[M2Blu]

Ok guys. I’m losing my mind and ready to dump the car off a cliff at this point. Been trying to resolve this issue for almost a year now and am not having any success. I’m tired of speculating and dumping money in to fix it. Long story short, I installed the revshift dual mount diff brace along with their track front and rear diff bushings and with their transmission bushings as well. Yes I know this adds NVH and vibrations, I have no issue with that. I’ve had stiff bushings on previous cars so I knew what to expect. However what I did not expect to get was this annoying persistent shaking between 2k and 3k rpm’s. Above or below that the car runs beautifully and feels wonderful. But unfortunately 90% of my driving is based in that 2-3k rpm range and as much as I would like to, I can’t drive full throttle everywhere.

Decided to take the car to 2 different bmw dealerships to have it looked at to make sure there’s no issues with the driveshaft as I did have to lower the subframe to install and both shops came back saying everything was installed perfect and that they could not see any issues. They claim that shaking is normal with stiffer bushings. Didn’t want to argue with them so I took the car and left.

Decided I’d start back where I started and try to figure it out myself. Reinspected everything from the subframe to the mount to the bushings and the flex disc. No visible deformities or other signs of damage. Figured swapping in softer transmission bushings would help alleviate some of the shaking so I went and replaced them. Cheap and easy enough to do so why not.

It improved the shaking ever so slightly but not enough to be a significant change. Ended up finding out about JXB and their driveshaft carrier upgrade. Figured since it was the only “stock” thing left on the driveline that it could be the weak link that’s amplifying the shakes I was feeling. Mind you these are no minor shakes. Imagine having bent wheels and driving at highway speeds over a cobblestone road. It can be felt throughout the entire car. Pedals, seats, steering wheel, floor, etc.

JXB part arrived, very impressive quality btw, and I went ahead and threw that on. Saw the greatest improvement with that. But still it was less than 10% better. Still foaming at the mouth from not being able to figure out what is causing it I made the decision to replace all of my diff bushings with the softest ones revshift has to offer. They claim them to be oem+ in terms of hardness. This meant redoing the entire diff job which was the furthest thing from fun.

I swear it’s worse. Maybe I’ve just gone completely mad and every little thing is setting me off but swapping in the softer bushings has taken away all of my fun race car noises and whines and left only vibration and shaking. However now instead of it being in the range of 2k to 3k rpm it is only between 2-2500rpm. That’s a plus right? Right? I’m going crazy here..plz help.

Anyways, all out of ideas now. I could revert it all back to stock but that’s not the solution I’m looking for. Afterall, there was a reason for me to upgrade my bushings. It wasn’t for nothing. All the reviews and people I’ve spoken to have all been positive and no one has had the issues with their kits as I have with mine. I could replace the flex disc but I don’t see it being a fix. No one seems to make an upgraded flex disc and I’m worried that it could make it worse. Does anyone have any suggestions or advice? Sell the car and get a Prius or roll it off the nearest cliff and just walk for the rest of my life?

I did just get my new wheels put on so that should put me at ease….as long as I don’t have to drive the car lol

Pictures are of the old green bushings that I replaced with the softer black bushings and the jxb carrier.

[Maynard]

Put it back to full stock. Fixed? if yes, then it's the bushings.
If no, then take it to dealer and if it is as bad as you described then they can find the reason (can't just punt it off to 'you changed bushings and this is normal') - I'm skeptical that they would have a good idea of what it should feel like, since dealerships probably don't see a lot of cars modded this way. I'm suspecting that if it isn't the bushings, you (or the new bushing setup) misaligned something in the process - pinion angle and total driveshaft deviation can be sensitive to even a degree or two of misalignment.
Failing all that, find a shop that does custom driveshafts and see if they can help; not that you need a custom job, but they'll likely know all the possible issues.

[M2Blu]

Originally Posted by Maynard

Put it back to full stock. Fixed? if yes, then it's the bushings.
If no, then take it to dealer and if it is as bad as you described then they can find the reason (can't just punt it off to 'you changed bushings and this is normal') - I'm skeptical that they would have a good idea of what it should feel like, since dealerships probably don't see a lot of cars modded this way. I'm suspecting that if it isn't the bushings, you (or the new bushing setup) misaligned something in the process - pinion angle and total driveshaft deviation can be sensitive to even a degree or two of misalignment.
Failing all that, find a shop that does custom driveshafts and see if they can help; not that you need a custom job, but they'll likely know all the possible issues.

