W124 Diesel 4spd Auto Rough Jerky Changes

pikeydave

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Over a relatively short period of time my E300TD Turbodiesel's autobox started giving me very rough gearchanges on all upchanges, feeling worse on the 3rd/4th change. It felt so bad that I worried about my diff being ripped out and the prop-shaft bouncing down the road following it.
First thing to do was drop the oil, change the filter and refill with fresh and cross the fingers that all the jerkiness flowed out with the old (and surprisingly clean) oil.
Quick test drive. No change. Bugger!

Now the trouble with auto boxes, especially of this vintage, is they're tough, reliable and aren't fussy about oil changes! Which means that you don't get to tinker with them much. Mr Haynes in his manual shies away from even touching anything oily in them!
So the thin section on auto boxes in the Haynes manual is only good for bog paper.

So I go and seek a professional autobox bloke's opinion who's fixed a couple of Merc boxes of people I know.
After a test drive he says the clutches are worn and to do an overhaul think of around £1200 give or take a ton.
It sounds plausible. When the clutch bands wear out maybe they go downhill fast? I don't know.
Then I post on here looking for options, ideas, suggestions and looking for a spare box.

Here's the rare sight of a turbodiesel under the bonnet of a W124. I think it's a great looking engine. No plastic covers and all quality components. (Note the optional heated washer bottle)

300turbo2.jpg



So starts the steep learning curve with getting to grips with auto transmissions and, more importantly, the vacuum systems that control the gearchanges. This lead to doing a little swapping around to test certain components.

Picture 1

vac1.jpg


This is the standard set up with the supply of vacuum on the right and the outgoing vacuum to the gearbox on the left with the green inline filter.

Picture 2

vac2.jpg


Now the unit is bypassed with vacuum coming straight from the pump.
Result. Smooth, soft gear changes.

So either the control unit is failing or the modulator valve on the gearbox needs more vacuum than the control unit can provide.

After feeling all smug that I've logically got to the bottom of the problem I look at the control valve bolted on to the Injector pump. It's an impressive aluminium casting that looks as though if contains 10,000 tiny springs assembled by a Swiss watchmaker, at great expense, in a clean room, in some laboratory, in Zurich and will explode when the cover comes off!
If this was a French car it'd look like a bit of Tupperware and be velcro'd on.
But hang on, it's only 3 pneumatic tubes and two 10m bolts holding it on, what have I got to lose.
I marked up its position with a scribe and unbolted it.

Here's the control valve in pieces off of the IP. Looks in good condition and only 1 spring!

vac3.jpg


Looking more closely though the inlet vacuum brass jet is blocked with a bit of gunge.

vac4.jpg


After a bit of careful cleaning the jet is remounted in the valve housing and reassembled.

vac5.jpg


After remounting back on the Injector pump, a bit of adjustment, and all is well again.
Seeing as some specialist test driving the car and wanting £1200 to overhaul the box and I was contemplating buying and fitting a secondhand gearbox (sorry Ian) I think this is a result and makes me appreciate MB engineering even more.
300TD.jpg
 

television

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Thank you and I have asked anyweb to move this excellent post to the DIY section
 

farters

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Does this just refer to the 4 speed auto, or is the principal the same for the 5 speed box? I have a Petrol 320, so not sure if that makes a difference to the box either, but when cold the changes are a bit jerky. I did the old changing of the oil trick, which was successful to a degree, but wonder if this might also help. Interesting guide though, thank you.
 

television

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Yes the 5 sped box is in principle the same a vacuum tube of or the modulator faulty will give jerky changes
 

dieselman

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Seeing as some specialist test driving the car and wanting £1200 to overhaul the box and I was contemplating buying and fitting a secondhand gearbox (sorry Ian)
Go back tot eh auto-box specialist and offer a deal. If he gets any more boxes doing exactly this fault he can charge the £1200 and then bring the car to you and you will only charge him £1000 to fix it.

He makes £200 for driving the car to you...
 

Doug1234

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Curiosity has the better of me.

Am I correct to presume that the cover with the jet in can be removed individually ?,it looks as if it just needs a 1/4 turn to release it and remove ?.

Adjustment,I can see how the unit can be swung and it's position altered ,but what changes when position is moved ? ,does it alter duration of vacuum ?
 

television

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You should check that the pipes are all good first
 

wireman

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I have just this weekend had a second go at this task, my car having developed a severe jolt when up changing on start off whilst cold.

I am reliably informed that the vacuum modulator is inside the gear box and translates the vac "pressure" to the hydraulic pressure which controls how the gearchanges are executed.

The device on the diesel injection pump (or the throttle pot on electronic M series pumps) is a manifold vacuum simulator which gives similar vacuum to that which a spark ignition engine would under various load conditions.
It has two functions, the provision of fast idle when cold via the thermovalve on the cylinder head and the black pipe to the devices body.
The variable vacuum is made from the two tappings on the simulators head, one to the transmission and one from the vac pump.

To remove the simulators top (black part) it must be taken off the car as some quite hefty levering off is required to release the 4 clip points around its outer ring from the body (white part) and lift out the top.

I have done this job once before with almost complete satisfaction just a few bits of jerk and thrutch remained, on my second go I have flipped over the rubber seal on which the nozzle/jet rides to a brand new undented surface.
The result is a much improved response and smooth gear change behavior.

To flip the seal the piston/diaphargm assy needs taking to bits, just pull the plastic bit on each side of the diaphagm and a spring and small piston falls out - piston on top, spring underneath.
The seal is held in by 4 small projections on the piston molding just lift the seal and peel it out.
As they say reassmbly is the reverse of disaasembly.

