ZF 5 HP-24A Teardown: Step 2: Torque Converter

We removed the torque converter from the front of the transmission, by pulling it forward and away from the transmission.

The input shaft for this transmission is a two-piece unit, with one shaft inside the other. The torque converter slides onto this shaft. Here’s a picture of the shaft (not of the torque converter):

2015-12-19 15.55.29

From what we saw in the repair manual, the torque converter locks up in both 4th and 5th gear. No electrical signals run to the torque converter though the process is no doubt initiated by an electric signal to a solenoid that changes the hydraulic fluid pressure.

The input shaft is the only way that the torque converter connects to the transmission, so the fluid pressure must come from the shaft. We have not yet figured out the fluid flow path; e.g, does the fluid flow into the torque converter from the inside of the inner shaft, and then out in the space between the inner shaft and the outer shaft? We don’t know.

When we remove a torque converter, we like to have, at the ready, a round drip pan with strong vertical sides, slightly taller and with a smaller diameter than the torque converter. That way, after removing the torque converter from the transmission, we can put the torque converter onto this drip pan and allow the fluid within to run and drip out.

We removed the torque converter while the transmission was on a large drip pan that in turn was on a wooden pallet, off the floor by a few inches but still low, so that if we were to drop the torque converter by mistake, it would not have far too fall.

We removed the torque converter after we’d thoroughly cleaned the outside of the transmission, to reduce the risk of dirt getting inside the torque converter or into the input shaft.

From what we see in the ZF spare parts catalog, all the C5 A6 Audis that use this transmission have an identical torque converter. Informally it’s known as the P35, with ZF part number 4168 026 394. The C5 S6 Audi, being a more-sporty model, has a different torque converter: Q35, with ZF part number 4168 026 395.

 

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