Downhill Decel Drive line clunk in rear end

[Driver Ed]

Hello, All-
I'm still a newbie to the site and Chryslers. Learning a lot. My car: 64 Dart Gt. 318, 904, 8.75 Dana w/3.23 (according to seller-still need to verify). Drive line is smooth, shifts well under acceleration,normal driving. I live in a hilly town. After cresting a hill and coasting downhill the trans upshifts into third as expected. When it does, there is a clunk from the rear end. Does not happen under acceleration or going uphill shifting into third. Where should I start looking?
Thanks in advance for any suggestions.
Driver Ed

 

[CFD244]

Excessive backlash maybe?

 

[George Jets]

Tighten up your upper shock mount bolts, loose in the upper cross member.

2 Full Turns > 2 Full Turns

Spray your rear leafs with PB blaster generously, so they move free, instead of jump and bang.


☆☆☆☆☆

 

[340sFastback]

Check for slack in U Joints

 

[volaredon]

8.75 DANA? I don't think so.

 

[RustyRatRod]

It's either a Dana OR an 8 3/4, but not both.

That said, the first think I would check is to make sure the pinion nut hasn't backed off. They are somewhat problematic there sometimes.

 

[Oldmanmopar]

All of the above plus. What could be happening is the trans is shifting hard into drive when leaving off the throttle cresting the hill. To much throttle pressure from out of adjustment or geometry off from carb to trans. Or line pressure turned up.

 

[volaredon]

I don't think it's in the rear end with "it only happens when....." you say. Noises and vibrations, klunks can "travel" some..... With all that metal and everything is connected somehow

 

[pauly]

Are the u bolts on the axle tight?

 

[Driver Ed]

Hello, All-
I'm still a newbie to the site and Chryslers. Learning a lot. My car: 64 Dart Gt. 318, 904, 8.75 Dana w/3.23 (according to seller-still need to verify). Drive line is smooth, shifts well under acceleration,normal driving. I live in a hilly town. After cresting a hill and coasting downhill the trans upshifts into third as expected. When it does, there is a clunk from the rear end. Does not happen under acceleration or going uphill shifting into third. Where should I start looking?
Thanks in advance for any suggestions.
Driver Ed

UPDATE to above on my '64 Dart:
Hello all-Thanks to everyone that posted suggestions on how to solve my drive line clunk. I have done the following so far:

• ensured pinion nut is torqued.
• ensured rear shocks are secured
• verified u-joints are secure and do not have play.
• verified rear end in 8 3/4 mopar, xxx741 center section
• verified the trans is a 904A
• verified the engine is a 1977 IH 318(although doubt that has anything to do with the clunk)

A follow on question: When doing the above, I noticed that whomever converted the rear end to the 8 3/4 did not install a pinion snubber. Again, I am new to mopar's. My understanding of the snubber is that it helps maintain the axel/driveshaft alignment under acceleration. Could the clunk I am experiencing on downhill deceleration shift into third gear be related to no snubber?
Thanks!
Driver Ed

 

[Dartswinger70]

nah I don't think its lack of a snubber not all cars came with a snubber so its possible to run without one youd just possibly have wheel hop at launch etc without it on th eother hand you could jack up the rear end, place on jack stands disconnect the driveshaft and feel for excessive slop at the yoke if youhave a backlash probllem you should be able to feel it turn cloickwise then back counter clockwise feel how the pinion is meshing with the ring gear

 

[Oldmanmopar]

When accelerating the snubber moves up toward the body. When decelerating it move down away from the body. So if it would be the snubber it would hit on acceleration.

 

[oldkimmer]

If u have a shift kit that’s the nature of the beast. Kim

 

[Bewy]

If original, it will have the ball & trunnion U joint up front. They wear & can make noise. Here is something very simple test you can to do to see if it is the culprit. Remove the 4 nuts holding the u joint. Install larger nuts that slip over the studs....or use a 3/8" washer stack to give about 3/8" thickness. Re-assemble & test drive.