Powerflex purple diff bushes - replace rear only?

[///Mobbin]

Does anyone know if it's possible to install the diff bushings without dropping the rear subframe?

[tlrid3r]

Originally Posted by ///Mobbin

Does anyone know if it's possible to install the diff bushings without dropping the rear subframe?

You don't have to drop the subframe but you do need to drop the diff

[wyatth]

Aluminum subframe and PF purple diff seem like the way to go to still. Curious, anybody try what the OP suggested - single rear PF bushing, stock 2 front rubbers? Looks like the guy above tried the opposite and still had whine.

[94jedi]

Originally Posted by wyatth

Aluminum subframe and PF purple diff seem like the way to go to still. Curious, anybody try what the OP suggested - single rear PF bushing, stock 2 front rubbers? Looks like the guy above tried the opposite and still had whine.

based on searching through all the threads, yes, this seems like the way to go for DCT cars but what about 6spd?

My car is making the dreaded diff "ping" so my shop is going to apply the TSB recommendation and pull/regrease the pinion. Figured it's worth throwing some subframe and diff bushings in there while the diff has been dropped.

Any ideas for 6spd cars?

[pbonsalb]

The shop may just pull the driveshaft for that job.

[wyatth]

I see no reason to deviate from aluminum subframe and purple diff for a 6MT. It's DCT where there is still some whine.

[Bartledoo]

Originally Posted by wyatth

I see no reason to deviate from aluminum subframe and purple diff for a 6MT. It's DCT where there is still some whine.

There is definitely whine with 6MT as well.

[strokemycocktus]

Originally Posted by ksteckba

There is definitely whine with 6MT as well.

Is the whine present all the time or just at certain speed? My 6MT on stock bushings has a silent but definitely audible whine at 70-80 km/h.
A short video with this setup would be much appreciated by many of us here

[Bartledoo]

Originally Posted by strokemycocktus

Is the whine present all the time or just at certain speed? My 6MT on stock bushings has a silent but definitely audible whine at 70-80 km/h.
A short video with this setup would be much appreciated by many of us here

Around 40 and 72mph (indicated speed rather than actual) it is quite loud imo. At other speeds the diff sound (including some added whirring) is still more prevalent than stock. I have test pipes and Corsa exhaust also, and I still hear it. Overall it was necessary and the feel is much improved, but the extra noise is definitely a drawback.

[pbonsalb]

I used harder 95A black and have faint whine that I can notice only in a limited rpm range — around 60-65 in 6th if I recall but I would have to check again to pinpoint it since I don’t really pay any attention to it anymore. If you have a modified exhaust the extra noise will mask some of the whine and if you have a convertible the extra sound deadening will mask some whine.

[strokemycocktus]

Do you have solid subframe bushings? I assume it would transmit more noise, and if I recall correctly ksteckba has these.
From my understanding subframe bushings give more improvement with no drawback, so I would definitely like to change them for solid. If then any poly diff bushing results in notably more whine noise in cruising speeds (100km/h and above) I would probably pass on that.

[pbonsalb]

I have 75D poly subframe bushings, which is similar to delrin. Subframe bushings make the most difference in feel. I changed the diff bushings because a few people have experienced failure that broke their finned diff cover and bent their subframe. This is why defi made a diff support brace years ago. In contrast, I have not read of any subframe failures from having stock subframe bushings. I did both “upgrades.”

[EricSMG]

Originally Posted by wyatth

Aluminum subframe and PF purple diff seem like the way to go to still. Curious, anybody try what the OP suggested - single rear PF bushing, stock 2 front rubbers? Looks like the guy above tried the opposite and still had whine.

You know that I'm not a huge mod guy but honestly, the rear end of this car is so planted in stock form I struggle to see the desire to stiffen things more at the risk of noise/clunks.

Seriously - I can't feel any lateral play in the rear end at all and only the slightest amount of diff 'rock' under heavy on/off load. The car also tracks perfectly straight under load over single wheel bumps, so there is little/no toe change happening in that scenario which means ultra stable rear end. BMW really did their homework on these rear suspensions.

The 46M is much less stable in stock form and that's saying something as it's a damn stable car. The E9XM is much tighter.

[pbonsalb]

I am not a track guy and could immediately feel the difference in how much more stable the rear was in hard driving on turns. There is noticeably less movement side to side.

[EricSMG]

Originally Posted by pbonsalb

I am not a track guy and could immediately feel the difference in how much more stable the rear was in hard driving on turns. There is noticeably less movement side to side.

Surely, no question.

My question is more - did you find the stock setup lacking in lateral control? Did it 'improve' something that wasn't an issue in the first place?

[Bartledoo]

Originally Posted by EricSMG

Surely, no question.

My question is more - did you find the stock setup lacking in lateral control? Did it 'improve' something that wasn't an issue in the first place?

It improved/reduced my car's tendency to snap diff bolts , and I agree it feels much better. It's hard to miss what you haven't experienced in this case, though.

[Shredicus]

I have had AKG 95A diff and solid aluminum subframe bushings for around 5k miles now and still don't much mind the whine at all. There are certain speeds and scenarios when its more audible but its pitch/tone is really not that obtrusive. More of a "whirr" that changes directions than a whine imo.

And yes the improved rear end stability is noticeable, especially during hard acceleration and cornering.

[SYT_Shadow]

I now have alu subframe bushings and powerflex purple diff bushings

It definitely and clearly whines on the road. If this were a DD I'd be seriously pissed

[strokemycocktus]

Meh, I will just do the subframe bushings and leave the diff stock. Car is my daily, I do about 50/50 city and highway, so it would probably piss me off. With about 2 trackdays a year I think I'm more than good with this setup.
I don't really complain about rear end grip, but would love to eliminate wheel hop.

[Shredicus]

Originally Posted by SYT_Shadow

I now have alu subframe bushings and powerflex purple diff bushings

It definitely and clearly whines on the road. If this were a DD I'd be seriously pissed

Interesting. I wonder if it's just perception or if other factors are at play namely diff clutch wear and fluid type. As an extra data point I have a pretty fresh fill of bmw fm+ fluid

[SYT_Shadow]

Originally Posted by Shredicus

Interesting. I wonder if it's just perception or if other factors are at play namely diff clutch wear and fluid type. As an extra data point I have a pretty fresh fill of bmw fm+ fluid

sometimes drone is relatively personal. I noticed the diff whine immediately. It isn't incredibly loud, but I can notice it

[pbonsalb]

Originally Posted by EricSMG

Surely, no question.

My question is more - did you find the stock setup lacking in lateral control? Did it 'improve' something that wasn't an issue in the first place?

No, the car handles pretty well stock. But I could feel the rear wiggle and it does not anymore. I assumed all that benefit is from the subframe bushings, rather than the diff bushings.

I changed diff bushings only to avoid breaking the diff cover and then possibly damaging the subframe. It’s happened to a few people. I think the stiffer diff bushings are what adds whine. You could try adding a damper to the subframe. Or not go solid on the subframe. I don’t complain about the minor whine I hear sometimes, but I went red poly on the SF and black poly on the diff. I have an E36 M3 with terrible diff whine that bothers me but I had no choice on that car due to the power.