722.6 sometimes downshifting to 4th and not wanting to upshift

[charlysays]

I replaced the springs on my 97' C250 TD this week... car was fine before.
New rear springs on and the first test drive it changes down into 4th when doing 60mph down a slight gradient and then doesn't want to go into 5th. I pull over, shift into N and back into D and it behaves itself for the rest of the drive.
Its done it a couple of times since now but seems to be getting less frequent.

I did the fluid, filter and O rings on the pilot bushing about 11k miles ago.
Checked the fluid again and it's a little overfilled (has been this way 11k miles) but I overfilled my previous C250 to a greater degree and it never played up.
When I did the fluid I'd run out of copper washers so reused the old ones and as a result the trans drain plug is dripping slightly so I'll sort this and drain off some fluid to get the level absolutely spot on. Will also check the multi plug isn't wet with ATF.

Anyone had this issue before?

Literally feels like the trans thinks its going down a steeper gradient than it is and the shifts themselves are normal.

 

[charlysays]

Just drained about 220ml from the box whilst replacing the drain plug washer. Multi plug is dry etc. Took car for test drive and it did it again. It's usually after I've been coasting it'll change down to 4th it seems. This time I just kept driving it, it hung on to 4th far longer than normal but then later on after slowing down for a 30mph limit it behaved normally again. Wondering if there could be a problem with a micro switch in the shifter.

 

[alexanderfoti]

The 722.6 tends to downshift from 5th to 4th when its overheating, or at least it thinks the gearbox temp is too high.

That wont cause it to hold 4th too long at lower speeds though

 

[Steve@Avantgarde]

Possible electro plate starting to fail or one of the valves on the valve body jamming.

 

[charlysays]

Something is on the way out for sure... time to get the codes read? It even held on in 3rd tonight then eventually changed into 4th and then 5th.

 

[Steve@Avantgarde]

Definitely..

Cant really go any further without reading them out...

 

[charlysays]

OK will get on with that tomorrow. I take it that it needs to be done on STAR?
Where can the parts be bought from? I heard there's a spring which is prone to breaking which should be changed at the same time and Sonnax sell it separately whereas MB will just sell you the whole valve body.

Seeing as I only did the fluid about 10k ago I take it I can leave the TC alone and save myself a bit on yet more fluid?

Lastly how is this likely to progress? Is it likely to just pack up completely and need recovering? I have another C250 sitting idle which still has a bit of MOT on it so I might clean the mold off the inside and get it going again lol.

 

[charlysays]

I just had an idea (last hopeful attempt at an easy fix). The battery is a few yrs old but I got it from a friend and it had been repeatedly discharged... I've been sort of getting the last legs out of it and it certainly doesn't have enough juice left in it to do a starting cycle after doing the fuel pipe O rings etc so it's not in its first flush of youth.
It had 12.4 volts after the engine had been running a few minutes. So I've fitted one which I know is much better and so far its not played up during the same test drive where it had been playing up. It played up last night worse than it ever had but it was dark and I'd done a few short trips.
Also the fact it started doing this after being on the ramp a few days and not in use.

It was just something I remembered- a tired battery causing issues. We'll see anyway

 

[John Laidlaw]

Worth sorting out the battery but it won't fix your issue sorry - as said needs the codes read on star...

 

[om613]

Charlie mate, did you see the Febi worksheets I posted here a few weeks back?
If not, search on febi 722.6, or search my posts.

You can pin-out the multi-plug with a DVM for some basic diags.
A poor battery is worth eliminating first.

 

[charlysays]

Charlie mate, did you see the Febi worksheets I posted here a few weeks back?
If not, search on febi 722.6, or search my posts.

You can pin-out the multi-plug with a DVM for some basic diags.
A poor battery is worth eliminating first.

I'm not sure I did but have a vague memory! Cheers mate will take a look Thank you.
The local independent has agreed to read the codes tomorrow with star after work however

Tbf, it behaved normally on the way to work today. Will be interesting to see what happens.

 

[charlysays]

It played up briefly this morning... bottom of a long hill where I'd been coasting a bit in 5th... just before the bend at the bottom it changed down to 4th, then as I was coming out of the bend down to 3rd... then held on a bit too long before changing up to an appropriate gear then behaved normally. It definitely didn't use to do that! Shifts themselves seem normal but it does change 1-2 a bit hard like my other one. Codes will tell all I hope.

I looked on ebay and there's a kit available for £137 with fast and free postage from sussex auto transmissions which includes the conductor plate, pilot bushing, filter and pan seal. It says the plate and connector are OEM and the other bits decent aftermarket. Good to go?

 

[Steve@Avantgarde]

I wouldn't order any parts until you have looked at the fault codes mate. It could have split K2 or K3 clutch pack inside the box or a split drum causing a hydraulic pressure loss.

A battery can lock the gearbox into limp mode, but that only usually happens on start up.

Fault - Diagnosis - Cure - that is the correct path.

 

[charlysays]

Geez... I didn't know the clutch packs could split in half?!

Star turned up basically nothing. Only codes were for an intermittent issue with the park interlock, nothing else :/

The mechanic did note that the adaptions look pretty crazy, but this is to be expected given that it's got a GT2871 turbo and a hefty remap so it's probably making 230-240hp.

I;m going to concentrate on ripping my donor car apart so I've got a good used trans on a pallet incase and just drive I think. Nothing on star, and the car generally drives fine 99% of the time. I will be more considerate to it for the first 15 miles now though lol

 

[television]

A low battery cannot cause this as the car runs on well over 12 volt, often as said the valve block are the cause, often one never knows if the fluid ever got changed

 

[charlysays]

A low battery cannot cause this as the car runs on well over 12 volt, often as said the valve block are the cause, often one never knows if the fluid ever got changed

Yeah the battery was definitely a red herring... it's been funny since that. It had 118k miles on it when I got it... fluid wasn't badly dirty tbh, I got 7.5 litres out and the pan was the cleanest I've seen. Was forever finding debris in my old one which had 250k miles on it (but it kept going fine, and I didn't give it an easy life!).
11k miles with fresh fluid and I was thinking I was on to another 100k miles of good motoring

 

[om613]

Yeah the battery was definitely a red herring... it's been funny since that. It had 118k miles on it when I got it... fluid wasn't badly dirty tbh, I got 7.5 litres out and the pan was the cleanest I've seen. Was forever finding debris in my old one which had 250k miles on it (but it kept going fine, and I didn't give it an easy life!).
11k miles with fresh fluid and I was thinking I was on to another 100k miles of good motoring

There's a '98 120K car with a short MOT going for 100 quid over on VOD, mate.

 

[Steve@Avantgarde]

Between which gears are the adaptions crazy?

That can be the clue to your problem.

 

[charlysays]

There's a '98 120K car with a short MOT going for 100 quid over on VOD, mate.

I'd better take a look at that.
was looking on dronsfields and a 722.612 is now £150 inc vat. less than half the price of 3-4 yrs ago

 

[charlysays]

Between which gears are the adaptions crazy?

That can be the clue to your problem.

2-3 was on -45 or something which was one which stood out. The guy described it as some pretty extreme torque limiting during shifting. This is the shift which usually takes the full brunt of the tuned OM605 turbo when I'm overtaking (it'll spin the wheels from 35mph).
I'm usually very gentle with it 1-2 due to the higher stresses on the bearings etc at the lower speed, but equally by the time you get to the top of 3rd you're already in banned territory speed wise.