A few months after I finished my auto to T5 tranny swap my Bird developed a very bad vibration. It starts at about 60mph, peaks at 65 and stops at 70mph. The car is pretty smooth everywhere else, faster and slower.

I asked this question a while ago ( https://www.thirdgen.org/messgboard/...ML/012643.html ) and got a few good responses.

I tried adjusting the pinion angle with shims to raise and lower the tranny. This did not improve the vibes and it might have made it worse.

If I jack up the car and run it up to speed on blocks, with or with out wheels, the vibes are still there.

I have tried two different driveshafts, both with new U-joints and had no change.

If I put it in neutral or push in the clutch or shut the engine off the vibes do not go away until the car drops below 60 or I run into a tree because the wheel is locked . So the engine speed is not important.

The car has new motor and tranny mounts.

The tranny was rebuilt (new bearings and syncros) and had no problems immediately after the install.

Sorry for the long post but I am going nuts and I would like to drive my car again!!

Thanks in advance!

Dale



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1986 FireBird
2.8L MPFI
1/2 CAI
Gutted Cat, No muffler
Was 700-R4 --> Now T5
**** Great cars aren't bought, they're built ****

 

Could easily be the extension housing bushing...

Check to see if the driveshaft has any side play in the back of the trans. If it does, call around to the various trans shops in you area until you find one that has the tool for replacing that bushing while the trans is still in the car. With the right tool it's about a 20 minute job and a $4 bushing, maybe a $35 or $40 ticket total.

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"So many Mustangs, so little time..."
ICON Motorsports

 

That's weird. That is exactly what my grandfather suggested about an hour ago.

I will check it tomorrow some time but I am almost certain that there is no side movement. I have pulled the driveshaft out many times and never noticed anything hinky back there but I will double check it.

Thanks
Dale

 

Well I checked the driveshaft for lateral movement and there was none.

Any other ideas??? Please Help!

Dale

 

Check both the driveshaft and the wheels for balance weights. If that checks out OK, then you could try removing the rear U-joint and turing the driveshaft 180 degrees.

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89 Transam GTA, 350TPI, auto, 3.27 rear, dual cats, gray.
Magnaflow cat-back,
K&N open element,
Best E.T. 14.63@95mph

 

I have run the car w/o wheels on and it still vibrates. I have tried BOTH of my available shafts (see above) and it vibrated. I then flipped them 180* and it continued vibrating.

I think I am going to try running the car with the drums off in case somehow something happened to them but I doubt it.


Could bad axle bearings be causing this? How about something in the diff? I am out of ideas.

Thanks
Dale

 

Axle bearings, pinion bearings, carrier bearings could all be the problem.


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350 with stealth intake, holley carb, 470 lift cam. 700r4 with .5 boost valve, vette servo, tci lock-up kit, B&M megashifter. Richmond 3.73 gears, powertrax locker, timkin bearings, synthetic lube. Custom 3 inch single into 2 2.5 pipes. 1 1/2 drop springs, 1 5/16 solid front sway bar, 1 inch rear bar, custom subframe connectors, custom LCA relocation brackets. Kobel ground FX, currant red metallic paint. Lots of other stuff...
82camaro

 

It's either the output shaft bearing (wiggling the drivesaft back and forth to check for play is not really a valid test) and/or the pinion bearing is shot. An out of balance driveshaft would have been my first guess but you have tried 2 different ones so it's unlikely they were both bad.

 

Ok, I guess that any bearing back there is suspect.

Now the question is: How do I narrow this list down a bit? What should I look at or measure to give me some clues? I just do not want to replace any more than is necessary.

When I rebuilt the tranny about 10K miles ago, I remember that I saw nothing wrong with the extension housing bushing but that does not mean much.


Thanks for the help!!!!

Dale

 

i guess u have way too much power then. in that case vibration is good. especially when the old ladies at the grocery store bitch u out for being a bad driver.hehe


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86 berlinetta
350cui w/.30 over
.526 hilift cam
hooker supercomps
3" duals
edelbrock streetmaster
holley 750 dp
bad asshauler

 

Say what?!