79 differential plug removal
Thread Starter
Instructor
Joined: Nov 1999
Posts: 233
Likes: 0
From: Downers Grove, IL, USA IL
79 differential plug removal
My 79 vette seem to be leaking from the plug. (I had it checked before the Hot Rod Power tour from IL to WI) I don't know if it just loosened or ??? but I don't know what to use to get at it. A 5/8's 12 point is to small and 11/16's seems to large. What's up? any suggestions? Metrics? I can't seem to get anything else up there with the spare and spring in the way. Thanks in advance.
Race Director
Joined: Sep 2004
Posts: 11,874
Likes: 263
From: Arlington Va Current ride 04 vert, previous vettes: 69 vert, 77 resto mod
Originally Posted by RJPvettes4ever
My 79 vette seem to be leaking from the plug. (I had it checked before the Hot Rod Power tour from IL to WI) I don't know if it just loosened or ??? but I don't know what to use to get at it. A 5/8's 12 point is to small and 11/16's seems to large. What's up? any suggestions? Metrics? I can't seem to get anything else up there with the spare and spring in the way. Thanks in advance.
if its the one i'm thinking about isn't it a square head? you would use an 8 point socket of the appropriate size, measure the width and any tool shop should have them...
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,443
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
It is a special item. I also have a 79. I stopped a SnapOn truck and he had it in 1/2 drive socket attachment. He knew exactly what I was asking for.
it's the filler cap, your refering to?
it's the filler cap, your refering to?
Melting Slicks
Joined: Aug 2003
Posts: 2,135
Likes: 2
From: Dayton Oh
I used a cresent wrench on mine. Can only get about 1/8" travel at a time but slowy was able to get mine out. Afterwards, it used a wire brush on the threads and applied a liberal coat of anti-sieze. Good luck
Tech Contributor
Joined: Aug 1999
Posts: 15,114
Likes: 3,900
From: Connecticut, USA
Should be a 5/8" square head -3/8" npt plug. I use teflon tape or Permatex high temp thread sealant on them to seal. I had one last year that was so tight it rounded off the corners. I had to remove the tire tub to get it off with 2' channel locks! This plug has a flange head too so you won't find the exact same type very easily. I used a 3/8" npt plug to replace it and it worked well.
Gary
Gary
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
10 Most Common Corvette Problems of the Last 20 Years!
Joe Kucinski
5 MOST and 5 LEAST Popular Corvette Model Years in History!
Joe Kucinski
2027 Corvette Buyer's Guide: Everything You Need to Know!
Joe Kucinski
10 Things C8 Corvette Owners Hate (But Won't Tell You)
Joe Kucinski
10 Best Corvettes Coming to Barrett-Jackson Palm Beach 2026!
Brett Foote
Every Corvette Grand Sport Explained! (C2, C4, C6, C7, & C8)
Joe Kucinski
Grand Sport & Grand Sport X Launch Alongside All-New 535hp LS6 V8!
Michael S. Palmer
5 Reasons Bad Drivers Crash & 5 Ways to Avoid a Costly Mistake!
Joe Kucinski
7 Bolt-On Upgrades From Extreme Online Store to Level Up Your C6 Corvette
Pouria Savadkouei
Le Mans Master
Joined: May 2000
Posts: 6,493
Likes: 6
From: Bloomington MN
Cruise-In II Veteran
Go to Home Depot and get a Rigid aluminum pipe wrench...18 inches should be fine. It will EASILY get the plug out and then you will have a nice pipe wrench for using around the house. 
Instructor
Joined: Aug 2003
Posts: 111
Likes: 0
From: South-western Ontario
I removed mine this past summer. I took the spare tub out first and used a crescent wrench to remove the plug. It was time consuming but got the thing out. I found it was very tight when truning, almost seemed like I was stripping the thread when taking the plug out and putting back in. I cleaned the threads on both but still found very tight. Is this normal?
Melting Slicks
Joined: Oct 2004
Posts: 2,662
Likes: 8
From: Knoxville Tennessee
I kept fitting 12 point sockets over the plug until I found the one that fit. Attached extensions until the ratchet cleared enough to turn the plug and the rest is history. Topped off the diff and reinstalled the plug. Still have a leak and think it is the rear cover which brings up another repair not associated with this thread. I hope that tightening your plug solves your problem.
Thread Starter
Instructor
Joined: Nov 1999
Posts: 233
Likes: 0
From: Downers Grove, IL, USA IL
I won't be able to get to it this weekend and I hope it's not the diff. but I have a place to start. As to those who suggest taking the spare tub off, I considered it but my bolts are pretty rusty so I will try that as a last resort because I can see that opening another can of worms. I am going to Chevy vette fest tomorrow in Chicago and will see about new tub bolts to just cut them off and put new ones on. Thanks for the tips.
Team Owner
Joined: Jul 2004
Posts: 40,239
Likes: 786
From: Redondo Beach, California
When I had my differential rebuilt by Toms Differential, they returned the differential with my stock plug, but also gave me one they suggested I use instead. It had a allen wrench socket drive and a magnet on the inside. The allen wrench drive really makes it a lot easier to remove and install the plug.
