will121
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| posted on 22/2/11 at 12:32 PM |
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tin top brake servo question
i run a zetec fiesta as a track day car, it has throttle bodies fitted and i have problems with brakes that i believe is down to insufficent servo
assist.
the vacuum pipe is connected to the throttle bodies and ive tried taking it from one and all four joined together but know different. I assume as
generally on track at open throttle little or no vacuum is produced in the inlet for the servo.
question is any idea's to resolve or other thought how do vacuum servo's work on turbo charged or Diesels do they have a separate vacuum
pump i could utilise?
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Mr Whippy
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| posted on 22/2/11 at 12:44 PM |
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why not first buy a vacuum gauge to see what the engine is generating before spending more money on something that might not be the problem. As far as
I can recall there is usually just one vacuum connection on even a multi carb manifold as there should be a one way valve to prevent the air getting
back into the servo.
If you run the car and then pull the hose off the servo there should be a big hiss and the will tell you if the servo is holding the vacuum properly,
even after a whole day with the engine off it should still hiss.
[Edited on 22/2/11 by Mr Whippy]
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loggyboy
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| posted on 22/2/11 at 12:55 PM |
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Whats the acctualty brake problem?
I assume the car is farily stripped and light? I had virtually no assistance on my Nova due to a crappy vacuum hose that collapsed under pressure, but
as it never effected the brakes I didnt change it.
I wouldnt expect you would need a servo if you have a decent set of brakes on the car.
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will121
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| posted on 22/2/11 at 01:05 PM |
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its basically limited power to the brakes so having to really push on the peddle, it works sometimes better than others so judging braking distance a
pain.
done track day at Snetterton on Sunday and at end of straight braking first stab of the peddle it felt like some assistance then if lifted of brake
and reapplied it was like all the vacuum assistance had been used and no more so case of push like hell.
vacuum seems to work and its second servo fitted with same problem with a working non return valve and problem seems i can test it when stationary on
tick over and a vacuum will be there its after a period at full throttle and repeated brake use is a problem.
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adithorp
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| posted on 22/2/11 at 01:17 PM |
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Do you still have the one way valve in the servo hose? Pump the brakes with the engine off to get rid of any vacuum then you start the car with your
foot on the brake. Do you feel the pedal go down a bit as the vac builds? Then switch of and pull the pipe off the servo. Do you hear a pop as the vac
is released?
"A witty saying proves nothing" Voltaire
http://jpsc.org.uk/forum/
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will121
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| posted on 22/2/11 at 01:58 PM |
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quote:
Originally posted by adithorp
Do you still have the one way valve in the servo hose? Pump the brakes with the engine off to get rid of any vacuum then you start the car with your
foot on the brake. Do you feel the pedal go down a bit as the vac builds? Then switch of and pull the pipe off the servo. Do you hear a pop as the vac
is released?
the one way valve is installed and seems to work and the pedal goes down initially, not tried to pull the servo pipe off to see if it holds vacuum
though, so will try that.
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JAG
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| posted on 22/2/11 at 02:03 PM |
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quote:
its after a period at full throttle and repeated brake use
This is the clue - engines only develop a vacuum in the inlet manifold when operating at partial or closed throttle. That's why there's a
non-return valve fitted.
It's the same for turbocharged engines although Diesel engines have a mechanical vacuum pump (either engine driven or electrical I believe).
Justin
Who is this super hero? Sarge? ...No.
Rosemary, the telephone operator? ...No.
Penry, the mild-mannered janitor? ...Could be!
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matt_gsxr
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| posted on 22/2/11 at 02:18 PM |
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Audi TT's use a separate electric pump.
Surprised that you don't get sufficient vacuum under braking though, as normally under braking the throttle plates are closed and the engine at
highish revs which results in lots of vacuum (if you can have lots of vacuum, but that is more of a philosophical point!).
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rusty nuts
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| posted on 22/2/11 at 07:56 PM |
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Might be worth using a belt driven vacuum pump from something like a Peugeot 405 diesel or possibly a Mercedes supercharged electric pump ? Transit
vans have a pump driven off the back of the alternator as I'm sure others do although you wouldn't need such a high output.
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