'70 Challenger. Noisy differential. What is it?

[DamianC]

Hi guys. I have a '71 Challenger that has a 440, Fairbanks 727 with manual reverse pattern valve body and limited slip diff. The previous owner couldn't give me any detail of the mechanicals as it was his fathers car before he passed. So after two years restoring I finally got it on the road for the first time today. All is good other than the rear end. The pinion bearings are noisy, and there is vibration. So I pulled the drive shaft and axle shafts - they all look good, but I will get them checked out for balance etc. I then pulled the differential. The oil was silver so I expected wear. The bearings on either side of the crown gear and diff unit feel and sound perfect. I marked the caps and removed the diff unit, opened it up and saw lots of damage to the spider gears. The gears that the spiders run in look fine, but are probably worn also. So obviously things need sorting out. My question is, am I right in saying it's an Auburn limited slip unit? I expected to see clutch plates, but see just springs. I assume, it would make sense to replace the unit rather than replace the parts individually? There was quite a lot of overall slack in the drive train before I took it all apart - if I span the pinion yolk by hand there was quite a bit of 'slack' before the axle shafts moved. Looking at the condition, I think it's been 'ridden hard and put away wet' over the years - nothing wrong with that lol. New ring and pinion and complete diff unit - or new spider gears/springs and call it good? What do you guys suggest? My first time delving into a differential, just need some advice on the best approach. Any advice gratefully received!

[TGGodfrey]

That is an auburn built unit.  Frankly I would just find a good used drop out with a clutch type sure grip unit.  Going rate is only 550.00 for a good dropout.  For added insurance do a rebuild kit for 125. and you are good.  No headaches.

If your ring and pinion doesn't have any noticable damage, keep it and use it or just sell it.

If you really want to use this one, send it to doctor diff and have him rebuild the whole unit.  The cone type are rebuildable but if the cone pockets need to be reworked, you will need a machine shop to do it and its more of a specialty.  You could simply replace the spider gears and hope for the best. Any time you replace spider gears like that, you should be replacing the mating axle gears too.

Terry

[DamianC]

That's great info Terry. The ring and pinion gears appear to be good, no marks left by trying to eat chunks of spider gear. From what you say, replacing the pinion bearings, spiders and mating axle bearings would be the cheapest route I guess, as long as the pockets don't have any damage. I will check out the pockets today. Thanks very much.

That is an auburn built unit.  Frankly I would just find a good used drop out with a clutch type sure grip unit.  Going rate is only 550.00 for a good dropout.  For added insurance do a rebuild kit for 125. and you are good.  No headaches.

If your ring and pinion doesn't have any noticable damage, keep it and use it or just sell it.

If you really want to use this one, send it to doctor diff and have him rebuild the whole unit.  The cone type are rebuildable but if the cone pockets need to be reworked, you will need a machine shop to do it and its more of a specialty.  You could simply replace the spider gears and hope for the best. Any time you replace spider gears like that, you should be replacing the mating axle gears too.

Terry

[DamianC]

I just re read your reply. You meant spend 125 of a rebuild for the sure-grip, I see that now. As above, I'll take a look at the pockets and go from there. Thanks again.

That is an auburn built unit.  Frankly I would just find a good used drop out with a clutch type sure grip unit.  Going rate is only 550.00 for a good dropout.  For added insurance do a rebuild kit for 125. and you are good.  No headaches.

If your ring and pinion doesn't have any noticable damage, keep it and use it or just sell it.

If you really want to use this one, send it to doctor diff and have him rebuild the whole unit.  The cone type are rebuildable but if the cone pockets need to be reworked, you will need a machine shop to do it and its more of a specialty.  You could simply replace the spider gears and hope for the best. Any time you replace spider gears like that, you should be replacing the mating axle gears too.

Terry

[Chryco Psycho]

You might want to find a good dentist for all those broken teeth !!
I would swap it out for a clutch type rebuildable unit .
IMO no point in wasting $$ on the auburn type repair or replacement .

[DamianC]

lol Being English I have to ask the question, "What's a Dentist?" lol. I actually got a good deal on a new replacement Auburn unit, already on it's way from Western Canada. There's a local Mopar restoration parts dealer near me in Ontario and they wanted $935 + Taxes!!!, got one for $660 from out west. I guess the rebuildable unit makes more sense. It's a done deal now though. Now I have to teach myself how to set up a rear end - should be fun?? Thanks for your input Chryco. 

You might want to find a good dentist for all those broken teeth !!
I would swap it out for a clutch type rebuildable unit .
IMO no point in wasting $$ on the auburn type repair or replacement .

[7212Mopar]

Dr Diff SureTrac for 8-3/4. It is a Torsen style LSD. Maintenance free, no special oil and quiet. No clutch pack replacement needed. I have about 2000 miles on mine and works great going straight and around corners.

[DamianC]

Actually I just got an email to say the Auburn unit I ordered although listed as in stock actually wasn't. So, back to square one. I have 30 spline axles and a 10 spline pinion. Credit card at the ready!! 

[DamianC]

Is this what you are referring to 7212 ?         https://www.doctordiff.com/8-3-4-clutch-type-sure-grip-powr-lok.html

Dr Diff SureTrac for 8-3/4. It is a Torsen style LSD. Maintenance free, no special oil and quiet. No clutch pack replacement needed. I have about 2000 miles on mine and works great going straight and around corners.

[DamianC]

Bought.     https://www.ebay.ca/itm/222352570243

[7212Mopar]

Bought.     https://www.ebay.ca/itm/222352570243

That is the reproduction of the factory clutch type LSD which will work. But the discs will be wear out and need replacement in the future. The Sure Grip is a Torsen style LSD that Dr Diff also sell. It cost more though. He offers the LSD by itself or packaged complete assembled in a third member. Best to call him to discuss. He reply really fast.