Bad Vibration at 70+ MPH

MattSVTContour · Mar 27, 2009

onefstsnake said:
Well Ive searched and have found alot of great info but nothing to solve my vibration problem.

Car is a 93 Coupe. TKO 600 trans, FMS Aluminum DS, Auburn Pro Locker, 31 Spline axles, and FMS 4.10 gears.

Vibration happens at 70mph and continues at higher speed but doesnt get worse.
No vibration under 70mph. I can put the trans into neutral and the vibration is still there. The vibration is so bad I cant see out of the rear view mirror.

Ive tried 2 sets of wheels/tires, U Joints have no play, and the wear patern on the gears looks good.

I also have a gear whine under deceleration.

Could a bad bearing in the rear cause a vibration like this?

Also how much play should there be between the splines of the axle and the internal splines in the carrier?

Any help would be awesome!

Thanks,
Ken

I had too much backlash (.020) and moving it down to around .015 took away my gear whine on decel. You might want to check that.

While I was in there I checked the axles and one of mine was bent pretty bad, .070 in the center if I supported the ends and spun it. After that, most of my vibration is gone.

phutch11 · Mar 27, 2009

+1 on backlash and +1 on driveshaft angle

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jhonda · Mar 27, 2009

More than likely its your rear tailshaft bushing on your transmission. Check to see if you can move the driveshaft up and down where it goes into the tranmission. Thats what mine is.

Strype · Mar 27, 2009

jhonda said:
More than likely its your rear tailshaft bushing on your transmission. Check to see if you can move the driveshaft up and down where it goes into the tranmission. Thats what mine is.

Smart man. Simplist things first. That'd be my guess.

fford · Mar 27, 2009

Had someone I knew and it was a bent shaft in the tranny. Everything shifted fine, sounded fine, but the tranny had a bent shaft.

wildstang90 · Mar 27, 2009

You still have the dog bone looking thing on the rear end? When I took mine off it did the same thing so I just put it back on.

onefstsnake · Mar 27, 2009

Driveshaft is bent.

I put it on a lift and lifted the rear susp. up and let the tires roll a bit and you can see the DS wobble.

Hopefully I can get it straightened out....

MattSVTContour · Mar 28, 2009

Strype said:
Smart man. Simplist things first. That'd be my guess.

Might be simple to check, but not so simple to replace!

KamiKaziDK · Mar 28, 2009

Straighten? Just hit up craigslist, there's enough people that buy aluminum driveshafts or wreck mustangs that you should be able to pick one up for 20 bucks......AND I just noticed you had a tko in there and am not sure if they require different driveshafts. HAHA. well.....glad you found the problem Double check all your seals to make sure the wobble didn't goof any up

onefstsnake · Mar 28, 2009

Yeah there is a local driveline shop that Im going to call and see if they can fix the DS.

Seals are good.

Im actually kinda glad its just the DS and not something in the rear end.

resistol · Mar 28, 2009

I just got my 87 gt a couple of months ago and I had the same problem but at 80mph. Turns out my front u joint was locked up on one side which caused my yoke to wear on one side due to the bushing in the rear of the transmission. The u joint fixed most of it but the yoke fixed it all.

BStevens · Mar 31, 2009

i've got the same issue basically...

I've tried a new tranny, new driveshaft, new wheels & tires... basically everything but a rear end, bearings & gears. i did have my brother in law whos a mechanic take a look at the gears and everything checked out ok.

kind of annoying...

thebullschmidt · Apr 1, 2009

im kinna leaning toward a bushing in the tranny my self. my car had a similar vibration at bout 85 but it was my pilot bearing... i figure its something similar except a little further back.

Bad Vibration at 70+ MPH

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