Borg Warner super t10 in place of 3 speed

[70 shorty]

My 79 Vette has it's original BorgWarner super t10 4speed in it and I just got a tremec tkx 5 speed conversion for it. I think I want to put the 4 speed from the Vette in my truck to back up the built 6cyl in it. I think I've read that it will bolt right in and even the.shifter would be in exactly the same place. The Vette has a Hurst shifter in it, so I would reuse that. What about a crossmember? Of course there is none with the 3 spd, but would I need one with a 4 spd, and if so what do I use? Looking for advice from those who have done a 3 speed to passenger car 4 speed swap. Thanks!

[Accelo]

Just use a cross-member for an automatic. It should mount right up and match the Borg just fine. I believe the drive-line will do the same. If you have a floor shift, which sounds like you have, it should be a fairly painless swap except for the removal of the cross-member. Access is poor and the rivets are a PITA to remove. I recently worked on a converted truck, and they used a torch to cut the center of the 4-speed cross member out. The riveted sections were still there. Looked like heck but functioned perfectly.

[LockDoc]

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The 3 speed just uses the bell housing mounts, no rear X-member. The 4 speed will mount the same. No rear X-member needed..... Just bolt it in, in place of the 3 speed.
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[geezer#99]

Leave the crossmember in place with the bh and hang the t10 onto the bh. The t10 is 20 lbs lighter than the Saginaw.
Depending on your t10’s first gear ratio you might be losing some gear reduction.

Another thing is to check the input shaft bearing housing diameter.

[MikeB]

Originally Posted by geezer#99

Leave the crossmember in place with the bh and hang the t10 onto the bh. The t10 is 20 lbs lighter than the Saginaw.
Depending on your t10’s first gear ratio you might be losing some gear reduction.

Another thing is to check the input shaft bearing housing diameter.

Very good advice. I was also thinking about input shaft spline count. The T10 is 10-spline like the Saginaw, but I just read that the Super T10 has 26 splines. I also read that the Super T10 has a larger output shaft diameter, which probably means a different yoke.


As for gear ratios, the Saginaw 3-speed has at least three different gearsets. The base six-cylinder engines have the lowest first gear ratio for better torque multiplication. The 292 six (and later the 305) got the next lowest, and then the 350 and big blocks got the tallest.

[geezer#99]

And now that I thought about it, it’s likely the shifter location isn’t the same. IIRC the t10 is a couple inches more rearward. Puts the handle right under the seat.

[MikeB]

About the gear ratios, I found the info below on the 3-speeds. 0-3 are the number of grooves on the input shaft. I would guess your six-cyl trans is 3.11 or 3.50, assuming it's original.

.................................1st 2nd 3rd
Saginaw 3-speed – 1 2.54 1.50 1.00
Saginaw 3-speed – 0 2.85 1.68 1.00
Saginaw 3-speed – 2 3.11 1.84 1.00
Saginaw 3-speed – 3 3.50 1.89 1.00

So compare total torque multiplication (1st gear ratio X rear axle ratio) to see which one will work best.