Subframe and differential bushings

[M3 Number 86]

Originally Posted by whats77inaname

Drive one that has been upgraded for comparison, and I assure you, you won't have these questions.

I don't need to even need to question these points is my point. The car works perfectly fine at the limit I can assure you that as well. If the stock parts work better than your driving abilities, what's the point? I don't mean to be harsh but it's just ridiculous. You get no benefit except now you have to maintain your car even more (if you actually drive it hard enough to now stress other parts of the car).

[whats77inaname]

Originally Posted by M3 Number 86

I don't need to even need to question these points is my point. The car works perfectly fine at the limit I can assure you that as well. If the stock parts work better than your driving abilities, what's the point? I don't mean to be harsh but it's just ridiculous. You get no benefit except now you have to maintain your car even more (if you actually drive it hard enough to now stress other parts of the car).

Actually, the stock parts *don't* work better than my driving ability, and I don't have to maintain the car even more. Quite the contrary, tbhwy. The primary reason for replacing the diff bushings is that the STOCK FOAM (that's right, FOAM!) bushing FAIL. You might want to check around the forum and view some of the threads about that, as people with diff bushing failures sometimes end up losing the diff as well, and BMW won't cover it. Simple solution? Delrin bushings. Now I have peace of mind as a result of this mod, as well as the knowledge that I've replaced a wear item with one that doesn't wear.

Regarding the subframe bushings, the F8x subframe bushing are aluminum as opposed to rubber. Do you think that BMW would have made that switch if it would stress other parts on the car? Methinks not. Prior to the subframe upgrade, when I planted my right foot, my rear end was not compliant and would move around quite a bit. This has nothing to do with my driving ability, as this would occur in a straight line. Afterwards, that was diminished greatly. Again, nothing to do w/my driving skill, but everything to do with the parts on the car.

I upgraded one to minimize having to replace damaged parts. I upgraded another as a precursor to handle more power (I eventually plan to introduce f/i). To me, it's a win-win.

[JEllis]

Originally Posted by M3 Number 86

I don't need to even need to question these points is my point. The car works perfectly fine at the limit I can assure you that as well. If the stock parts work better than your driving abilities, what's the point? I don't mean to be harsh but it's just ridiculous. You get no benefit except now you have to maintain your car even more (if you actually drive it hard enough to now stress other parts of the car).

As has been stated, BMW has moved to full solid subframes on all modern M cars. Prior to the current batch of M cars, BMW supplied all solid subframes on the M3 GTS.

There are multiple reasons. From a structural point of view, when the rubber bushing fails from age or hard use, the subframe bolt will start wiggling around under load. After a while this will cause tears in the unibody (see E46, E36 horror stories). The rear diff main bushing is actually not rubber but soft foam. My guess is to reduce diff noise as much as possible. The foam fails quite quickly especially with harder use in 6MT cars. The rear main diff bolt will lose stability from the degraded foam and start moving around, hollowing out the bushing. This causes Diff knock and eventual failure of the bolt itself which can cause a lot of other damage to the driveline.

[squartus]

Originally Posted by M3 Number 86

I don't need to even need to question these points is my point. The car works perfectly fine at the limit I can assure you that as well. If the stock parts work better than your driving abilities, what's the point? I don't mean to be harsh but it's just ridiculous. You get no benefit except now you have to maintain your car even more (if you actually drive it hard enough to now stress other parts of the car).

Because the stock mounts are garbage, tons of slop also causes wheel hop and in many cases snapped rear diff bolts from the excessive movement.


Then your diff is sitting on your exhaust, some people had some pretty terrible things happen when it let go.


After putting in solid rear diff mounts... Its night and day difference in how the car behaves under agressive driving

[pbonsalb]

I am worried about the diff damage. That is why I plan to change at least my diff bushings and I am inclined to go ahead and do the subframe as well. I would like to be able to run at the dragstrip without concern, and manual trans cars are very hard on the drivetrain.

[squartus]

Originally Posted by pbonsalb

I am worried about the diff damage. That is why I plan to change at least my diff bushings and I am inclined to go ahead and do the subframe as well. I would like to be able to run at the dragstrip without concern, and manual trans cars are very hard on the drivetrain.

Yea I snapped mine in the pic above on the street running 265s in the rear N/A.
Now running sticky 315's in the rear supercharged after rear diff mount change shes rock steady, the bolt that snapped mount also had to be reshaped since it was more egg shaped from all the slop.

[M3 Number 86]

I understand the mega horsepower and hard launching guys with sticky tires as that would be some hardcore abuse and damage is probably around the corner.

