Lets 3.46 differential my '01 M-Z3 coupe, part 1 [Archive] - bimmerfest

Ron Stygar

04-14-2002, 09:34 PM

The '99/'00 M-Z3 coupe with the S52 engine has a 3.23:1 differential.
The '01/'02 M-Z3 coupe with the S54 engine has a 3.15:1 differential.
Based on the 7600 rev limit on the S54 engine, the 3.15 differential is not a good match for the car in my opinion. Have no idea why BMW really did this.
Looking to change this, I first focused on the 3.38:1 based on the numbers, and settled on the 3.46:1 used in the Z3-3.0's with automatic.

<img src="http://www.unofficialbmw.com/images/z3differentialchart.jpg">

Back then, I had no idea if this unit would fit or work with the M. At the time we knew that the rear covers were different. We also knew that the output flanges were different, but based on the parts data the M ones would swap right in. The driveshafts are different lengths too.
But based on both differentials using the same input flange, we assumed it would work.
Al Corey (took the chance) purchased one to see. The differential retails for $2200.00 with a $100.00 core charge. So, if you want, you can keep your stock differential for $100.00.
He installed it and it fit fine. When we took it out for a test drive there was no speedometer reading. Turns out the speed signal generator (spider) is different, diameter wise between the two differentials.
Since BMW no longer sells internal differential parts, there was no way to check this since the internal parts no longer show up on the parts CD. They show up if you know the part number, but that's another story.
Al modified his speed signal sensor so that it would go in more. It worked.
Randy Forbes swapped out the speed signal generator (spider) with the one from his M differential and it worked too.
I had my machinist modify a speed sensor based on what Al found out. He also made me a plate to accommodate the shortened sensor.

<img src="http://www.unofficialbmw.com/images/new346-9.jpg">
<img src="http://www.unofficialbmw.com/images/new346-10.jpg">

After three unsuccessful tries, the fourth differential I ordered showed up undamaged.
Time for me to finally 3.46 my '01 M coupe.
Last time I swapped out a differential was over forty years ago in my '61 3 speed Chrysler. Used to swap back and forth a 4.11 with the stock 3.23 as needed. Looking back, I have no idea how I did this.
I remember slam hammering the axles out and removing the rear cover.
Five years earlier my first car was a 40 Ford Deluxe coupe.
Pontiac V8 with a '39 Lasalle tranny and Ford rear end. No idea how I did this either. At fourteen, I never finished the car. The guy I sold it to did though. My older brother, being into cars, got me into cars.
Part 2 to come.
Preview: I got the stock differential out.

<img src="http://www.unofficialbmw.com/images/new346-8.jpg">

SilvyinLA

04-15-2002, 03:49 PM

Will this make the car easier to drive when in 5th gear?

My brother has a 95 M3 and in 5th gear on the freeway it revs sort of high. I thought a 6th gear would make the car easier to live with on long drives.

Is this the same sort of thing what you are doing will do? Lower the rpms when in 5th gear....

Sorry for such a simplistic question.

By the way the bottom of your car is too clean...you need to drive it more.

Ron Stygar

04-15-2002, 05:57 PM

The 3.46 is roughly a 10% change which will increase the RPM's for any given speed. 70 MPH in fifth gear is 3250 RPM. Based on the S54 engines 7600 redline the 3.46 is a better match for the car.
With a six speed, sixth gear is an overdrive (.83) so it would make the 3.46 differential look like a 2.87 one.

blackdawg

04-16-2002, 05:55 AM

lesser men would have sensed fate against them after the first 3 damaged differentials!

please keep updates coming along.

i'll bet the car just flatout rips with the new rear-end.

cheers,
coky nguyen

Steve Borsse

04-16-2002, 09:28 AM

Thanks Ron, looking forward to the remainder of the installation. Thanks for pointing out to me "bimmerfest." :thumb:

Shawn Fogg

04-16-2002, 05:33 PM

Ron,

Glad to hear you finally got a diff intact! Took them enough tries. I've been checking part numbers for my fathers 330ci... he is thinking about a diff upgrade for it.

Shawn

Christian

04-19-2002, 01:50 PM

Ron, just curious as to whether you've finished your rear differential intall or not. I'm very interested to hear the end result.

Ron Stygar

04-19-2002, 06:07 PM

Finished the install Monday night. Have around 200 miles on it since then. No droning, vibrations or leaks. Still breaking it in.

