Engine and Transmission Tech

Tech question ?

I recently installed a Ford 8 inch Positraction limited slip differential in my RV8 GT2 car.

After one race weekend and the 2 SCCA National Races, the Driver reports loss of traction - wheel spin - on the right side, especially in tight, right hand turns. Like the Positraction differential isn't working. Before the Ford 8 inch Positraction was installed, we were using a fully locked MGB differential. Driver liked the locked MGB
differential, however a few races destroyed the ring and pinion.

Question ..... concerning Ford 8 inch Positraction gear oil ?

Obviously not thinking the conversion all the way through - I now realize that the Ford Positraction 8 inch differential might profit from using the correct Positraction gear lube in the differential. I had installed new "regular" differential gear lube - only to discover that Ford recommends "their" own Positraction gear lube - which is "89 W 90 Premium Rear Axle Lubricant ... and their Motorcraft Additive Lubrication Modifier. They said I need 3 quarts of their oil and 1 small bottle of their additive.

So ok ... I will change out the rear axle oil with the Ford Positraction oil, but I wonder if the oil can really make a difference in allowing the Ford 8 inch Positraction differential to work correctly.

What do you think ?

keep them on the track,

phillip g

The Ford Additive is to stop the clutch pack from popping. It is super slick. Perhaps the preload to the clutch pack is incorrect. Later 8.8 R/E have a S type spring to preload the pack. Some racers use the S-type spring from a F-150 to give better lockup than the std. car.. Sounds like the Trac-Loc is not properly set up. Ford's limited slip is Trac-Loc vs GM who's is Posi-Trac.
I did my own 8.8 Trac-Loc and it works great. No special tools needed, but I did use OEM additive and oil.
SAFETY FASTER!

I have an 8.8 w/Trak-loc like Kelly.
Ford calls for 80W90 oil and 4 oz of friction modifier part # C8AZ-19B546-A or CM-19546-A1 (3.8 oz)

> I wonder if the oil can really make a difference in allowing the Ford 8 inch Positraction differential to work correctly.

Just to be clear, we are talking about a drop out 3rd mmeber style 8" rear end
with a Trac-Loc clutch type limited slip, not the late model 8.8". For street
use, the usual street use recommendation is to use non-limited slip gear lube
and add the Ford friction modifier until the unit stops chattering on tight turns.
The friction modifer lowers the coefficient of friction so will allow more slippage
between the two sides.

Dan Jones

[api.viglink.com]

The above link has rebuild instructions for track use.

Jim

Great link Jim. Thanks for sharing.
Mike

Phillip and clan, Perhaps it's wise to have a look at those clutches ? Maybe they are toast/glazed ? I suspect this makes the "carbon" clutch plates more desirable. If the budget allows, the Gleason Tork-syn design, is most durable and proportunate. Of course, you can always install a spool, to make the driver happy. Good Luck, roverman.

The 8" & 9" Trac-Loc should function like the later ones. Ford has a suggested assembly order of the steel and friction discs. I used the Old Racers Order that changes the order and adds an extra friction disc. That mod changes from the OEM S-S-F-S-F to F-S-F-S-F or similar. ck to be sure. You will use the best old disc in your original pack to complete this. I got the clutch pack info from the 9" instructions and used the assembly order for the 8.8" on the S- spring. Maybe try the assembly order used by us "Old School Guys" The carrier type should not effect the mechanical operation.