Transmission Update

PIC of Trans Adapt Kit June 28 2012
TH350-400-700R4-200 4R and PG to early Chevrolet & GMC 6 cylinder engines
With the advent of the Stovebolt Transmission Adapter the installation of the GM TH350, 200 4R and 700R4 is made possible. This requires an “open” driveline and cannot retain the torque tube. In addition to the rear axle, the installation of a transmission cooler, shifter, and T.V. cable mounting make this a project not intended for the novice. It also requires a 12 Volt system for the starter.


We strongly encourage the use of a 200 4R in combination with a 3.73 or 4.10 axle ratio so your efforts will result in a satisfying combination of low speed performance and highway cruising at modern speeds up to 70 MPH. The THM 350 could be used at a substantial loss in low speed and highway cruising (both). The use of the Powerglide is strongly discouraged.
The original design of our transmission adapter used measurements from 25 engines and 50 bellhousings. We found that GM was off as much as .020″ from centerline on many manual shift engines, and even on some matched set Hydro-Matic engines. We then took the average to build our adapter. In occasional cases of too much run out (.012″), the use of eccentric dowels will be required. Currently, however, both dowel pin location specifications are the exact factory blueprint dimensions machined exactly by CNC technology and assured on every adapter by assembly and dial indicator. Checking on your block and with your transmission is recommended.
To start, unbolt the four bolts that hold the factory transmission to the bell housing, and pull out the transmission. Remove the throwout bearing, the pressure plate, and the clutch disc.
We are now down to the flywheel which must be removed before the bell housing. The flywheel is held on by bolts that are retained by a flat metal strip that has tabs that are bent over to prevent the bolts from turning. Use a chisel to flatten the ears before removal. After the bolts are out, carefully remove the flywheel. Now you are ready to remove the bell housing. Remove the 6 retaining bolts and now remove the bell housing. Clean the grease and dirt off the back of the block and install the adapter plate.
Our kit comes complete with a spacer for the crank and a flexplate that has been re-drilled to Chevrolet 6 cylinder bolt pattern. Remove the 3 dowels from the crankshaft and install the spacer then the new flexplate using the special washers provided.
Set the transmission on a transmission jack and strap it down. Carefully install the converter to the transmission turning it with light pressure to insure it slips into the pump. Lift the transmission into place and install mounting bolts. Now turn the converter to line it up with the flexplate and slip it forward. Install the mounting bolts. It’s a good idea to use LOCTITE on these.
This kit requires the use of a 250 Chev 6 starter (part # Delco 323-236). It may be necessary to make a slight notch in the starter housing for clearance to the flywheel teeth. We strongly recommend purchase of this starter from Langdon’s Stovebolt to assure proper engagement, shimming and clearancing. Use the shims provided as a starting point. Your kit has been tested with these shims.
Rear support for your transmission
Chassis Engineering in West Branch, Iowa (319-643-2655) makes a good selection of kits for supporting the transmission at the rear mount. This will work well if your engine is side mounted but will not be adequate if you are using the front mounting plate typical of 1937-1951 cars and ’37-’54 trucks. In these cases it will be necessary to fabricate mounts similar to the original bell housing type mounts typical of ’55-’57 Chevy passenger cars.
(rev: 30 July 2012 bas)