From BMW:

<img src="http://www.unofficialbmw.com/images/new346-11.jpg">

I'm not sure what the above statement means. I assume 2/3 of maximum speed in 5th gear, which is not a problem over here.

Mileage appears better (based on the OBC) with the new differential cruising at 71 MPH. Also measuring differential temperatures etc. Will try to post part two of the how to Sunday night. Have a lot of pics to edit etc. Going to Limerock tomorrow so it won't happen then.
We have planned testing of Al's car with Shawn Fogg sometime soon.
As mentioned, the 3.46 is a nice match for the car.

Preview:
Coming out. Since the differential weighs 83 pounds, having a nice jack makes this much easier to do.

<img src="http://www.unofficialbmw.com/images/new346-12.jpg">

Christian

04-19-2002, 07:00 PM

Have fun at Lime Rock!

Ron Stygar

05-23-2002, 11:50 PM

As mentioned, we modified the stock M sensor to go in more so that the smaller diameter speed spider in the 3.46 differential would mate with it.
The covers and sensors are different between the M and the 3.46 differential. If you were to keep the 3.46 cover using the 3.46 sensor everything would work fine. If you want to use the M cover with the 3.46 differential you have to change out the speed spider or modify the sensor.
I modified the sensor and it appeared to work fine initially. The sensor Al modified when he did his car is still working fine.
Depending on the drive time the speedometer signal becomes intermittent. This has been driving me nuts for the last couple of weeks. Appears to be temperature related. Thought it might be wiring based on me not disconnecting the plug when letting the differential down. Thought it also may be related to the many mods I've done using the speed signal.
Have a 3.46 sensor coming tomorrow so that I can compare things dimension wise. I have both the M and 3.46 covers.
If you place a scope across the speed sensor you will see a 5 volt square wave referenced to ground when working. When its not working the square wave goes away and you see a line on the scope at ground.
Wasn't sure how the sensor worked. Took one apart tonight to see.

http://www.unofficialbmw.com/images//pulsegen-1.jpg

In one prong of the sensor is a switch. In the other a magnet.

http://www.unofficialbmw.com/images//pulsegen-2.jpg

The magnet closes the switch (ground). When the magnet is interrupted by the speed spider blade, the blade shunts the magnetic field and the switch opens (5 volts).

http://www.unofficialbmw.com/images//spiderz3m.jpg

I have a thermocouple attached to the differential case to measure temperature, which goes to a meter in the passenger seat.
I also have a lead paralled with the sensor going to a scope in the passenger seat footwell.
Knowing how the sensor works, I can now place an ohmeter across the sensor leads when it fails and hopefully figure this out.
Come this Winter, I will be installing the M spider in the 3.46 differential.

Gus

05-24-2002, 07:57 AM

Ron,

I am going to go for a drive later to day and check out the RPM/Speed ratio, as I believe that my car revs higher at the speeds posted. I am not 100% sure about this, but I will "have to" :D to out now for a drive! Will post the results. Give the incredible traffic here, its bound to be a challenge to do so...

Gus

Steve Borsse

05-24-2002, 09:30 AM

Hay Gus!

If you'd like me to check my RPM at a certain indicated speed, let me know what numbers you want checked. Just not anything over 5k in fifth!!! I have the 3.15 rear end in my 01 M///Roadster.

Have a great weekend, looking forward to seeing you a couple weeks! We'll see what we can do about adjusting your hood. I've been practicing "mi Espanol cada dia": "Tiene una cervezas muy fria, tenemos sed!!!" ;) ;)

Gus

05-24-2002, 12:25 PM

Keep practicing that Spanish! :thumb:

I am the one who is going to verify for Ron the RPM to speed ration on my car and see if its a 3.15 or what that I have in there.

I promise not to go over 6K rpms in 5th :angel: Maybe not?:lmao:

Z ya soon!

