C1 Differential Drain Plug
Thread Starter
Instructor
Joined: Oct 2013
Posts: 181
Likes: 1
From: Honolulu Hawaii
C1 Differential Drain Plug
Hi Corvette gang!
The drain plug on the rear differential is leaking. Upon removing plug I found metal washer that cannot be removed. The plug have 4-machined cuts across the threads, so I can't back out the washer.
I cannot find new drain plug on any of the catalogs, Corvette Central or Paragon. Not sure if NAPA would have a new plug.
Can anyone please offer any help? I did not want to chance my dog ingesting the gear oil from her pawls.
Aloha,
Eric
The drain plug on the rear differential is leaking. Upon removing plug I found metal washer that cannot be removed. The plug have 4-machined cuts across the threads, so I can't back out the washer.
I cannot find new drain plug on any of the catalogs, Corvette Central or Paragon. Not sure if NAPA would have a new plug.
Can anyone please offer any help? I did not want to chance my dog ingesting the gear oil from her pawls.
Aloha,
Eric
Drifting
Joined: Apr 2005
Posts: 1,526
Likes: 61
From: TU CUM CARI NEW.MEX.
Hi Corvette gang!
The drain plug on the rear differential is leaking. Upon removing plug I found metal washer that cannot be removed. The plug have 4-machined cuts across the threads, so I can't back out the washer.
I cannot find new drain plug on any of the catalogs, Corvette Central or Paragon. Not sure if NAPA would have a new plug.
Can anyone please offer any help? I did not want to chance my dog ingesting the gear oil from her pawls.
Aloha,
Eric
The drain plug on the rear differential is leaking. Upon removing plug I found metal washer that cannot be removed. The plug have 4-machined cuts across the threads, so I can't back out the washer.
I cannot find new drain plug on any of the catalogs, Corvette Central or Paragon. Not sure if NAPA would have a new plug.
Can anyone please offer any help? I did not want to chance my dog ingesting the gear oil from her pawls.
Aloha,
Eric
Race Director
Joined: Mar 2001
Posts: 14,636
Likes: 4,685
From: Mustang OK
2026 Corvette of the Year Finalist - Modified
2025 c1 of the Year - Modified Winner
2024 C1 of the Year Finalist - Modified
2023 C1 of the Year Finalist - Modified
2015 C1 of the Year Finalist
It sounds to me like the typical oversize drain plug. Those 4 cuts across the threads were to allow the larger threads to be cut into the hole. As mentioned, a brass washer under the head of the plug MAY and MAY NOT cure the leak. From the factory, the drain plugs had a sealing washer under the head.
The ONLY sure way to stop the leak is to either fix the hole by welding around the hole and then tap new, correct size threads, OR, remove the housing from the car and have a nut welded to the inside of the housing to provide more threads for the drain plug to get a tighter grip without stripping the threads, as shown below.
The ONLY sure way to stop the leak is to either fix the hole by welding around the hole and then tap new, correct size threads, OR, remove the housing from the car and have a nut welded to the inside of the housing to provide more threads for the drain plug to get a tighter grip without stripping the threads, as shown below.
Last edited by DZAUTO; Jan 27, 2016 at 10:22 PM.
Team Owner
Joined: Aug 2007
Posts: 58,061
Likes: 7,146
Army
I don't know why those drain plugs are so hard to find...still haven't gotten a replacement for my rounded off '61 plug. Tom has given you good advice (as always). Now, I'll give you the Bubba fix.....I cut a round gasket out of some gasket material available nearly anywhere and used it to seal the drain plug. No more leaks.
Someday I'll pull things apart and do a permanent fix...
Someday I'll pull things apart and do a permanent fix...
Drifting
Joined: Nov 2007
Posts: 1,711
Likes: 179
From: Hightstown NJ
It sounds to me like the typical oversize drain plug. Those 4 cuts across the threads were to allow the larger threads to be cut into the hole. As mentioned, a brass washer under the head of the plug MAY and MAY NOT cure the leak. From the factory, the drain plugs had a sealing washer under the head.
The ONLY sure way to stop the leak is to either fix the hole by welding around the hole and then tap new, correct size threads, OR, remove the housing from the car and have a nut welded to the inside of the housing to provide more threads for the drain plug to get a tighter grip without stripping the threads, as shown below.
The ONLY sure way to stop the leak is to either fix the hole by welding around the hole and then tap new, correct size threads, OR, remove the housing from the car and have a nut welded to the inside of the housing to provide more threads for the drain plug to get a tighter grip without stripping the threads, as shown below.
The next time you do one of those conversions, instead of drilling holes through the nut why not use an upside down castle nut?
Verne
Race Director
Joined: Mar 2001
Posts: 14,636
Likes: 4,685
From: Mustang OK
2026 Corvette of the Year Finalist - Modified
2025 c1 of the Year - Modified Winner
2024 C1 of the Year Finalist - Modified
2023 C1 of the Year Finalist - Modified
2015 C1 of the Year Finalist
I didn't have one available at the time --------------------- and NO, I still haven't touched the 56 yet. Right now, I've got 3 FI units on the workbench for customers which I need to get done soon because I'm getting the other knee replaced in 2wks (I'll be lucky to have 2 of them done before then).
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Race Director
Joined: Apr 2015
Posts: 17,571
Likes: 3,460
From: Fresno California
For the drain plug, a strand pulled off of a floor mop and wrapped around the plug under the head one or two revolutions will serve as packing and will seal right up. An old timer taught me this 35 years ago, and it really works. Trim off the excess after the install and it's invisible, too. On the diff gasket with oil weep, the only real cure is to take it back apart and use sealer on the mating surfaces and around the bases of the studs. Or install small copper washers under each nut..
Drifting
Joined: Jun 2005
Posts: 1,747
Likes: 192
From: nj
I don't know why those drain plugs are so hard to find...still haven't gotten a replacement for my rounded off '61 plug. Tom has given you good advice (as always). Now, I'll give you the Bubba fix.....I cut a round gasket out of some gasket material available nearly anywhere and used it to seal the drain plug. No more leaks.
Someday I'll pull things apart and do a permanent fix...
Someday I'll pull things apart and do a permanent fix...