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-   -   540i Manual Rear Differential Upgrade! (http://www.bimmerfest.com/forums/showthread.php?t=683443)

e39530i5speed 03-19-2013 06:55 PM

540i Manual Rear Differential Upgrade!
 
Hi,
The 540i with manual transmissions has horrifically tall gearing. It has a 2.81:1 rear differential. I want to upgrade it to shorten the gearing. I know that 3.15:1's came stock on the 2003 M-Sport and M5 as well as all of the automatic 540i's. However, 3.15 isn't quite a large upgrade.

I look around and all of BMW's cars that use V8's such as the M62 and N62 of variety of sizes all tend to use differentials of 3.23 or 3.38. I think 3.46 is a bit too much, however 3.38 sounds reasonable as does a 3.23. These came on E60's and E65's 5&7 series cars.

I obviously want to buy a used open differential. I cannot however find anywhere if the flanges are interchangeable between differentials and if its a drop in replacement from the old ones meaning that they bolt to the frame in the same spots and you're good to go.

Thanks for any help!

edjack 03-19-2013 07:15 PM

What are you trying to accomplish? With the prodigious torque and 6 speeds, I am never at a loss for the proper gear on the street. Perhaps you should enroll in a BWW CCA high-performance driving school. Ya think?

e39530i5speed 03-20-2013 12:35 PM

Quote:

What are you trying to accomplish? With the prodigious torque and 6 speeds, I am never at a loss for the proper gear on the street.
I am trying to accomplish better acceleration and shorten my gearing. A 2.81 rear end really bogs down the car's acceleration and reduces its potential power delivery over time.

Quote:

Perhaps you should enroll in a BWW CCA high-performance driving school. Ya think?
What does that have anything to do with the question I asked? I see no relevance. Maybe I'm missing something.

kimokk 03-20-2013 12:46 PM

Quote:

What does that have anything to do with the question I asked? I see no relevance. Maybe I'm missing something.
I think he's saying you may learn some new techniques to overcome the perceived differential gearing shortcomings.

e39530i5speed 03-20-2013 02:48 PM

Quote:

Originally Posted by kimokk (Post 7458389)
I think he's saying you may learn some new techniques to overcome the perceived differential gearing shortcomings.

Maybe he should first learn how differentials work as well as how they affect acceleration of a vehicle ...if he doesn't already. Then maybe he should just answer the question asked... if he knows the answer or skip it if he doesn't.

Either way, I'm trying to figure out if the bolt pattern on the differentials cover is the same for the future generation difs of E60, in which case that cover can be changed so it can be bolted properly to the E39 subframe. Can't find anything on it though.

Any help would be appreciated.

granlund 03-20-2013 08:51 PM

Even though the gasket is the same on many 220mm diffs, the cover and the diff housing itself clearly is not. The only reasonable option as I see it is a 3.15.
http://www.realoem.com/bmw/partxref.do?part=33111214448

I do not know if you can gut the interior of an E53/E60/E63/E64/E65/E66 higher ratio diff and use it in an E38/E39 housing, which would be a more involved upgrade.

LaCrosse540i6 03-20-2013 09:04 PM

There is another member on this forum who just upgraded his M5 diff with 3.46 gears from and e46 M3.

It's documented in his lq9 swap thread, check it out.

nsogiba 03-21-2013 06:57 AM

The E46 M3 ring and pinion (3.62 ratio) are definitely compatible with the M5 diff. However, I don't know if the internals of the M5 diff are compatible with the 540i diff, which means the M3 3.62 may not be compatible with your 540i diff.

If I were you I'd buy a stock E39 3.15 out of an auto car as it is a direct bolt in. Before I took my car off the road for the LQ4, I swapped in one of those to replace my OEM 2.81 and enjoyed the better acceleration; highway cruising was only slightly more annoying (higher revs), but above 80mph the engine was really screaming. I would do it again.

If you really have time and money to burn, buy a used E46 M3 ring and pinion and see if it's compatible with the 210mm M3 housing. I probably wouldn't run that combo on the street though-too many revs while cruising on the highway.

e39530i5speed 03-21-2013 11:57 AM

See thats the thing, I'm not really a highway cruiser...rarely get on. I drive on backroads and traffic where shorter gearing is not only helpful but also more fun.

nsogiba 03-21-2013 12:02 PM

For what it's worth I drove a LOT on the highway and didn't terribly mind the 3.15, so that's what I would recommend for your driving habits.

I would absolutely buy this, good price and it's from a reputable seller.

http://www.ebay.com/itm/BMW-Parts-3-...c95bee&vxp=mtr

geargrinder 03-23-2013 05:39 AM

The drill on the M5 diff is you need either the M5 axles OR get different flanges for the 540 axles. I think there's an E34 or 7er flange or something you can use. I'd have to look it up... I've thought about it...

Few more comments:
- there's a buncha places that can regear your diff or any core you have to whatever you want including gearing AND LSD components including diffsonline
- myself, i'd really not bother screwing around w/ the diff without going to LSD at the same time unless yer on a super tight budget. tossing an E46 or M5 LSD in adds to the ROI for sure.

Lastly, as any racer will tell you, there's no "right" empirically "better" gearing and despite street urban legend to the contrary, higher geared diffs don't "put more power down", they just put it down at different wheel speeds. yeah the car might "put more power down" in first coupla gears and that might be great for your driving style and on the street most people will feel it as "more power" at the stop light drags. But for a tracked car where 1st gear doesn't even come into play, a lower diff might very well shift the 3rd/4th gear peaks into a much worse spot (and I'm not talking about top speed, talking about where the gearing is optimized for your track). Lots of E46M3 n00bs go running after low geared diffs (4.11's) so they can win more stoplight races... If that's all you do that's great, but some find later that tracking the car the rest of the gears aren't really where you want them to be... On other hand a lot of track setup cars are dog slow in 1st because everything is optimized for 3rd and up on the track...

Don't take that as an argument against OP doing the diff swap BTW - I LIKE the 3.15 in my Touring, just take it as an argument against not arguing for one or the other - whatever floats someone's boat as long as it works.

e39530i5speed 03-23-2013 10:40 AM

Quote:

- myself, i'd really not bother screwing around w/ the diff without going to LSD at the same time unless yer on a super tight budget. tossing an E46 or M5 LSD in adds to the ROI for sure.
An LSD is absolutely a pointless waste of money for me. This 540i is a daily driver to get from point A to B...5.3 miles one way. I can get a used open 3.38 for $260 with shipping included and swap it in within a few hours assuming I flanges are compatible. If already checked and the rear cover has the same bolt pattern and uses the same gasket.

Quote:

Lastly, as any racer will tell you, there's no "right" empirically "better" gearing and despite street urban legend to the contrary, higher geared diffs don't "put more power down", they just put it down at different wheel speeds.
So many people assume that a 540i 6-speed must be tracked or some sort of performance machine. Its just a daily driver LOL. I'm not trying to race it or do anything that I wouldn't do if I had a Toyota Corolla. A shorter differential ratio will shorten my gearing so I can have power on tap when I need it. I don't mind shifting a bit more often.

As it is right now...take an E46 M3. Its gearing (example of 1st gear) is 24.6% more multiplied than a stock 540i. In 1st gear, a 3.38 will yield me less 20% more multiplication. So my gearing will still be taller than any stock E46 M3. Not that bad if you think about it. 1st gear will still be plenty useful while 2nd-4th will provide phenomenal traffic drivability and passing power. For highway, 6th gear will keep the engine way below 3000rpm anyway.

And lastly, it will make it a lot more fun!


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