Just went out to grab lunch and it’s getting unbearable to the point I don’t even want to drive the car. So this was my main concern from day 1. I know how delicate the balance of the driveshaft is which is why I avoided removing it when doing the job. After the vibrations started I was concerned that the driveshaft was out of whack. I ended up calling a few shops around here and unfortunately not one gave me hope. Most either didn’t work on BMW’s or were unfamiliar with doing this kind of work on a bmw. Unfortunately St. Louis is a joke when it comes to European performance shops. Even called a place that specializes in driveshafts and asked if they would be able to test mine to see if it is balanced and they claimed “yeah that’s not something we can do here”…..at a fucking driveshaft shop…

My guess is the actual diff mount brace is what is causing the issue. Maybe it’s defective or something as there was no difference in feel between the 95A durometer bushings and the 80A durometer bushings that I have on the car now. In fact the only difference was the noise which was never an issue for me personally. I loved it.

I hate the idea of going back to the stock diff mount. Main reason I upgraded was because mine were feeling loose and there was an excessive amount of clunking from the rear. Not to mention how strange it is for such a high performance car to have a single mount instead of dual but the bmw engineers must have done it that way for a reason. Will most likely keep my front diff bushings and just revert the rear to stock and try that. After all this isn’t costing me anything but my time.

My only gripe is that it happens at such a specific rpm. Regardless of speed and load on the engine.

I do have to say though that with the softer bushings in currently, that it has pinpointed the shaking to be coming from the rear of the vehicle. On deceleration it is the most noticeable

[Brandt51]

I’d go back to stock and verify it’s ok. Too many variables right now it seems. That’s a tough pill to swallow I bet. I wouldn’t expect there to be issues either with just fancy mounts. But if you go back to stock, and start installing those hard core mounts in one area at a time, you’ll prob have a good chance of sorting it out. That’s more of a niche race car thing and not a lot of testing with it perhaps.

Good luck, I’m very curious to see what happens with it. Don’t give up!

[Telluride]

Sorry to hear and feel your frustration... through the roof, right?! Considering all the hours and work you have put into this, bah!

Wish I had further insight but letting you know I had a KMP rear diff bracket and bushings, installed at a BMW specialty tuner shop in my area. Like you, I wanted to clean up the bad habits of the rear end, especially the occasional but dreaded wheel hop. Outside of a ssk, all my other mounts/bushings/drive shaft carrier, etc. remain stock.

I have zero driveline shake you describe and actually minimal NVH added, other than 'gear whine'. The lack of material NVH being introduced was a pleasant surprise. My gear whine really starts kicking in at 60mph and increases in volume with additional speed. 85mph+ it's a glorious sound and very pronounced within the cabin.

You are not crazy! And I agree the rear diff really improves the handling and planted feel of the rear end while under power/load. Good luck with your identifying and solving issue.

[M2Blu]

Originally Posted by Brandt51

I’d go back to stock and verify it’s ok. Too many variables right now it seems. That’s a tough pill to swallow I bet. I wouldn’t expect there to be issues either with just fancy mounts. But if you go back to stock, and start installing those hard core mounts in one area at a time, you’ll prob have a good chance of sorting it out. That’s more of a niche race car thing and not a lot of testing with it perhaps.

Good luck, I’m very curious to see what happens with it. Don’t give up!

You’re probably right. We are definitely a niche within a niche when it comes to these cars. I’m just dreading doing the job for a third time lol especially since I’d be crawling on my back once again. I think before I do that I’m going to call my buddy at bmw and see if I can pick one of their master techs brains for a few minutes and see if they have any tips. Maybe the driveshaft is slightly out of balance and is causing this. I could have damaged the flex disc or the U-joints somehow when I first did the job or when I was putting the SSK in. Who knows, my fear is that even with the stock parts back on that it will still shake then I’ll be forced to dump the car lol I’ll probably tackle this job next weekend and update here if it gets fixed

[M2Blu]

Originally Posted by Telluride

Sorry to hear and feel your frustration... through the roof, right?! Considering all the hours and work you have put into this, bah!

Wish I had further insight but letting you know I had a KMP rear diff bracket and bushings, installed at a BMW specialty tuner shop in my area. Like you, I wanted to clean up the bad habits of the rear end, especially the occasional but dreaded wheel hop. Outside of a ssk, all my other mounts/bushings/drive shaft carrier, etc. remain stock.

I have zero driveline shake you describe and actually minimal NVH added, other than 'gear whine'. The lack of material NVH being introduced was a pleasant surprise. My gear whine really starts kicking in at 60mph and increases in volume with additional speed. 85mph+ it's a glorious sound and very pronounced within the cabin.

You are not crazy! And I agree the rear diff really improves the handling and planted feel of the rear end while under power/load. Good luck with your identifying and solving issue.

Absolutely, the difference in how the car felt was just night and day! And man I miss those sounds lol these softer bushings are way too quiet for me