Driveshaft vibration starting @ ~75mph (long post)

[muppetman342]

Adding my experience here as well, as I'm still chasing vibrations in my car: even "reputable" driveshaft rebuilders were selling me driveshafts that vibrated worse than my worn out original. I think I went through three different sellers back in 2019-2020?

I ended up going with an expensive OE driveshaft, which seems to have largely solved my issues, or at least gotten me to the point where I think my problem is wheel-related.

[twright]

Great! Thanks for the followup.

It just goes to show how really small things can make a difference. (And harder to find when youi have a problem.)

[84svoracer]

Hey all, so I spoke with the shop Monday morning and they were totally cool about it and agreed there should not be any play and told me to bring the driveshaft over and they would take care of it. So this afternoon I was able to stop by, they re-staked the axis of the u joint with play and re-balanced the driveshaft. I installed it tonight and it's fixed! The car drives perfect with no vibrations or anything, such a great feeling to not have to continually check all those things and having a BMW capable of more than highway speeds haha.

Maybe I just had very bad luck with the first few driveshafts? I didn't actually really change much of anything or how I installed any of them. Oh well

Anyway, thanks to all on here for your help and insight on this.

-Cheers

[84svoracer]

econti I totally agree, I am not. And yes, that is the procedure I follow when installing the driveshaft. Now given the play in the driveshaft I have my fingers crossed that this was causing the issue.

twright I will try to check the wheel runout too, as I could see it being a potential contributor to things. Will check before putting it back together next round. But It will probably be a couple weeks for me getting the tires, planning on visiting family in the midwest in early to mid October first.

[84svoracer]

So I was putting the car back together and noticed I have almost .020" of play on one of the planes the rear u joint to the diff! The other plane on the cap 90degrees is fine with only a few thousandths play. One thing to note on this current driveshaft, the shop did not rebuild the u joints because because I was reusing the one that they (same shop) rebuilt ago 5 years under the previous owner, however I told them to do what was needed and was originally quoted for a full rebuild which was okay by me. I figure either the shop didn't check this or, or its something new caused from the vibration, however I find the latter highly unlikely as I have only driven ~200 miles or so on this driveshaft and kept speed under 70mph for most of the driving, most of which were driving back and forth to the shop. I will be calling the driveshaft shop Monday when they open, will keep you all posted when/if I get this resolved with the shop. This seems like a never ending saga, however I have no idea how I missed this before.

[twright]

While you have the tires off, put the bare wheels on the balance machine and spin them. Any runout past about .5 millimeter will cause the vibration you're seeing.

[econti]

I wouldn't be stressing about those numbers. I also wouldn't necessarily be stressing about the angle of the shaft, remember that light-medium duty trucks (not the 4x4 things that your pretend rednecks drive) use multi piece driveshafts with uni joints at large angles, and they don't vibrate either.

I assume you tighten the centre nut after the ends of the shaft are tight and the CSB is preloaded?

[84svoracer]

tomstin I plan on updating all on here with any of my findings as this forum and many others have been helpful for me on figuring some of these things out.

twright I'm not very concerned on the .004" as that's literally a sheet of paper and highest number after checking the mid/low/high diameters where the bolt holes are. Plus it bolts to the rubber flex disc which probably won't even have those tolerances itself. Yes, the driveshaft does fit snuggly on the end of the output, it does have a new (and greased) bushing and I could feel the slight friction of it just taking off the driveshaft last night. I think at this point I might put it back together, and just try forcing the driveshaft forwards as much as possible before tightening the center slider bolt. For some reason when I did this with more force than normal last time it seemed to help a bit. After that I think I will go ahead and order some new tires as the ones on the car are older all seasons that are ever so slightly out of balance and down to ~%30 tread. I was planning on the tires anyway because the current ones have some minor cracking and would also perform hideously at a track day.

Maybe there is some weird harmonics with the slight out of balance tire issue because it feels like the vibration with no wheels on the car and suspension loaded at speeds over 80mph from the other night seemed to be half of what it was with the wheels on actually driving those speeds?

[twright]

I totally agree it's very strange, but much more frustrating. I measure the run out perpendicular to transmission/diff flange mounts and it varies .004" at most. I also checked the runout of the transmission output shaft and it was only .002", so I think I can safely cross those off the list as causing any issues. The only somewhat off thing I noticed is that my output flange has '265' stamped/cast on it. See the pic below. The raised center portion is still lower than the flex disc and I don't see how that would make any difference, but is this the correct part for a getrag 260 in this car? I know the trans is a later model 260 and not a 265, its not an removable bellhousing or anything and doesn't have the crank trigger mounting stuff like on the older ETAs.



Additionally, I have messed around quite a bit shimming the transmission/rear diff mounts quite a bit to basically have 0 felt change in anything. The only thing that seemed to have helped a bit was pushing the driveshaft forward very hard before tightening the center locking thing for the driveshaft length.

I'm not sure if .004" is close enough. I was hoping for .001-.002'. If it were my car, I would try to put a small shim or two on the offending pad and see it that helps.

Another thought: Does the end of your driveshaft fit snugly on the pilot of the transmission shaft?

[tomstin]

I hope you figure this out and please post your results. I've been fighting, what I believe is a drive line vibration, and can't seem to figure it out.

[84svoracer]

I totally agree it's very strange, but much more frustrating. I measure the run out perpendicular to transmission/diff flange mounts and it varies .004" at most. I also checked the runout of the transmission output shaft and it was only .002", so I think I can safely cross those off the list as causing any issues. The only somewhat off thing I noticed is that my output flange has '265' stamped/cast on it. See the pic below. The raised center portion is still lower than the flex disc and I don't see how that would make any difference, but is this the correct part for a getrag 260 in this car? I know the trans is a later model 260 and not a 265, its not an removable bellhousing or anything and doesn't have the crank trigger mounting stuff like on the older ETAs.



Additionally, I have messed around quite a bit shimming the transmission/rear diff mounts quite a bit to basically have 0 felt change in anything. The only thing that seemed to have helped a bit was pushing the driveshaft forward very hard before tightening the center locking thing for the driveshaft length.

[econti]

Very strange. Driveshafts don't actually have to be dead straight - as long as its balanced correctly and components in good condition it can be at angles and still be fine.
I'd experiment with spacing the trans up or down using washers on either side of the mounts, and also spacing the CSB down using washers, to see if that makes any difference. Good bit is its cheap and easy to do.
Other than that I'm largely out of ideas, and I've spent a lot of time diagnosing vibrations in my cars.

[84svoracer]

ADEN I wish I had another transmission, if you know of a cheap getrag 260 laying around in good shape let me know

twright, I'll check it out, I'm thinking the rear is probably fine, but am more suspect of the transmission. Will pull the driveshaft and check those after work and report back

[twright]

Mount a dial indicator somewhere close to the rear diff and sweep the pads on the differential. Make sure that they are all in the same plane, within a few thousands of an inch. Do the same with the rear flange of the transmission.

These surfaces have to be square with the driveshaft.

[ADEN]

After reading all this the guy knows alot about cars and covered all possible causes, Since he developed the vib. after tranny swap then i would only suspect engine to transmission alignment i once had a vibration due to misalignment when suddenly deaccelerating from 5k rpm but mine was rpm related.

At the end try to swap another working tranny and see.