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I have a 8 3/4" diff head with a clutch type suregrip that I want to check out of the car. I have read that there should be .020" clearance on the clutch plates but I can't see where I'm supposed to check this. Can someone please tell me how to do this or post some pics, videos of how to check this clearance & any other important things I should look for. My 60' times were getting slower & a mate at the track swore my car was one wheeling so I swapped out the head & now I need to do something with it so it can go back in.

Thanks in advance.

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There is no way a stock 8 3/4 Dana clutch type unit came from the factory with .020 free play in between the clutch plates, the curve bevel washer(plate) on each side prevents that Take it apart and look at the driven and drive discs, (clutch plates) for wear or damamge Mark the case halfs before disassembling the carrier Make sure and put the case halfs back together like the came apart Dr Diff stocks replacement and rebuild kits for them If and when you reassemble it you should put the axles into the carrier all the way through all of the driven cluth plates, you can see the axle splines when there in all the way before you tighten the case bolts to put crush(preload) on the bevel plates, don't ask me how I know about that I do remember a Mopar sponsered factory racer saying that( a long time ago) they ran .020 clearances inside the clutch type posi unit on there Dana 60, that it mod. was worth a tiny bit of MPH, the bad thing about doing that according to him is you had to remember to let the cluch out slowly in first gear behind the starting line after backing up from a burn out to set the preload on the spider gears on the axles up agianst the carriet halfs to make the posi work properly, if you didn't and rev the motor up without preloading the posi unit that way and let the clucth out the posi wouldn't work, it would act like it was still in nuetral I never treid not setting the preload in that rear end, I never had a problem with his posi rear end that we had. We where running a 727 also so it wasn't a big deal to let it creep slowly into the staging lights

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I've never tried to check one the way you describe. My own method is pretty practical, but it does involve sacrificing two old axles. Cut the splined ends off leaving about six to ten inches of axle shaft beyond the splines. Weld a nut to the end of the unsplined ends. Put one nuted end in a large vice or enlist the services of a large and STRONG friend to hold that end with a socket and breaker bar. Place the unit to be tested on the splines. Insert the other splined stub axle in the other end of the unit. Use a torque wrench on this end and see how much torque it takes to turn the stub axle. Should be a minimum of 100 ft. lbs.

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As a side point what oil should I be running? the local Mopar dealer told me to run Castrol LSX90 Limited slip diff oil & Mopar limited slip additive, ia this right?

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That lube will work. Don't use the additive and live with a little chatter around corners - especially if you are going to race it. While it's out just rebuild it ( not that expensive for a new clutch pack ). Put it in. Drive it for a short. Than do a torque / breakaway ( ft lbs )test on it. That will be your base line for a good clutch pack. My 9 1/4 with spicer clutch disc set up was around 100 lbs break-a-way torque new. At about 40 lbs, it was time for a new clutch pack. Those #'s probably won't apply to your unit. What kills them real fast is the burnout box. One tire will usually bit ( get dry ) before the other and, with slicks, you will spin the wet tire and eat up the clutch pack in no time. I've had them last as few as 11 passes. With street tires they will last a long time. FYI, I have lots of videos of one tire - than the other tire - burnouts. Serious racing with lots of HP - ya gotta have a spool. If you have bad chatter without the additive, lots of times you can make it better by just doing some circles in both directions to get some lube in to the discs. IMO, additive is a last resort, as it some what defeats the objective. It's for sissy's - and now to return to .