A correct adjustment has left me a little puzzled, so I connected a vac gauge with a tee into the pipe to the gearbox and temporarily fitted the pipe from the centre of the simulator (vac supply) to check for any leak on the tubing, gauge read 25.5"hg, this and all that follows was done with the engine running.

Then the setup was returned to normal with the gauge still in the line to the box, gauge read 11"hg with the simulator off the pump, turning the operating peg caused the vac to fall off to zero. I do not know whether this vac figure is correct it is just as high a vac that I could get on my car.

With the simulator back on the pump the body was rotated untill the vac just began to fall, this point was found to be at the marks I originaly made before taking off the unit.
Slight proding of the throttle caused the vac to fall so a road test followed.

A little lack of smoothness remained and the simulator body was turned a further 1.0mm (at the bolt flange ) clock wise, result nice and smooth gear changes and reasonable cold start jerking changes. On driving at very slight throttle settings the vac stays up at 10-11" as the throttle is increased the vac falls off to zero at about 1/4 throttle.

I have not investigated the fast tick over aspect of the device, I will have to wait for winter when it is noticable that the fast tick over is reduced when the engine warms a little.


Aplogies for being long winded and thanks to Pikeydave for giving me the courage to fiddle with the simulator in the first place.
 

Doug1234

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Excellent explanation thank you.

I have spent some time trawling the net looking at vacuum diagrams and reading page upon page looking for info and this one thread explains it all.

A big thanks pikeydave and wireman
 

chizzel89

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Where and how did you get your Turbodiesel W124??!! I'd love one, even if it is L/H drive. Talking of which, how do you find the LHD thing?
 

wireman

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I've had further troubles with my vac thingy since my last input to this topic, in my investigations I discovered that the fast tickover is not controlled by the simulator but is controlled by the thermal vac valve in the cyl head and a vacuum bellows capsule on the back end of the pump govenor housing, during the 2010 winter the pipe some how became detached from the tickover bellows and some realy vicous/rough gear changes were the norm untill the engine had warmed sufficiently to shut the CH vac valve (the head lights assumed a supper low dip position due to the total loss of vac in their system caused by the massive leak).

I again removed the simulator and took it completely to bits, piston part and all, atop of the moving "piston" is a small (6diax1mm thick) rubber baffle disk which covers the nozzle to control/set the vacuum in the transmission control line.
The rubber disk was somewhat tatty and a replacement was made from an odd sheet of silicone rubber found in my extensive collection of to say the least junk.

Along with the reconnection of the tick over pipe (fault found only as I re-installed the thingy/simulator) this has further improved my cars gear change behaviour, its behaviour is now almost faultless.

My thinking is that the original blockage of the nozzle was a piece of the rubber baffle.

My only remaining question about this part of the vac system is what does the black vac tube that dissapears to the bulk head do? It comes from the thermal valve on the CH, but where does it go to?
 
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pikeydave

pikeydave

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Where and how did you get your Turbodiesel W124??!! I'd love one, even if it is L/H drive. Talking of which, how do you find the LHD thing?

It came from Germany!

I picked it up whilst working over in Berlin for easyjet a few years ago. Nearly all the Turbo TDs are very miley and are getting tired now. Mine's been "VOR" for over a year now whilst I work on refurbishing the running gear. I recently finished overhauling a 300TE-24V also LHD and manual for use in Italy. Also have a 250TD LHD for a project as well. Prefer LHD to right, maybe because I'm left handed?!!
 

chizzel89

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It came from Germany!

I picked it up whilst working over in Berlin for easyjet a few years ago. Nearly all the Turbo TDs are very miley and are getting tired now. Mine's been "VOR" for over a year now whilst I work on refurbishing the running gear. I recently finished overhauling a 300TE-24V also LHD and manual for use in Italy. Also have a 250TD LHD for a project as well. Prefer LHD to right, maybe because I'm left handed?!!

I was wondering if there were any contacts out there who will arrange sales. Like an english speaking used Mercedes diesel specialist or something. Thanks for the advice. I may have to go looking for one! How much did you pay for your one?
 

television

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My only remaining question about this part of the vac system is what does the black vac tube that dissapears to the bulk head do? It comes from the thermal valve on the CH, but where does it go to?

Fuel consumption gauge ?
 

Richard Elliot

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I was wondering if there were any contacts out there who will arrange sales. Like an english speaking used Mercedes diesel specialist or something. Thanks for the advice. I may have to go looking for one! How much did you pay for your one?

Have a look on www.mobile.de

Or try this link

http://suchen.mobile.de/fahrzeuge/s...985-01-01&maxFirstRegistrationDate=1996-12-31

Any cheap one with a mileage under 400000km has probably been clocked. Most dealers will speak a bit of English. You just need export plates and a temporary insurance, its all quite easy.
 
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pikeydave

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I wouldn't get one from Germany again. too much body rot.
It's easier to overhaul engines,gearboxes, brakes and running gear than start welding inner wings (always under the washer bottle!) replacing outer wings and stopping the rust in the boot section(too many to mention)

The next one will be coming from Italy (have my eye on a 250TDturbo already) of south of France (the 190e has come from Monaco)
 

mej

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Where does the black one go?

It goes to the passenger compartment, and in my E250D estate LHD appears at the right side of the (rear of the) binnacle, but isn't connected to anything. Seems too far from the distributor valve for the pods to be involved with it in any way, and my flaps appear to work perfectly. The WIS has this diagram from which I draw my information above, but my query is; should the black (sw) pipe be unconnected in this way? I've blocked it for the moment, and nothing is behaving any differently.
 

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