TH400 Conversion from M6

Transmission Mount Install
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Tools Needed
15 mm socket
17 mm socket
You will need to order a transmission mount. I looked high and low for a trans mount locally. No luck. So I did what I should have done to begin with, I called Madman and ordered one. A few days later, I have a mount, with an upper preload plate.

This is important to note. None of the local part stores offered the upper preload plate. I wouldn't run a trans mount without one.

Energy Suspension 3.1108G Transmission Mount for G.M.

Set 3-1108 (Gold Plated) OR Set 3-1132 (Chrome Plated)
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Tech Note: You will need a special transmission cross member for this installation. BMR, and I assume others, sell a special TH400 conversion crossmember just for this installation. Please check which crossmember you need and order accordingly.

Install the mount with upper preload plate above the mount and the radius toward the rear of the car.

You should have a bolt, split washer, and flat washer. Go ahead and snug the upper transmission mount to the transmission. Using a 17 mm socket I tightened the bolts to 42 ft-lb (
Your Risk). I have no idea if this is correct but it is the general rating for a course thread Grade 8 bolt of that size.
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Raise your transmission cross member up and get a few threads started on each of the four bolts that attach to the body. Let this piece remain loose as getting these bolts started may prove to be a pain in the butt.

Using a 15 mm socket, tighten the four transmission cross member bolts to 66 ft-lb (
GM Service Manual 1999 7-317) for the 4L60-E.

Use one bolt, split washer, and flat washer through the cross member and into the middle hole boss. Just get this bolt started a few threads. Torque the lower transmission mount bolt to 42 ft-lb (
GM Service Manual 1999 7-137) using a 17 mm socket.

This was the specification for the 4L60-E and per Energy Suspension, I should use the factory torque specification. Since this is a TH400 in a T56 LS1, we will do just that since I don't really have a true factory specification within hands reach.
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