cookstar

iTrader: (6)

My sister in law has an A series Merc,(auto) and she is describing a problem pulling away that sounds like a slipping clutch, - revs rise with no road speed then eventually bites and off she goes.

skinner

Have you checked the fluid level .You need to check it with engine running .

cookstar

iTrader: (6)

No, didn't know you had to, could low level of fluid cause this then, I have only had a phone call about this so far, so haven't seen or driven the car.

what would scooby do

A class gearboxes are known to be weak and often break

cookstar

iTrader: (6)

Surelu if the gearbox had let go then it would be mashing itself to bits, it drives fine from what I can gather after its managed to pull away.

TonyBurns

iTrader: (3)

Yes low fluid levels can or else its probably the torque converter but either way if the low (possably low) fluid level hasnt been sorted for a while your probably going to have to replace the torque converter anyway

Tony

skinner

i have just repaire a toyota that was finding it hard to get gear and then lost drive due to fluid loss through a rotten pipe to auto fluid oil cooler.Some auto boxes have a filter in this could be blocked if you ring mercerdes parts they will tell you if it has a filter inside the box .I have changed filters on mercerdes auto boxes before.

what would scooby do

I can't remember the exact symptoms and causes I read about - something to do with valves. Give me a min and I will see if I can find it again.

what would scooby do

found it..

A Class Gearbox Woes - MBClub UK Forums

cookstar

iTrader: (6)

Ok cool, I'll have a check of the fluid then, will this be on a dipstick on the gearbox? Or is it another fluid I need to check, like I say I have never done any work whatsoever on anything auto.

skinner

just like a engine oil dip stick that goes in to auto box.

The Zohan

Yup and it must be done with it running

Adidas

Cookie,

Promise us one thing. Whatever it is, you won't be working on it!!

cookstar

iTrader: (6)

Good link that, thanks.

cookstar

iTrader: (6)

By the sounds of it, the only "work" I will be doing on it, the less YOU know about it the better.

cookstar

iTrader: (6)

The gearbox let go completely the next day, first gear disintegrated, in the garage now having a £1500 rebuild.

ALi-B

iTrader: (1)

Actually to be pedantic, it will be the clutch pack for first gear that will have disintergrated. The lining material and metal particals from the failed clutch discs will contaminate the valve block and the rest of the gearbox, necessitating a total strip down, clean and replacment of all the seals, valve block, solonoids, actuators and other clutch packs. Running the gearbox low on fluid also does similar damage as the clutches are wet plate clutches (designed to be used in contact with oil), if the clutches run dry, the friction material quickly wears out (its only a few mm thick).

The physical gears used for first gear is also the same gears for second third and fourth etc. Sorry, just I find epicyclic/planetary gears fascinating with how they obtain different ratios just by using a few brake bands and clutches. Also give good insight in how a automatic gearbox works.



Here's some of pics of a old BW automatic with a failed front clutch pack (used for 1st and reverse IIRC) that I rebuilt (click to enlarge):

Sump metal sludge:

Valve block seperator plate, more metallic sludge (all the black stuff is sludge - its a stainless steel plate):


Metallic sludge in clutch actuator:


The source of the metal (front clutch pack, one of the steel discs):
What it should look like:

The source if the sludge (one of the friction discs from the front clutch - whats left of it):
What it should look like:

stilover

My old man has this problem on his Auto X-Trail. Slight clutch slim at low speeds.

Told him to book it in for them to look at. He hasn't of course.

hodgy0_2

it might help to think of an auto box as a big hydraulic pump working at v high pressure

that is why fluid level (and quality) is important -- low = low hydraulic pressure hence slippage

cookstar

iTrader: (6)

I guess she will have to be more carefull with checking her fluid levels in future then, thanks for the explanations as to the workkings of an auto box, I can't see the pics at the mo as work PC blocks them.