Gus

Ron Stygar

05-24-2002, 05:34 PM

Reference the picture below.
The Z3-3.0 speed sensor arrived today. Compared it dimensionally to the M-Z3 one.
From taking the M one apart last night, I now know how they work. Based on this I checked the trigger point on the
Z3-3.0 one. Although the 3.0 one is shorter, its trigger point is further out towards the tip of the prong than the M one. Bingo.
Looking at the pic the stock M one trigger point is .074" away from the end of the spider blade tip. By modifying the sensor to go in around .1" the tip just goes over the trigger point. On Al's car this has not been a problem, yet. On my car it works fine initially and stops working after the differential heats up.
On the 3.0 unmodified one the blade tip is past the trigger point by .328". More then enough margin.
Keep in mind that why this is necessary is that the speed spiders are a different diameter between the 3.46-3.0 and 3.15/3.23 M differentials, The 3.0 cover (where the sensor mounts) is thinner than the M one.
So now, instead of swapping spiders or modifying a sensor, you just have to replace the M sensor with the 3.0 one.
Finally!

http://www.unofficialbmw.com/images//pulsegen-3.jpg

bmwRobert

06-09-2002, 08:37 PM

We did it. Last week we installed a 3.46 diff (from a 2000 Z3 auto)in a 2001 M coupe. Thanks to Ron Stygar who did the R&D and showed us the way. The car drives as it was ment do drive. What was BMW thinking putting a 3.15 in that car.
We got the diff from Pasific BMW for $1750. Install is a straight bolt on. We even used the Mcoupe diff cover so everything looks stock. We did have to swap out the Mcoupe speed sensor with a 2000 Z3 3.0 speed sensor (as Ron recommended) to make everything work correctly.
This weekend the car was driven 1000 miles (600 miles per BMW recs) as part of the break in period for the diff.
Now it just ROCKS!
THANKS Ron you are the GURU! http://community.webshots.com/photo/32881575/32881676bvwevy

kaiwang

06-10-2002, 09:25 AM

With the new Diff, it would be interesting to see 0-60 and 1/4 mile times.!

Randy Forbes

06-10-2002, 07:58 PM

I hope to get my car out to the strip for some timed runs sometime this summer.
I got out late last fall and was only able to make two passes on a very busy "test-n-tune" night.
The car only had around 3000 miles on it, and I've since learned that it isn't a "fast track" as far as times go.
My best that night was a 13.8 at maybe 104mph with the 3.15:1.
The plan is to make it over to Norwalk (?) where they have some kind of high traction surface. That and a 3.73:1 should make a world of difference. Plus mounting the Hoosiers on the rear only.

caylan

07-23-2002, 01:21 PM

Limited Slip Diff?

Ron Stygar

07-23-2002, 01:26 PM

Originally posted by caylan
Limited Slip Diff?

Torsen style. Torsen style only used in the non M-Z3's based on my research

phrider

07-23-2002, 02:47 PM

Originally posted by Ron Stygar
Torsen style. Torsen style only used in the non M-Z3's based on my research Ron, to avoid confusion for all of us that are contemplating this now or in the future, what is the full part number on the Torsen 3.46 differential?

Thanks for your R&D efforts.:thumbup:

Ron Stygar

07-23-2002, 07:31 PM

Originally posted by phrider
Ron, to avoid confusion for all of us that are contemplating this now or in the future, what is the full part number on the Torsen 3.46 differential?

http://www.unofficialbmw.com/images//diff4513-1a.jpg

The part number shown is for the remanufactured differential which is basically like a new one, based on the four I got to look at.
The new part number is the remanufactured number minus 1.
Don't think that the new part number is available through the parts system.
This minus one thing works on transmissions too, and I assume other things.
Knowing this, if you had a part number list of the new differentials used in Z3's that were Torsen style, you could add one and see if they were used only in the non M-Z3's or whatever.
I went with the 3.0 from BMW because it was a Torsen style and it was like new. Torsen folks said that it would have no problem handling the M's power. It appears, so far, to work very well with the M DSC.
The differential retails for $2200.00. For an extra $100.00 you get to keep your stock one. Good deal in my opinion.
No history on this when this was first done, so a back up was nice. Sell the car, switch back the stock one and easily sell the 3.46.
Paul McLaughlin (1-800-883-7278) at South Motors BMW in FL will discount 25% from true suggested retail plus shipping. He's sold eight of them so far and has the packing down, so that you will only have to order one of them:).
45 ring teeth divided by 13 pinon teeth = 3.4615
Quiz: Does the driveshaft turning around once make the wheels go around 3.46 times, or does the driveshaft going around 3.46 times make the wheels go around once?

Christian

07-23-2002, 07:36 PM

Driveshaft rotates every 3.xx times for each time the rear wheels spin. Correct?

