126 Tranny Rebuilt @ 160,000 miles.

[ymsin]

Its finally in the workshop with the tranny unit taken apart. The clutch plates looked a little worn and the coupling was a little loose. This would be the first ever rebuilt and I'm looking forward to getting it out of the workshop by Tuesday.

I learnt a great tip while talking to the boss: NEVER EVER REV THE ENGINE WHILE PARKED IN P.

I never knew that the gears are engaged in P and revving the engine could damage the clutch plates.

[BenzOnline]

Really???? oops

[David C Klasse]

Then what about neutral!?

[ymsin]

I was advised N is fine.

[BenzOnline]

Well, how much damage would you do if did rev the car in park? How would you know their is damage done to that?

[dpetryk]

I would like to know why reving the engine in park can damage the clutch plates. That dosent make sense to me. Can you explain it to me?

Hmm.... interesting. Not that I do that, no need to rev my car, but I'd like to know why. Inquiring minds want to know

[MikeTangas]

Park should just be neutral with a ratchet (pawl) holding the car stationary. Shouldn't damage anything, but you could cause a timing chain to jump (had that happen on a 70's Mopar ).

[FineOlBenz]

Parks are for cruising. oops Transmission Park.

I haven't checked the transmission flow chart because I don't have one for the MBZ. Many manufactures say to check the transmission fluid level in neutral with the motor idling. The reason for this is that the transmission front pump is not circulating fluid through the transmission in Park. But in neutral there is full circulation of fluid. So If you are reving up the motor in Park with no fluid circulating, there could be damage. You should not be overly concerned with normal idling or running the engine in Park though. Mopar transmissions do not pump fluid through in Park either. I've never heard of a failure due to running the engine in Park. (21 years of police vehicle maintenance experience I've never come accross a problem of engines running in Park).

By the way, does the MBZ book tell you to check the fluid running in neutral? I don't have a book.

[Ali Al-Chalabi]

According to alldata, it says to check the fluid level while in park.

[stevebfl]

Don't know a thing about mopar but the front pump on all trannies Ihave ever seen including MB is turned by the torque convertor which is spinning every time the engine is.

As Mike says park is just like neutral with the added locking feature.

I suppose that reving the trans in either neutral or park could eventually do damage from reving as the gears are always engaged in an automatic (except Hondas). They use planetary gears which involve three gear groups which are attached to the clutches and drums that are locked in the application of clutches or bands (clutches make two pieces rotate at the same speed - coupled, band stop members relative to the case). Since a reved motor will have clutches spinning in oil against themselves; some plates moving and the others not, they will be wearing some and overheating. At some point the oil left between them acts sort of like the lock-up feature of the torque convertor.

I have never seen any of this do anything to an MB but BMW had a real problem with their mid-80's ZF trannie. Due to internal leakage theforward clutch always had a small amount of pressure on it. I think it was Texas that first found out about this in emissions testing. They were doing in park testing under part throttle conditions. The partially applied clutches burned and wouldn't pull the car out of the stall after the test.

I had the same thing happen on a 86 735 after charging the A/C at 2000rpm in park. We now do this in neutral with the cars wheels off the ground on those models.

[ymsin]

Steve's explanation was close to what I was told.

Anyway, the 126 drives like never before. Smooth upwards and downward changes with no jerks. Its like sitting a new ride again.