help diagnose driveline noises after diff install

**rs4eva** · 05-19-2018, 06:26 PM

I need some forum wisdom.

I purchased a rebuilt 3.64 diff and experienced noises right away. A clang when shifting gears or going over a bump. I only really noticed at lower speeds but assume it was there at higher ones as well.

I drove a few miles to try and figure out the source of the noise, and then it started vibrating really bad in the steering wheel and generally felt throughout the car. Again all low speed/RPMs.

I put got under the car to check things out and found if I twisted the drive shaft I could easily reproduce the clang noise. It was coming from the u-joint and CSB area. If I spin the rear wheels back and forth there is a good amount of play. The CSB was also making a terrible squeaking noise.

https://youtu.be/4l8KP44uR9Y

Take the driveshaft out to test the diff flange. It does have some play in it. I don't know if this is normal or not.

https://youtu.be/qdLV134bZxE

Here is the original diff for comparison

https://youtu.be/8vMwGR1PESY

The CSB looks to be intact although there is a little bit of cracking but no tears. And the metal flange is distorted and squeaks like hell.

The u-joints have a very slight wiggle to them

https://youtu.be/iq4TGdJ0YnI

https://youtu.be/5bcQFClvOcM

--------------------------------- Update 5/20 ---------------------------------------

I removed the diff today and while it was out of the car I checked the input flange again. Zero play. Only components left are the axles. Weird that neither the noise or the vibration where there before I replaced the diff.

My rear subframe bushings are deteriorated around the perimeter. The insides look ok and I don't feel any significant movement in them.

IMG_0576.jpg IMG_0578.jpg IMG_0584.jpg IMG_0583.jpg

--------------------------------- Update 5/21 SOLVED ---------------------------------------

I was puzzled as to how the diff exhibited play when the driveshaft was attached, so I attached it to the original diff. No play.

Now when I connected it to the new diff. Ding! ding! We have a winner. The flange bolt holes are slightly larger than the driveshaft bolts causing them to slide back and forth even when tight.

Things I've ruled out:

Front and rear Diff bolts are tight
Guibo is in good shape
Old diff didn't have vibrations or noise

**bluptgm3** · 05-19-2018, 07:24 PM

Did you separate the drive shaft halves replacing the differential?
Realign the two half’s on re-installation?
Ideally, slop in the drive shaft and differential should not be overly significant.

Sent from my iPhone using Tapatalk

**TostitoBandito** · 05-19-2018, 08:40 PM

+1 on making sure your drive shaft is aligned exactly in the same bolt holes as it was before. If you don't know, unbolt, rotate it 90 degrees and rebolt it, then test it. Repeat up to two times until it either fixes it or you've tried every combination.

Other than that, if you only changed the diff and not anything else, then it has to be the diff. Perhaps the flange or crush collar are messed up.

**rs4eva** · 05-20-2018, 08:02 AM

Originally Posted by TostitoBandito

+1 on making sure your drive shaft is aligned exactly in the same bolt holes as it was before. If you don't know, unbolt, rotate it 90 degrees and rebolt it, then test it. Repeat up to two times until it either fixes it or you've tried every combination.

Other than that, if you only changed the diff and not anything else, then it has to be the diff. Perhaps the flange or crush collar are messed up.

Thanks for the suggestions

I didn't separate the driveshaft, just r/r the diff.

@Tostito Are you saying that the bolts where it attaches to the diff flange need to be in a certain order?

**TostitoBandito** · 05-20-2018, 12:22 PM

No I'm saying that the driveshaft is balanced and is in theory only supposed to go onto the diff flange only a certain way. If for example you needed to disconnect the shaft from your diff for whatever reason you're supposed to mark where the drive shaft and diff flange lined up so you can put them back together the same way (with the same two sides facing each other). With an entirely new diff this is obviously impossible, but it could just be on there in a way that the drive shaft doesn't like. What I suggested is to spin the drive shaft so that it lines up differently with the diff flange and then try. The drive shaft and flange are a square, so I think there's four different orientations in which you could attach them. Sometimes one or two might be ok and one or two might be bad.

That said, I'm skeptical that this is your issue. Sounds more like the flange coming off the diff is crooked or damaged or something like that. If you didn't touch the rest of the drive shaft there's no way it should be an issue. Who built your diff?