Ron Stygar

07-24-2002, 02:13 PM

Originally posted by Christian
Driveshaft rotates every 3.xx times for each time the rear wheels spin. Correct?

Correct. Email me your address and I'll send you a prize.

M Power

07-29-2002, 06:11 AM

I've upgraded my differential from 3.15 to 3.46 about a week ago. This thread has been very helpful in making my decision. The total cost of upgrade was about $2500 from a local BMW dealer that includes BMW warranty as well.

As for performance, the car noticeably pulls faster in each gear as it was mentioned already. Definitely a worthwhile upgrade, IMO.

Tommy V

07-29-2002, 12:13 PM

Ron,

Very appreciative of your post here as well. It was instrumental in my choice to change diffy"s.

Very happy with the change! Car pulls hard through all gears like it should have. Also notice that bogging in first up to 2K RPM is mostly gone as well.

Tommy V
02 Steel Grey MCoupe
Ground Control Suspension: 450F/600R Eibach - Koni SA
Ground Control Rear Mounts
Supersprint Dual DTM
UUC Short Shift & Tranny Mount
UUC Big Boy Clutch Stop/Rob Knob III
HMS Harness Bar/Schroth 4pt
3.46 Differential - Great!
Valentine 1 Hardwired
SS CL Stut Bar

M Power

07-29-2002, 02:50 PM

Are you following me around, Tommy? :D :D :D
Hey, have you thought of oil cooler for our cars? I wonder if it will provide any performance increase?

JonM

07-29-2002, 02:59 PM

All S54s have oil coolers.

M Power

07-29-2002, 03:57 PM

I see. Thanks for the info.
Actually, I was referring to aftermarket oil cooler for additional heat dissapation effect. My car has it's oil temperature at about 260 even when the car is not driven hard. Have you notice this? I know it's summer and all but it's getting awefully close to that red line.

JonM

07-29-2002, 06:10 PM

Mine runs at 200-210 on the road during hard driving.

Have not had the car on the track, so no data in my case.

5 Rakete

07-30-2002, 07:25 AM

I see the same indicated oil temperature as Jon, 200-210 degrees. 260 seems rather high, as if the thermostat to the cooler isn't opening or something.

Tommy V

07-30-2002, 07:34 AM

Hey Sean,

Ive gotten as high as 230 on a really hot day (90+) driving hard. Ive only seen that figure once. Most of the time its like the other guys stated 190 to 210 area on the gauge.

As far as cooler running ideas, (ive thot about these and may do if I find heat becoming a prob as I drive/track the car more)

Remove AC/fan and cooling tubes in front of radiator to give free air access to radiator as opposed to having all that stuff in front of the radiator. I never use A/C. Would eliminate about 30lbs weight.

Move oil cooler to behind spoiler mesh for more free flowing air. To be honest I cant even see the oil cooler now....

Note: you could have a sensor issue like stated above. If its running hot like that all the time, Id take the car into the dealer, possibly consult ahead of time with a solid inde shop as well.

Prob should change the thread as this is starting to go off topic......

M Power

07-30-2002, 07:45 AM

Hey, Tommy.
So it is abnormal then. I guess I will ask BMW of Sterling to look at it when they are replacing my 3.46 with a new one. Tommy!!! my 3.46 is still making that "whinning noise". It's as loud as turbo boost sound when I had Stealth RT/TT. I don't think it's a healthy sound at all. Does anyone with 3.46 have this problem? I can hear turbo-whinning-sound(?) like when I am in high gear and accelerating. The car drives perfect otherwise though.

Tommy V

07-30-2002, 07:53 AM

Sean,

Drive the car mellow and take it in immediately to an independent shop and have the noise analyzed.

Take it to the dealer second after youve had this initial prepwork done. I dont trust dealers very much....

Have them check that the right diffy oil went in BWM lifetime....and the correct weighting.....

Do this right away to play it safe in case their are any problems.

I hear a whiny noise myself but this is coming from the engine at high RPM'S...... :D

Check on the oil cooler. That seems quite hot for our cars equipped with a cooler....

