ML270 autobox slipping?

[greenfingers]

After a little more than a month of ownership, I have been very satisfied with the performance of my Merc, until today when I towed a newly acquired caravan back from the Forest of Dean. I am suddenly concerned that my autobox is failing:-

I have had a few automatic cars, and I recognise that there is always a degree of clutch slip (torque converter?) on acceleration. For example, when you increase the throttle, say at 50mph, the engine revs increase before the road speed does. With a manual gearbox, this is not possible without the clutch plates slipping, since the gear ratio is fixed.
My last VW tiptronic autobox however, would lock in above a certian speed in top gear.

The revs when driving my ML270 auto normally, seem to float from around 1500 to 2500rpm as it progresses through the gears, according to the amount of throttle. Today, when I towed back 1300kg of caravan, the tachometer was reading more like 2000 to 2800rpm. What I found particularly worrying, was that it never seemed to lock into a fixed ratio - even cruising at around 55mph. What I am basically trying to say. is it feels like a slipping clutch.

Please, can anyone tell me if I am justified in fearing the worst? I will get the fluid changed ASAP (done 75000 miles), but are these symptoms normal? If not what do they suggest, and what will it cost?

 

[eric242340]

Having read this post several times, I dont think there is a problem. Normal shift point is 2.5K, However towing a caravan 2.8 is acceptable. The car is beyond 60K therefore it is better to do an oil and filter change. To change the filter means dropping the oil pan, but this is a straight forward job. Inside the base of the pan are two/three magnets and these collect and metal filings, from this you will see if there is any serious damage. Also check for sludge. (black sticky stuff). Smell the old oil for burning. When done put four litres of Transmission fluid and start the engine, dip the transmission and check the level with the engine running. Foot on brake run it through the gears and back to park then check the fluid level again with the engine running.

 

[greenfingers]

Thanks for the reassuring words Eric.
Yes, the first thing I will do is get the fluid and filter changed. A local independant seemed to understand the procedure when I asked them previously, so I am hoping they can do it next week. I will ask them to keep the excrement for examination.

However, I didn't explain the symptoms very well, so to clarify:-
The change up points seem normal, but if I increase throttle in any gear, then the revs increase while it stays in that gear. When towing, I noticed that more throttle gives more revs, so that cruising at 55mph with light throttle=1800rpm; if I push the accelerator, revs go up to as much as 2800 while still in top gear at 55mph! Just like a slipping clutch.

 

[Uncle Benz]

Are you sure it was still in top gear? Downchange from 5th to 4th can be pretty seamless if you have load on the back. The surest way to tell is to flick the tiptronic down to 4 and see if the revs change.

I have had people come in before saying their auto is slipping when towing, but actually there has been nothing wrong!!

 

[eric242340]

Are you sure it was still in top gear? Downchange from 5th to 4th can be pretty seamless if you have load on the back. The surest way to tell is to flick the tiptronic down to 4 and see if the revs change.

I have had people come in before saying their auto is slipping when towing, but actually there has been nothing wrong!!

Good thinking uncle benz, and there is one thing missing here. When you remove the caravan does the transmission revert to normal? Ttransmissions dont behave too well under severe loads.

 

[greenfingers]

Are you sure it was still in top gear? Downchange from 5th to 4th can be pretty seamless if you have load on the back. The surest way to tell is to flick the tiptronic down to 4 and see if the revs change

That was my first thought, but when downshifting there was a pronounced step up in revs. I also tried going into second and third gears manually while climbing a gradient, and although the change of gear was noticable, I could still increase the revs by applying more throttle - regardless of which gear was engaged.

Yes Eric, I would say it behaves normally without the caravan. Having said that, I have only had the car for 1000 miles, and I don't really understand how an 'electronically controlled' autobox is supposed to behave. I guess the engine temp increasing to around 90 degrees when towing is expected?

My towing experience has worried me lots, because I am convinced something is wrong. I remember my Dad cursing as we were trying to ascend the Alps with a caravan in tow, and a badly slipping clutch - you wonder when the force of gravity is going to defeat the power to the wheels!

 

[OmniCognateNeutronRangler]

Hi Greenfingers, I've had my Merc now for about a year and have found the gearbox to be "eratic" at best. I've had the oil and filters changed and it made a difference for about a week and now has gone back to its old ways again. It can be very lumpy and make some odd choices about when it should change gear. I had a loaner C220 with only 5k on the clock and found that to be just as bad.

I have had quite a few auto's in the past and never had these sort of problems. I'm afraid what you are describing just sounds like normal MB autoboxes to me.

 

[oigle]

Unlike a lot of auto transmissions, MB trannies like the one in your ML don't have a "lock up" torque converter. They use a progressive arrangement which gradually reduces the amount of slip as the speed rises but it never completely locks. This may be what you are experiencing. I also tow a van and find the slippage increases with load. I try to manually select a lower gear on hills rather than allow the larger amount of slippage to occur in the higher gear, as I believe that just adds to the heat produced in the gearbox, and heat is the biggest enemy.

 

[psmart]

Wouldnt worry about it, from brand new when I towed the twin axle spectrum (circa 1700kg) the revs were always well above the actual per-gear rate, ie. 3000rpm would drop by over 500rpm when you let off the accelerator. We drove the ML down to Austria with over a tonne of gear in (looked wickedly cool as it looked lowered!) and same scenario. I was suprised no lockup seemed to be occurring, but got and still get good economy, so must be locking up at some point.

The ML towed the Spectrum down to South of France and back when it was new, in hot summer and didnt blink an eyelid (or gear cog), so from what Ive seen, you havent got a problem.

