No servo support...

TyroleanRover

Active Member
Dear community,

Maybe someone has a idea where i should check.
The Problem is, my servo does not deliver support to braking.
There is no difference in braking power whether i pull the vacuum hose of the engine manifold or not.

The brakes itself are working.
I can stop the car by pressing real hard (without servo power)
The brake works on all four wheels.

I already checked:

- the little white servo valve. (I opened, cleaned, the diaphragm looks good and feels soft, when pressing the pedal the valve opens and you can hear the pressure equalization)
- the brake servo. (the diaphragm looks also good, feels soft.)
- replaced all hoses with new ones (also used hose clamps)
- the engine delivers a remarkable suction on the manifold, this is enough for sure

what should i do?
 
Sounds like the piston connected to the diaphragm has seized. If you can open up the servo and get behind the main cylinder try moving it manually.

Alternatively, you say it hisses when you depress the pedal. Is it a continuous hiss or just do a second? It should only be for a second if not I would suspect a leak around the diaphragm.
 
There are two. One large conical spring that helps the diaphragm return and one inside the main cylinder to return the piston if I remember correctly.

To release the large spring open the unit, push down the diaphragm plate and let the metal key drop out, you should be able to remove the plate then.
 
Sounds like the piston is stuck. If its the one with a band wrapped around the outside secured by a bolt,like this one,you can remove the end safely as the spring is a return spring and should be held in place by the clip mentioned.
I rebuilt my servo,nothing too hard about it if you work methodically and lay the bits out carefully as you remove them.
Try pressing the pedal again a few minutes after the engine is turned off,if you dont hear the servo 'cut in' you have a air leak somewhere. If you empty the servo by pressing the pedal a few times,then start the engine with your foot on the pedal you should feel the pedal go down a bit as the servo is energised.

servo.jpg
 
Thank you all guys, for your answers

I was on holiday for a few days.
Next weekend i will check trough the possible faults you wrote

@sdibbers:
It is just a short hiss. As it should.
I removed the hoses to the servo to check the vacumm.
If the little valve opens you can feel a stronger vacuum on the diaphragm site facing back. That's what it should do i suppose.

@Hairyrover:
Yes, i have this one.
I already opened this one and checked the diaphragm. I can push the diaphragm in and it comes out (spring powered) again. But i guess this doesn't mean anything as @sdibbers wrote?
"One large conical spring that helps the diaphragm return and one inside the main cylinder to return the piston if I remember correctly."

Do i have to remove the servo to check it?
The diaphragm holds in place by a sort of cap? is it enough to remove this to get inside?

I have to try the test with the servo "cut in" after a few minutes, i never tried this.
The pump test does not work. If i press the pedal, it always feels quite hard. And the pedal is not sucked in after starting the engine.
As i wrote, the car brakes (not really safe, but i can stop it with real foot power), but no matter if the vacuum hose of the servo is connected to the intake or not.

thanks
Simon
 
Thank you all guys, for your answers

I was on holiday for a few days.
Next weekend i will check trough the possible faults you wrote

@sdibbers:
It is just a short hiss. As it should. Sounds good!
I removed the hoses to the servo to check the vacuum.
If the little valve opens you can feel a stronger vacuum on the diaphragm site facing back. That's what it should do i suppose. Yes, You should have no vacuum to diaphragm when brakes are released.

@Hairyrover:
Yes, i have this one.
I already opened this one and checked the diaphragm. I can push the diaphragm in and it comes out (spring powered) again. But i guess this doesn't mean anything as @sdibbers wrote?
"One large conical spring that helps the diaphragm return and one inside the main cylinder to return the piston if I remember correctly."

Do i have to remove the servo to check it? I'm afraid so.
The diaphragm holds in place by a sort of cap? is it enough to remove this to get inside? You remove this once inside the servo. Once you remove this you can dismantle the main cylinder and piston assembly.

I have to try the test with the servo "cut in" after a few minutes, i never tried this.
The pump test does not work. If i press the pedal, it always feels quite hard. And the pedal is not sucked in after starting the engine.
As i wrote, the car brakes (not really safe, but i can stop it with real foot power), but no matter if the vacuum hose of the servo is connected to the intake or not.

thanks
Simon
 
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