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Automatic gearbox


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I bought my Golf Mk3 VR6 with an automatic gearbox fault (unknown at the time). It would run perfectly for up to 14 miles and then shift randomly between 3rd and 4th.

 

So I spent quite a lot of time finding out how it worked, testing it and finally diagnosing the problems.

 

I think the later 01M unit in the OBD2 cars seems to superior to the 096 in the ealier cars. Both are only 4 speeds, so not very efficient by modern standards.

It needs an oil and filter change every 80k miles or so. Only use genuine VAG fluid which is quite expensive @ 50 ish.

 

The gearbox computer is under the rear bench seat. This connects to the gearbox by about 50 discrete wires. There is no ECU in the gearbox. The shifter bar moves a lever on the gearbox. This directly acts on the internals to engage reverse or park. It also moves a switch (the famous Multi-Function-Switch). This is connected back to the ECU to tell it what gear has been selected. There is also a connection from the ECU to the brake switch, the kick down switch and a data bus connection to the engine management unit. It also connects to an number of discrete speed sensors on the gearbox.

 

This is how the ECU works out what to do and adapt to driving styles.

 

The wiring is basically the achilles heel of the system. There is a wiring harness on top of the gearbox for the sensors plus MFS and another one that goes inside the gearbox to work the solenoids. All of this is routed back through the bulkhead to the ECU.

 

So look out for wiring damage and bad earths.

 

When the gearbox is working properly it is brilliant and serves up smooth driving with snappy kickdown when required. Another feature is that there is very little creep when in drive. There is a noticeable delay between engaging forward and reverse. Don't give it any gas until it has engaged!

 

Mine, after fixing two wiring faults and a fluid change is perfect, having done 107K miles. I think the complexity (for 20 years ago), plus also the confusion with the very different operation between 096 and 01M types meant that a lot of people went for a manual conversion when there was a serious problem. You need a proper VAG diagnostic scanner to check it properly, but you can do basic continuity checks with the manual.

 

If the internals have truly gone then reckon on £1500 from an auto gearbox specialist for a rebuild.

 

If it's a solenoid or the flexi-circuit wiring then you can change this yourself when the pan is off, if feeling brave. You can get new kits from the USA, or salvage the bits from a used gearbox.

 

Cheers Pete

 

Edited by red_rocket
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