brake servo

#1
Got a bit of a weird problem that maybe someone on here can help me with? my Buick has got a high lift cam in it and my brakes are--lets say not very good--I got 4 pots and vented discs for ages now --they were really good with the 3.9 yet since fitted the Buick they're poor
The problem-I think is vacuum lower due to cam--am I right --if so would smaller servo help?
 

colnerov

Well-Known Member
#2
Hi, the servo doesn't directly make the brakes better, it just makes the pedal effort lighter.
Which I suppose makes it easier to press the pedal harder. But I think you're on the right track,
so check the operation of the servo, how many applications do you get before the pedal gets
harder. Another quick fix is to fit a vacuum reservoir to help, P5b,s had one under the offside
front wing. But I suppose an easier source would be off a more modern car. I have seen that
Mercedes Benz have them, they look like three plastic balls joined together. It would certainly
be cheaper than an engine driven vac pump, if you can find one nowadays that isn't nailed on
the back of an alternator.

Colin
 

sowen

Active Member
#4
I've recently removed the servo off my P6 as I wanted the extra space, pedal effort is a bit higher but still out-brakes everything I've got! My plan is to fit a smaller master cylinder and nothing else!

Years ago I found an article than went into depth on servo assistance and how to size servo's for non-original applications, giving examples of fluid pressure for given master cylinder sizes, loads, moments etc. Very interesting but I've never been able to find it again :(
 
#5
well now ford is done I am starting on rover re vamp --wedgewood blue and white--or maybe another early color
the brakes themselves are fine-its the amount of effort needed so today i got a smaller servo--will try that first then take it from there
 

colnerov

Well-Known Member
#6
Hi, why do you think a smaller servo will give you more assistance? You need a greater
surface area to increase the effect of air pressure.

Colin
 
#7
colnerov said:
Hi, why do you think a smaller servo will give you more assistance? You need a greater
surface area to increase the effect of air pressure.

Colin
I'm thinking that a smaller servo would be better as vacuum is lower
 

colnerov

Well-Known Member
#8
symes said:
colnerov said:
Hi, why do you think a smaller servo will give you more assistance? You need a greater
surface area to increase the effect of air pressure.

Colin
I'm thinking that a smaller servo would be better as vacuum is lower
Hi, Vacuum is vacuum, Basically when the brakes are operated the servo has vacuum one side
of the diaphragm and atmosphere the other so the air pressure pushes the diaphragm into the
vacuum giving assistance to the hydraulic part. So the greater the size of the diaphragm the
greater the assistance. This explains it in more detail if you want.

http://www.mgb-stuff.org.uk/servo.htm

I know you're going to ask about partial vacuum,so that's why there is a non return valve in the
vacuum hose or one of the fittings so the servo chamber acts a reservoir. But when you come
off the throttle to apply the brakes there is maximum vacuum available from the engine anyway.

Colin
 
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