Hope this helps

Ron Stygar

08-10-2002, 07:38 PM

Been sorting through the pics I took changing out my '01 M coupe 3.15 differential to a 3.46 differential used in the 3.0 automatic Z3's. Have them selected, cropped etc. minus annotations.
Not a how to, but you will get the idea. Will eventually annotate the pics. Will eventually do a how to. Will post some more pics soon. (you have to come up with a pic, annotate it and come up with some words to go with it.)
The following pics show my car jacked up to swap out the differential.
Keep in mind that if whatever system you use to elevate your car fails, that you may fail with it.
First pic shows the front wheel chocked in place using Tru-Cut chocks chained together by Ron. I do this on both front wheels. Doing this keeps the car from going back and forth. Car can't go up, only down.
Have a modified set of Tru-cut chocks for sale for $50.00 plus shipping. Someone asked me to make a set and never came through.
Note the blue powder coated calipers.
Note the bumper clear lenses.
Note that the wheel center logo caps are lined up.
Note that the wheel lug bolts are covered with the SAAB caps.
Note the front mud flaps.
Note that the rotor edge is not rusted.
Note that the hood is opened and not because of installing a strut brace. BMW spec. on body gaps is 5mm (.197 inch).

http://www.unofficialbmw.com/images//new346-16.jpg

Second pic shows the rear of the car up on stands and ramps.
Note the blue powder coated calipers.
Note that the wheel center logo caps are lined up.
Note that the wheel lug bolts are covered with the SAAB caps.
Note the rear mud flaps.
Note that the rotor edge is not rusted.
Note the jackstands with adapters to fit the Z3.
Tru-Cut ramps are mainly to keep the wheels up. Also a back up if the jack stands fail.

http://www.unofficialbmw.com/images//new346-17.jpg

Third pic shows the car up, and the Lincoln jack with the plywood adapter that I made to fit the cup on the Lincoln jack. This piece keeps the frame of the jack from interfering with the differential cover cooling fins when jacking on the differential case forward of the fins.

http://www.unofficialbmw.com/images//new346-18.jpg

bob lindquist

08-11-2002, 05:35 AM

Ron would you have a speed/RPM chart for the 2000 M coupe? I would like to find the right ratio change for my s52. I understood you could just have the gears changed and increase the slip ratio, using the existing unit. Is this true?

Ron Stygar

08-11-2002, 02:46 PM

Originally posted by bob lindquist
Ron would you have a speed/RPM chart for the 2000 M coupe? I would like to find the right ratio change for my s52. I understood you could just have the gears changed and increase the slip ratio, using the existing unit. Is this true?

http://www.unofficialbmw.com/images//z3mdifferentialratios.jpg

Ron Stygar

08-11-2002, 06:23 PM

To remove the differential you have to remove the 12 output shaft bolts and the 4 driveshaft nuts along with the speed sensor connector at the differetial rear cover. The following pics show the differential part.
You have to remove the rear cover rubber mount point hardware.

http://www.unofficialbmw.com/images//new346-20.jpg

This lets you lower the differential which allows access to the four top mounting bolts.
Doing this is also a good way to change out the springs without stressing the output shaft joints. Alan Alfano just did this on his E30 and said it worked well.

http://www.unofficialbmw.com/images//new346-19.jpg

http://www.unofficialbmw.com/images//new346-13.jpg

http://www.unofficialbmw.com/images//new346-14.jpg

http://www.unofficialbmw.com/images//new346-15.jpg

Ron Stygar

08-12-2002, 09:07 PM

Car jacked up with the exhaust off.

http://www.unofficialbmw.com/images//new346-21.jpg

Outpt flange bolts.

http://www.unofficialbmw.com/images//new346-22.jpg

http://www.unofficialbmw.com/images//snaponE12.jpg

Driveshaft nuts.

http://www.unofficialbmw.com/images//new346-23.jpg

Ron Stygar

08-13-2002, 03:07 PM

http://www.unofficialbmw.com/images//new346-24.jpg

http://www.unofficialbmw.com/images//new346-25.jpg

http://www.unofficialbmw.com/images//new346-26.jpg

Bottom fins of differential cover rest on the jack keeping it from tipping.

http://www.unofficialbmw.com/images//new346-27.jpg

Adding fluid.

http://www.unofficialbmw.com/images//new346-28.jpg

Ready to go back in.

http://www.unofficialbmw.com/images//new346-29.jpg

bob lindquist

09-10-2002, 10:55 AM

Ok so all you S54 guys have been getting these 3.46 hams. What about us s52 people? Is this a good swap for us?

Randy Forbes

09-10-2002, 01:48 PM

What about us s52 people? Is this a good swap for us?

