P reg C280 gearbox advice please.

Tetleysmooth

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I'm going to view a P reg C280 today. I spoke to the seller yesterday and he told me sometimes the gearbox 'clonks' a bit. He said it's fine when he's just waffling around, but as soon as he gives it a bit of throttle, the gearchanges hang on for a bit longer and are harsh when they do change.
I though this was quite normal behaviour for an autobox, regarding the staying in gear for longer, but must admit the harsh changing has got me a little wary.
He also told me he's taken the car to Mercedes to have the gearbox scanned, but the fault reader came back with no faults. He told me this a few times, so I can tell he's concerned about the 'box.
Has anyone here experienced this sort of thing? It'd be great if it's just a split or blocked vacuum pipe, or something of that nature, as he's willing to part with the car cheaply.
Sorry if this all seems a little vague, but I'm just relating what the seller told me.
Thanks in advance.
 

kth286

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you need the full vin so that you can check which gearbox it is.

it's probably the older (non electronic) box and so will have nil diagnostics.

and indeed maybe a vacuum problem.
 

dulayj

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I doubt it will be as simple as a vacuum pipe
Likely needs more diagnostic work first of all to find real cause-this needs factoring into equation before purchase especially if gearbox fails !
 
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Tetleysmooth

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I doubt it will be as simple as a vacuum pipe
Likely needs more diagnostic work first of all to find real cause-this needs factoring into equation before purchase especially if gearbox fails !

That's what I'm a tad worried about :eek:
 

shorty

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Has the level of the ATF been checked , this couls just be low or need changing
 
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Tetleysmooth

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Has the level of the ATF been checked , this couls just be low or need changing

Well, I bought the car. Collecting on Sunday. Couldn't really find much wrong during the test run. Bags of power and no slippage. The seller did say he might just be being over cautious. I agree with him. All will be revealed from Sunday onwards, watch this space......

Thanks for the replies.
 
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Tetleysmooth

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Update!! The gearbox is a 722/6
Well, I've had the car a week now, and this gearbox 'niggle' is really baffling me. As said before, if I use light throttle, the car drives perfectly, but as soon as I get a bit enthusiastic, that's when the niggle starts.
I took it to my local autobox specialist yesterday and he came up with a range of possibilities, but I think he suspects the control plate or valve chest as he put it. He quoted me £400 to replace the control plate. Is this excessive? Any specialists on here that could do it cheaper please?
The car is going back for a full diagnostic check next Monday. The gearbox bloke also said there may possibly be a couple of faults which may not have been cleared yet, and once cleared, the 'box may be ok - if I'm lucky.
He also mentioned the brake light switch. Can someone please tell me how this affects gearbox performance? Maybe it's my imagination, but it seems like the harder I put my foot on the brake pedal, the gear selector is easier to use!!! Probably me being thick.
Any help/advice will be most welcome.
Oh, the ATF level was ok.
Thanks.
 
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Tinkerer

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That sounds like the same gearbox as I have, you have to have your foot on the brake to take it out of park but from then on I think you should be able to move it without the brake, can't say that I have really tried though as I always have the brake applied when shifting from D to R. why would you want to move the selector when driving? other than if you have the tip function?

I have heard that if the brake light switch fails it puts the car into limp home mode which does not sound like what you have.

Have you tried the gearbox reset procedure which was posted on here recently, it certainly made a difference on my car especially with gearchanges.

Hope this helps & good luck.
 

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It could be a number of things causing your issue. It needs proper diagnosis with a Star to check some of the adaptaion values and a road test to see how bad it is.

Was the fluid that was repalced the correct type?
 
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Tetleysmooth

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why would you want to move the selector when driving? other than if you have the tip function?
Thanks for that Tinkerer. I don't move the selector while driving, just from P to D. It seems as though with a light brake pressure, the selector is harder to shift. With heavier brake pressure, it seems easier. Probably just my imagination.
I did try the reset procedure as posted on here, but didn't seem to make a difference.
 

Adam230K

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Try and diagnose the problem yourself while driving.

You need to figure out whether the gearbox is actually causing the banging, or drive train related. Does it do it when the car is cold? If you were 'enthusiastic' when the car is cold does it still do it? If not, then it only happens when the car is warm and i'd be more inclined to blame the gearbox - it could be a cooling issue, or even the incorrect fluid which heats up more than it should causing the gearbox to bang - whole range of stuff to blame here and much harder to diagnose

Say for example if you floor it on a straight and try to stop very suddenly and harshly, do you get any clonks? This would be drive train mounts, could be any of them though, ranging from gearbox/engine mounts to propshaft mounts.

Its so easy for someone who isn't competent in these things to blame the gearbox when it could be something entirely different.

Trial and error is your friend
 

Adam230K

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Just saying that when I had 'gearbox' problems on a previous car (bmw) 2 specialists just kept blaming the gearbox and were really pushing for me to let them do the work for £1600.

It turned out to be the gearbox cooler which was £280 from ECP and fitted takes just over an hour. The only way I found out was I turned the heater on at full blast when my gearbox went into limp mode and it seemed to correct itself and come out of limp mode, it was a 'Eureka moment for me, and I didn't have to fork out half the price of the car on a gearbox I didn't need.

good luck
 
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Tetleysmooth

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I reckon it's the sensor plate, but of course I'll wait for that to be confirmed on Monday.
If it is, I've heard these can be bought, and I've got a very competent mechanic living a few doors away, so maybe it won't be the end of the world.
 

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