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Transmission Swap

Provided to us by Tom Langdon at Langdon's Stovebolt Engine Parts Company

The following is provided by our friends at Langdon's Stovebolt Engine Parts Co. 47950 Robin St. Utica, MI 48317 (810) 739-9601 Business hours are 10 a.m. - 7 p.m. Eastern Time Monday - Friday. Or check 'em out online!

Mating 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, 400, 700R4, 200 4R and the aluminum Powerglide is made easy, usually one day to install the transmission itself. This requires an "open" driveline and cannot retain the torque tube.

    In designing our transmission adapter we originally measured about 25 Chevrolet and GMC blocks, and about 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 HydroMatic engines. We then took the average to build our adapter.

    In very rare cases of too much run out (.012"), the use of eccentric dowels will be required. In a continuing effort to provide our customers with the best possible products, Langdon's Stovebolt now machines the adapter to exact factory blueprint specifications and dial indicates every adapter plate on a bell- housing. We also check starter engagement and actually crank the flywheel.

    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 that 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 over the original dowel pins. Use special washers supplied with the adapter kit. Our kit comes complete with an alignment ring for the crank and a flexplate that has been redrilled to Chevrolet 6 cylinder bolt pattern (the GMC does not require this).

    Remove the 3 dowels from the crankshaft and install the spacer, then the new flexplate using special washers, which are also supplied. Now you are ready for the transmission.

    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 LocTight on these.

    This kit requires the use of a 1970 250 Chevy 6 (automatic trans.) starter (part # Delco 323-236). It will be necessary to make a slight clearance notch in the starter housing for flexplate tooth clearance.

    Rear support for your transmission can be done in several ways. It's best to check with us regarding the availability of our kit for this. For '40-'49 cars we have a weld-in type kit that looks very nice when installed in that it retains the x member.

    We also carry a dropped X member with drops from 2" to 8". This works well in most pick-ups and in a lot of cars. This is a bolt in kit, as are most of our products. Whatever method is used to mount the engine, torsional rigidity must be provided to absorb engine torque. This can be achieved by using side motor mounts ('58-'62 blocks) or bell housing mounts on other years. Failure to do this will result in excessive engine rocking.

    Langdon's Stovebolt recommends that a qualified technician familiar with conversion type installations should always install the transmission cooler, shifter, driveshaft, and neutral safety switches.

v. Jan 05

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