Transmission Mount spacer ?

[uncle]

I’m replacing a turbo 350 with a turbo 400 in one of my trucks and I’m wondering if the spacer that was with the transmission is needed. It’s about a quarter inch tall. Was that for use with the big block trucks only or haul trucks equipped with a turbo 400? I believe it goes between the mount and the transmission. My truck is a small block. Thanks.

[Steeveedee]

You will need to measure your driveline angles to determine if you still need the shim.

[72SB]

OP, before you remove your TH350, measure from floor to center of tail shaft spline. Do this once truck is raised to work on so when you get the 400 in, make the same measurement. You want it to be the same as the TH350 measurement so if you need to add the shim back, delete it or use a different thickness, do so to maintain your DL angle.

[Accelo]

I never figured out when GM used the shim and when they didn't.
If someone knows I would find it interesting.

[72SB]

Originally Posted by Accelo

I never figured out when GM used the shim and when they didn't.
If someone knows I would find it interesting.

My guess is when the drive trains were installed on frames (before body) the DL angle was checked and "if needed" shim(s) were added. This is because of minor differences in each frame welding or even differences in rear axle location (height) due to heavy or regular springs.

For after the fact, people use them more when truck is lowered so adding trans shim and or pinon angled shim is needed to correct DL angle.

Typically the shims for trans are 1/8" thick and 1 or 2 are used as needed. I have a 96 that has 2. I don't recall seeing any on my 72 C10 Saginaw 3 speed

[uncle]

Thanks for the input.