R129 - no reverse

[finleyfishface]

Hi everyone.
I have searched the forum on this, but couldnt find any similar problems.
Has anyone ever suffered loss of reverse gear on the 500 SL auto ?
When car is cold, everything is fine....when reaches operating temp, forward gears select, but when reverse is selected, its as if its in neutral, ie it just revs.
As soon as it cools down, it works again.
Its currently with a specialist MB garage at present, who has 40 plus years experience, and has ever seen this once, (as in reverse going, but forward gears perfect), and that was a 220 which had a sticking valve body in the box, caused he thought by mere lack of use !!!.
We have changed the filter etc etc and checked pressures, ie the usual starting points, so now its back in for box removal
So, just interested if anyone has had this ?
When I find out what the cause / remedy is, i will post results as it is so unusual.
Regards to all

 

[Richard Moakes]

Sounds like the B3 clutch pack is worn, this controls reverse gear. Or the valve controlling fluid flow isn't operating correctly when the fluid is warm.

Has it been getting progressively slower to engage reverse?

Cheers,

 

[finleyfishface]

Hi Richard,
Thanks for taking time to reply...
No, its always worked fine, then one day, it didnt !. From then on, its works when cold, doesnt when warm ! This is whats puzzling the specialist, forward gears are as positive as ever, reverse is fine until everything reaches operating temp, then it doesnt clunk into gear.
Cheers

 

[finleyfishface]

ps Richard, the car has only done 95,257 miles..........
cheers

 

[Xtractorfan]

Is R coming up on the dash when u select reverse..no drinks or anything spilled around the gearshift module?

 

[finleyfishface]

Hi there,
dont have the display mode on dash, too old !!! I dont recall spilling any drinks no, good thought though, i have been known to sit in the car with the hi fi on with a tin when the mrs starts nagging, but dont think ive spilt any !!!!
cheers

 

[Richard Moakes]

Hmm, well there is a valve controlling the pressure to the B3 piston in the valve body, however my money would be on the B3 piston itself having leaky seals, this would allow the warm oil to bypass the piston and not engage the clutch pack.

Unless your mechanic is a transmission man, then I would recommend you find an auto transmission specialist who will have more experience in diagnosing transmissions.

PM me your email address, and I will send you some .pdf files which will assist anyone working on the gearbox.

Good Luck,

 

[finleyfishface]

Hey thats interesting because his best thought so far is, as he puts it, "sticking valve",
how do I pm you ??

 

[finleyfishface]

ok Richard, pm'd you
cheers

 

[finleyfishface]

further thoughts, he has done some initial checks on pressure, could be he was checking pressure on seal, as you suggested ? He said there was various things to do before taking box out, this must have been one of them, but what threw him, was pressure was fine which indicates no leaky seals..... this is why he told me to try it again and use it more, but it didnt get any better, and thus it is now in the operating room !
Cheers

 

[finleyfishface]

received thanks Richard, thats good of you.....
I will think of a way of showing it to him without offending him !!
I think (as in one of the benefits of this club) that any help should always be received positively, so he should really have a read of it.
many thanks again, and when I find out what it is I will post. I am confident though, that as the guy said, weve done all we can to avoid dragging the box out, but its now inevitable !
Thanks again

 

[Richard Moakes]

You are welcome, it's good to share info and help others.

I hope it turns out well for you.

Regards,

 

[finleyfishface]

yeah, its not the sort of problem you want on one of these is it ! Ill keep you posted, and your help and advice is appreciated.

 

[finleyfishface]

Hi everyone,
just an update in case anyone is interested.
Got car back today, the B3 piston had failed, over a long period of time, prob because i dont use car regularly, causing damage to friction plates. The specialist said this was only the second time he had come accross this in 40 years !!!! which made me feel loads better !!!!!!!!!!!!!!. Anyway,all fixed now, and as it was a nice sunny day, i treated the car to an Autoglym polish, as I was glad to have it home !
Thanks once again to Richard Moakes ( he was spot on as it happens, in his suggested diagnosis, and also to Xtractorfan.
Cheers.

 

[Richard Moakes]

Thank you for your kind words, I am so pleased you have it sorted out.

I am surprised he sorted it out so quickly for you, thats most impressive.

Enjoy the car, I spent the day working on mine and then went for a drive in the sunshine on Dartmoor

 

[19657]

Hi Richard,
well I had a different problem in my A170cdi auto, putting in reverse would give an impulse in the car (after 1 second -gear delay). It I am pressing brake pedal I have this impulse (car trying to move) every 4 seconds more or less. If i press slightly gas pedal, it stops. It feels like clutch tries to engage but then understands not too good....
could it be oil level? i am about to do oil renew and filter and sump.

Also, during a CO2 test, they put my car on rollers, front wheels, and run the car at speed/revs and they were getting ASR fail, then my auto gearbox got into "F" mode. now I can not reset this, but I will do the oil change same.

Could you send me your info on auto gearbox?

Many Thanks

Nuno
A170 cdi 1999 automatic

 

[Richard Moakes]

Hi Nuno,

Sorry to hear of your problems, regrettably the documentation I have isn't applicable to your car, it's only for the 722.xxx series of transmissions fitted to R129/W124 etc...

I believe your transmission has a much greater degree of electronic control, and will need some computerised diagnostics to assist in resolving the problem.

I do hope you get it sorted, my best advise would be to contact a transmission specialist or preferably one of the specialist MB mechanics who regularly post on the forum.

Cheers,

Richard

 

[television]

I do not know much about the A class,,but "F" in the display means that the shift valve has gone, the fault code for this is P1844 with the code no other valve should be replaced.'

There is nothing about the reverse problem listed, but could the above part cause this

 

[Cole@MBS]

Just as a "add-on" to what Malc said, a faulty selector lever will also put F on the display!

 

[19657]

My gearbox is 722.7 so the info you have should be convenient.

About that Valve, where do I find it and is it expensive? Easy to replace?

About Selector, this would be one of the possibilities I thought also, but does anyone know what this selector does? I have seen a webpage by lofty where I have picture of this selector. I see a cable that will connect to gearbox, and will select drives. I see a kind of switch that should be P related. Does it have any other electronics?
I am electronics man so I could take a look....

Regards
Nuno