**rs4eva** · 05-20-2018, 12:59 PM

Originally Posted by TostitoBandito

No I'm saying that the driveshaft is balanced and is in theory only supposed to go onto the diff flange only a certain way. If for example you needed to disconnect the shaft from your diff for whatever reason you're supposed to mark where the drive shaft and diff flange lined up so you can put them back together the same way (with the same two sides facing each other). With an entirely new diff this is obviously impossible, but it could just be on there in a way that the drive shaft doesn't like. What I suggested is to spin the drive shaft so that it lines up differently with the diff flange and then try. The drive shaft and flange are a square, so I think there's four different orientations in which you could attach them. Sometimes one or two might be ok and one or two might be bad.

That said, I'm skeptical that this is your issue. Sounds more like the flange coming off the diff is crooked or damaged or something like that. If you didn't touch the rest of the drive shaft there's no way it should be an issue. Who built your diff?

Ok, I understand what you are saying now. I bought the diff from a seller on ebay.

I removed it today with the intention of sending it back to him. After I had it out I decided to rotate the flange to see if there was still play. There was zero. So now I am leaning to one or both axles being the source of the vibration and play.

**ArcticM** · 05-20-2018, 02:09 PM

Replace your driveshaft. Any play in the ujoints and any cracking in the csb your asking to be under there again in the next year to replace it. Buy a rebuilt one message me for a great source for one that I recently dealt with.

Also know(which I didn’t until recently..) that any time you work on anything connect to that driveshaft you should resize it for proper figment meaning when you get it in place loosen the lock nut and make it sit flush on the guibo and diff flange.

**rs4eva** · 05-22-2018, 07:49 AM

--------------------------------- Update 5/21 SOLVED ---------------------------------------

I was puzzled as to how the diff exhibited play when the driveshaft was attached, so I attached it to the original diff. No play.

When I connected it to the new diff. Ding! ding! We have a winner. The flange bolt holes are slightly larger than the driveshaft bolts causing them to slide back and forth even when tight.

**TostitoBandito** · 05-22-2018, 09:52 AM

Nice, so it looks like the wrong flange is on there. At least now you know.

I think the flange on my diff isn't round, but is more square with scalloped sides. I'm not sure if all 96-99 M3 diffs are like this or not.

**rs4eva** · 05-22-2018, 10:07 AM

Well one other detail I remembered.

With the driveshaft off and rotating the rear wheels, There was some play back and forth. Is that normal?

**TostitoBandito** · 05-22-2018, 11:29 AM

Originally Posted by rs4eva

Well one other detail I remembered.

With the driveshaft off and rotating the rear wheels, There was some play back and forth. Is that normal?

Yes, if you grab a rear wheel and spin it with the drive shaft detached (or just with the car in neutral) it's normal for there to be a little play in the diff as you start to spin the wheels back and forth. Once it's moving it should be smooth, but the first engagement in either direction has a little play until everything is engaged.

**rs4eva** · 05-22-2018, 02:48 PM

That is what I thought but wasn't sure. Now the million dollar question, why are the holes bigger?

**NotUrAvgM** · 05-28-2018, 10:10 AM

Originally Posted by rs4eva

That is what I thought but wasn't sure. Now the million dollar question, why are the holes bigger?

Holes are always oversize to some degree. If the flange bolts were sliding back and forth when tight, I guarantee they weren't tight.

Also, if your ujoint is shot you need to find a shop that is capable of replacing it, or find used driveshaft. No sense in bolting it back together with a known issue.

**rs4eva** · 05-31-2018, 02:48 PM

Okay, still working on this problem.

Now I can get the differential to exhibit some play. Is this a normal amount for a 3.64 with 40% lockup?

**tjm3** · 05-31-2018, 03:12 PM

Was it originally a 3.64 or were the ring and pinion changed?

**rs4eva** · 05-31-2018, 03:20 PM

I think it was changed, or at least rebuilt.

**tjm3** · 05-31-2018, 04:18 PM

There's a big difference. Not that this is the problem here, but a change of ring and pinion requires the pinion depth to be reset properly and becomes the basis for most of the other clearances. Who knows what a rebuild is.