W124 E300d. Auto gearbox gone clunky suddenly.

[tpv01]

ok so i had my manifold off at the weekend (write up to follow when i have time) and changed plugs, cleaned it out (unbelievably grimey!), plugged EGR and changed the fuel lines. also got a new battery.

it all went back together ok and runs fine and starts better so im happy with the work.

however, since it has been running after the work the gearbox has gone really clunky. particularly low gears and going down as well as up. It is actually quite violent and jarring. cant be good for the car. It has had a gone run, mostly motorway so not alot of changes, and it hasnt got any better. still kicks down ok and dont think i am missing any gears. changes were really smooth before i did the work this weekend.

what have i knocked and done during the work i did that has made it do this??

not sure how the autobox works but my educated guess would it having something to do with the vac system which now doesnt pull on the EGR?

 

[Number_Cruncher]

>>the gearbox has gone really clunky

There are 2 possibilities;

1) There is a problem with the vacuum system, and not enouh vacuum is reaching the modulator valve on the gearbox. To check on this, remove the crossover pipe, and you should be able to see all of the important vacuum cannections.

2) The so-called bowden cable has been disturbed. This is quite a sensitive adjustment, and for a start, it should be adjusted so there is no tension on the cable at the idle position. i.e., pop the cable connector off, and turn the threaded adjuster until this is so.

 

[tpv01]

>>the gearbox has gone really clunky

There are 2 possibilities;

1) There is a problem with the vacuum system, and not enouh vacuum is reaching the modulator valve on the gearbox. To check on this, remove the crossover pipe, and you should be able to see all of the important vacuum cannections.

2) The so-called bowden cable has been disturbed. This is quite a sensitive adjustment, and for a start, it should be adjusted so there is no tension on the cable at the idle position. i.e., pop the cable connector off, and turn the threaded adjuster until this is so.

where can i find these 2 things so i can check it out?

I was thinking there was too much vaccuum as EGR not in use any more so it was pulling too hard but your idea sounds more likely.

 

[Number_Cruncher]

The vacuum connections are under the manifold, but, you can get to them by takig the crossover pipe off. There's also the vacuum amplifier down by the air filter which is part of the circuit.

If you had too much vacuum at the modulator valve, the shifts would be very soft and mushy.

The bowden cable is the one which leaves the accelerator pivot connection on the inlet manifold, and goes under the crossover pipe, and down to the gearbox adjacent to the gearbox dipstick.

 

[Dieselman]

The Bowden cable will make upshifts earlier or later, the vacuum controls the speed of shift.
As N-C says it's a lack of vacuum.

 

[tpv01]

>>the gearbox has gone really clunky

There are 2 possibilities;

1) There is a problem with the vacuum system, and not enouh vacuum is reaching the modulator valve on the gearbox. To check on this, remove the crossover pipe, and you should be able to see all of the important vacuum cannections.

what do i do then to check it is all ok?
i guess i could of knocked a vacuum pipe off when i was putting the manifold back on. I remember there being a pipe going to the crossover pipe and one to a box secured under the manifold. Are these the resonance flaps?

>>
2) The so-called bowden cable has been disturbed. This is quite a sensitive adjustment, and for a start, it should be adjusted so there is no tension on the cable at the idle position. i.e., pop the cable connector off, and turn the threaded adjuster until this is so.

Is this a rod that goes down through one of the gaps in the manifold? it is highly possible this system got disturbed when i was removing the manifold. how do i make the adjustment? is it the grey thing circled in green in the pic? i have just been out to look at it and it seemed a bit loose under idle to tightened it up a bit and dont think it made any difference but maybe i didnt tighten enough.

PS found this pic on one of Derek's aka Silversaloons thread on a similar thing but i am still a bit clueless on what i need to do to sort my problem...

 

[Number_Cruncher]

>>The Bowden cable will make upshifts earlier or later, the vacuum controls the speed of shift.

This is largely true, and I think it's far more likely that the OP has a vacuum problem than a bowden cable problem.

