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Brake Servo Problem



 
 
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  #1 (permalink)  
Old October 23rd 03, 05:08 PM posted to uk.rec.motorcaravans
Mike Williams
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Posts: 56
Default Brake Servo Problem

I have an Elddis 270 on a Peugeot Talbot Express 2.5 diesel chassis (1990).
For some weeks now I have had a brake servo problem. When slowing down or
coming to a stop (approaching a roundabout, for example) I get normal
"servo" action the first time I press the brake pedal. If I then release the
pedal and press it again within a second or a few seconds the pedal "goes
hard" and there is no servo assistance. The servo assistance does not return
to normal until after I have then driven normally for a further minute or
so. I took my van to a special Peugot garage and they examined the brake
system and replace two rear brake cylinders which they said were beginning
to leak and four flexible hoses which they said were slightly cracked,
saying that they couldn't check the rest of the circuit until they had done
that. They charge me just under 400 and the brake servo problem is still
the same. I have a distinct feeling that I have been ripped off! They now
say that the next thing they would need to do is to replace the vacuum pump
(the unit driven by the engine) and then the brake servo vacuum unit itself
if that didn't fix it. They want about 300 for the vacuum pump alone, with
no guarantee that it will fix the fault. I asked if they had actually
measured the vacuum and they said that they had, but I had to press the man
hard before getting him to tell me the reading (which he said was about 12
inches on mercury).

I've now had a little look myself and I can definitely feel a vacuum at
engine tick over if I remove the pipe from the servo unit and hold my thumb
over it, but I have no idea what reading it is. I've also checked that the
vacuum unit is actually holding a vacuum, because if I switch the engine off
and return the next day I can still hear a "pop" as the vacuum is realeased
when I pull the hose out of the unit.

Does anybody have any idea what could be wrong?

Mike


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  #2 (permalink)  
Old October 23rd 03, 07:12 PM posted to uk.rec.motorcaravans
riccip
external usenet poster
 
Posts: 25
Default Brake Servo Problem

"Mike Williams" wrote:

pedal and press it again within a second or a few seconds the pedal "goes
hard" and there is no servo assistance. The servo assistance does not return
to normal until after I have then driven normally for a further minute or
so. I took my van to a special Peugot garage and they examined the brake
system and replace two rear brake cylinders which they said were beginning
to leak and four flexible hoses which they said were slightly cracked,
saying that they couldn't check the rest of the circuit until they had done
that.


Absolute ********. They should have completed the diagnosis first
then quoted you for the entire job. They've returned the vehicle
with deficient brakes which simply isn't on after a brake repair,
could even be illegal.

They charge me just under 400 and the brake servo problem is still
the same. I have a distinct feeling that I have been ripped off!


You have, because presumably the last MOT examiner was quite
happy with the hoses. "Beginning to leak" sniffs of BS too -
either the wheel cylinders are leaking or they're not. You should
definitely complain to the agency's manager and threaten them
with the trading standards to get at least a partial refund.
They'll comply if you stick to your guns and kick up a stink.

They now say that the next thing they would need to do is to replace the vacuum pump
(the unit driven by the engine) and then the brake servo vacuum unit itself
if that didn't fix it. They want about 300 for the vacuum pump alone, with
no guarantee that it will fix the fault.


You're joking? You should avoid main dealers like the plague on a
vehicle this age. "Specialists" are just as bad, posing as
manufacturer qualified when they're clearly not. Ask around until
you find a trustworthy and reliable mechanic. He should be able
to repair the pump, which is probably down to the diaphram (not
uncommon on Peugeot diesels) and easy to fix. Unless Peugeot want
too much for the parts in which case get a used pump from a
breakers (around 15).

I've now had a little look myself and I can definitely feel a vacuum at
engine tick over if I remove the pipe from the servo unit and hold my thumb
over it, but I have no idea what reading it is.


There should be a *lot* of suction there. If you put your thumb
over the pipe it should hurt a little. You should also hear it
sucking the air. Check also that the pipe isn't kinked, split or
collapsed. If not then it does sound as though the pump's on it's
way out.

I've also checked that the
vacuum unit is actually holding a vacuum, because if I switch the engine off
and return the next day I can still hear a "pop" as the vacuum is realeased
when I pull the hose out of the unit.


