Saginaw 4-speed

Transmissions

December 27, 2020 0

When I bought my 1969 Oldsmobile F85 it had a 355ci SBC and a TH350 automatic transmission. After I broke the transmission in a bad way I decided to swap the car to a manual. Parts came from a 1968 Cutlass that was going the opposite direction to a TH400 automatic.

The Saginaw did fine for the most part but would often not want to downshift from 3rd to 2nd. You had to go (while keeping the clutch in) from 3rd to 1st to 2nd then let the clutch out. It also occasionally made a bad screeching noise when taking off in 1st gear.

I decided I wanted to LS swap the car so I pulled the engine and trans out sold the engine and set the trans outside thinking somebody would scoop it up for $100. Instead it sat for a couple years getting rained on and covered in mud. Just before winter I cleaned it off best I could and brought it back inside with a plan to take it apart to see if I could figure out what was wrong with it just to do it.

Side cover off. Mainshaft up top countershaft below with reverse idler gear on bottom right.

Shift forks in place. They slide left to right to engage gears.

Up front is the 3/4 syncro hub assembly.

Slider removed, hub visible with 1 of 3 strut keys up top.

Hub removed. It is press fit but I was able to pry it off.

Hub with strut keys and springs still wound.

Taken apart. You can assemble this by hand.

I left the countershaft in as I read it can be a real disaster.

I had to use the press to put it back together.

I can’t seem to find a picture with the shift levers connected but it shifts into all gears on the bench!

In the end I did not identify any problems so the shifting issue remains a mystery. All the blocker rings seemed to grab the gears fine and i did not note any wear on the engagement teeth. Disappointing but I really enjoyed doing this and it gave me the confidence for my next project.

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