[joes455]

So I've finally got rid of the high speed 130mph full throttle I was getting,but now at that speed when letting of the throttle I'm getting a driveshaft vib that will knock ur loose dentures out it goes away about 110mph.Your thoughts?

[steve25]

If the driveshaft is a stocker then it’s likely giving you notice that it’s going to rip apart on you.

Is the trans mount new?

[Gary H]

Possible that the pinion angel is off? What did you do to solve the acceleration vibration?

[AG]

Have you checked the pinion angle and condition of the U-joints? Might be time for a new aftermarket driveshaft.

[joes455]

New 1350 shaft,pinion flange ,th400 output shaft and balanced.Shimmed pinion up 2° very bad vibration that would begin at 110mph,no vibe on let off.Shimmed pinion down 2 no vib up to 135 but bad vibration off throttle.Put it back no shim no vib up to 135 ,bad vibe off throttle .I'm right back where I started trying to solve this issue.Shaft had to be balanced 2x to solve vibe at load up to 135.My output shaft bushing does have up and down movement and gear back lash seems excessive.

[joes455]

On a side note my shaft is not centered in relation to body tunnel,its off to the right.Is this typical with 2nd gen f bodies ?

[DaleO]

Originally Posted by joes455

On a side note my shaft is not centered in relation to body tunnel,its off to the right.Is this typical with 2nd gen f bodies ?

So I watch you big dogs from afar but this question is very interesting to me because I am looking into a new rear to replace my 8.2 10 bolt. I've learned the GM 12 bolt is 1/2 inch off center and the 9" is 15/16 off and an inch or so lower than GM's. I've wondered the potential impacts of these deltas. Obviously there isn't a problem as so many run 9" and I'm not far enough along to ask Quick Performance or others about this. I am curious which rear end you have?

[AG]

I would take the TH400 tail off and get the bushing replaced and retry, there should be no play. I use a pinion angle of 4 degrees down on my Caltrac suspension with split mono leafs and don't have any vibration crossing the line at 134 mph. I doubt the backlash is contributing to the issue. What is your pinion angle?

[joes455]

It's a 10 bolt 8.5 no full throttle vibration anywhere in the rpm range ,its just on deceleration from 135 mph( the fastest this car will go)down to about 110mph with just engine braking.When feathering throttling the vibe will come and go at high speed.Ill recheck pinion angle and post results.I have noticed slight gear wind when just cruising at constant speed the noise goes away with adding slight throttle or engine braking.

[Elarson]

Originally Posted by AG

I would take the TH400 tail off and get the bushing replaced and retry, there should be no play. ?

Agree. If the output shaft bushing is loose, the angles of the front u-joint are probably all over the place and the driveshaft is orbiting; not rotating about it's centerline.

Eric

[george kujanski]

Reading this with interest. My son has a 2000 T/A which had a vibration issue on decel after going to a STRANGE S60, new driveshaft, etc. AFter much work at a local "go-to" shop, symptoms changed but never cured. I was helping to diagnose the existing problem and noticed there was about 1-3/4" clearance on the driveshaft-to-output shaft. This really should be about 5/8" from what I understand. I firmly believe this was the original cause of his vibe during decel, caused by the front of the drivesaft not being constrained correctly when back driven during coast.

Sounds like yours with excessive bushing clearance. My 2cents.

George

[wolf]

Stupid question: is the pinion nut tight? I had one loosen off on an old truck many years ago, and had similar symptoms. Under acceleration, the pinion is pushed out against the bearings, but under decel, it will fall into the ring gear and all hell breaks loose.

[joes455]

Yes nut tight and indexed to check movement, pre load 20" lbs.No question is stupid, I've once had it go loose well backoff

[aaronman]

Recheck your ring and pinion and clearances.

[blueghoast]

Originally Posted by Elarson

Agree. If the output shaft bushing is loose, the angles of the front u-joint are probably all over the place and the driveshaft is orbiting; not rotating about it's centerline.

Eric

X2 on this

GT