brake servo issues

jimberlake

jimberlake

0
H all... Strange problem, so a new brake servo fitted but as soon as you for up the engine the brakes lock up fully to the point where it won't move. Turn engine off and after a minute they release again. It's all fitted correctly and would rather not have to take it all off again otherwise will mean bleeding the bleeding brakes again... Any ideas to fix all I can think is a pressure relief cable sticking out something...aahhhhhhh

Cheers

Jim

Hasta la supervista baby
 
It sounds like there is an air leak into the space behind the diaphragm, possibly the air valve. If it is leaking then it could be possible that the brakes operate by themselves

servo4.jpg


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Founder of the Non-Facebook Club
 
Yes think you must be right, wasn't sure how they quite worked till see that...so guess the pressure in the rear of the servo stops the brakes operating by themselves under the vacuum, as you apply the brakes it lifts the piston which opens the air valve to release that pressure and the the brakes become assisted.

Cheers

Hasta la supervista baby
 
Sort of, as the brakes are applied the piston raises the air valve and allows atmospheric air onto the back of the piston. As the other side of the diaphragm is under vacuum it is pushed forward by atmospheric pressure to assist the brakes, when the brakes are released the piston drops, the air valve closes and a port opens up to equalise the pressure within the servo and create a vacuum on both sides of the diaphragm so removing the assisted pressure. If the air valve is stuck open then the servo assistance is permanently on[xx(]

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Founder of the Non-Facebook Club
 
Perfect Panky...ill take a look, mind you bit scary if it jammed on at 55! Maybe ill get a newun :)

Hasta la supervista baby
 
Would also explain why the brakes release a few seconds after the engine is turned off, a good servo would hold that vacuum for quite a while, must be jammed open.

Hasta la supervista baby
 
Probably more likely that the piston is stuck in the bore and holding the valve open as Greg suggested.

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Founder of the Non-Facebook Club
 
Thankfully theres no need for a servo on my Commer, running standard drums, but imagine you're stuck at the traffic lights and your brakes are on solid. To add insult to injury, there are people muttering that old vans are no good and should be banned :(
Be prepared to disconnect the vacuum hose from the servo and bung something in the end to stop air rushing into the manifold...

Haven't you considered a rebuild kit, Jim[?]

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The simpler the better
 
It's already bunged up now so working fine or as was. It's a brand new Servo so a bit of a pain, not an issues getting it swapped I'd have thought but the pain is taking it off and mainly bleeding everything up again - nightmare!

Hasta la supervista baby
 
Ha ha...from Martin, not his fault its not working and he's fine with it, I've just not got time to go up there before hols start, was gonna try to fix it but thought it might cock the warranty up so gonna leave it I reckon.

Hasta la supervista baby
 
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