When it comes to doing it right, it’s always best to ask someone who’s successful in the field. My friend, Dave Hammond, owner and operator of Atlantic Torque Converters, was kind enough to show me what doing it right looks like.
First, let’s look at a few different types of converter clutches (Figures 1a – 1d): The standard type clutch is bonded to the clutch housing and is compressed against the converter cover. The clutch pack used here is from a Mercedes; it uses a piston, clutches, and a snap ring, just like clutch packs in most transmissions.
The captive clutch uses a pressure plate and a clutch that is compressed between the cover and pressure plate. The triple disc — the most commonly requested upgrade for Dodge turbo diesels — uses a plate with a clutch on both sides and a plate with a clutch on one side and a steel surface on the other, compressed between a pressure plate and the cover.
There are many different types of clutch materials available, though it’s important to match the clutch material to the application and fluid. The bonding process is equally important: The standard process is to apply glue to the piston plate and the clutch, then compress and heat these components to 400ºF (205ºC) for a specific amount of time. Dave preheats the piston plate before beginning the bonding process to improve the plate and clutch bond.
Setting the proper endplay is as critical in the torque converter as it is in the transmission. Most of the time you adjust endplay with shims. But the TMBX bearing support lip (Figure 2) on the stator support is too short for shims. Using shims can allow the bearings to move off the support and damage the converter. On these units, the best method for adjusting endplay is to use different thickness bearings on either side of the stator.
Hondas have a single race bearing riding against a surface on the impeller side of the converter. This configuration generates a lot of heat. When this surface becomes damaged or softens from excessive heat, the impeller won’t be reusable; you’ll need to replace the impeller hub or the entire impeller. By machining the stator cap (Figure 3), and installing a bearing with two races, you can save money and increase the durability of the converter.
Honda also has an issue with the spring retainers becoming damaged. Small welds to hold the retainer to the clutch housing (figure 4) adds extra support and helps prevent these retainers from breaking off and damaging other parts of the converter.
Installing Mercedes clutch pistons with their square cut rings can be difficult and, if they get cut, they can cause clutch chatter or slip. Another common problem that causes clutch chatter is improperly prepared steels. Dave recommends bead blasting over any other method. He must be right: Over the years I’ve never had one of his converters chatter or slip.
The AS68RC converters have a common issue with the pilot hub on the back of the converter breaking (figure 6). There’s an aftermarket hub that’s much thicker to correct this problem, but it requires special tooling to install.
As with any other part of the transmission, your torque converter is only as strong as its weakest link. Use the right fluid, check your valve bodies and pumps for wear in the valve bores, replace the stator bushings and sealing rings, and check the surfaces they ride on. Overlooking the small things can lead to spending a lot of money on a comeback.