I have an 85 IROC Z with a posi rear end. Got the whole car for $800 because it wouldn't fire (someone swapped in a 350 and didnt wire the distributor correctly) its been a fun car despite being a bit of a beater...

Anyway I put it on stands to change the tires and I noticed the back wheels are really hard to turn by hand! I thought it was the brakes because it kind of surges when breaking from about 5 to 0 mph. Figured they needed some tlc, but even after removing both drums it still is hard to turn the axle forward and almost impossible to turn in reverse. (Yes, it is in neutral with park brake off. Even the drums are removed.)

The car seems to drive alright but of course if it has been like this the whole time they maybe I just don't know what right is. I don't have any experience with a posi rear end so I don't know if this is normal, but I have had other vehicles with open diffs and LSDs and never had something like this happen. The only thing I can compare it to is the open diff on my 84 project car which spins fairly freely... Is this a posi thing?

Again jacked up, in neutral, wheels and brakes off. It is hard to turn forward and almost impossible to turn in reverse. I haven't pulled the cover yet because I don't have the time and I'm kinda afraid to see what's going on to be honest. Don't want to dump more than the whole car is worth in a new diff...

Anyone had this happen before? Thanks!

 

You are feeling resistance from the transmission. It has nothing to do with the rear end. If you remove the drive shaft then the rear end will turn easy. The reason that your other rear ends turn easy is because the standard differential allows the other axle to turn in the opposite direction and the drive shaft is not trying to turn the transmission. The LSD in the '85 IROC is forcing the drive shaft to turn because the opposite axle can not turn the other way, so you are feeling internal resistance in the transmission. If you have someone hold the opposite axle in one of your other cars and you try to tun it you will feel the same resistance in them because the drive shaft will have to turn.

 

Right but it still seems excessive. Going backwards I can literally barely turn the wheel. Forwards it is about 1/2 that resistance but still very hard to turn. I'm very mechanically inclined and know how various LSD'S work but it just seems off... I guess I'm just being paranoid. Either way replacing the diff is more than I want to invest into this thing, I just want to keep it until my other one is on the road. Hopefully I'm wrong with my worries!

 

In neutral with drums removed it should be very easy to turn. Remove thw drive shaft and try to turn the rear end. If no change then you have an issue inside the axle.

 

BigGearHead is absolutely right. When you turn the wheel on an LSD, since the carrier will not differentiate, it MUST spin the driveshaft. The 700R4 turns hard one direction, and a little bit easier the other direction (in neutral). Both give resistance due to the nature of a planetary geared automatic transmission design. My Trans Am is exactly the same and has a Torsen in it that I built personally, and a race built 700R4. This is completely normal.

GD

 

Ok yeah you guys are right I just popped off the drive shaft and sure enough it spun fine! Grabbed the driveshaft and it would have a lot more resistance going in one direction which was what I was feeling spinning the wheel in reverse. Strange! Like I said I've had vehicles with LSD's before but they were either manual or the Allison in my duramax and none had this behaviour. This is my first th700 though!

Thanks for learnin me something new! Best part is I can save the money working on the diff for my other project car haha.