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3.46 variable lsd installed

4111 Views 7 Replies 5 Participants Last post by  karlblomquist
I received my final drive back from Metric Mechanic yesterday via Fed-Ex (well-packed, no box/packaging damage).

Spent the better part of the evening installing it. It was lot easier getting off than getting back on! Aligning this upper bolts while on a creeper on the ground (car on ramps) was not fun considering the 80 lb block I had to work with. But eventually it went in OK.

Took the opportunity of having the mufflers off to replace them with Supersprint DTMs. Questions about that later.

Re the final drive - I had the following done by Jim Rowe:
- gear change to 3.46
- extra clutch plate
- mod Limited Slip (25%) to Variable Limited Slip (20-100%).

Re the feel - launches are tremendously better. I expect this is mostly because of the variable mod. Jim says that when pushed his mod allows the clutch grab to creep up to 100% lockup. I can launch much more aggressively now and not see a flicker from DSC.

With the new gearing red-line comes up noticably faster in 1st & 2nd gear. I'll need to adjust my timing for enthusiastic shifing. :)

Takeoff might seem a little better (probably more the lockup than anything), but where I really see the difference is around 3rd and 4th at highway/secondary road speed. Downshifting into 3rd at 130 (km/h) and cranking it produces noticably more pull than before - and the pulling is relentless all the way to redline. The car could really use an extra 500rpm of red-line in my opinion.

Similarly, 2nd gear at 70-80 and stepping on it produces tremendous amounts of thrust.

I agree with Ron - 3.46 gearing is such a better mate to this vehicle.

My only remaining concern is that now sharp corning seems to kick the DSC on more often than usual. This could be a function of the increased torque to the wheels causing easier wheel spin on sharp corners, or perhaps the new clutching needs to "break-in". I'll be keeping my eye on this new trait - maybe it just requires adjusting my throttling through corners. Of course, I can always turn DSC off, but I've gotten too used to it saving me from myself. :yikes:

Re the Supersprint install - man those things are hard to get lined up the same. After 2:00am rolled around I said screw it and just tightened them up. They're not well-aligned right now, but I just wanted to drive a bit before tackling that again.

Anyone have any tips on methods to get these mufflers lined up properly? The passenger side one hangs too low and pulls to the driver side. I have the mod'd bracket per Ron's note about passenger side hanging. The driver side is not too bad.

Cheers , Karl
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Your new gears!

Excellent report Karl! Thank you. Glad to see you're so happy with the 3.46s.

Anyone have any thoughts on the difference in highway mileage that these 3.46s will make vs. the 3.15s? I normally cruise at 80 (and that's MPH!) here in Florida. (Everyone goes close to 80 or even above on the interstate down here.) I take a lot of weekend road trips all around the state, and I really don't want to see my mileage suffer too much. Love the 23 [email protected] 80-85 MPH!

Even though the RPM is roughly 500 more with the 3.46s at 80 MPH, possibly the load on the engine is lighter, negating the effect of the higher RPMs on the mileage? Karl, Ron, Randy, Big Al?
Re: Your new gears!

Steve Borsse said:

Even though the RPM is roughly 500 more with the 3.46s at 80 MPH, possibly the load on the engine is lighter, negating the effect of the higher RPMs on the mileage? Karl, Ron, Randy, Big Al?
Put in a 6-speed and you'll be fine:D
6 spd will make the 3.46 look like a 2.87

We have several drives planned for April, May and June. Will check mileage and also watch what the OBC does. It goes down directly with the gas pedal.
RE: SuperSprint install

There is a front and rear mount on each muffler. There is a rubber band mount which allows back and forth motion. The mount that holds this band is adjustable up and down. The connection to the cars middle pipe is rotating flanges with a metal donut like gasket. The trick is to adjust the two muffler mounts on each muffler to your liking with the flanges disconnected and the band mount floating. Once these are adjusted raising the band mount lowers the tips. If you adjust this with the system connected to the middle pipe, raising the band mount moves everything up. Raising the band mount also gives you more ground clearance. Position the flanges with the flat horizontal for max clearance as well. On my car from the floor to the bottom of the flange measures 5 1/4 inch.
I started by locking in the rear muffler mount on each muffler. This is the pipe that looks high on most installs so you are locking this in at its lowest point without any washers to lower it more. On the drivers side I was able to get the pipes level with clearance with plenty of adjustment either way up or down at the muffler mounts. On the passenger side the front muffler mount comes out with adjustment either way. The rear muffler mount ends up at its lowest point. To get this bracket so it has adjustment either way, I had my machinist weld on to the top end a .4 inch piece of stainless and mill out the slot. It came out really nice. I had purchased a 6 foot piece of stainless to make the brackets from scratch.

Once installed the mufflers do not move to the side as they heat up. They do move down though. Keep this in mind when adjusting yours.
On my '01 M coupe the inner tip on the drivers side sticks out about 1/16 inch more than the passenger side.
When I removed the exhaust for the differential install, I undid just the bottom rear muffler mounts. Left the top ones (which adjusts the up and down) as is. Once I had the exhaust out, I noticed scuffs on both exhaust pipes directly in line with the rear cross member (axle support).

Based on the scuffs, when I reinstalled the exhaust Monday evening I raised the center mounts full up and locked them in place. The drivers side came out the same. The passenger side was lower about 1/4 inch. Tips stayed level on each side. This tells me that the center mount on the drivers side was initially all the way up and the passenger side was not. To raise the passenger side back up to where it used to be, I will undo both pipes from the center pipes. I will then raise the muffler up using the top muffler adjustment points. To get it right, you may have to go back and forth a couple of times. Once set up, it will stay if you leave the center mounts in a known place (like all the way up) and just disconnect the mufflers at the lower section of the mounts.
what about a 3.46 on a '99?

The S52 engine in the 98/99 M coupes don't have quite the RPM range but I find that at the end of 3rd gear and into 4th the car really feels slow.

Would anyone like to give an opinion about the benefit (or lack there of) of putting it a 3.46 in a pre-01 M coupe?

after running a 14.33 in the 1.4 mile at the local track I am looking for ways to give the car a little more "umph"

3.46 in a pre '01 = 6.6% change

Sure. Forgot the rev limit on the pre '01's. With the Conforti software, second gear at the new redline would be 59.8 MPH.
After some regular and aggressive driving over the past 300km I have to say that the Metric Mechanic modified final drive is great!

Enough has been said about the gearing... the car pulls like a rocket in gears 1-4 and cruises nicely in 5th (not too high rpm).

If anyone is considering doing a 3.46 upgrade you can get gearing only done by Jim Rowe of metric mechanic for $1445 + shipping. This is an alternative to purchasing a 2nd complete final drive. The total prices are close and you can't go wrong either way. Of course, if you want to have the 3.15 as a "backup" then purchasing a 2nd assembly is the only option. However I understand they are not exactly plentiful in supply, plus here in Canada they list for CDN$4000.

Jim states that their failure rate of re/re final drive assemblies is 0% (i.e., no failures).

Realistically any good mechanic with access to a machine shop or machinist can swap gearing in a final drive, but the main problem is sourcing the parts. It's a hunt for a good set of matched r/p gears and it's almost guaranteed that some machining of bearings or shims will be required to get proper fitment... I've been through this twice now (Quaife in E39 540 and now the M Coupe gears).

Anyway, just wanted to give a thumbs up to

Cheers, Karl
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