Ben Harold: haroldbr@muohio.edu Tom Harold: harold2@iquest.net

The Project Car History Engine Vortec Heads Transmission
Differential Suspension Steering Interior Racing
Street Machine Nationals Dyno Test

The 10 Bolt

The car came with a 10-bolt open gear differential which we never officially determined the gear-ratio of. We believe that it is 3.08:1. Needless to say, this had to go. It is now resting comfortably in a shed.

The 12 Bolt

A fellow named Carlo posted an add for a 12-bolt posi unit with 3.73 gears out of a '69 El Camino. This fits perfectly under our car, with only rim backspacing to deal with. The 68+ Chevelle differentials are about one inch wider than 67 and earlier. Basically, this was exactly what we really wanted. Amazingly enough, it wasn't too far away. We drove up to the middle of downtown Chicago to get lost before we got miles north to Carlo's house. Incredibly, this deal was all it was cracked up to be, and we drove 45 minuites out of our way home with the massive differential in the back of Tom's minivan.

Preperation and Installation

For the next few days I used a power wire brush to clean up the new rear end. After then sitting underneath some shelves for a couple of weeks, I cleaned the entire thing with a metal etch. On June 15, I mixed up the primer and applied it. The next day I painted the whole thing black. About a week later we installed the massive hunk of metal. The polygraphite bushings and thrust washers on the control arms made it a considerably difficult task to mount the differential. We ended up using two hydraulic jacks and a come-along to get the bolt holes lined up.

Click on a thumbnail for a larger image
differential primered differential painting the differential
The differential midway through cleaning The differential after being primered I'm painting the differential
foot in a bucket tom and a differential ben torquing bolts
My foot in a bucket of paint Tom and the differential Me torquing down bolts

The Project Car History Engine Vortec Heads Transmission
Differential Suspension Steering Interior Racing
Street Machine Nationals Dyno Test