W140 driveline/transmission issues

[s class]

My W140 500SEL ('92) is an early version with the basic 4 speed torque converter tranny. It seems similar to 70's and 80's benz transmissions in design.

It is not slipping at all, in fact the gear changes are a little hard if anything. Recently is has developed a tendency to 'shudder' as it changes gear. This is most noticeable on the 1st to 2nd change, and is worse under full throttle conditions.

I've used the word shudder, but its quite tough to describe, but that's the best term I can find. The shudder is very brief - perhaps half a second. There is no obvious slack in the diff, sideshafts or driveline.

I FINALLY got underneath the car to have a look this evening. The front flex disk is in a fairly advanced stage of developing the Don King hairstyle......

The rear flex disk looks OK.

I'm unsure how to judge the state of the centre bearing - visually it looks OK. I can deflect the shaft sideways with modest pressure applied to it near the bearing. Does this sound reasonable? Any tips for diagnosing centre bearings?

I think I also have an engine mount problem. Recently its been feeling like the engine bounces around undamped when going over sharp corrugations etc. I had assumed there were mounts and separate dampers as on the 70's benzes, but this appears not to be the case. The engine mounts appear to also perform the damping function.

 

[Styria]

Hi S-Class, if your W140 has a similar centre mount/bearing set up to the 116/126 range, it is perfectly normal for there to be sone up and down and sideways movement. After all, the bearing is encased in a rubber housing. As I have said previously, they are long and well lasting units.

Obviously, with an 'Afro style' haircut, the flexible coupling should be replaced. In fact, just a small crack or fracture, will cause the coupling to transmit vibrations to varying degrees. One needs to remember that by the time hairline cracks appear, the rubber component of the coupling would be rock hard already.

Whilst I am not familiar, with your W140, S- Class, I suspect that the old 116/126 engine mount set up has been replaced by oil (more than likely) or gas filled mounts for better cushioning effects. Regards Styria

 

[s class]

Thanks for the help styria. Thoroughness would be to change both flex disks and the centre bearing, buy W140 components are a little dear, and my instinctive judgement tells me the centre bearing is OK. The front flex disk was a real shock to see. It has bunches of cords sticking out, and some of the metal 'eyes' have come adrift already. I will replace it as a matter of extreme urgency.

 

[Styria]

Talking about flexible discs - genuine 6.9 units sell for quite a bit more than those for 280's and even 450's. although I am not sure if, due to standardization (again ! ?) 6.9 units are no longer available.

Physically, of course, the units are interchangeable and from time to time I have seen non 6.9 units that were fitted in place of the genuine item - obviously with cost savings in mind. I should really illustrate the difference between the various units.

I have the further belief that similar sentiments apply to engine mounts, but with those it is only the composition of the rubber itself that differs. Physically, there is no difference, but you have to look out for left and right variations (not always) as well as early and late types. At those times, chassis numbers may have to be quoted. Regards Styria

 

[mathew]

G'day S-Class don't not drive that car any further with that flex disc like that, when it goes it will rip the drive shaft through the transmission housing very expensive!!!!!!!!!!!!!!

W140's are very heavy cars and flex discs that are worn will give way really quikly, your shuddering would be that I have worked on a few of these. Engine mounts are common in 140's they are good for about 100,000km and thats it.

Replace all the flex discs, it is very rare for the centre bearing to go, however drive with that flex disc and you are putting an unwanted load on the bearing.
If you need an OEM parts supplier outside the MB network PM me I can give you a couple of guys in Sydney that will look after you and not break the bank.

Cheers Mat

 

[s class]

Thanks Mathew, I know the risks of driving like this, but 'ive done it again' to myself :

The 280SE is on stands awaiting new front brake calipers
the blue 6.9 is on stands with half its mechanicals disassembled
the red 6.9 is on stands for lack of a suspension distribution valve (parts borrowed to copy for the blue car)
the 450SL is on stands waiting for a chain tensioner.



I have a flex disc now, I will fit it this evening. In the meantime, I am creeping around with very gentle throttle application.

Yes I know the engine mounts are shot on my W140, the strange thing is it seems to have come suddenly. The car was nice and tight, and then just one day I started to notice the engine oscillating around.

I have located the flex discs, engine mounts, and other items I need like upper control arms at AutohausAZ, for typically 25% of what the MB dealer wants.

The reason my present mobility (or lack thereof) has arisen is I've been so focused on the blue 6.9, I've neglected the W140 for some 6 months - not a wise way to treat one's daily driver.

There is hope though, I get back the red 6.9's hydraulic bits today, I will finish the 450SL this weekend, and I will get the 280SE's calipers back from ultrasonic cleaning on Tuesday - and I'm on leave next week, so I hope to get 3 or 4 cars running.

Note to self - don't put so many cars on stands at once next time....

 

[s class]

Well here's the horror picture : (excuse the poor phone-photo)

 

[mathew]

You are one lucky son of gun with that flex disc. As for the engine mounts mate that is exactly what they do one minute there good, next minute the oil diafragm lets go and the engine does the rock and roll!
Cheers Mat