hubert

I have a 97 C280 with straight 6 and when i accelerate to like 40Mph(not with the gas to the metal just regular acceleration) and them i stop I can feel something loose or moving under my feet.It just happens whem the trrany shifts from 2 down to 1. it feels like the car stops faster than the trrany shifts or like somebody hits my rear bumper very lightly. I also changed my trrany mount(did not help), meaby i need to change the motor mounts too or this hve nothing to do with the trransmision. IF anybody knows something please let me know what could it be. Thanks in advance.

David C Klasse

Sounds like it's a problem within the tranny. 97 was the first year in the C-class with this transmission. There were many TSBs, and this sounds like it's common with the early 722.6s. Ask your dealer, maybe they'll take care of part of the cost..

Good luck!

mbtech208

Has it always done this, or have you just started to notice it? If its done this for as long as you can remember, I'd have to say it might even be normal. If it's just started to do it, check your motor mounts and flex discs. I'm not aware of any TSB off the top of my head regarding slow speed clunks, but given the number of TSBs Mercedes puts out each month, its entirely possbile.

David C Klasse

One of the most common procedures on this (97) tranny was an upgrade to the transmission control module.

TSB No.: 980501980501
Summary Description: Replacement of automatic transmission 722.6 with transmission serial numbers up to and including 880338 TP 951700. *YC (However, this might only apply to the 97 E420)

It's also common for the dealer to replace electronic transmission control module.

There was also a major upgrade with the software and the valve bodies in these early transmissions.

Though i'd bet you need to update the software in the transmission control module and have the valve body swapped out with the upgraded one.

Flex disc usually starts wearing out at about 80k miles. Mine was changed at 115k miles, and I drive the SHlT ouf of my car! Do you hear/feel a clunk when shifting into D or R, or what about when shifting from D to R, or from R to D? Part for this is usually about $75.

There were a number of early model faults... but they have been worked out, and the transmission has proved to be a remarkable unit. THough I'd still change the tranny fluid at 60k miles, albeit the "LIFE FILL," $225 roughly is a good cost vs possible replacement of a $4,000 transmission!

I alsoread this, might be worth something:

"MBNA recently released a 722.6 service summary pack detailing problems, corresponding symptoms and fault codes, and service solutions (both hard and software). There is a software upgrade available for your vehicle. Check with your dealer again; he should have this summary pack."

hubert

HI and thank you for all this. I changed the transmission fluid at 60K and after like month i startred to notice that and also when i shift from P to R a can feel something moving feels like the rear diff is loose but realy i dont know what to think. THANX.

hubert

One more thing what are flex discs and TSB. Sorry to borher.

David C Klasse

The flex disc is a round (hard) rubber peice that connects the drivetrain to the engine. Over time, it becomes brittle, and will cause a loose connection from the driveshaft to the engine/transmission. If you do have a clunk when shifting from P-R the make sure you have it checked. THere are two actually, but the front one is culprit.

Good luck.

TSB = Technical Service Bulletin

hubert

In other words you say to change the flex disc and see what happens and also the front flex disk you change that or no.Thank you again.

David C Klasse

I suppose it is possible to change yourself. But you must be atleast an ADVANCED beginner to intermediate, to do the job properly, in my opinion. Also, the flex disc can easily be inspect to see if it's cracked or chipped or worn. Kind of hard to explain...

But it's under the car, where the transmission meets the drivetrain... there is a black rubber (round) peice that connects between the 2 with 6 screws total. I'd try a good inspection... use a flashlight too. If not, have it inspected by a reputable mechanic or the dealer. How many miles are on your car?

hubert

-I have 65,000 miles on the car and from you were saying that seems to be the problem.
-And what do I say to the dealer when I go with that transmisson upgrade?
-Is the rear flex disc is easier to change then the front one?
Thanks alot for your help

David C Klasse

Tell the dealer that you want the valve body replaced with the upgraded one and a software upgrade... They should have TSBs regarding the matter with your early-make 722.6 transmission.

The rear one usually lasts more than twice as long... I wouldn't worry about that one.

hubert

Thanks Im going to the dealer right now see what they say.

hubert

One more thing wirh spark plugs do i go wit stock or somebody makes somthing better. And how does the thing with cables work because they not acctually cables and do you replace those with new ones. Thank You again.

David C Klasse

Go with stock spark plugs! NO PLATINUM IN MERCEDES ENGINES. They break apart. Don't worry about the wires with your mileages.

hubert

I made a appoitment but its on april 30. When i said that i want to upgrade my valve body and software she said that its not true that they dont do that but than i told her that it happend when they changed transsmisiom oil right away she gave me an appoitment. We"ll see what happens hopr its going to help. O and also she said thet you can ajust the tranny to. And can you tell me where is the valve body located is it inside the tranny or outside. THANK YOU .

BrabusCClass

My C36 did something like that at 75,000 miles. It was the flex disc. I would not recommend doing that unless you are a shop.

hubert

Thank you BrabusClass