Rebuilt gearbox borked

[simonpoulton]

Hi guys,

Has anyone got any insight into the following? I haven't had much time to look into it yet, just mentally preparing myself for another engine pull

The gearbox has been rebuilt by professionals with 2k on the clock.

Its going straight into limp mode with the following codes:

P1850 - 35-10 Missing message from ECU - intermittent
P0730 - 35-10 Gear Ratio Monitoring - Incorrect Gear Ratio - intermittent
P0731 - 35-00 Gear 1 - Incorrect Ratio

All I have done so far is pop it on the ramp, warm to 40c and check the oil level (Seemed fine, a little came out when I opened up the fill plug).

Originally it started having problems on a short run up the road, it felt like it was randomly disengaging through all gears and thumping back into them, with it finally going into limp mode. Now as soon as I set off, it goes into limp mode.

Feels like it could be an electrical problem rather than a mechanical one...

Cheers
Simon

[Shoppinit]

Clear the codes then see if anything comes back without starting the engine.

Here is what I would try:

Then start then engine and see if any codes turn up.

Then put it in tiptronic and stay in first and drive it round the block without changing gear. Any codes come up?

If so then clear them (after noting them) and change into second. Do the same.

This feels like a mechanical problem, ratio problems almost always mean a major mechanical fault, but it's worth investigating a bit further.

There might be some useful information you can log using the Vagcom. Do you know how to log data?

[simonpoulton]

Thanks Shopp, cleared the codes and had a quick go in it yesterday.
- Only the P0731 - 35-00 Gear 1 - Incorrect Ratio came back. The others must have been historic.
- Still misbehaving
- Tried the tiptronic mode, still disengaging
- When it was disengaging, it was jumping gears, sometimes 2 or 3 at a time. At one point it jumped into 5th at 20mph.
- Seemed slow to switch gears

What bits of data are best to log for gearbox diagnosis? I had a graph going yesterday but my laptop battery died. I might have a crack at getting some data tonight to look at as that sounds like a pretty wild friday night!

Cheers

Simon

[Shoppinit]

You should log the input and output speed for the box. This way you can see if it's not transmitting power correctly or whether a sensor is playing up. The data should tell the story. You can also log the F125 position and the gear selector position. Can't think of any other data offhand that might be useful. Doesn't sound like a TC issue, but if the previous logs don't show any promising leads you can look further into what other data is available.

It's a real pity you can't log the ATF pressure. It sounds like that's what might be causing an issue in yours. That could be pump or conduit. Maybe a blockage in the valve body.

If you can get it into second without it faulting out, can you drive it normally staying out of first? Even if you have to clear the fault code while driving (getting a passenger to do it obvs).

[RS2]

I have an RS6 gearbox here for spares if you need/want anything.

MG
07989 333437

[simonpoulton]

OK so an update on this. I must have messed up the top up procedure somehow as I managed to get another litre of ATF in and it's running a lot better.

Questions I have now are how I managed to screw it up twice and why it went from fine to not working in overnight. I'm guessing as soon as the level gets below the bottom of its filter, it basically has no oil and starts sucking in air and any hydraulic effect ruined.

I might have a look at the filter next and check that it's the right length and not cracked (read of that before) which I assume would cause similar symptoms to low oil.

Thanks for you help on this one guys.

@RS2 thanks - I already have a spare broken gearbox but might be interested in a second spare, I do want to start dissecting these and finding out how they work. Will PM you!

[simonpoulton]

Hi guys, an update for this. Finally got some time to work on the wagon.

Drained the transmission fluid and popped off the sump... and found the smoking gun.The filter was badly cracked.

It was a Filtran filter - did someone mention having issues with these before?

[Shoppinit]

Never head of Filtran. Is this the filter the gearbox people put in?

[bam_bam]

Filter cracked, check the pickup length, if it's too long. Wrong filter.
Post up the last number of you have it .

[simonpoulton]

Yeah it was the one that was put in after the rebuild. The part number on it was 0501006460.

The replacement one had no issues fouling on the sump and looked identical in size, pick up tube length etc.

What's the actual pickup length meant to be?