[heze]

Good morning all,

(this thread is transferred from the non-turbo forum)

I have problems with my ZF 8HP45 transmission (E70, LCI, 2010).
In ISTA, I got several codes;
- Gear ratio monitoring, Clutch A, B and D
- Gear ratio monitoring, Clutch A and B
- Gear ratio monitoring, Clutch B

So I removed and opened the mechatronic unit. Some valves were stuck, so I removed and cleaned all the valves and hydraulic channels again. Some valves needed lots of force to come loose… One small spring was broken, so I replaced the spring with a new spring (I’m not sure that the spring gives exact equal force) and bolted everything together with a new plate in between.

After mounting everything, the errors from above were gone. The transmission shifts correct to gear 5 but it will not shift to 6. It will give the general transmission error (limp home mode) and in ISTA I got this error:
- Gear Ratio monitoring, 5 to x

So to be sure that the gearbox itself is not damaged, I disassembled the complete gearbox, checked every part and discovered that the friction material on 3 clutches were loose, so I replaced all the friction plates. The clutches were in decent shape (I tested all of them with air pressure). I re-assembled everything again, applied new original ZF oil and again:
- Gear Ratio monitoring, 5 to x

This is the current status. From the table in the attachment I discovered that all clutches are on and off in gears 1-5 and park and R, except for Clutch B: is always enabled during gears 1-5, park and R and that it is disabled at gears 6-8. So the fact that gears 1-5, park and R works fine, but gears 6 (and possibly 7 and 8) are not working, sounds like something wrong with clutch B.

Clutch B is a special clutch: both engage and disengage are hydraulically operated (no spring involved) and both circuits has 2 valves (so in total 4 valves are controlling clutch B). See also attachment for hyraulic schematic.

So before disassembling the complete transmission again, can it be the mechatronic unit which causes this? Or is the B clutch faulty?
Normaly, when a clutch fails, the error in ISTA also points to a clutch, but this time the error is saying nothing about a clutch…

Has someone experience with this error?

Thanks in advance and best regards,
Hendrik Zeilstra.

[Murf 530]

Hi Hendrik,
I was just wondering if you had any joy with the issue on your 8hp gearbox? I have the exact same fault on my 8hp 70 in a 530 D , I also removed the mechatronic , split and cleaned ,found no obvious damage reinstalled and changed the oil and sump/filter. I didn't strip any further as I was not as courageous as you and also because it is hard to figure out where the fault may lie after this , strangely as well you know all the clutches are activated from gears 1 thru 5 . The only code I have from my obd is 420351 Gear monitoring during gear 5>x which there is very little info on the net to help. At the moment the car is driving fine from gears 1 to 5 but stalls a little as it attempts 6th and then defaults to Limp mode. I would really appreciate any feedback on this as it would be great to fix it myself without have to recondition or replace with a second hand unit.

Cheers Keith

[juld0zer]

ISTA is very limited in diagnosing transmission issues. There are no repair guides further than replacing the mechatronics. The test modules will almost always lead to replacing rhw transmission in these situations.
What I do know is that there is a lot of back end data that it can see and capture but cannot display. I wonder if Rheingold is any better at this? ie less locked down?

Have you tried viewing and then resetting the transmission adaptations? It's a service function in ISTA. I don't think it will fix your problem though

[heze]

Originally Posted by Murf 530

Hi Hendrik,
I was just wondering if you had any joy with the issue on your 8hp gearbox? I have the exact same fault on my 8hp 70 in a 530 D , I also removed the mechatronic , split and cleaned ,found no obvious damage reinstalled and changed the oil and sump/filter. I didn't strip any further as I was not as courageous as you and also because it is hard to figure out where the fault may lie after this , strangely as well you know all the clutches are activated from gears 1 thru 5 . The only code I have from my obd is 420351 Gear monitoring during gear 5>x which there is very little info on the net to help. At the moment the car is driving fine from gears 1 to 5 but stalls a little as it attempts 6th and then defaults to Limp mode. I would really appreciate any feedback on this as it would be great to fix it myself without have to recondition or replace with a second hand unit.

Cheers Keith

Good morning Keith,

When I disassembled the mechatronics, I noticed that lots of plungers of the valves were stuck due to the presence of water. With some plungers it needed lots of force to get it moving again. I think that one of the plungers was still moving a little stiff. The problem solved itself after some time.

I now only have the problem that with cold engine, the automatic needs to shift up, but accidentally it shifts down, somewhere around gear 2 or 3. This only happens very rare. I'm affraid that one of the plungers is still not moving freely or the plunger housing is scored (very tight tolerances). Clearly the water did the mechatronics no good... If I can find a decent second hand piece, I will replace the mechatronics to get rid of this problem...

Best regards Hendrik.

[Murf 530]

Hi All ,
Thanks very much for your replies, I tried the adaption reset before I carried out any physical work on the transmission without any luck but never thought to try it again, I'll give it a go next week as I am currently away from home. Hopefully I might have the same luck as you Hendrik and the mechatronic might start to settle down and behave, although I have to admit the original oil in the transmission was black and it smelled so bad that I was not allowed to bring my overalls into the house! Maybe later if the issue does not improve I might strip the mechatronic again and have a closer look at clutch B's 4 operating valves?
I have also seen a little online about a software upgrade for the TCM , have you had or heard of any experience on this? Might be a waste of time , thanks again for your time and info.

Cheers Keith

[juld0zer]

8 speed oil reeks. If i got it on my clothes I'd throw them away.