Rear end woes

[mjb765]

70 Cuda with 8 3/4 489 rear. Started with a one legger and I wanted to upgrade. Bought a complete unit from Randy's ring and pinion. Started making a loud clunk on hard turns so I changed fluid, added the suggested additive, etc and still making the noise. Drained the fluid again and a chink of gear came out.....instead of shipping it back to them I brought the center section to a local guy and he tore it down and replaced any broken parts. Re-installed and still making the noise. This is not just a click or little clunk..this is a clunk that the car shakes and you expect and axle to be broken. It only happens on tight parking lot turns or when backing out of the driveway and cutting the wheel hard then going forward in the street. 

I do not want to have this center section rebuilt again by some one else---or should I? Could it be the case since I didn't have the clunk with the one legger?  Or buy another center section from Dr Diff...or just buy a Dana S60 end to end from Summit racing??  I know the center comes out in 30 minutes, but this is still getting old........

[GoodysGotaCuda]

So I went through something similar when I rebuilt my SureGrip and it worked itself out with the help of more friction modifier.

I didn't assemble the clutches after being soaked in limited slip additive, rather i used gear oil [wrong]. The axle felt broken, very broken, like the broken axle you mentioned. After talking with Dr. Diff [Cass], he suggested to keep driving the car easy and work toward tighter turns and using Ford friction modifier.

In the end, I have 1.5 bottles of -Ford- friction modifier [recommended by Cass] and worked up to figure 8's. Now the diff works perfect, no chunks or missing pieces however.

[mjb765]

So I went through something similar when I rebuilt my SureGrip and it worked itself out with the help of more friction modifier.

I didn't assemble the clutches after being soaked in limited slip additive, rather i used gear oil [wrong]. The axle felt broken, very broken, like the broken axle you mentioned. After talking with Dr. Diff [Cass], he suggested to keep driving the car easy and work toward tighter turns and using Ford friction modifier.

In the end, I have 1.5 bottles of -Ford- friction modifier [recommended by Cass] and worked up to figure 8's. Now the diff works perfect, no chunks or missing pieces however.

The gear chunks were the first time I took it out--when it was built by Randy's. Haven't opened it up this time yet. They specifically said the Mopar additive in this one. I'm gonna guess from what I remember there is probably about 1 1/2 to 2 bottles of the Mopar stuff in it now.

[GoodysGotaCuda]

How many miles are on it now?


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[1 Wild R/T]

Like Mike said, use the Ford stuff... I'd consider drawing it, inspect it then reinstall & refill with the Ford stinky stuff...  In the past I went straight to figure eights.. Work the stuff in good, then park it for a day.... ext time you drive it the noise should be gone....

[mjb765]

Like Mike said, use the Ford stuff... I'd consider drawing it, inspect it then reinstall & refill with the Ford stinky stuff...  In the past I went straight to figure eights.. Work the stuff in good, then park it for a day.... ext time you drive it the noise should be gone....

I will give it a try..

Thanks for the suggestion.

[JS29]

Another vote for Ford friction modifier! 

[mjb765]

Just to update this thread...added the Ford friction modifier, did some figure 8's (thought I was gonna break something it was banging so bad) and then parked it. Took it out just now...it didn't chatter going around the first turn so I thought that maybe this worked. Went into the parking lot and did a few tight turns and BANG--noise still there. So apart it comes.....

Thanks for the suggestions and help......

[Brads70]

What do you have for the diff, like true trac , sure grip?  I wonder if it's an axle preload/clearance  adjustment issue?

[Scooter]

What do you have for the diff, like true trac , sure grip?  I wonder if it's an axle preload/clearance  adjustment issue?

Don't think you have these issues with Tru-Trac. I'd bet Detroit locker by the sounds of it... no pun intended. 

[Brads70]

What do you have for the diff, like true trac , sure grip?  I wonder if it's an axle preload/clearance  adjustment issue?

Don't think you have these issues with Tru-Trac. I'd bet Detroit locker by the sounds of it... no pun intended.

If it's a tru trac with 8 3/4's I've read a lot of issues. I think I read where Cass stopped selling them for 8 3/4's for awhile? I have one in my Dana and love it and I've had zero issues with it.

[usraptor]

Had the same issue with my original '70 'Cuda 8 3/4 sure grip 3:55 gear set.  Was fine when I took delivery.  Thinking I was doing the right thing I had all the fluids, engine, trans and rear end changed at 1K miles.  Rear started clunking on turns or pulling into driveways like gas stations.  It was so loud people would stop and look.  Like you said it sounded like it was going to break at any moment.   Turns out when they replaced the rear end fluid they didn't put in the proper fluid for a sure-grip.  Took it back, had it changed again and problem went away.   Current 'Cud has a Dana 60 with sure grip.  Added the friction modifier along with the "posi" gear oil and haven't had any issues at all with it.  Good luck with yours.

[scf100]

Good stuff....same issues

[mjb765]

What do you have for the diff, like true trac , sure grip?  I wonder if it's an axle preload/clearance  adjustment issue?

I got their standard limited slip unit--the part description is "USA Standard Gear Powr Lok Positraction for Chrysler 8.75"

I wasn't racing it or anything so I didn't really think I needed the upgraded units......but now I will end up with one. The guy that it is going to build it has done a few for me in the past. When I ordered this one from Randy's it just seemed easier than taking mine out and getting it rebuilt. One day---out with the old and in with a new one.....bad decision on my part. I spoke to him today and I think he said he wants to do a Tru-Trac..he does this everyday so I am just going to go with it....Hopefully will drop the center section off to him on Saturday.

[Brads70]

What do you have for the diff, like true trac , sure grip?  I wonder if it's an axle preload/clearance  adjustment issue?

I got their standard limited slip unit--the part description is "USA Standard Gear Powr Lok Positraction for Chrysler 8.75"

I wasn't racing it or anything so I didn't really think I needed the upgraded units......but now I will end up with one. The guy that it is going to build it has done a few for me in the past. When I ordered this one from Randy's it just seemed easier than taking mine out and getting it rebuilt. One day---out with the old and in with a new one.....bad decision on my part. I spoke to him today and I think he said he wants to do a Tru-Trac..he does this everyday so I am just going to go with it....Hopefully will drop the center section off to him on Saturday.

I'd do some more research on using a Tru trac in a 8 3/4   Just looked at DrDiff site and he doesn't even offer it as an option anymore in a 8 3/4 rear end , Dana 60 yes.  I'd hate to see you get into another mess?
https://www.doctordiff.com/drivetrain/