Positraction total drain before refill
Thread Starter
2nd Gear
Joined: Nov 2008
Posts: 2
Likes: 0
Positraction total drain before refill
My 77 Vette (4200 mi.) appears to have its original positraction lubricant. We've drained as much as we could and refilled, but I'm still hearing an occasional grinding noise. If we start over, how do we suction out ALL fluid rather than most of it? (We now have 4 oz. bottle of GM lube additive--something we didn't know about before. Any ideas or suggestions?) Thanks! "Second 77"
Safety Car
Joined: Oct 2006
Posts: 3,930
Likes: 15
From: Calgary Alberta
My 77 Vette (4200 mi.) appears to have its original positraction lubricant. We've drained as much as we could and refilled, but I'm still hearing an occasional grinding noise. If we start over, how do we suction out ALL fluid rather than most of it? (We now have 4 oz. bottle of GM lube additive--something we didn't know about before. Any ideas or suggestions?) Thanks! "Second 77"
Le Mans Master
Joined: Mar 2002
Posts: 8,575
Likes: 3
From: On an island surrounded by sharks Hawaii
That's not good...and I doubt it will go away after you replace the oil. How many bottles of additive and gear lube did you use? It should be 2 of each in the diff. If that didn't do anything, then it sounds like one of your clutch plates is broken...which requires a total rebuild.
Must have gear lube additive
Tech Contributor
Joined: Aug 1999
Posts: 15,135
Likes: 3,939
From: Connecticut, USA
You can try up to 2 bottles of additive and use Lucas 85-140 gear oil- non syn.
Look at the endplay in the yokes as well, you may have worn yokes hitting the housing. The mid 70's cdiff were not the best. Q/C in some areas went down during this period, the units themself are good the posi clutches, RG bolts,and side yokes were junk. Hopefully you don't have internal issues, if the additive doesn't work your only option is to drop it and check it. If the yokes are worn more then .100 replace them. Look up my threads on this work and you'll find a lot of pictures. If you can't find them PM me or someone here will probably link you to them.
If you have questons you can contact me.
Good luck
Look at the endplay in the yokes as well, you may have worn yokes hitting the housing. The mid 70's cdiff were not the best. Q/C in some areas went down during this period, the units themself are good the posi clutches, RG bolts,and side yokes were junk. Hopefully you don't have internal issues, if the additive doesn't work your only option is to drop it and check it. If the yokes are worn more then .100 replace them. Look up my threads on this work and you'll find a lot of pictures. If you can't find them PM me or someone here will probably link you to them.
If you have questons you can contact me.
Good luck
Pro
Joined: Sep 2002
Posts: 624
Likes: 1
From: Melbourne, Fla. 6 months- New Middletown, Ohio 6 months
Back to your original question, I have a drain plug on my differential. Mine is just a 1/8" pipe plug. Here is a link to some pictures of where other members have installed drain plugs.
One of the comments in the link below was that drilling a hole in the case would weaken it. When mine was drilled it was offset about 1/2" to the passenger side. Can not see where that 1/4" diameter offset hole would of weakened the case that much. My guess is that the only reason the person who tapped the hole offset it was that he thought there might possible be a weak point where it looks like there were two halves to the case. Haven't looked at it enough to determine how the casting was made.
http://forums.corvetteforum.com/c3-t...rain-plug.html
One of the comments in the link below was that drilling a hole in the case would weaken it. When mine was drilled it was offset about 1/2" to the passenger side. Can not see where that 1/4" diameter offset hole would of weakened the case that much. My guess is that the only reason the person who tapped the hole offset it was that he thought there might possible be a weak point where it looks like there were two halves to the case. Haven't looked at it enough to determine how the casting was made.
http://forums.corvetteforum.com/c3-t...rain-plug.html
Last edited by Red 71; Dec 6, 2008 at 03:12 PM.
CF Community Team
Joined: Oct 2004
Posts: 19,354
Likes: 5,240
From: Cape Cod, Mass.
2025 C6 of the Year Finalist - Unmodified
2025 C8 Z06/7/E-Ray of the Year Finalist - Unmodified
2023 C3 of the Year Finalist - Unmodified
2021 C8 of the Year Finalist Unmodified
2020 Corvette of the Year Finalist (performance mods)
2019 C1 of Year Winner (performance mods)
2017 Corvette of the Year Finalist
2016 C2 of Year
2015 C3 of Year Finalist
If you've already suctioned out most of the fluid and re-filled it just add the 4 oz bottle of GM posi additive (really preferable to put the lube in first and then fill).Take the car out and do some figure eights in a parking lot to work the posi lube into the clutches. That should help. Then drive it for a while. If that doesn't work you may have some internal issues.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)
Joe Kucinski
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Top 10 C9 Corvette MUST-HAVES to Fix These C8 Generation Flaws!
Michael S. Palmer
10 Revolutionary 'Corvette Firsts' Most People Don't Know
Joe Kucinski
5 Reasons to Upgrade to an LS6-Powered Corvette; 5 Reasons to Stay LT2
Michael S. Palmer
2027 Corvette vs The World: Every C8 vs Its Closest Competitor
Joe Kucinski
10 Most Common Corvette Problems of the Last 20 Years!
Joe Kucinski
Tech Contributor
Joined: Aug 1999
Posts: 15,135
Likes: 3,939
From: Connecticut, USA
Back to your original question, I have a drain plug on my differential. Mine is just a 1/8" pipe plug. Here is a link to some pictures of where other members have installed drain plugs.
One of the comments in the link below was that drilling a hole in the case would weaken it. When mine was drilled it was offset about 1/2" to the passenger side. Can not see where that 1/4" diameter offset hole would of weakened the case that much. My guess is that the only reason the person who tapped the hole offset it was that he thought there might possible be a weak point where it looks like there were two halves to the case. Haven't looked at it enough to determine how the casting was made.
http://forums.corvetteforum.com/c3-t...rain-plug.html
One of the comments in the link below was that drilling a hole in the case would weaken it. When mine was drilled it was offset about 1/2" to the passenger side. Can not see where that 1/4" diameter offset hole would of weakened the case that much. My guess is that the only reason the person who tapped the hole offset it was that he thought there might possible be a weak point where it looks like there were two halves to the case. Haven't looked at it enough to determine how the casting was made.
http://forums.corvetteforum.com/c3-t...rain-plug.html
