LSD off of an automatic

[hickatew]

I'm considering buying a used LSD off of an automatic ZHP. I don't see why it would make a difference that it's automatic but looking at the listing for the MFactory LSDs (https://www.ecstuning.com/News/BMW_E...004_2005_2006/), they differentiate between auto and manual transmission. My ZHP is manual, will it work?

[slater]

it should work - just confirm that the diff has a 6-bolt input flange.

[Sockethead]

The axle flanges are different than the manual but they can be swapped

[hickatew]

The axle flanges are different than the manual but they can be swapped

That for sure? I found this too https://www.bimmerforums.com/forum/s...ft-Differences

[Reasoned1]

I assume that's a 3.64--I just ordered one from M-Factory... REALLY looking forward to installing and driving it. I'm no expert but, in all my research (which has been extensive, to say the least), I never encountered any cautions about manual versus automatic--quite the contrary, in fact. They get mixed and matched all the time. The most important consideration, as slater mentioned , is the flange type (input and output, but input is what really matters since the output flanges can be easily swapped with your current ones). Of course, we're talking about RWD vehicles only here... otherwise, there are other, extremely important considerations.

[Sockethead]

The LSD diff I got from Diffs online had automatic flanges... different bolt pattern. You can pop them out with a pry bar and swap your manual flanges... that's what I did. The Pinion flange needs a little more work since it should be pre-loaded. Mine already had the 6 bolt pinion flange on it.

I believe it's the non ZHPs that have the 4 bolt pinion flange but I'm not entirely sure...

[slater]

The LSD diff I got from Diffs online had automatic flanges... different bolt pattern. You can pop them out with a pry bar and swap your manual flanges... that's what I did. The Pinion flange needs a little more work since it should be pre-loaded. Mine already had the 6 bolt pinion flange on it.

I believe it's the non ZHPs that have the 4 bolt pinion flange but I'm not entirely sure...

basically all 5-speed E46s got the 4-bolt flange... we didn't see the 6-bolt until 3/03 when the 6-speed 330's because available.

and yes, the axle flanges are easy to swap. my MFactory diff also came with 5-speed axle flanges (and a 4-bolt input flange... not a welcome surprise... but it wasn't their fault).

[hickatew]

Great info, thanks all!

Sent from my LG-H918 using Tapatalk

[cornercarver]

A 3.64 ratio is going to make 1st gear almost useless, but should make 2-5 a lot more fun.

edit; BTW hickatew - is this the diff you asked about in GDMChRiZ's classified thread? How do you know it's an LSD?

[Reasoned1]

Torque and speed are proportional to gearing. So, since 3.64 is 7.7% greater than 3.38, redline speed in any gear will be 7.7% lower for 3.64 than for 3.38. Thus, if I currently redline in 1st at 35mph with my 3.38, I divide 35mph by 1.077 to figure out I’ll redline at 32.5mph in 1st with the 3.64. The difference, while significant, isn’t dramatic and won’t make 1st gear useless, in my opinion. My biggest concern in going with 3.64 is excessive rpm at highway cruising speed, but the calculations show I’ll still be under 3,400rpm which, for me, is tolerable (especially since this car doesn’t see much Interstate) and is worth the benefits.

Another tantalizing calculation is that, assuming my modified car is making 225lb-ft of peak torque at the flywheel, the torque multiplying effect of the shorter, 3.64 gear ratio will make the wheels see a torque 18.5% greater than that seen with the stock, 3.07 gear box—as if the engine were generating a peak torque of 267lb-ft! That’s why changing the final drive ratio is known as a “poor man’s supercharger”.

Of course, there are trade-offs—the big one being reduced top speed, but the calculations also show the 3.64 still has a theoretical top speed in excess of 160mph which is both impractically fast and getting to the point where drag makes going faster impossible for available power anyway. Another possible trade-off, for some people but not me, is that the shorter gearing makes it necessary to shift sooner and changes the position of shift points relative to speed.