Servo/Vacuum Symptoms on 300TD

[harpoonlouis]

Just had a fright, thought I would ask around before heading for the workshop.

I know I have slight vacuum leaking causing transmisson thump but I just had the brakes/servo lock the pedal hard up for a few seconds after start up before they became normal again, happens each time I start the car. Also the car runs on after I shut down the ignition. These two faults have started today in very cold weather, never had this before.

I am suspecting a major failure in the vacumm system?

Anyone recognise this combo of faults?

Thank in advance

John

 

[television]

Is the car a 124 or 210

 

[harpoonlouis]

Model listed as E300, not sure what you mean by 124 or 210

 

[wireman]

124 or 210 is the model type number, E300 is just the label on the back, merc seem do this to bolix us all up.
The ID plate under the bonnet has WDB xxx bodynumberetc, where xxx is the 124 or 210.

Brakes, Could be frozen water in the servo valve, not common but its either that or the servo is faulty. A vac leak would cause poor braking efficiency, you would need to push hard to stop it.

Engine, the stop mechanism is vaccum and needs vac to stop, this may be the "switch" on the ignition lock, a leak in the pipes or a dud stop capsule on the fuel pump. Look around the forum you will find some more info on this.

There are several (many?) bits of rubber tube that connect the 4mm nylon tubing used for the vac system, these get tired and can leak once disturbed so be ready to do a campain change of 30mm long rubber tubes.

If there is a leak the vacuum system could draw in water from the leak and unpredictable things will happen if this is the case.

 

[harpoonlouis]

Wireman, thanks for that.

I'm a 124 apparently, never realised there was a subdivision within 300E range.

It has been unusually cold so I suspected freezing initially but it is still there even after running well up to temperature.

They all started happening at once so I suspect s a commom element and that seems to be vacuum.

The brakes are most likely to be effected just after start up but not every time and more commonly after giving the engine a short footful of throttle so something sticking is more likely. It causes the effeciency to drop to almost nil AND harden the pedal up. Vac feed to servo s the single large line isn't it, checked this already and it's fine. Could be sticky vac pump. What mechanism is the vac pump?

Thanks a bunch

John

A stock of that tubing seems like the next investment.

 

[television]

Your vacuum system.

http://www.detali.ru/cat/oem_mb1.as...983&GA=722.320&GM=717.430&CT=F&Cat=15S&SID=80

 

[television]

And some more gearbox vacuum

http://www.detali.ru/cat/oem_mb2.as...M=717.430&CT=GA&cat=09Y&SID=27&SGR=001&SGN=01

 

[glenluceblue]

Your brake problem sounds a bit like mine (W210). I have posted a couple of times on this forum but no solution has been found so far. When I start the car (with foot on the brake) I can feel the sevo pick up and the pedal moves. If I then take my foot off the brake (but don't touch the accelerator) then crawl forward the brake pedal then stiffens and the servo seems to have gone. I only need to up the engine revs slightly for this fault to disappear although it returns if I put the car into reverse gear (again if I was to touch the accelerator the problem goes). The brakes are excellent and to be honest I'm now that used to it I haven't bothered following it up

 

[ernieh]

Vacuum Brakes

Your brake problem sounds a bit like mine (W210). I have posted a couple of times on this forum but no solution has been found so far. When I start the car (with foot on the brake) I can feel the sevo pick up and the pedal moves. If I then take my foot off the brake (but don't touch the accelerator) then crawl forward the brake pedal then stiffens and the servo seems to have gone. I only need to up the engine revs slightly for this fault to disappear although it returns if I put the car into reverse gear (again if I was to touch the accelerator the problem goes). The brakes are excellent and to be honest I'm now that used to it I haven't bothered following it up

Apologies if this has been covered before, but it sounds as though either there is a massive leak in the vacuum system or the Vacuum Pump which supplies vacuum for the brakes and other auxiliaries is getting tired and taking time to build up a head of vacuum. In addition, I don't know about Mercs specifically, but in other cars I have worked on, there is a non-return valve (NRV) on the servo unit which prevents the vacuum reservoir 'draining' when the engine is turned off. When operating properly, this valve allows a couple of applications of the brakes before the pedal goes hard due to the loss of vacuum assistance. I would doubt if the NRV could be bought separately from the servo unit.

It does sound as though the problems described could be due to loss of vacuum somewhere.

Hope this helps.


Ernie

 

[glenluceblue]

Apologies if this has been covered before, but it sounds as though either there is a massive leak in the vacuum system or the Vacuum Pump which supplies vacuum for the brakes and other auxiliaries is getting tired and taking time to build up a head of vacuum. In addition, I don't know about Mercs specifically, but in other cars I have worked on, there is a non-return valve (NRV) on the servo unit which prevents the vacuum reservoir 'draining' when the engine is turned off. When operating properly, this valve allows a couple of applications of the brakes before the pedal goes hard due to the loss of vacuum assistance. I would doubt if the NRV could be bought separately from the servo unit.

It does sound as though the problems described could be due to loss of vacuum somewhere.

Hope this helps.


Ernie

I have heard about the NRV causing problems but to be honest I couln't locate it ! I traced the hose back from the servo to the engine but nothing obviously resembling an NRV jumped out. The correct way to go would be to order up the hose / NRV assembly from the stealers then I would know what I was looking at / for and then change it out.

 

[wireman]

Often the NRV is fitted within the adaptor from the hose into the servo body usualy a white nylon molded elbow connection. On my 124 its a moulded nylon valve in the pipe work. On some older (petrol) cars its in the connection at the inlet manifold.

When you press the pedal after the engine has run (and is stopped) there should be sufficient remaining vacuum to assist the brakes at least once maybe twice but after this the pedal will harden and assitance (and efficacy of the brakes) will be virtualy nonexistant.

 

[type49]

The valve on the main vacuum pipe to the servo does cause this exact fault. Only happens for one or two applications of the brake pedal (the pedal is rock solid) & then all returns to normal again. The valve comes with the pipe so replace the lot. Can't remember the price but it's OK & much cheaper than a servo.