Lateral thinking=Why worry about your gearbox if it aint broke? Why spend money on perceptions? When you stop dead or can no longer tow the van, then its time to worry! Changing the oil though would be a good move.

 

[psmart]

MB trannies like the one in your ML don't have a "lock up" torque converter. They use a progressive arrangement which gradually reduces the amount of slip as the speed rises but it never completely locks.

This explains why Ive never seen lockup, even at 120/130mph, the revs off throttle are always lower than on throttle.

 

[television]

Unlike a lot of auto transmissions, MB trannies like the one in your ML don't have a "lock up" torque converter. They use a progressive arrangement which gradually reduces the amount of slip as the speed rises but it never completely locks. This may be what you are experiencing. I also tow a van and find the slippage increases with load. I try to manually select a lower gear on hills rather than allow the larger amount of slippage to occur in the higher gear, as I believe that just adds to the heat produced in the gearbox, and heat is the biggest enemy.

Must check this out,As psmart says nice to know.I will read about it later and see if any other models do this.

Malcolm

 

[greenfingers]

Wow, it is a huge relief to hear that I have misdiagnosed a fault. I was convinced that all those revs were going to cook something.
Thanks to all of you for your wise words.

Oigle, I have read posts by you before, and appreciate your wealth of hands on knowledge. Your explanation of the autobox behavior convinces me, but I am surprised that it is designed to slip so much, since surely this causes more heat and wear plus less efficiency?

Psmart, I have also read a lot of your tales of ML ownership, and it is reassuring to hear you describe the same symptoms as being no problem.

I am still going to get the fluid changed and inspect the effluent. When completed, I will post a report on the findings on this thread.

 

[greenfingers]

Today I took the car and 4 litres of Mercedes autobox fluid, one strainer, one sump gasket and one plastic clip, to an indie who already had the dipstick and reassured me that he knew what he was doing.

About an hour later the job was done. I was a little alarmed by the colour of the effluent - not burned, but sort of black. There was a little gunge on the bottom of the sump, but nothing metallic on the magnet. Almost exactly 4 litres came out, and they replaced it with exactly 4 litres.

It may be my imagination, but I think the gearchanges could be a bit smoother. Otherwise, I cannot notice any differences.

So should I worry that the blackness indicates worn friction plates?
I am thinking the only way to really know if my discs are slipping excessively, is to drive a similar ML.

I am still worried, especially since I know the previous owner had towed with it - he even admitted to pulling his friend's Range Rover after it broke down!

Can anyone reassure me please?

 

[television]

Today I took the car and 4 litres of Mercedes autobox fluid, one strainer, one sump gasket and one plastic clip, to an indie who already had the dipstick and reassured me that he knew what he was doing.

About an hour later the job was done. I was a little alarmed by the colour of the effluent - not burned, but sort of black. There was a little gunge on the bottom of the sump, but nothing metallic on the magnet. Almost exactly 4 litres came out, and they replaced it with exactly 4 litres.

It may be my imagination, but I think the gearchanges could be a bit smoother. Otherwise, I cannot notice any differences.

So should I worry that the blackness indicates worn friction plates?
I am thinking the only way to really know if my discs are slipping excessively, is to drive a similar ML.

I am still worried, especially since I know the previous owner had towed with it - he even admitted to pulling his friend's Range Rover after it broke down!

Can anyone reassure me please?

Yes why not, its been a cold day today so always a little bit harder to judge.

Towing can over heat the fluid so that it goes black and seldom does that much damage to the box, I think that over the next few days you will forget all about it.


malcolm

 

[greenfingers]

Thanks Malcolm. One day I might sing you a lullaby.

 

[psmart]

I drained mine at 58K and it was black. The car has done about 1000 miles of towing, the rest a mixture of sedate 80mph cruising, 120mph cruising and going off the beaten track! From reading others posts about changing the fluid, this seems normal and puts to bed the Mercedes notion of sealed for life.... not!

Ive done over 10K since changing the oil and the only problem Ive noticed is that the 4x4 thunk is more noticeable (ie. from stop, a thunk as the 4x4 engages power, which my Grand Cherokee used to do more noticeably from brand new). I replaced all the oils though, gearbox, transfer case, both axle housings.

One other thing Ive noticed is after a reset, the gearbox is lovely and smooth, but after about a K, is not so smooth, mind you there are several people driving the ML at the moment, so its probably confused as per driver style

 

[rio678]

It's not only the MB boxes that do this, same happened to me in my Audi A6

 

[eric242340]

It's not only the MB boxes that do this, same happened to me in my Audi A6

Audi have a bigger failure rate than Mercedes, but the box is an entirely different design. But all transmissions suffer, its quite simply a matter of manufacturers trying to say their boxes are better. ie the sealed for life thing that both MB and BMW are pushing at the moment. Its simply not true. Nothing is sealed for life, or should I say that depends on what you define as life and they dont define it.

 

[rio678]

Not too bad, lasted until 170K before it went Bang, But i am one for servicing so perhaps that helped. Auto-Boxes are always going to be troublesome though, i do prefer a manual any-day.

 

[Hibbo]

Not too bad, lasted until 170K before it went Bang, But i am one for servicing so perhaps that helped. Auto-Boxes are always going to be troublesome though, i do prefer a manual any-day.

I'd disagree with that from what I've seen of 200k+ Merc autos.

How many 15+ year old daily drivers with a couple on hundred thousand on original manual boxes do you see? Although manual Mercs are so rare it's difficult to make a like for like comparison.

Might have something to do with not being able to thrash and grind and auto, and power delivery will be smoother owing to the TC instead of a left foot.