It’s hardly earthshaking to say that today’s transmissions are advancing technologically every day. But what you may not realize is that today’s torque converters are changing, too.
When transmissions had two and three speeds, the torque converter was a relatively simple part of the equation. But things have changed and today’s torque converter rebuilders need to keep up with those changes.
The TCRA Technical Committee meets every month to examine issues they’ve identified in their shops, or that have been brought to their attention by other TCRA Members.
Here are some examples of subjects that the committee has addressed in recent months that may be of interest to the transmission rebuilding industry. The first is about Mercedes 722.9 pumps: Early units had a bushing in the front pump; in later units, the bushing was replaced with a bearing. The issue here is that the hub for a bushing may be too soft to work with a bearing.
If you purchase a new pump, it’ll probably have a bearing, so make sure the converter you’re using has a hub that’s suitable for use with a bearing. There are a number of ways to check the hub harness, but one of the more cost-effective solutions is to purchase a file set designed especially for this purpose (figure 1).
In fact, having this type of tool would be useful for gauging the hardness of a variety of metals, making it a terrific addition to your shop tools. Several different manufacturers offer similar hardness files.
Another situation has to do with the 4L80 in panel vans equipped with a Cummings 4-cylinder 4BT engine. There have been cases where the lockup clutch drags at low speeds. The problem traces back to a lack of pump capacity at low engine RPM. The fix is to install one of the aftermarket pressure regulator valves that provide more clutch release oil.
A major failure with a Ford 5R110 converter shows up if someone installs an aftermarket 4R100 boost valve during the rebuild. This valve creates excessively high mainline pressure, which can deform the lockup piston or OEM converter cover, and cause the converter clutch to slip or fail entirely. The fix is simple: Install the correct boost valve.
While we’re discussing the 5R110, keep in mind that the outer pump gear is directional: The identification mark faces the pump cover (figure 2), while the chamfered edge on the OD of the outer gear faces the pump body. There have been cases where incorrect assembly has caused the pump gears to seize up and damage the converter impeller hub.
The TCRA technical committee is happy to receive feedback or input on any converter-related issues you run into in the shop. If your converter supplier is a member of TCRA, there’s a forum they can access to post a question. If they aren’t members, encourage them to join TCRA: It’s to their advantage… and yours.
You can also access the TCRA web site at www.tcraonline.com for membership and contact information.