But, there are one off's to everything - that doesn't make it necessary does it? Regarding F8x, everything else has been re-engineered to compensate the solid bushings don't you think? In that case, we should swap to turbo engines because of known rod bearing issues.

And on top of all this, from a guy who installed a bbk upside down and straight up said it was correct - I'm sorry did air move down? The same guy who posted a picture of him in "opposite lock" and got called out for lying? From a guy claiming -2.5 camber was optimal for track usage because of pyrometer testing he did when everyone was saying otherwise (who btw doesn't believe in 2.5 anymore)?

[squartus]

I wouldn't say its something you HAVE to get done, but it is a week point in the rear and if something is going to let go it will because of the very squishy bushings.
Many options for it, you dont have to go solid. The purple bushings work as well and are still a huge upgrade over OEM. If your not really thrashing the car it could be something you just have done when you need to have some rear diff work done or something so you can just lump it together and wont cost much in time or money.

[JEllis]

Originally Posted by M3 Number 86

I understand the mega horsepower and hard launching guys with sticky tires as that would be some hardcore abuse and damage is probably around the corner.

But, there are one off's to everything - that doesn't make it necessary does it? Regarding F8x, everything else has been re-engineered to compensate the solid bushings don't you think? In that case, we should swap to turbo engines because of known rod bearing issues.

And on top of all this, from a guy who installed a bbk upside down and straight up said it was correct - I'm sorry did air move down? The same guy who posted a picture of him in "opposite lock" and got called out for lying? From a guy claiming -2.5 camber was optimal for track usage because of pyrometer testing he did when everyone was saying otherwise (who btw doesn't believe in 2.5 anymore)?

No you don't have to do it.

The E92 M3 GTS also had solid mounting points from BMW.

The best way to think about it, if you haven't seen the mounting points, is a long 5-6" bolt that is holding the subframe to the car at four points. There is about 4" of bolt that is stabilized only by the subframe bushing. The OE bushings are made of rubber, as you know, and the bolt itself is torqued onto the bushing.

Solid and Delrin bushings are offered by Turner Motorsport, EAS, MRF, Motorsport24 ect.... the benefits of them have been realized by many manufacturers and motorsport teams to include BMW.

[kerrit]

did anyone hear back from malek on his custom solution to the diff whine?

[pbonsalb]

I think he tried a stock BMW differential sound absorption device from another model subframe. The E36 328i, for example has a stub on the subframe that looks like another bushing going sideways, but the E36 M3 subframe does not have this. However, both subframes have the threaded boss to mount it. The one that fits the E90 M3 may be from a 1M.

Might help a little but won't make solid bushings as quiet as stock.

Supposedly the stock rear bushing is more foam like than rubber. Just replacing this bushing with an aftermarket like a 95A poly one might be enough to stabilize the diff for those who are primarily interested in avoiding diff damage.

Maybe solid or delrin or 75D poly subframe bushings would be best matched with 95A diff bushings for street cars. I hope to get to this project later this year, so I am reading all the feedback. A really loud exhaust would help cover some of the whine, but I don't have one.

I am curious what seems to make DCT cars whine more noticeably than 6MT cars. The only thing I can think of is that the DCT cars spend more time in a whiney rpm range due to their different gearing.

[kerrit]

Thanks. I'll probably be doing the 95A diff bushings and solid subframe.

Wheel hop comes on fast with the blower on my car and it makes me worry about the rear diff bolts snapping.

The rear end also sways side to side at higher speeds when I'm doing a pull.

Those are the only real problems I'd like to fix. Since it's my only car I don't really want to increase NVH.

[Longboarder]

Originally Posted by pbonsalb

I think he tried a stock BMW differential sound absorption device from another model subframe. The E36 328i, for example has a stub on the subframe that looks like another bushing going sideways, but the E36 M3 subframe does not have this. However, both subframes have the threaded boss to mount it. The one that fits the E90 M3 may be from a 1M.

Might help a little but won't make solid bushings as quiet as stock.

Supposedly the stock rear bushing is more foam like than rubber. Just replacing this bushing with an aftermarket like a 95A poly one might be enough to stabilize the diff for those who are primarily interested in avoiding diff damage.

Maybe solid or delrin or 75D poly subframe bushings would be best matched with 95A diff bushings for street cars. I hope to get to this project later this year, so I am reading all the feedback. A really loud exhaust would help cover some of the whine, but I don't have one.

I am curious what seems to make DCT cars whine more noticeably than 6MT cars. The only thing I can think of is that the DCT cars spend more time in a whiney rpm range due to their different gearing.

I'm getting a very subtle "clunk" during acceleration and going in this week for subframe and diff bushings. I'm going with the poly diff with the added 1M rubber bracket in an attempt fully diffuse the feedback since I'm DCT. Goal is zero additional NVH from stock.