Bob,

The jump from 3.23:1 to a lower 3.46:1 isn't going to be as noticeable as the spread between a 3.15:1 and a 3.46:1.

If it were me, I would look into a 3.73 or even a 3.91:1. Granted top speed will suffer (which I don't use anyway) and rpm for a given road speed will be higher, but it is still not excessive.

There are plenty of ratio RPM vs Road Speed charts available (E-mail me if you want the one I use) so you can see what the trade off is.

For the record, not all of us S-54 guys went to a 3.46, there is at least one running a 3.73;)

scottn2retro

09-10-2002, 02:00 PM

Originally posted by Randy Forbes

For the record, not all of us S-54 guys went to a 3.46, there is at least one running a 3.73;)

Randy, what was your mpg to/from HC2002?

Randy Forbes

09-10-2002, 05:31 PM

Randy, what was your mpg to/from HC2002?

First off, let me say that I rarely drive with the intention of getting good gas mileage.

That said, I don't check my mileage very often either.

We did however check it a couple times while on our trip to HC

While still in the flatlands of Ohio, I had a tank run over 23 mpg while doing 80 (indicated...) on the Interstate.

I checked it again when I fillled up after running The Dragon a few times (I use 2nd & 3rd gears, Sue used just 2nd) and that tank yielded about 17 mpg.

There are some that would complain (makes me laugh too), but the most fun I ever had with the car was getting 11.8 mpg at the Evolution School!

scottn2retro

09-11-2002, 07:20 AM

Originally posted by Randy Forbes

While still in the flatlands of Ohio, I had a tank run over 23 mpg while doing 80 (indicated...) on the Interstate.

That's pretty respectable for using a 3.73 :)

M Power

09-11-2002, 08:00 AM

And there is at least one of us (S54 owners) who has 3.46 and Super Charger (being installed this weekend). :thumbup:

Zeegar

09-11-2002, 11:22 AM

I love this post, only thing that could make it better is Silvy in some stylish oufit pointing to all the items in Ron's pics. This is entertaining, educational and gets my imagination going. Imagination going is NOT just 'cause I picture Silvy in a stylish outfit. :thumbup: :thumbup: :thumbup:

Randy Forbes

09-11-2002, 11:26 AM

And there is at least one of us (S54 owners) who has 3.46 and Super Charger (being installed this weekend).

Just curious, but what precautions are taken when supercharging an engine with 11.5:1 compression ratio?
I would think that detonation would be a big factor.
Are you using an intercooler?
Or water injection to cool the charge?

The results will be very interesting, and I am certain that I am not the only one that wants to know how big of an improvement it will make.

Keep us posted!

M Power

09-11-2002, 05:04 PM

There was a rumor about water injection while RMS SC for S54 was going through its development phase. I honestly do not know much detail at this point. I do know that it will run 6.5psi pressure and maximum power will happen around 7k rpm.

I just dropped off my car at Curry's auto center. It will be dyno tuned and ready to go by Saturday. As soon as I find out more information, I will keep you guys updated. Wish me luck!

badkarma

09-12-2002, 07:46 AM

I get about 240 miles to a full tank now, down from about 280. Now the car pulls like my chipped Audi S4

Dadofour

10-22-2003, 10:42 AM

Ron Stygar

10-22-2003, 11:21 AM

I have ordered a 3.73 Differential for my 2001 M Roadster. My questions is:

Will the Z3/3.0 Speed sensor work in the 3.73 differential with the M Roadster back plate installed?
>>>Haven't been there yet.
If not, do you have any suggestions.
>>>Order a 3.0-3.46 Torsen.

bob lindquist

07-25-2004, 07:31 AM

where does this go?

What is required to change it?

Randy Forbes

07-25-2004, 08:54 AM

where does this go?

What is required to change it?

This is where it goes (visible just inside the case on the right)

http://www.rfdm.com/Randy/BMW/pics/projects/01%20M%20Differential/3%2073%201%20Differential.JPG

And this is what it takes to change it (really very easy). You do not have to do any "setup" just put everything back where you found it. Note that four (4) of the bolts that go through the bearing retainers (side covers) need to have thread sealant on them as they go all the way through the casting (and could, I guess, potentially leak oil).

http://www.rfdm.com/Randy/BMW/pics/projects/01%20M%20Differential/changing_spider.JPG

A new roll of duct tape makes an excellent mandrell to drive the spider back on (stacked on end: differential carrier, spider, roll of duct tape, 4 x 4 x 8 and top it off with a dollup from a BFH).

