75 Diesel Auto Box Issues
 

Hello everyone.

Firstly I'd like to say this forum looks very informative and helpful. I've been browsing over the last couple of days to try and help with the problem I'm experiencing with my car.

The auto box has always been somewhat of an issue. Occasionally when it changes up from 2nd gear to 3rd gear it jumps, temporarily missing the gear resulting in engine revs increasing followed by judder, bang, lurching as the gear engages. It's very quick to happen, a split second and its all over with the gear engaged and car pulling on forwards. I have noticed it seems to occur more often under more acceleration and never happens when pulling away slowly.

Thanks to this forum I read a similar post with a user experiencing exactly the same issue but the car in question was a V6 petrol. The fault was caused by a cracked reverse piston. I'm not sure if the gearboxes are exactly the same regardless of engine and so I'm not sure if this could be my problem.

The next issue is a little more worrying because I can't find any threads with anyone detailing it...

sometimes the car looses top gear. As the box is changing up through the gears when it gets to changing to 5th/top gear it seems to miss it resulting in engine increasing in revs as if the box has gone into neutral. The only way to get the gear back is to drop off the throttle until revs return to almost idle and then the engine revs pick back up until there is a slight clunk and judder which lets me know the gear is engaged. I can then apply throttle to regain my lost speed. Sometimes this can happen and be resolved quickly and sometimes it doesn't...

When it doesn't it's usually because the car has lost too much speed to maintain 5th gear so it goes back to 4th. Sometimes then the change from 4th to 5th goes smoothly and other times it doesn't and the process is repeated.

These 2 issues have been a constant in my 3 years of ownership. The gearbox had a fresh oil change and check over several months into my ownership but still these 2 issues have remained.

Then, just the other day something more worrying happened...

The box simply refused to change from 3rd to 4th even with engine revs up to 3.5-4k with just gentle throttle to try and coax it to change. I pulled over, put it in P then back down to D and set off again. I got the usual lurchy 3rd gear change I described earlier but no 4th gear until 3.5k when it suddenly banged into gear with a massive thud. After this EP was displayed instead of D on the dash and the box appeared to be stuck in 4th with no attempt to change to 5th. When I stopped at a junction it felt like it was trying to pull away in a high gear so I pulled over again, put it in P and switched off the engine. After a few minutes I restarted with the EP gone from the dash. I was able to drive home and the problem hasn't reappeared but the typical 2nd to 3rd and occasional loss of top gear remain.

Can anyone suggest with possible issues?

By the way the car is a 2003 75 CDT Connoisseur SE Auto with 143k miles

Hi
If the fluid level is correct and has had fluid changes as it should I would suggest a T4 session that should be able read any codes in the JATCO box, as a thought I wonder if the solenoids ever been changed. 2/4 duty solenoid is normally a issue.
I do believe that a low level can cause some of these problems.
Best to contact Phil T-4 he's super.

Dampness in the transmission controller can cause harsh gear changes and failure to engage solenoids, varying between intermitent and persistent, and including the EP error. It may show up on diagnostics as a canbus error. Definitely worth checking behind the glove compartment for damp.

Harsh gearchanges are caused by the pressure duty solenoid not activating, this regulates the hydraulic line pressure to the solenoids.

The state of the gears with solenoids unpowered is 4th, this usually occurs when EP shows on the dash and the transmission controller has shut down for whatever reason.

The wiring to the gearbox runs from behind the glovebox out through the wing and loops around behind the headlight. If the wheelarch cover is missing or damaged mud can get in and overheat the loom.

Live sensor data from the controller is very comprehensive and should show more than enough to identify the fault when the car is moving.

The controllers themselves seem to be quite tough, but if it does need changing you can change them over without any reprogramming, best to get one from the same engine type although the mapping in these controllers appears to be so minimal I think it works it all out from speed, throttle position and load.

I can vouch for the efficacy of oil replacement.
I cannot tell you if this is the problem, but my box went from harsh to good, especially shifts into 2nd and 3rd, if my memory serves me well.
Just an addendum, make sure you know exactly which bolt to remove for drain. Check it carefully, or your box might suffer damage if you remove the wrong bolt!

Thanks for all the replies guys. Very informative.

My worry is that after doing the oil change a few years ago it made no differences to the issues.

OK, planning a fresh fluid change for the auto box and have retrieved the invoice for the fluid that was used in the box before. It was Fuchs Titan ATF 4000 that required 2 trips to the garage to change, 4 litres at a time, 500 miles apart.

Is this fluid OK for the auto box?