I'm curious if this sounds like a problem to anyone. This morning on my way to work, I stopped for gas. Since there were a couple SUV's in the way I had to stop as I was entering the driveway to the gas station.

I'm sitting there, front wheels on the driveway, steering wheel cranked over to the right, rear wheels still out on the street. Once I had a clear path to the pump I pressed the accelerator to proceed. However, the engine just reved and I went nowhere.

I hit the gas again and still I'm going nowhere, but I can now here the right rear wheel spinning. I then shifted into reverse, rolled the car back a little bit, eased off the steering a tad and drove up the driveway to the pump.

This happened once before, only it was while trying to turn left into a steep driveway. Similar situation – I was at a stop, front wheels on the driveway, rear wheels on the street. When I tried to turn left up the driveway the car wouldn't move and just spun the left rear wheel. Since the driveway was so steep, and I value my air dam, I just parked on the street.

Does this sound like the limited slip in my 9-bolt is going bad or is it normal? When turning the limited slip is supposed to disengage, but I was also under the impression that if one wheel lost traction, then it should engage to supply power to both wheels.

ttt

Don't know Brett. Even with one wheel turning, it should have moved. You might want to check the spider gears. One might be missing some teeth.

That's what was weird. Both times this has happened, the car sat still while one of the rear wheels just spun, I assume due to a loss of traction at that wheel.

Now IIRC, the last time I nailed the car from a stand-still at a stop sign, it spun both wheels. Also, the last time I changed the gear oil, everything looked fine. No mashed or broken teeth. Plus, I don't pound on it. I never drag race and rarely hammer it from a stop.

It's also worth mentioning that I was not making a straight-on approach up the driveway. In both cases, my car was more parallel to the driveway. When the rear tire broke loose it was essentially in the gutter area of the street at the lip of the driveway.

Could synthetic gear oil cause this? At the last change, I switched to Red Line synthetic. I wonder if it's affecting the posi unit.

Redline, that says it all to me. Which Redline did you use? Jack one rear tire and try to turn it. If it spins easy, the posi is shot. Hoopers used have the parts to rebuild 9 bolts.

IIRC, I used the 75W90 Redline synthetic gear oil. Nothing unusual. After checking out the Redline web site I see they offer a 75W90 NS oil without the added friction modifiers. Hmmmm.
http://www.redlineoil.com/products_g...60&subcatID=20

I'm thinking the standard Red Line stuff is too slippery for the cone style posi in the 9-bolt.

From the Red Line site:
75W90 Gear Oil - the preferred product in nearly all car and light truck differentials, both conventional and limited-slip. 75W90 is preferred for most racing applications. It contains friction modifier which is recommended for limited-slip units. 75W90 Gear Oil can be used in many
transmissions and transaxles; however, other Red Line lubricants have better frictional properties for rapid synchronization.
Exceeds API GL-5.

75W90 NS, 75W140NS - GL-5 lubricants which do notcontain the friction modifiers for limited-slip hypoid differentials. This makes the transmission synchronizers come to equal speeds more quickly, allowing faster shifting and much easier low-temperature shifting. Can also be used
in racing limited-slip differentials where weak spring design causes too much wheel spin. These products provide significantly more lockup. Some Limited-Slip Friction Modifier may be required for optimum preformance.

Well, I have been doing a bit of hunting online regarding limited-slip rear ends to better understand what is taking place in the rear end.

I found this and thought others may find it useful:
Positractions & Limited Slips:
Transmits equal torque to both wheels when driving straight ahead. However when one wheel spins due to loss of traction, a patch of ice, mud, too much throttle, etc., the unit automatically provides more torque to the wheel that has traction. Recommended for daily driving, works well in ice, rain, mud and snow. However, in situations where absolute lockup is needed, a limited slip is not the best choice due to the fact that limited slips do slip in some situations.

Positraction is a type of limited slip and is a term that is used very loosely as another name or description for limited slip differentials. A positraction is not more aggressive than a limited slip or vice versa. The name "positraction" was used by General Motors for their limited slip differential and the name has been associated with limited slips for many years.

Don't forget, a 9-bolt is a cone not clutches.

If you are looking for a posi, Check www.tomsdifferentials.com
He set up the one in my car 12 years ago and after "many" autocross races I have never worn or broke the posi . I don't know if he has diffs. for 9 bolts but it wouldn't hurt to check it out.
He is in the city of Paramount.

I haven't forgotten. In fact, I'm wondering if the standard Red Line 75W90 gear oil is too slippery for the cone-style posi. I may need to switch to the 75W90 NS to get better lock-up.

I'm going to read thru my Helm manual this weekend and see if there is any information regarding gear oil in the 9-bolt.

Bret:
It may need some attention..such as tightening up (w/shims).

Okay, I've done some reading in the Helm manual and it appears the rear end is fine.

Here's a quick synopsis of what the manual has to say:
--------------------------
Limited Slip Rear Axle (Cone Type)
The clutch energizing force comes from the thrust of the side gears. Consequently, a free spinning wheel may not have enough resistance to drive torque to apply the clucth cones. If this occurs, apply the parking brake a few notches which will provide enough resistance to energize the clutch cones.

Under certain conditions where one wheel is on a very slippery surface and the other is on dry pavement, wheel spin can occur if over acceleration is attempted. Continued spinning may cause audible noise, such as a whirring sound, due to the cones lacking sufficiant lubricant. This does not necesarily indicate failure of the unit.

During regular operation (straight ahead driving) when both wheels rotate at equal speeds, there is an approximately equal driving force delivered to each wheel. When cornering, the inside wheel delivers extra driving force causing slippage in both clutch cones.
--------------------------

Like I said in an earlier post, I been out.

Now from an autoxer point of view. We use the RedLine N/S when the posi started to go. The posi will wear out faster with the N/S. Use you use the GM fluid and add only a half bottle of additive. YMMV