However, the load dependent control pressure (or kickdown pressure) does influence the quality of shifts. It does this in the so-called shifting pressure control valve, where working pressure is reduced to shifting pressure. In determining the reduction from working pressure to shifting pressure, the modulating pressure (i.e. vacuum derived pressure) and the kickdown pressure *both* act to increase shifting pressure, i.e., to make the shifts harder.

It's actually closer to the truth to say;

The bowden cable adjusts when shifts occur and has an effect on the firmness of shift, while the vacuum controls the firmness of shift.

 

[Dieselman]

It's actually closer to the truth to say;

The bowden cable adjusts when shifts occur and has an effect on the firmness of shift, while the vacuum controls the firmness of shift.

True, but the o-p hasn't said the shifts are taking place higher up the rev range, just that they are more abrupt.
Has the bowden cable been adjusted, not as far as I can see, so it should retain the original setting when reconnected.

As you, my money says vacuum problem.

 

[Number_Cruncher]

The Bowden cable is No 1 on the piccie. All you need to do to check it is to pop the cable off, and make sure the cup sits by the ball when the cable begins to take up tension (you'll feel it plainly enough once you've popped the cable off)

Yes, it's highly likely that a vac pipe isn't properly connected. Take the crossover pipe off [for the 3rd time in this thread!], and check them.

 

[tpv01]

Yes, it's highly likely that a vac pipe isn't properly connected. Take the crossover pipe off [for the 3rd time in this thread!], and check them.

ok will give this a try thanks for the advice everyone.

 

[bolide]

The vacuum pipe to the resonance flap under the centre of the inlet manifold cross tube has come adrift

Nick Froome
www.w124.co.uk

 

[Smiley]

Nick,

I agree - this is the most likely cause - it is easy to forget to re-connect it after replacing the cross over pipe.

 

[tpv01]

is this the one that is under the crossover pipe or the manifold?

it was to hot to work on last night when i got it home so i will investigate tonight.



Also, out of my own interest what does this flap do and how does it affect gear changes?

...and one final thought. Is it possble to get to glowplug #2 (second from the front) with just the crosspipe removed. This was the only one i wasnt able to change at the weekend as I couldn't start the engine to warm up the block to free it up.

 

[bolide]

The flap doesn't affect gearshifts - it changes the apparent length of the inlet manifold, thus changing the resonant frequency & tuning of the manifold to help breathing

When the pipe drops off the vacuum disappears - this is what screws up the shifts

Nick Froome
www.w124.co.uk

 

[Number_Cruncher]

>>is this the one that is under the crossover pipe or the manifold?

You need to check both.

 

[Smiley]

It is very easy to forget them - if I remember they drop down and get covered up with the cross over pipe.
By the way did you replace the injectors and GPs?
When I replaced the injectors on mine I was surprised how noisy the engine became - there was a lot of diesel knock going on - it has taken about 10k miles to settle down.

 

[tpv01]

didnt replace injectors. i have noticed it sounds a bit knocky when it settles to idle initially but not sure if it has always done that or maybe has something to do with this vac line issue.

 

[bolide]

The serpentine belt damper top mount breaks up & rattles at idle

Nick Froome
www.w124.co.uk

 

[tpv01]

ok so i fixed this last night. I took off the crosspipe and it wasnt the vc pipe under the crossover or the manifold but in the mess of of vac pipes under the crossover including from a green plastic jobby directly under the crosspipe.

It is a well and good to have vaccuum controlling things on the car but when the vac connections are so weak that if you breathe on them they pop out its not to easy to work on the car.

anyway my tip would be to check and be very careful of all the vac connections when putting things back together.

one thing i noticed was what looked like the ball from a ball and socket connection (like the throttle linkage) that is not connected to anything [green circle]. moving it shows it is the same pivot as the rod that comes vertically up from under the inlet manifold to connect to the throttle linkage. can find a rod to connect to it and the car runs fine. Could it be for cruise control which my car doesnt have??

 

[Smiley]

great that you have fixed the clunky gearbox.
re the unconnected linkage it is a while since I did my manifold job - I remember the linkage and am pretty sure it is connected to something - I am sure I would have puzzled over it (like you are) if it had not been connected. I do not think it would be cruise control. Does your kickdown work OK?