hgoodwiniii

Can anyone let me know what (if anything) is recommended for rear end differential fluid replacement for a 1991 coupe with automatice transmission? How often should the fluid be topped off or changed? I can't find that the GM service manual covers this. If changing the fluid is recommended, can anyone let me know the best fluid to use? I'm sad to say, I've never changed the fluid. Seems as though I recall reading or hearing the factory fluid never needed to replaced when I first bought the car back in 1991. Also, the fill plug on my car sits side ways and faces between the underneath of one of the interior storage compartments. It looks almost impossible to remove the old fluid or fill with new fluid. Any ideas? Thanks.

geogolf

it time you change your fluid, i used redline 75/90 gear lube it has the limited slip addtive already in it. you have to suck out the old lube with a suction gun not easy to get it all but most of it comes out, if you can put car up on a lift makes job a lot easier there is only one hole in case you drain and fill from that hole, lube called royal purple is good too after you take old out you fill the gun with new and squirt it back in the hole you drained lube out of, when lube starts to pour from hole its full

CentralCoaster

The fill plug requires a 3/8" allen key.

bogus

www.c4guru.com - Changing Differential Fluid

hgoodwiniii

Thanks everyone. I'll give it a try.

runner140*

I followed your pics/instructions on the above web sit. Easy 15 minute job. Worst part of the job is getting the synthetic 75/90 W "OUT OF YOUR HAIR".

bogus

oh, man, you ain't kidding. That stuff is slick honey. yuck-o-matic.

hgoodwiniii

Ok everyone, just when I thought things got simplier, I decided to purchase the GM differential fluid. The service manual calls for SAE 80-90 GL5 (GM part #1052271). However, when I went to pickup the fluid only SAE 80W-90 GL4 (GM part #89021671 was available. I was told this replaced the fluid recommended by the service manual. Can anyone let me know if the replacement fluid will work in place of the recommended. What's the difference between GL4 and GL5? Also, what's the recommended change interval on power steering fluid? Is it hard to change? Once again Thanks.

onedef92

I used the Mobil 1 Synthetic Gear Oil and two bottles of the GM rear axle additive. Bogus' instructions are spot-on. I followed them, too.