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diff drain plug '71?


Well-known member
Dec 27, 2000
Florence, SC (Timmonsville SC)
71 War Bonnet Yellow VERT 71 BH Blue CPE (SOLD)
Okay...go ahead and laugh now, but...I'm trying to find a drain plug in the differential of '71. Possibility diff is not year-correct. No, I don't have a manual. But, other cars' rear ends had drain plugs...please tell me this one does too...and I just don't know where to look...or it's covered w/grime. Haven't had the car too long and it's my first vette...have it in the air now doing other repairs and engine overhaul...would really like to drain it and replace with fresh gear oil and posi goo. After you've finished goofing on me...please inform?
Drain plug?


You aren't nuts. The carrier is basically like other GM centers in that you have to remove the rear cover to drain it. To drain the rear end you need to loosen the bolts that hold the carrier to the rear cover which in a Corvette also happenes to be the spring mount. You can spread them apart enough to allow the fluid to drain without removing the drive shaft. Be careful not to damage the gasket or force the drive shaft into the rear of the trans.

Refill with GM Multi- purpose Differential Lube and be sure to add a bottle of Posi-traction additive. It keeps the posi clutches from glazing and getting hard causing chattering and jerking going around corners.

Tom: Thanks for your diff drain info. I'll try "carefully" loosening the rear cover. I do know where fill plug is! Right about other GM 10 & 12 bolts...just pop the cover. But, It seems to me that GM's Advanced Quality Planning and Design Review failed on this app. FOMOCO just as lax...about as silly as spark plug r&r on big block 68 cougar.
Not laughing at you, more like with you

Jack said:
Okay...go ahead and laugh now, but...I'm trying to find a drain plug in the differential of '71. After you've finished goofing on me...please inform?

I know the '71 pumkin is different than the one in my '81, but I have to tell this little story, It's TRUE.

I took my '81 out to the local Chevy garage to have the rear end drained and new lube and GM Posi Additive put in. I dropped the car off and my wife and I went for breakfast. Got back to the dealer in a couple of hours and the service writer said We're sorry but you'll have to make an appointment to have the fluid changed, we're unable to do it in the lube shop. I said what is the problem, they told me the rear end didn't have a drain plug. hmmmmmmmmmmmmmmm I brought the car home and crawled around under it looking for the drain plug, yep sure enought NO drain plug.

I have the assy manual and the Shop Manual, but couldn't figure out what it was saying for sure. So I asked the question on the old L81Registry and right out of the box a Tomlin explained where it was, sure enough there it was on the passagers side on the top side of the pumkin. So I called the Chevy dealer and took it back out to them and showed them where it was, "They were somewhat embarassed and changed the fluid and put in the GM posi additive and only charged me $12.50 for the fluid and additive.

How this relates to your '71 I'm not sure, but maybe, just maybe your '71 is similar. And another point here is to be sure to use the GM additive part #1052358. GM lube #1052272 is also recommended.
vacuum it out?

Thnaks Rare81 for your info. I'd thought about (still thinkin') sticking a poly hose in the fill hole and trying to suck the old lube out. Whether I pry it out (separate cover) or suck it out, I'll replace with the good stuff you recommended. Regards, Jack
Make sure you buy a new one

hey Jack,
Borrow the "Turkey Baster" and a little poly tubing from the local fish story. Just be sure to buy mom a new Turkey Baster before next Thanksgiving:J
Just a note, but I have been told by more than one source to add 2 bottles of posi additive when changing the diff fluid.


It sucks

I use a suction pump, looks like a grease gun, but has a poly tube.Just suck the old out. When refilling I us the suction pump to fill also. I clean out the pump, stick it in the bottle(I premix the additive in first with the gear oil) then refill. As far as getting the plug out, we use a crow's foot (63-79) with extention. I too, have been told to use two bottles of additive, however I don't necasarlly agree with this. After refilling with new, take your car to a large parking lot(I know that you can't right now if the motor is out) and do "slow" figure 8's, this will force the clutches to work, and get the new grease in them. If, after doing this, you still have a "hopping" while going around slow corners(like at stop lights) then do it again. I doubt that adding 2 bottles of additive will hurt anything, and it may even help, but that's not what Chevy called for, not that they are always right, they didn't put a drain plug in:) Hope this helps......Steve
jack, i have a 71 454 4sp conv it does not have a diff drain plug. started to just suck it out but glad i didnt. went ahead and pulled the cover and found small particles of metal in the bottom of the diff. gears and bearings all checked good looked like just 80 thousand miles of wear. dont know the condition or how long yours has been in survice but it something to think about.i got two bottles of 1052358 limited slip axle lubricant additive from gm about 8 dollars a bottle. hope this helps robert
turkey baster & crazy 8's

Thanks Steve, Jim, Bud, Robert and Tom for the info. Finally, I do have a use for either of two "inherited" turkey basters...twang,twang "she got the gold mine...I got the (sic)basters." My "new" old beater's probably rolled over twice...and had been badly neglected. I should consider pulling cover to get at any tramp metal...maybe flush/spray out with kero or brake cleaner...if only GM'd put 1/2" npt hole down there it'd been perfect for a 2 buck mag plug. I do like that figure 8 tip. So far the rear's not so noisy nor "hopping" but, like Robert's BB, it probably has some metal. One bottle or two...I've heard either. A typical American; I might use two.
Regards, Jack

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