Limited slip differentials

**BlackHawk99** · 05-04-2009, 03:19 PM

I am about the replace the leaky rear differential gasket on our 97 Tahoe. I have a new seal and 2 quarts of 80W90 gear lube. But, I'm not sure if this truck is a limited slip or not...and if it is, do I need the limited silp additive? If so, how much is necessary?

Anyone know for sure? I want to make sure I do the job right.

**MrShorty** · 05-04-2009, 04:23 PM

If you are reasonably sure it has the factory diff in there, look on your RPO code list for "G80": the RPO code for the factory "gov-lock" differential.

Either way, though, the factory doesn't call for the LS additive for either the conventional open diff or the G80. The gov-lock is not a typical clutch type LS, so it doesn't need the additive that clutch type LS's call for.

**Jimmiee** · 05-04-2009, 07:53 PM

An easy way to tell if you need the additive is to jack up the rear end. With the transmission in park or in gear if it's a stick see if you can turn one wheel. If you have an open diff one wheel will turn forward and the other will turn the opposite way. If you have a posi then the axles will be locked together and the wheels will not turn.

**MrShorty** · 05-04-2009, 11:22 PM

Originally Posted by Jimmiee

An easy way to tell if you need the additive is to jack up the rear end. With the transmission in park or in gear if it's a stick see if you can turn one wheel. If you have an open diff one wheel will turn forward and the other will turn the opposite way. If you have a posi then the axles will be locked together and the wheels will not turn.

Except in the case of the G80. The G80 will behave just like an open diff: spin in opposite directions.

**1st Synthetics** · 05-05-2009, 07:36 AM

Either Diff you possibility have does not call for the additive. You are going to need at least 1 more quart of gear lube.

Differential, with 10.5 ring gear Dana Rear..........5.5 pints
Differential, with 10.5 ring gear EX Dana Rear..........6.3 pints
Differential, with 11 ring gear Dana Rear..........8.4 pints
Differential, with 8.5, 8-5/8 ring gear Rear..........4.2 pints
Differential, with 9.5 ring gear Rear..........5.5 pints
Differential, with 9.75 ring gear Rear..........5.5 pints

**Jimmiee** · 05-05-2009, 07:50 AM

Originally Posted by MrShorty

Except in the case of the G80. The G80 will behave just like an open diff: spin in opposite directions.

Exactly! Even though it's a "posi" it doesn't require the additive because it is not locked in turns. The conventional Auburn style is always locked and will chatter in turns without the friction modifier.

**BlackHawk99** · 05-05-2009, 07:54 AM

Thanks for the help, guys!

I do have the G80 RPO code and have no reason to believe the rear end has ever been swapped out. But it sounds like I don't need the additive anyway.

I'll pick up another quart of gear lube. AutoZone told me the capacity was 1.75 quarts. LOL That's what I get for listening to those guys! I'm going to tackle the job tomorrow night

**BlackHawk99** · 05-09-2009, 08:16 PM

I swapped out the gasket. What an act of congress it was to get the 10 bolts off! 12 years of rust really made things a challenge.

So...got it all swapped and drove it about 50 miles. The leak is back. I'm so irritated. UGH. I wire wheeled the cover and removed all the gasket residual from the mating surface on the rear diff. Set the new gasket in place with RTV on both sides. Cleaned the bolts with a wire wheel and used PB Blaster on them before torquing them down. I torqued them to 165 inch lbs (13.75 ft. lbs.). Did I do something wrong? This feels like a waste of what should have been a really easy job.

**MrShorty** · 05-09-2009, 10:13 PM

Are you certain the leak is through the gasket? A lot of times other seals (especially a leaky pinion seal) will look like a leaky gasket because the oil flows down the housing and drips off the bottom: right where the gasket seal would drip.

I've had trouble sealing up a diff before because I used the wrong "stuff". Don't take offense, but are you certain you used RTV silicone? There's another product out there that calls itself a "gasket maker" but isn't RTV, and it doesn't work on gear oil.

All sealing surfaces looked clean without imperfections/scratches/pitting/etc.? Housing flat? Cover flat and not bent?

**1st Synthetics** · 05-10-2009, 01:08 AM

I swapped out the gasket. What an act of congress it was to get the 10 bolts off! 12 years of rust really made things a challenge.

So...got it all swapped and drove it about 50 miles. The leak is back. I'm so irritated. UGH. I wire wheeled the cover and removed all the gasket residual from the mating surface on the rear diff. Set the new gasket in place with RTV on both sides. Cleaned the bolts with a wire wheel and used PB Blaster on them before torquing them down. I torqued them to 165 inch lbs (13.75 ft. lbs.). Did I do something wrong? This feels like a waste of what should have been a really easy job.

Did you use a synthetic gear lube? You can not use RTV with synthetic lubricants. They react and cause seal failure.