Transmission Oil
Instructor
Joined: Dec 2002
Posts: 242
Likes: 0
From: Port Orchard Washington
Your 1970 4 speed takes the same lube as the rear end (90 weight). Synthetics will work with the seals. I have used from 80w to 140w with no issues, but I don't like to mix weights or blends (personal preference).
Melting Slicks
Joined: Nov 2001
Posts: 2,668
Likes: 43
From: Eastern US XX
Originally Posted by 70vert
What fluid should I use in my 4 speed? Anybody using synthetic? Are synthetics compatable with old seals? What weight?
Safety Car
Joined: Aug 2000
Posts: 3,711
Likes: 43
From: San Antonio TX
What type of lube depends on how you drive the car. If you drive it like a normal, sane person you can use a synthetic and experience a little better shift smoothness. If you do high-rpm shifting, like in a drag race, you're better off with the regular mineral oil lube. The higher your gear speed the more grip you need on the syncros and blockers. Synthetics don't provide as much grip and it can be harder and take longer to make a high-rpm shift.