That's a good sign at least.
  #3 (permalink)  
Old October 23rd 03, 07:33 PM posted to uk.rec.motorcaravans
Niall
external usenet poster
 
Posts: 15
Default Brake Servo Problem

On Thu, 23 Oct 2003 18:08:27 +0100, "Mike Williams"
wrote:



I've now had a little look myself and I can definitely feel a vacuum at
engine tick over if I remove the pipe from the servo unit and hold my thumb
over it, but I have no idea what reading it is. I've also checked that the
vacuum unit is actually holding a vacuum, because if I switch the engine off
and return the next day I can still hear a "pop" as the vacuum is realeased
when I pull the hose out of the unit.

Does anybody have any idea what could be wrong?


Not familiar with the actual vehicle but assuming the servo is the
usual type mounted behind the master cylinder, there will be a rubber
seal between the servo and the master cylinder, which may be split.
I had intermittent loss of servo assistance on a Bedford CF which was
due to this cause. As the brake operating rod passes through this seal
pressing the brake pedal may be releasing the vacuum.

Even if the pump is deficient there should be enough vacuum in the
accumulator for several applications, which is why I suspect a problem
with the servo unit, but it would be as well to check the vacuum hose
isn't collapsed internally or if there is a filter anywhere in the
line it isn't choked, as a restriction in air or vacuum pipes doesn't
limit the ultimate static pressure or vacuum which can be acheived,
only the rate at which it can be reached.

If you suspect the servo unit itself, when I had the problem with the
CF I got a servo unit from a scrapyard and found that there was
sufficient movement in the brake pipes to remove and replace the servo
unit without disconnecting the brake pipes. When I removed the master
cylinder I immediately spotted the split seal, so I replaced it with
the intact one from the other unit.

HTH
--
Niall
  #4 (permalink)  
Old October 27th 03, 10:05 AM posted to uk.rec.motorcaravans
Chris[_5_]
external usenet poster
 
Posts: 7
Default Brake Servo Problem

I agree with ricip. Also I think you are posting in the wrong group, you
will get much more info. if you repost in: uk.rec.cars.maintenance.

I think you have been outrageously ripped off, two wheel cylinders & four
brake hoses can't come to anywhere near 400! It's about an hours work with
a 15 minute fag break in the middle. Don't take your MH back there; you
don't need a Peugeot specialist for this kind of work.

You should ask the garage for a proper breakdown of the work carried out
with prices for labour & parts, also ask what their hourly charge is. If
you are a member of the AA, RAC or similar then ask them for advice,
otherwise go to Trading Standards.

As for the problem, the suction according to the workshop manual should be
500mm/Hg (about 20 inches of mercury) or 700 mbar, so 12 inches is well
under spec. The vacuum pump is quite a simple piece of kit & it wouldn't
surprise me if there's a repair kit available for it if it's faulty. But
first I'd check the hose for cracks particularity at the ends.



"Mike Williams" wrote:

I have an Elddis 270 on a Peugeot Talbot Express 2.5 diesel chassis (1990).
For some weeks now I have had a brake servo problem. When slowing down or
coming to a stop (approaching a roundabout, for example) I get normal
"servo" action the first time I press the brake pedal. If I then release the
pedal and press it again within a second or a few seconds the pedal "goes
hard" and there is no servo assistance. The servo assistance does not return
to normal until after I have then driven normally for a further minute or
so. I took my van to a special Peugot garage and they examined the brake
system and replace two rear brake cylinders which they said were beginning
to leak and four flexible hoses which they said were slightly cracked,
saying that they couldn't check the rest of the circuit until they had done
that. They charge me just under 400 and the brake servo problem is still
the same. I have a distinct feeling that I have been ripped off! They now
say that the next thing they would need to do is to replace the vacuum pump
(the unit driven by the engine) and then the brake servo vacuum unit itself
if that didn't fix it. They want about 300 for the vacuum pump alone, with
no guarantee that it will fix the fault. I asked if they had actually
measured the vacuum and they said that they had, but I had to press the man
hard before getting him to tell me the reading (which he said was about 12
inches on mercury).

I've now had a little look myself and I can definitely feel a vacuum at
engine tick over if I remove the pipe from the servo unit and hold my thumb
over it, but I have no idea what reading it is. I've also checked that the
vacuum unit is actually holding a vacuum, because if I switch the engine off
and return the next day I can still hear a "pop" as the vacuum is realeased
when I pull the hose out of the unit.

Does anybody have any idea what could be wrong?

Mike


 



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