knock when on/off gas

[Atcogas]

Here's the scenario. Have a knock from the tranny / rear end area when I apply throttle then let off and so on. I have a 88 mustang drive train. Otherwise everything is smooth as butter. I'm thinking just some slop in the old mustang drive train. I've been under and everything seems solid, Only have 300 hundred clicks on it so drive shaft should be ok. Maybe the angle? Dunno. Input would appreciated once again. Thanks.

[Slider]

was the knock there from the beginning (First drive) or did it appear after driving for awhile? Can you "feel" it, or is it just audible? Is it there all the time, or just when cold, etc.... I'm sure you've gone through these questions yourself... just trying to narrow down a bit...

[Atcogas]

was the knock there from the beginning (First drive) or did it appear after driving for awhile? Can you "feel" it, or is it just audible? Is it there all the time, or just when cold, etc.... I'm sure you've gone through these questions yourself... just trying to narrow down a bit...

I didn't really notice at 1st but I only have a couple 270 km's on it . the noise is just audible and it does it hot or cold. If u can imagine doing the on/off throttle at low speeds. that's when it's noticeable.

[riptide motorsport]

bad universal joint...............its sloppy.

[nursedude]

Assuming solid axle: put the car in neutral and rotate the drive shaft to feel if there is slop in the universal joint as mentioned... Or if it is in the differential itself...

My old land cruiser had a rebuilt rear end with the ring and pinion not torqued to spec, the first sign of trouble was an audible clunk as the gears took up slop... That turned into a mess quick.

[Mustang Man]

What suspension? If you're using the donor four link you could have sloppy control arm or upper differential bushings. Pretty common on old/high mileage Fox Mustangs. Mine clunks on the 1-2 upshift (AOD).

Mark

[Atcogas]

What suspension? If you're using the donor four link you could have sloppy control arm or upper differential bushings. Pretty common on old/high mileage Fox Mustangs. Mine clunks on the 1-2 upshift (AOD).

Mark

I have the 3 link set up. universals are good.. I've had it on stands and there is a bit of slop in rear end it self. I just don't know how much is normal. I do plan on replacing the 3:08's with 3:73's this winter so hopefully if there is an issue there it will get me through the summer.

[Dan Babb]

Check the engine mount and transmission mount bolts. If something is loose, the engine could slide just a bit and that could be what you're hearing. Had a similar sound on an old car of mine (1993 trans-am) and it was a broken transmission mount.

[68GT500MAN]

Check the bolts holding the rear u-joint to the differential....one of the many things that I learned over the years.
Doug

[Atcogas]

Check the bolts holding the rear u-joint to the differential....one of the many things that I learned over the years.
Doug

Thanks guys. I'll run the wrench over all that stuff tonight. It does seem like something is moving. I'll Let u know what I find... Ken

[willy]

had this too could be the diff if the discs in the diff are wore out you will have slop in the diff and have a clunck when changing the direction of the axel ie starting off or going forward to reverse, lift the car and see if you rotate one side is the other moving or it may move but it is easy to stop one side and rotate the other.

[Atcogas]

Thanks guys. I'll run the wrench over all that stuff tonight. It does seem like something is moving. I'll Let u know what I find... Ken

Nailed it Doug. the bolts from the shaft to the diff weren't quite loose but the they certainly were not as tight as they should be. Yes I did put lock tight on. I did that and I found the sidepipe hanger is about a 1/16'' away from the body and when I lifted up on it. the same sound was heard. which ever it was ...The noise is gone . Thanks guys.

[riptide motorsport]

i just love a happy ending!!

[nursedude]

i just love a happy ending!!

*Cough *cough... "That's what she said!" *cough *cough

[Sapper 3]

I have the low speed on/off gas thump described above that appears to be coming from the middle of the car. I can feel it in the frame. I've had it on the lift and pushed pulled and put my fingers on every nut/bolt and nothing will budge. I didn't put a wrench to the diff/axle nuts (Doug's recommendation). There is the smallest amount of play in the universal joint and with the trans out of gear and the emergency brake off I can turn either rear wheel about 1/8 to 1/4" before the other wheel or axle will start to move. I was leaning toward replacing the universal first then looking elsewhere.... I think I'll try Doug's recommendation first... Love this forum!

[riptide motorsport]

probably a broken engine or tranny mount or both, the torque of the engine would force the tranny up and over and hit the frame.