Servo problem

[glenluceblue]

I'm still having a bit of bother with my servo (W210 2000/X) although it's intermittant and only on initial start up. When I start the car I can feel the servo kick in through the pedal but if I then select reverse gear it's as if the servo fails to operate and the pedal becomes very stiff. This will remain in the forward gear until I pick up speed then all is well with no further problems until start up again. The problem also seems to be remedied by revving the engine in neutral. I spoke to a mechanic mate and he thinks it could be a check valve from the vaccum pump but I don't know where that is or whether it is a possible cause. The car is an E200K and any help or advise would be gratefully recieved.

 

[television]

150 in the link is the only vacuum pipe there.

http://www.detali.ru/cat/oem_mb2.as...GM=716.622&CT=F&cat=66G&SID=42&SGR=060&SGN=03

The other one that I am not sure about is this one

http://www.detali.ru/cat/oem_mb2.as...GM=716.622&CT=F&cat=66G&SID=42&SGR=110&SGN=05

I will try and find more later

 

[glenluceblue]

Cheers Malcolm, looking at those details I don't see anything about a check valve / non return valve so it looks like the advise I did recieve might be wrong.

 

[television]

Sorry about this but you do have one just in front of the servo, this joins into the vacuum pump

 

[type49]

Sounds like new servo pipe complete with valve is required

 

[television]

Sounds like new servo pipe complete with valve is required

You must start posting earlier my Keyboard packed up on computer 2 took ages

 

[glenluceblue]

Can you tell me the item number in the detail which shows the valve, as I just don't see it. If I get a part number then I'll get one ordered through parts site.
Thanks again for all your help so far.

 

[television]

Sorry,I cant see it there, so I am stuck, maybe Type49 will recognize it

 

[type49]

As Malc said 150, it's part of the pipe.

 

[wireman]

To test your servo's non return valve:-

Be aware that a cold engine will not generate as good a vacuum as a hot one due to the cold start idle enhacement (fast tickover).

With engine stoped press brakes several times to use up any stored vac.

Depress brake pedal and start engine, the pedal should move a little further down as soon as the engine sucks hard enough to generate vacuum. (It seems that you have already found this to be the case)

release the brake pedal and reapply the brakes, the pedal should feel just the same as it did after the engine start, release brakes.

Stop engine and reapply brakes, the pedal should still have assistance and the same feel as above. Repeat the brake application (engine still stopped) the assitance will fall off as you use up the stored vacuum.

Repeat the start check, stop the engine and wait a few mins then repeat the engine stoped tests. If the assistance is reduced on the first go you have a dud non return valve.

An alternative method (I can't recomend that this be done to often on health and safety grounds it tastes horrid) is to remove the valve and suck the servo end then slide your tongue over the end and it should stick to your tongue, if it falls of youve got the leak either in your hand or on the floor.

The valve is as others say in the vac pipe that runs from the inlet manifold to the servo vc chamber, on my 124 (diesel it runs from the vac pump) the NRV is in the pipe about 1/4 way along. some servos have the valve built into their vac chamber as part of the fitting where the vac pipe connects, some use a valve in the fitting to the manifold, it seems to be a value engineers choice where it is, but there is one somewhere.

I know that this may not apply here, but if the car is a carburetor model damage will occur to the servo itself each time the engine is stopped or operated at large throttle openings by a tiny amount of petrol vapour being drawn into the servo as the servo vac exceeds the manifold vac, the condensate of petrol in the servo will destroy the diaphragm of the servo and it will fail totaly.

 

[glenluceblue]

Thanks for the help and some excellent advice gents. I'll have a go at the tests as above but if a new pipe/NRV is required It'll be a couple of weeks before I can get the job done as I head offshore on Thursday. I will however get back on and tell you how it went.
Thanks again

 

[glenluceblue]

Can you advise whether I'm looking for a pipe or hose ? :-(

 

[television]

Can you advise whether I'm looking for a pipe or hose ? :-(

A hose as it will be flexible

 

[glenluceblue]

I tried the NRV test procedure by starting and stopping the engine but the results went as expected i.e all was ok. As I expained though the problem only comes about if on intial start up (or very soon after) the reverse gear is selected.
Can you tell me if the hose connection at the servo should simply pull out ?

 

[wireman]

If it has a rubber gromet around it into the servo diaphragm body probably yes