And here's why you want to know this ;)

http://www.rfdm.com/Randy/BMW/pics/projects/01%20M%20Differential/spider%20comparison.JPG

jpropane

09-12-2004, 06:48 PM

Has anybody toyed with the idea of using a 3:73 with the new Z4/E46 6 speed transmission yet?

L84THSKY

01-19-2005, 07:04 AM

Hello

May I please jump into this forum for a few quick questions. I saw a 2001 Z3 M coupe 3.45:1 limited slip diff for sale. The seller says it came from a 5 speed tranny. All the research I can find tells me it the 5 speed from that year was a 3.15:1 ratio. Can someone confirm this is a LSD 3.45:1 diff from the pics I will attach? I realize I must swap driveshafts too, any other issues?

I've upgraded my differential from 3.15 to 3.46 about a week ago. This thread has been very helpful in making my decision. The total cost of upgrade was about $2500 from a local BMW dealer that includes BMW warranty as well.

As for performance, the car noticeably pulls faster in each gear as it was mentioned already. Definitely a worthwhile upgrade, IMO.
http://www.geocities.com/triumph1518/Mdiff1.JPG http://www.geocities.com/triumph1518/Mdiff2.JPG http://www.geocities.com/triumph1518/Mdiff3.JPG http://www.geocities.com/triumph1518/Mdiff4.JPG

Randy Forbes

01-19-2005, 10:05 AM

Hello

May I please jump into this forum for a few quick questions. I saw a 2001 Z3 M coupe 3.45:1 limited slip diff for sale. The seller says it came from a 5 speed tranny. All the research I can find tells me it the 5 speed from that year was a 3.15:1 ratio. Can someone confirm this is a LSD 3.45:1 diff from the pics I will attach? I realize I must swap driveshafts too, any other issues?

http://www.geocities.com/triumph1518/Mdiff1.JPG http://www.geocities.com/triumph1518/Mdiff2.JPG http://www.geocities.com/triumph1518/Mdiff3.JPG http://www.geocities.com/triumph1518/Mdiff4.JPG

Looking at the tag on the top of the case (... 3.15:1), tells me that is the differential that was removed to make way for a lower ratio. Those are the stubaxles and rear cover of a non-M (Z3/M) differential.

Only way to know the ratio for sure would be to rotate the input flange and count the turns until the output flanges have made one (1) rotation. Or, remove the cover and count/divide the teeth on the ring and pinion.

Are you sure you'll need to swap driveshafts? I'm not familiar with the 318 range, but we don't swap driveshafts when installing a lower ratio in our cars.

ShifterKart Guy

01-19-2005, 01:51 PM

Randy Forbes

01-19-2005, 03:39 PM

he thinks the 3.15 on his 99 with 350+ at the wheel is completely necessary. The 3.46 would bang off rev limiter in 3 gears immediately.

I am assuming that you guys with the s54motors were experiencing the opposite- the 3.15 was too tall for the HP / power curve of your motor and you need to shorten up the gears to get more acceleration?

I have the 00 M coupe- does that have a 3.23?

The S-54 has a broad power band and pulls strongly right up to the 7600 RPM redline (unlike my S-52 that gets wheezy before it hits 6500). The 3.73:1 that I have puts the redline in 5th gear right around 150 MPH. That's way faster than I ever go. But I do like to get to 80 MPH as quickly as possible! It was plenty quick with the 3.15:1, now it's just awesome :yikes:

Your S-52 came from the factory with a 3.23:1

bob lindquist

01-19-2005, 05:49 PM

(unlike my S-52 that gets wheezy before it hits 6500).

For this symptom add eurosport cam kit and call me in the morning.

You will see rev limiter quite often.

ShifterKart Guy

01-22-2005, 06:27 PM

Randy Forbes

01-22-2005, 08:00 PM

I have an S 52 M coupe that I will be blowing this winter. Since many of you are going to
the 3.73 ratio- I am going the other way to get more top end.

Is anyone looking to unload the diff for a reasonable price?

I'm sure there are a lot of 3.15:1 units out there, maybe even some 3.23s.

My 3.15 barely has 3000 miles on it (3.73 was installed 1/02) but I don't have any plans to sell it (although, a Plasma cutter would be more useful...).

