clunk in the powertrain

[fgross2006]

So this weekend I installed springs all around, ball joints, control arm bushings, sway bar links, sway bar bushings, front wheel bearings, U joints, motor mounts, tranny mount. I was on a mission to tighten up the entire front end and power train. had the car aligned at Mavis.

No doubt the car is tight, but there is still a profound clunk when I stomp the gas, or release the accelerator after passing on the parkway. I cant determine if the play is in the rear end or the tailshaft of the tranny.

I know the spider gear in the rear can start to leave play and there is also a bearing and bushing in the tranny tailshaft. Other than the clunk, the tranny shifts perfect. No slippage, no hard shift. Its only when I get on the pedal that the clunk runs through the power train and makes a bang in the rear under the passenger seat.

Any suggestions? ideas?

Also, all new parts are Moog. No cheap durlast junk used.

[83gtstang]

Does the rear hum at all, I think my 8.8 is going out and does the same. My car vibrates bad under acceleration, mostly feel through the shifter. I'm thinking could also be universal joint.

[fgross2006]

Does the rear hum at all, I think my 8.8 is going out and does the same. My car vibrates bad under acceleration, mostly feel through the shifter. I'm thinking could also be universal joint.

No hum, just a clunk. It has to be either the rear or the transmission tail shaft.

[Travis T]

Did you put a thread locker on the driveshaft bolts? If not, they're probably already loose. That will definitely clunk.

[Jerry peachuer]

Wiggle the h pipe and the mufflers and look for any signs of rubbing to floor board the best way in my opinion is use ramps that way the car is loaded and at ride height on the ramps otherwise your rear end will droop along with your driveshaft and springs will be unloaded as well

The easiest way to check the rear is to un hook drive shaft 12mm wrench don't pull it out of the tranny use a coat hanger or your choice of sling old belt is perfect
Anyhow this will disengage the axle from tranny and move the tires in and out on the axle and rotate them back and forth see if there is anything extremely loose
Axle bearings can be toast they spin ridiculous RPMs and usually been known to hum like stated above
The in and out tire play shouldn't be more that half of a 1/16 or don't get to caught up with that number if the posi trac wears it will be more but the clunking could be excessive back lash in ring pinion or trans mount or motor mount

The motor is twisting to the right or passenger side so is the transmission that's why you hear it on the passenger side if you can't find or see any thing look at your torque boxes where your upper control arm meets body and lower control arm meets body that is worse case scenario
you could also load the passenger rear tire by jacking the car off the ground and see if there's any bottoming out of the body to driveline also look at the pinion snubber above the rear axle and see if it's a adjustable unit with no preload or if it's missing the rubber portion
Either way you have to do more visual than mechanical at this point
If it we're mechanical it would clunk most of the time or all the time
Good luck on your hunt

[mustangxtreme]

The 7.5 I had in my 83 had a clunk from the day I got it. It lasted 194,000 without any other strange noises.

[63roundbody]

Universal joints.

[webestang]

You say you changed the u-joints.......,Maybe a snap ring came off a u-joint and it's coming loose? Did you grease the u-joints after install?

[GIXER7502006]

My clunk was the upper control arm bushings alowing the rear end to move enuff to make it clunk as you have stated

[fgross2006]

All new parts are Moog problem solvers, including the U joints. They were pre greased but I am going to hit them up again with a grease gun.

this clunk only happens at high speeds. Crushing 55 on the highway then passing will cause the clunk both upon acceleration and deceleration.

There is an AOD adjustment cable that I wonder if it could be causing this clunk when passing if its out of adjustment. the thing is I don't know how to check it for proper adjustment. I think im going to take it a tranny shop near me where the owner is very honest and helpful. I'll let him take it for a test ride.

Im inclined to think this is coming through the tranny.

[83gtstang]

They adjust the tranny with a pressure gauge I believe. I would definitely have it checked, the plastic piece near the throttle body or carb, if it is worn or broken, can cost you your tranny or damage it really bad if that's what it is.

All new parts are Moog problem solvers, including the U joints. They were pre greased but I am going to hit them up again with a grease gun.

this clunk only happens at high speeds. Crushing 55 on the highway then passing will cause the clunk both upon acceleration and deceleration.

There is an AOD adjustment cable that I wonder if it could be causing this clunk when passing if its out of adjustment. the thing is I don't know how to check it for proper adjustment. I think im going to take it a tranny shop near me where the owner is very honest and helpful. I'll let him take it for a test ride.

Im inclined to think this is coming through the tranny.

[fgross2006]

They adjust the tranny with a pressure gauge I believe. I would definitely have it checked, the plastic piece near the throttle body or carb, if it is worn or broken, can cost you your tranny or damage it really bad if that's what it is.

The plastic grommet is new. replaced over the summer

[83gtstang]

Good, that's the number one AOD killer. There is a constant pressure kit available now for the AOD, so no more relying on adjustment for proper pressure.