Rebuilders go back to basics

Rebuilders go back to basics

ImageImageImage  It's hard to believe the GM TH350 torque converter debuted over 35 years ago and is still going strong. Rebuilding was a simpler time then, and profits were high. This simple, non-lockup torque converter required few replacement parts: a new hub, set of bearings, thrust washer and to the welder she went. Yet, even the simplest converters need to be built correctly, so let’s review how simple this converter is to rebuild.

After opening the converter and cleaning thoroughly, many rebuilders remove the impeller hub and perform a register cut across the front surface of the impeller. This is a critical indexing point and all further measurements will be dependent on its accuracy. Both parallel and perpendicular runouts will be taken from this point (see top photo).

Next, the inside diameter for locating the front bearing may be checked for concentricity with the outside diameter. This diameter should be no larger than 1.550 inches. The locating diameter of the bearing race is approximately 1.510 inches. This will leave .040 of an inch clearance for locating. This should be considered a maximum clearance.

Replacement of the impeller hub must be within .010 of an inch of the center. The closer you can hold this tolerance, the easier balancing will be. Upon inspection for any loose impeller or turbine fins, a decision must be made if any brazing or peening needs to be addressed. The turbine spline can be checked at this time to determine if any wear has occurred.

We will now focus on the disassembly of the stator, a simple yet overlooked component. After inspection of the inner and outer race and condition of rollers and springs, the cleaned stator can be reassembled, including a new stator cap. Lubrication should also be applied.

As for the front cover, any weld material protruding past the original diameter needs to be removed on a lathe, and at this time the thrust washer surface can be re-machined. After this has been accomplished, inspection of the pilot diameter can be made. If build up is required, it should be done at this time. Many ways to renew this surface include brazing, welding, re-machining and replacement and to create a knurl. All are satisfactory methods of renewal.

We are now ready to set the stack height. This converter needs to be assembled for a overall height of 6.150 inches. After assembling the converter and height is verified, it can b e adjusted up or down using a selective cover-to-turbine washer. The converter is now ready to be welded, leak tested, balanced and checked for total indicated runout. We have now completed rebuilding our basic converter.

Found in issue April 2005