8 3/4 issues

[63PlyMoepar]

I have an 8 3/4 742 354 posi. At low speeds especially backing up and turning into a parking spot I am getting what seems like a grinding noise.The rear end was built by someone with decades of experience so mechanically I believe it to be done right. Going down the road at almost any speed it is smooth as glass. Any thoughts would be appreciated.

 

[T2R9]

Did you add friction modifier when it was installed? Sure grips require it.

 

[63PlyMoepar]

I just purchased the car a few months ago. I have no idea what’s in it.

 

[63PlyMoepar]

Did you add friction modifier when it was installed? Sure grips require it.

What product would you recommend?

 

[davek]

rebuilt? New gears?

 

[T2R9]

What product would you recommend?

Add some, see if it helps. I like the Motorcraft stuff.

https://www.amazon.com/dp/B000NU5LP6

 

[dadsbee]

Go do figure eights in a parking lot. Start wide and go tighter and tighter for 10 minutes. If that doesn't work drain 4oz of fluid and put in a bottle as noted ^^^ and then go do those figure eights again.

 

[63PlyMoepar]

rebuilt? New gears?

I believe to be rebuilt with new axles.

 

[Don67Satellite]

Noises when turning and low speed, maybe someone threw a "Lincoln locker" in it, I'd pull it and see what you have.

 

[63PlyMoepar]

I’m definitely sure there isn’t one in it.

 

[Don67Satellite]

I just purchased the car a few months ago. I have no idea what’s in it.

I’m definitely sure there isn’t one in it.

I based my suggestion on the first one.

 

[63PlyMoepar]

Go do figure eights in a parking lot. Start wide and go tighter and tighter for 10 minutes. If that doesn't work drain 4oz of fluid and put in a bottle as noted ^^^ and then go do those figure eights again.

I don’t quite understand. Is something not seated or something?

 

[63PlyMoepar]

I based my suggestion on the first one.

Sorry, my dad built the car years ago and has since passed. I acquired the car from the guy that got it from him 12 years ago.

 

[DanielSlocum]

Some aftermarket clutch discs for the sure grip are very aggressive and tend to make noise when turning because they dont slip easily enough.

 

[dadsbee]

I don’t quite understand. Is something not seated or something?

You need to get the clutch disc's moving against each other to get the lube and additive worked in..

 

[Macdon221]

I had the exact same issue with my 3.23 sure grip a few years ago. It was 741 clutch type not cone.

I bought a new clutch kit (discs)...installed them as per factory...lubed it all up during install and it worked fine for about 9 months and started again. It sounds like something is getting destroyed in there!!!! But no so.

I did the entire process over again....nothing changed...used the same friction modifier and lube.....was careful to put it all back with proper torque values....and this time no issues for past 5 years. Not sure what i did different. The clutches from the first time were not worn either. Who knows.

I would follow all the advice above first....maybe change the oil....add a bottle of friction modifier. Dare I say it...I used the ford friction modifier...zero issues since.

Here is my newbie previous thread.

Charger “metal torsion sound” very slow speed turns

 

[63PlyMoepar]

I had the exact same issue with my 3.23 sure grip a few years ago. It was 741 clutch type not cone.

I bought a new clutch kit (discs)...installed them as per factory...lubed it all up during install and it worked fine for about 9 months and started again. It sounds like something is getting destroyed in there!!!! But no so.

I did the entire process over again....nothing changed...used the same friction modifier and lube.....was careful to put it all back with proper torque values....and this time no issues for past 5 years. Not sure what i did different. The clutches from the first time were not worn either. Who knows.

I would follow all the advice above first....maybe change the oil....add a bottle of friction modifier. Dare I say it...I used the ford friction modifier...zero issues since.

Here is my newbie previous thread.

Charger “metal torsion sound” very slow speed turns

I am going to drain a fill with the additive. Thanks for the info!
I had the exact same issue with my 3.23 sure grip a few years ago. It was 741 clutch type not cone.

I bought a new clutch kit (discs)...installed them as per factory...lubed it all up during install and it worked fine for about 9 months and started again. It sounds like something is getting destroyed in there!!!! But no so.

I did the entire process over again....nothing changed...used the same friction modifier and lube.....was careful to put it all back with proper torque values....and this time no issues for past 5 years. Not sure what i did different. The clutches from the first time were not worn either. Who knows.

I would follow all the advice above first....maybe change the oil....add a bottle of friction modifier. Dare I say it...I used the ford friction modifier...zero issues since.

Here is my newbie previous thread.

Charger “metal torsion sound” very slow speed turns

 

[33 IMP]

The figure eights, and the Motorcraft additive, are superb suggestions. Follow them.

 

[beanhead]

And when all the suggestions above don't cure it, take it back to the shop/guy that put it together....

I went through this a few years back.
Yes I added extra Ford fluid (on the right nights I swear I can still smell that crap in my garage!!) Did the figure 8s. Did all of it and still no joy.
Had a VERY reputable axle shop rebuild my 742 and after TWO fails, the consensus was shitty parts from Yukon (their supplier for that stuff at the time)....
Upon trying for yet a third warranty claim Yukon tried to blame me for "doing burnouts" and "launching it on slicks"....which the shop agreed with me that even if I was doing that (I was NOT) the clutch plates shouldn't be galling and breaking spiders with less than 450hp in front of it.

My shop finally told Yukon to pound sand and installed for me an Eaton tru-trac, free of charge...and that thing's been flawless even now that I've upgraded to the 600+hp/tq range.
Apparently they had other issues with parts from Yukon at the time, so it wasn't just me or "Mopar stuff."

Maybe it's your problem, maybe not....the point is you just never know with "new" parts these days even when they're put in by good guys.

Now THAT SAID if you're getting "grinding" noises that could be axle bearings which have nothing to do with the diff. And to add, some 'chatter' isn't necessarily an indicator of badness with a clutch rear if it's set up on the tight side, but really nobody can know that without hearing it in person.