Hi,
I know I read a thread on this forum about syn vs. non-syn diff. oil. My question is about the drain plug. Mine is either very tight or it has seized. It doesn't seem right that a steel plug would seize in an aluminum housing, but I'm not sure. What does everyone else do when they want to drain/change the diff oil? Suck it out through the fill hole? Any information or advice on this job would be greatly appreciated.
Glen

 

did you try an impact gun on it?

 

Go tp http://www.corvettecentral.com then search the on line catalog for "drain plug". They have a kit there for $59.95 where you can drill and tap your diff in order to drain the fluid. As far as getting the upper plug out in order to fill it goes - don't know, maybe someone else has an idea. According to a Bloomington Gold seminar I attended you should put two containers of GM positraction additive in before you put the synthetic gear oil in. Good luck! Just thinking here, if you buy the kit and send it to me after you are done I will pay you $30, then I can use it and pass it on to someone else! All I would have to do is buy the plug at the hardware store to make it work. :cheers: :lurk:

 

I have a 96 and the lower bolt on the differential is not a drain plug as a Chiltons manual described compared to a GM service manual does not mention a drain plug at all. I used a small suction pump that is driven by a electric drill to suck the fluid out through the fill hole. I originally bought the suction kit from a boat store and when the little pump went bad I was able to purchase a new pump at my local Menards store. I also did use AMSOIL synthetic gear lube.

 

I use a suction gun to pull old fluid out. I am not a fan of synthetics although others will argue that statement. I use gm lube and 2 bottles of the gm posi additive. Some guys drill a hole in the bottom of the housing and put a plug in it. I wont do this. 1 more potential leak spot.

 

Same here; wasn't aware of a drain plug on stock Dana's. Unless the PO put one in, you'll have to suck the lube out through the fill hole.
I, too, use the GM lube and additive.

Larry
code5coupe
:seeya

 

Thanks for the information. I confess I did not check the GM service manual regarding this procedure. That hex bolt on the very bottom of my Dana 36 sure looked like it was a drain plug. Can't imagine what else it is supposed to be doing there. Does it strike anyone else as a particularly stupid idea to have to suction this diff. oil out rather than simply drain it out? What's next - spark plugs you can't reach to replace?!?! Oh well...time to add a suction gun to my tool inventory.
Glen

 

why dont you unscrew it and see?

 

- changing the differential oil on my 96 is on my "to-do" list, and i'll have to get a siphon pump. NAPA has a small unit for around $5 that seems to get decent reviews on other forums. as many times as i'll use it, $5 seems just about right.

 

There is no drain plug, I would love to see one try to get a impact on the fill/check plug, yeah right. You have trouble getting a hex socket or allen wrench on the plug.

Aftermarket kits to install a drain plug are available. As noted. Personally I run Redline Oil 75W90 Full Synthetic Gear Oil in the diff. Requires no posi additive. I added none when I changed mine and I run the heck out of my car with no problems. If you run your car hard, I would recommend their shockproof heavy weight gear oil, that is what I should have put in, but for whatever reason I did not.

 

I too thought the lowest cap screw holding the differential to the batwing was a drain plug; it's not. So the first time I changed the differential lube I used a suction gun and flexible hose fed through the fill hole.

Later, when I had my differential on the bench, I drilled and tapped the bottom for a 1/8" allen head pipe plug...which is a little small, but there ain't a lot of metal to work with. With the plug removed, it drains slow, but it does drain ...but here's the catch, it's difficult (almost impossible) to get to the drain plug with the exhaust system on. I think this would be true with the aftermarket kits too. So whenever my exhaust is off, I make a point to also change the differential lube.

Even when my differential was opened up and on the bench, it took forever to drain, clean, and remove all the original fluid. You will never get all the old fluid out with either a drain plug or suction gun / pump.

So....which ever way you choose, change the differential fluid and change it often.

And I do like that Red Line shock proof oil; kinda hard to find though.

 

I use a liquivac that works well to change the differential oil.

 

1984 to 1996 C-4 Corvettes do not have a differential drain plug. Google Petris Enterprises, formally Corvette Clinic and look at Product SKU 198496, 84-96 Differential Drain Plug Kit, $66.95. This kit is long drill, tap, drilling template and plug to install the drain GM left out. Installed mine years ago in my 95 and change every 2 years. The template and drill stop welded on the drill bit protect the ring gear from damage.