It will for sure help with launching this sucker as I've never really bothered much with all the power. Looking forward to it after the fix and with a new set of PSS in the rear. Will do some 0-60's to see what's it's capable of in street form.

[kerrit]

Originally Posted by Longboarder

I'm getting a very subtle "clunk" during acceleration and going in this week for subframe and diff bushings. I'm going with the poly diff with the added 1M rubber bracket in an attempt fully diffuse the feedback since I'm DCT. Goal is zero additional NVH from stock.

It will for sure help with launching this sucker as I've never really bothered much with all the power. Looking forward to it after the fix and with a new set of PSS in the rear. Will do some 0-60's to see what's it's capable of in street form.

Please post review!

Also - have you gotten your ACM icebox solution yet installed for your blower? I wanted to hear about that install as well.

[Longboarder]

Originally Posted by kerrit

Please post review!

Also - have you gotten your ACM icebox solution yet installed for your blower? I wanted to hear about that install as well.

Of course will do.

I ordered the Powerhaus Performance 5 gallon water tank and hopefully it arrives while my car is at MRF getting the bushings so it can all be done at the same time. Also doing rod bearings and some other TLC while it's in. Car will be ready to race again

[pbonsalb]

Originally Posted by Longboarder

I'm getting a very subtle "clunk" during acceleration and going in this week for subframe and diff bushings. I'm going with the poly diff with the added 1M rubber bracket in an attempt fully diffuse the feedback since I'm DCT. Goal is zero additional NVH from stock.

It will for sure help with launching this sucker as I've never really bothered much with all the power. Looking forward to it after the fix and with a new set of PSS in the rear. Will do some 0-60's to see what's it's capable of in street form.

On some late models, not sure whether the E9xM3 is included, BMW noticed a clunk problem and has a recommended fix.

[Longboarder]

Originally Posted by pbonsalb

On some late models, not sure whether the E9xM3 is included, BMW noticed a clunk problem and has a recommended fix.

I've just started noticing this clunk 32,000 miles in. But that's not the sole reason I was going to do the upgrade. I was doing it anyway, and then two weeks ago I started feeling the clunk.

Curious what is BMWs recommended fix?

[pbonsalb]

Read the PDF that I attached to my post. Basically, remove and reinstall the diff input flange and lubricate the splines. BMW says it is not an internal diff problem. It is possible this does not apply to the M differential, or that M diffs suffer different problems.

[Longboarder]

Originally Posted by pbonsalb

Read the PDF that I attached to my post. Basically, remove and reinstall the diff input flange and lubricate the splines. BMW says it is not an internal diff problem. It is possible this does not apply to the M differential, or that M diffs suffer different problems.

Ok thanks. I actually tried to replicate the clunk but couldnt' this morning. It was in my head. Or my ass

[Exclusivs]

Originally Posted by DrFerry

Well, the new diff and driveshaft have now been installed. I also returned to the oem diff bushings, but I kept the solid subframe bushings. The diff whine noise and M-clunk have now both gone. The car drives as quietly as the day it was new.

The 3:45 ring and pinion gear ratio makes the car feel quicker off the line, with an increased sense of urgency, but I am still breaking the new diff and Quaife LSD in for the next 1200 miles or so. My initial impressions are that the car feels more responsive, especially in the lower gears.

When the time comes (>= 1200miles) when I can get on the gas hard and go WOT I'll report back.

See my earlier posts and videos on this thread for more background if needed.

Glad things worked out and another confirmation majority of noise is generated by diff bushings.

[ONE_slow_m5]

Originally Posted by Lucrecio84

I have an appointment on Monday to drop my car off at MRF to get the differential and subframe bushings done. Does anyone have these switched out yet? Thoughts?

Update: Picked up my car yesterday from MRF. Ended up doing diff and subframe bushings. All I can say is it was totally worth it. Car responds and just feels noticeably better. Taking corners and acceleration are a huge difference. The whine is definitely there but something I think I'll get used to. With the windows down or music on, it can't be heard. I want to thank Malek for the work, he did an amazing job. Not only is he extremely knowledgable but I loved how neat and clean his shop is. Will definitely use his services in the future! Anyone contemplating this modification should definitely get on this, you will not be disappointed!

care to share part numbers or links? I am thinking of doing this before some upcoming track days.

[Lucrecio84]

Originally Posted by Blown__m3

care to share part numbers or links? I am thinking of doing this before some upcoming track days.

Don't have any links or part numbers, but I know the differential bushings are made by Derlin, and subframe ones are by turner motorsports.