ShifterKart Guy

01-23-2005, 09:59 AM

Seriously- if you change your mind let me know. ( whats a the going price by the way for used 3.15 diff from a private owner- and please don't sy about the price of a plasma cutter since i have no clue on that either! I know what the criminals at Dinan would charge :yikes:

This fall I had Ben at Rogue install his LTW FlyWheel, HD Pressure Plate and m % Clutch package in the car. Since I am waiting ( like many I hear) for the Twin Screw to come out from Eurosport, I thought I would throw in a 3.73. The guys at Rogue got me a used on for a great price. They said it was noisy so they took it out. they tried again- same problem?? So I left the 3.23 in it.

I know that the clutch upgrades are noisier parts- but I am hearing a lot of whinning out of the rear end when the car is coasting and / decelerating in gear. Since the clutch pieces are in the front...what gives? Could the noise be traveling down the shaft or do I have some issue that should be checked out.

My old 944Ts use t o make this noise...then one day the I was begging Porsche NA to warranty the Trans.

robrez

01-23-2005, 10:12 AM

I have an S 52 M coupe that I will be blowing this winter. Since many of you are going to
the 3.73 ratio- I am going the other way to get more top end.

Is anyone looking to unload the diff for a reasonable price?
There are probably a few 5 speed 3.0 Z3 owners like myself who might be looking to swap our 3.07 Torsen diffs. for a 3.23 or 3.46. I'm still doing the research, but those are two diffs. i'm looking at swapping in.

ShifterKart Guy

01-23-2005, 10:31 PM

Don't want to make any promises to you- Being that I spend most time at 140 or lower :thumbup: .........I may not need the taller gearing.

The only place I need more top end is at Pocono so I can stay with the 911's and the Vipers :) Since thats a once or twice a year occassion- maybe I should see how the car drives once I install the SC. ( that makes too much sense for me)

I mostly go to LRP or the Glen- the east coast guys reading this know that at LRP I don't need the gearing and at the Glen- I am unlikely to see over 150 on the back straigh before the buss stop. With the modest gains in power from the Stage 5 Dinan crap (did I say that :yikes: ) and the 3.23 diff - I inch over 130 before the buss stop today. More power- I can get more speed- but now I have to brake sooner- the more I think about it-the more I have to see how it goes...

The 3.23 is probably more than enough, for top speed that is. My other concernms will be mid corner gearingso that I can use all the handling of the car with out being out of the powr band. When racing karts- a change in ratio can change you shift points and find some significant time for you.

Maybe I am over analyzing this rear diff thing too much-

After I get the SC installed I'll see if I can get through the 1, 2 and 3 with out dropping the diff on the street..Maybe I'll follow some of the other guys and go shorter - as in a 3.4?

I figure the S54 probably want to get on the power band sooner so they are going to the
3.73? But with the s52 motor that leaves me topping out at 137..back where I started when I bought the thing :mad:

ShifterKart Guy

01-23-2005, 11:01 PM

ANy thoughts on this???

I know that the clutch upgrades are noisier parts- but I am hearing a lot of whinning out of the rear end when the car is coasting and / decelerating in gear. Since the clutch pieces are in the front...what gives? Could the noise be traveling down the shaft or do I have some issue that should be checked out.

Those of you with Clutch upgrade- what is your experience. Other than the rattle cuming out of the assenbly when you disengage the clutch??

Do you hear a whining sound when you coast...almost like a zhuugh zhuugh zhuugh sound

do that 3 times :D

robrez

01-24-2005, 07:21 AM

Just wondering if somebody could please show me how to calculate RPMs and given speeds using different differential ratios. I see that Ron Styger used such a chart at the beginning of this thread. I want to see if I'd be better off going with a 3.23 or 3.46 diff. My car currently has a 3.07 and the rev limit is 6,900 RPM, and redline is 6,200 RPM, but I also have Dinan software which raises the rev limit. I also run 255, 40, 17 rears. I think Shifterkart guy is looking at going from 3.23 to 3.15 or maybe 3.07, maybe his numbers could be run as well. Thanks alot for the help, this is way beyond my current knowledge, but the chart Ron Styger lays out seems like a must-do when considering swapping diffs. Might car is a daily driver and sees a fair amount of highway driving, but I also want the change in the low end to be enough to make it worth doing. Thanks for the help.