1975 4spd tip
Thread Starter
Racer
Joined: Mar 2012
Posts: 396
Likes: 13
From: New Bern NC
1975 4spd tip
I had shifting issues with my tranny. Grinding into 1st and reverse, difficult to get into gear. I thought I needed to adjust the linkages but decided to go with the basics first. I drained the fluid and replaced it with 5oz of 40 weight motor oil and then topped her off with the 75-90 gear oil. After a 20 mile drive she was smooth as could be. Its been a 100 miles since then and she is still buttery smooth on the shifts. So if you are having issues and your fluid is old, change it first before your pull out the wrenches. 
Had a 1976 L-82, 4-sp
Joined: Mar 2011
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From: Some days your the dog and some days your the hydrant.
Royal Canadian Navy
Thread Starter
Racer
Joined: Mar 2012
Posts: 396
Likes: 13
From: New Bern NC
It is starting at the basics but it seems that the first recommendation on posts about hard shifting result in adjusting the shift linkages. I couldnt find the spacing tool to make the adjustments so I changed the fluids instead.
The 40 weight oil is to help thin the gear oil a little to help it get into tight places. The gear oil I used was GL5 so I am good there. I wanted to go synthetic but everyone said that synthetic is hard on the brass synchros. I know it sounds crazy but it works and the shifter doesnt get hot anymore. Others have used straight 30 weight but I dont have the guts to go that thin.
The 40 weight oil is to help thin the gear oil a little to help it get into tight places. The gear oil I used was GL5 so I am good there. I wanted to go synthetic but everyone said that synthetic is hard on the brass synchros. I know it sounds crazy but it works and the shifter doesnt get hot anymore. Others have used straight 30 weight but I dont have the guts to go that thin.
Last edited by ATIS; Jun 15, 2012 at 06:20 PM.
Drifting
Joined: Jun 2007
Posts: 1,404
Likes: 1
From: Ansonia/NYC CT
It is starting at the basics but it seems that the first recommendation on posts about hard shifting result in adjusting the shift linkages. I couldnt find the spacing tool to make the adjustments so I changed the fluids instead.
The 40 weight oil is to help thin the gear oil a little to help it get into tight places. The gear oil I used was GL5 so I am good there. I wanted to go synthetic but everyone said that synthetic is hard on the brass synchros. I know it sounds crazy but it works and the shifter doesnt get hot anymore. Others have used straight 30 weight but I dont have the guts to go that thin.
The 40 weight oil is to help thin the gear oil a little to help it get into tight places. The gear oil I used was GL5 so I am good there. I wanted to go synthetic but everyone said that synthetic is hard on the brass synchros. I know it sounds crazy but it works and the shifter doesnt get hot anymore. Others have used straight 30 weight but I dont have the guts to go that thin.
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Had a 1976 L-82, 4-sp
Joined: Mar 2011
Posts: 5,338
Likes: 1,213
From: Some days your the dog and some days your the hydrant.
Royal Canadian Navy
It is starting at the basics but it seems that the first recommendation on posts about hard shifting result in adjusting the shift linkages. I couldnt find the spacing tool to make the adjustments so I changed the fluids instead.
The 40 weight oil is to help thin the gear oil a little to help it get into tight places. The gear oil I used was GL5 so I am good there. I wanted to go synthetic but everyone said that synthetic is hard on the brass synchros. I know it sounds crazy but it works and the shifter doesnt get hot anymore. Others have used straight 30 weight but I dont have the guts to go that thin.
The 40 weight oil is to help thin the gear oil a little to help it get into tight places. The gear oil I used was GL5 so I am good there. I wanted to go synthetic but everyone said that synthetic is hard on the brass synchros. I know it sounds crazy but it works and the shifter doesnt get hot anymore. Others have used straight 30 weight but I dont have the guts to go that thin.
Race Director
Joined: May 2006
Posts: 16,528
Likes: 53
From: Dayton, Ohio
Drifting
Joined: Aug 2005
Posts: 1,372
Likes: 4
From: Springfield VA
It is starting at the basics but it seems that the first recommendation on posts about hard shifting result in adjusting the shift linkages. I couldnt find the spacing tool to make the adjustments so I changed the fluids instead.
The 40 weight oil is to help thin the gear oil a little to help it get into tight places. The gear oil I used was GL5 so I am good there. I wanted to go synthetic but everyone said that synthetic is hard on the brass synchros. I know it sounds crazy but it works and the shifter doesnt get hot anymore. Others have used straight 30 weight but I dont have the guts to go that thin.
The 40 weight oil is to help thin the gear oil a little to help it get into tight places. The gear oil I used was GL5 so I am good there. I wanted to go synthetic but everyone said that synthetic is hard on the brass synchros. I know it sounds crazy but it works and the shifter doesnt get hot anymore. Others have used straight 30 weight but I dont have the guts to go that thin.
The numbers on differant oil types can't be compared 1 to 1 like you are thinking. 40wt engine oil is thicker cold and slighty thinner when warm when compared to a 75w90 gear oil.
The CsT of Chevron 40wt is...
40 = 136
100 = 14.7
Mobil1 75w90 is...
40 = 99
100 = 15.2
So in the end you probably ended up making it a little thicker, not thinner.
Le Mans Master
Joined: Mar 2008
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From: Oxford MA-----You just lost the game!!!!
Ever stop and think that maybe your transmission is shifting nicer just because you changed the fluid, and it may have nothing to do with the snake oil?
Keep the shiny side up!
Scott
Keep the shiny side up!
Scott
Drifting
Joined: Mar 2011
Posts: 1,886
Likes: 9
Your symptoms sounded to me like the clutch wasn't releasing fully.
Can't imagine that engine oil is the right choice in a manual trans. You could try putting in a bottle of the positraction additive into the transmission to improve shifting performace. Worked for me.
Can't imagine that engine oil is the right choice in a manual trans. You could try putting in a bottle of the positraction additive into the transmission to improve shifting performace. Worked for me.
Race Director
Joined: May 2006
Posts: 16,528
Likes: 53
From: Dayton, Ohio
Thats what I thought when I read the OP. I doubt that 5 oz of motor oil is going to hurt a standard trans,it just thinned the 90 a bit.
Thread Starter
Racer
Joined: Mar 2012
Posts: 396
Likes: 13
From: New Bern NC
I didnt mess with the clutch at all so the fluid change fixed it. I did think that maybe it just needed a fluid change since it was 37 years old (but had less then 7,000 miles on it). I changed the the diff at the same time.
Race Director
Joined: May 2006
Posts: 16,528
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From: Dayton, Ohio
Glad the lube change fixed it for you.
Thread Starter
Racer
Joined: Mar 2012
Posts: 396
Likes: 13
From: New Bern NC
Thanks, I was calling around to a dozen places looking for someone that could adjust the linkages after I couldnt find the tool on line. I live in a small town and it was a no go. I have only found one guy that will even touch a Carb and he is an old school racer. Most of the guys and gals in the Corvette club take their cars 2 hours away to get them worked on.