Time to change the fluid in the differential--and I need the Vetterinarians' expert opinions on which method to use.

The garage nearby says they don't pump the pumpkin out, preferring to remove the case cover and drain it that way. Takes out more of any metal bits that might be in there, they advise. Makes sense to me.

But there's the small matter of access to that cover that concerns me. The spare tire holder and rear spring may pose potential problems (time=$, in plain English; and I don't have much of the latter to spend now).

So which way is better--pumping out or drop 'n drain? Or doesn't it make a whole lotta difference to the differential?

(I already have the GM brand lubricant and positraction additive on hand, either way)

I pump mine out. I got the pump from Boater's World. The kit has several hoses with different diameters. I drove the car to get the fluid hot and less viscous. The pump worked great. I also used the pump to inject the new fluid and additive. Put the additive in first so you use the entire bottle then add the differential fluid..

My 75 had terrible chatter in the posi-clutches. After the fluid change it is as smooth as silk.

Good Luck
Scott

I pump mine out,you wont get all of it,just move the hose around and keep suckin ,you'll get most of it.they do sell a plug kit which you can install on the cover,but I would want to take the cover off to install it,so as not to get any more metal in the differential like you said its a lot of work to get it off,you have to drop the spring off too,sometimes when you try to take the spring bolts off,it cracks the cover.do the pump thing

Check harbor freight for nifty little hand pumps... sometimes on sale they are only $4-5 bucks or so....

If the rear is not leaking, making any whining, chattering or clunking noises, pumping the gear oil out is fine. Make sure you use GM Positraction Additive when you refill. A cheap and worthwhile investment is also replacing the plastic vent cap on the top of th cover!! A few second worth of work. LukesVette2006-11-15 19:36:43

I'm wid ya'll!! Iffin it ain't makin no noise, or chatterin when ya turns da corners, jest pump it!! It will be mooch easier to do this if it is hot, like Scott said. The gear lube will be thinner, and easier to pump out.
Also, when pumping in the new lube, put the bottles in a bucket of hot water for a long time before putting it in...this will make it easier to pump the stuff back in. Put the posi additive in first, as was also mentioned.

I've pumped mine. Use the biggest hose that will work with the pump. I was able to get a good siphon working and just walked away from it for a couple of hours. Came back to find most of the fluid removed, enough to satisfy me. Poured it into an empty milk jug to see how much I had. At least 1 1/2 qts.

Filling it I was able to just use the squeeze bottle. Squeezed a little in and then added the posi lube to the bottle. Finished up as much as I could of the first bottle then poured what I could of the second bottle into the first to make sure all the posi lube got in. Kept adding to the first bottle til I got it all in.   Mike

I'm always looking for ways to improve the whole car.  That big, ugly metal spring weighs 34 lbs.  I would remove the spring, and replace it with a light weight fiberglass unit, or coil-overs.  While you're doing that, remove the diff. cover and clean everything out.  

I just realized that I've been scammed by the forum's computer.  It posted this post as a pop-up on my screen and I thought it was new.   Oh well, now I know.... 

Not yer puter doin that...it's the new stuff Adam has added, at the bottoms of the pages. I've fallen for it a couple of times myself....

I was wondering why you were pulling up such an old thread...