Hey all,

I have read here that I should try adding some Posi additive to my differential to see if it helps with the horrible crunching sound I am hearing. The stupid question of the day, where is the drain plug? I can see the full level bolt on the side but where is the actual drain plug?

I also read to remove the spare tire tub to get in there. Do the "T" bolts that hold the tub just simply unscrew from the frame, or is there some other way to get the tub off. The bolts are pretty rusty so I don't want to haul on them too hard unless I know for sure that it is the correct thing to do.

|UPDATED|11/14/2003 12:36:13 PM (AZT)|/UPDATED|

There is no drain plug,you have to syphon the old grease out.go down to your local auto shop,I got mine at advance auto.get a cheap syphon pump,2 quarts G.M. Posi Lube,2small G.M. posi lube additive for limited slip differentials.jack up right rear wheeel of car remove wheel.take out filler plug put syphon hose as far in and to the bottom as you can,syphon out as much of the grease as you can,next add the 2 bottles of additive first,then add the lube to fill it up untill it just reaches the bottomthreads of the filler plug hole.put the plug back in put the wheel back on take it for a ride.after4or500 miles if its still making noise repeat the whole procedure,drain and refill.If the noise doesnt stop,youve got major problems inside.the noise is usually the limited slip clutches that are sticking together inside the rear end the additive cleans the clutches so they can slip like they are supposed to.Ihad to do this 3 times to my 78,its got74000 miles on it,dont think the lube had ever been changed.try it,you'll like it. P.S. no you dont have to take off the spare tire tub to do this. Ron 78 |

Hi Jeremy,

I don't know about the spare tire tub bolts, but there is not a drain plug on the differential of stock, standard cars. If there is one it is because it was drilled and tapped during a rebuild, or because it is an aftermarket case.

You need to siphon the gear lube out and that is best done on a warm day so that the stuff is a little less like molassas.

Thanks guys, I had a suspicion of what you are saying, a mechanic told me there was 2 openings, I guess he wasn't familiar with vettes.

I am pretty new to this whole corvette thing, I have been wanting one for years and finally got a 72 LT-1, what a blast!

You'll have a great time with your car,if your not mechanically inclined,your buddies will help you,everybody likes to hang around vettes.just make sure you do repairs right the first time,some parts can be very expensive,dont try to cut corners unless you know it will work.take your time ,dont forget this car is over 30years old,nuts and bolts will need to be nursed out,lots of wd-40,replace them with new ones whenever you can.just take care of it,baby it and she'll serve you well,you own a car that almost every man and some woman have wanted all thier lives,and some of us got lucky enough to get one.when your out driving it you'll be surprised at all the people who will stare ,point and wave at you,and another plus its a chick magnet,they love em. Ron 78 SAVE THE WAVE , SHARKS RULE

I took a look under there, I see the bolt no problem, but it looks pretty tight in there, what is the best tool to use I don't think a standard socket will fit on the square bolt very well and even if it does there really isn't much room to turn it out.

Any suggestions?

I just used a large socket that would fit on it without slipping,and a couple long extensions,and a ratchet,you may have to break it loose with a crescent wrench or an open end wrench.b-4 you put it back in put some oil on the threads.by the way when you syphon the grease out drain it into a drain pan to check ifthere is any metal in there,ps its gonna smell real bad.

Changing fluid could help, make sure you use GM plus the additive. I have also seen the bolts that hold the ring gear come lose in the rearend especially on 1970-72 corvettes. I had a noise in mine and it turned out to be 3 lose bolts on the ring gear. Hope the fluid change works. Good Luck

Mike

OK, this is a project that I was planning on taking on today 'cause I'm taking a long trip to Florida for Thanksgiving, then on to Daytona Beach for the Turkey Run. I took my '80 in to a quickie lube place and the guy said he couldn't get the filler plug out 'cause it was "wallered out". I think mine has the kind that takes a 3/8ths ratchet to get it out, but y'all mentioned the kind with a square head on it? I'll figure it out when I get under there. My real question is how do I know if I have a posi unit or not? I don't thrash on my car, but I did kinda gas it in my driveway and there were 2 patches of rubber left, so does that mean I have a posi unit for sure? Would using the GM posi lube and additive mess up a non-posi unit? Sorry, I've never really messed with the 3rd members before...

As far as I know they all have posi,the lube wont hurt if it doesnt.