Knocking sound from drivetrain on deceleration/coasting

[MystichromeVert]

I took the car out last night for the first time since I replaced all of the rear-end bushings... it definitely needs a 4 wheel alignment, but I think there may be bigger problems.

Anywhere between about 25mph and 55mph there is a noticeable knock coming from the driveshaft/rearend every time I lift off the gas. I'm pretty sure its present at all speeds, its just harder to hear when its going really fast or really slow. It happens in every gear and in neutral, while decelerating and while coasting. The only time I don't notice it is when I'm accelerating in any gear at any speed.

I replaced the IRS bushings, the upper and lower control arm bushings, the differential bushings, the tie rod ends and sway bar endlinks. However, I can't see how any of that stuff would cause a knock in the drivetrain. MAYBE it has something to do with the aluminum differential bushings transferring a lot more drivetrain noise into the car? (if the knock was always there and the pliable rubber bushings absorbed enough of it that I've never noticed it before???)

Any ideas on what it could be? I'm clueless on this one...

 

[SpectorV]

i would start out by checking every bolt and make sure everything is set to specifications. Review the install how to's on MM's site and make sure it was al done correctly.

Did you take off your driveshaft and put it back on exactly how it came off?

 

[MystichromeVert]

The driveshaft is reinstalled in the same position as I took it off. I'm 100% positive the rear is in the same place. I may be off a tooth left or right on the tranny output shaft.

The half-shafts may not be in the diff at the same positions, but if they are out of balance, wouldn't that cause a vibration? What I'm experiencing is a knocking sound with no noticeable vibration.

I did all the work myself and followed MM's directions exactly.

 

[SpectorV]

hmmm just to be sure go back and double check everything and while you are checking look around for potential noise problems that could cause your issue, just looking around good may solve your problem.

 

[JB]

make sure driveshaft bolts are still tight

mine had all worked loose so I'm loctiting them this time

 

[MystichromeVert]

make sure driveshaft bolts are still tight

mine had all worked loose so I'm loctiting them this time

Would that help explain why the sound only occurs while coasting or slowing down and not under acceleration?

 

[UBNSTRK]

I have the same problem.... I can be at any gear... I am completely stock... If I left off the accelerator and then get back on the drivetrain sort of shifts and knocks??

Can some one please help?

 

[neckdemon]

I have the same problem.... I can be at any gear... I am completely stock... If I left off the accelerator and then get back on the drivetrain sort of shifts and knocks??

Can some one please help?

that's basically normal. late model mustangs are famous for clunking.

 

[cm svt 03]

that's basically normal. late model mustangs are famous for clunking.

This is true, normal for these cars. The transmission is where the noise/play is coming from