Hello, I have a 1985 Z51 with a 4+3 transmission. The car has about 93k on it. I want to change the fluid in the tranny and diff because Im not sure when it was done last. However Im having a hard time nailing down the capacities of these things

I have read the following capacities while searching the forum:

4-speed = 1qt
OD unit = 1.7qts
Diff = 1.5qts + 4-8oz of limited slip additive

These capacities seem a bit low to me so Im looking for someone to verify these or give me the correct ones. Also, I found a additive called "Trans-X" at my loca auto store and it says its compatibile with vehicles that use the GM brand additive. Anyone have any experiences with this?

-Thanks

 

http://www.amsoil.com/mygarage/vehic...LET+CORVETTE+8

There is not only a list of recommended fluids but scroll down to find the capacities for all the fluid systems.

 

Thanks for the link! very helpfull. That just seems like very little fluid to me but this is my first vette.

 

If you do a search on "4+3" you can find lots of info on the fluids for the manual tranny.

First off do not use a synthetic ATF in the OD unit. You may risk getting leaks into the 4-speed portion. Use a Dexron III ATF fluid. The filter is the same one used in late 60's thru early 70's Ford FMX auto trans. These were used in some Mustangs, Cougars, Fairlanes and F-150's. Cost about $8-$10 at a parts store. Change the fluid and filter annually or every 12-15K miles.

The OD unit will use about 2.2 quarts if you flush the cooler lines. Remove the two lines from the OD unit and use 10psi of air pressure to blow out the old fluid. Re-connect the lines, install the filter and add ATF thru the filler hole until it runs out. With a rear wheel off the ground, spin the tire for a couple minutes. This causes the pump in the OD unit to push fluid thru the coolant lines. Go back and top off the OD unit and insert the drain plug.

Both the 4-speed and the rear diff use a GL-5 80W-90 gear oil and the diff needs one bottle of the GM posi additive.

You have to suck the old gear oil from the diff so the amount you get out determines how much goes in. You should be able to get 90% or more out with one of the cheapie Harbor Freight pumps. Use the same pump to push in about half a bottle of gear oil, stop and add the bottle of posi lube and empty the bottle. Keep adding until gear oil runs out of the hole.

When you service the 4-speed, make sure you can remove the fill plug before you remove the drain plug. If the fill plug won't come out, you will have fun getting oil back in.......

 

Thanks everyone! How about using "Trans-X" as a diff additive? Also, I got Royal Purple "Max Gear" 75-90 for the tranny and diff, any thoughts?