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Brake Bleed Woes.. Should My Pedal Eventually Go Down?


DaveBMX

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trying to sort out an issue i had a while ago with my restoration.

 

 

I put on some volvo calipers a few months ago and tried a different cylinder which a few of you guys helped me with and then i got bored of the brakes and moved onto other jobs.

 

Well i'm back at the brakes now and have reinstalled the original 2002 cylinder.

 

I have a dual booster setup

 

I have bled them all around using my dad as a "pumper" :lol: and the pedal now appears to activate about half way down the stroke is good.

 

However if i hold hard pressure on eventually the pedal will seem to give out, as if fluid is escaping and go down to the floor.

 

Is this fluid slipping back past the valves of the MC? im pretty sure its not leaving the system as no fluid on the floor and the reservoir doesnt go down?

 

Is this actually normal as you wouldnt really do this in normal driving or should the pedal stay hard permanently until you release?

 

Now just so you know i have a 10lb residual valve for the rear drums as the original one isnt on the cylinder and also a 2lb on the front as i have had to move the front booster up on top of the rear booster to fit the engine in and it is higher than the MC.

 

Im trying to get it all sorted as the car is going to paint on the 2nd  :D

 

 

I would be greatful for anyones views!!

 

kind regards

 

 

Dave

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Something about seeing a doctor after four hours...

Anyway, I'm not sure what effect the dual boosters would have, but if the pedal sinks slowly to the floor, and there are no leaks, chances are the master is shot. If it just feels spongy, bleed on.

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I've heard of old units failing when a combined with a new caliper, etc. But to clarify, the pedal goes down half way and stops, feels hard, but slowly sinks if you keep pushing? Have you tried it with the motor running? A spongy pedal is just that - it never feels solid.

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Good idea on bleeding again. You know the sequence I assume - RR, LR, RF, LF. And then sequence for calipers - but I'm not sure about Volvo ones  - do they have one bleeder? You need to move a bit of fluid to get fresh stuff to the back. I have  a vague recollection of something special with those dual boosters...RHD?? Sometimes starting motor and thus activating booster will firm things up.

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Yep right hand drive so rear left then rear right. Then however i go to front right before front left as that hose has to travel to the far side of the car and back so is much longer. There are bleed screws on the top of the boosters that i have been using. volvo caliper has 3 bleed nipples but. Im only using the highest one. Should i also be using the ones on either side half way down?

Regards

Dave

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Normally, the idea is to start with the cyl furthest away from the master and work back in order. As I recall, for RHD, Hayne says to start with cyl on remote servo first, then the rears. AS for calipers, I can't see why you wouldn't do them like BMW calipers with 3 nipples  - top, lower in, lower out.

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FYI I had a new factory master cylinder fail with less than 10k miles on it, so such things can happen...

 

A sinking brake pedal with no external leaks and well-bled wheel cylinders/calipers is usually the sign of a M/C passing fluid past its internal seals.

 

cheers

mike

'69 Nevada sunroof-Wolfgang-bought new
'73 Sahara sunroof-Ludwig-since '78
'91 Brillantrot 318is sunroof-Georg Friederich 
Fiat Topolini (Benito & Luigi), Renault 4CVs (Anatole, Lucky Pierre, Brigette) & Kermit, the Bugeye Sprite

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Many times when you have an older master cylinder pushing the pedal to the floor ruins the rubber seals. I have had this happen. I have had new MC out of the box be no good. If you are not getting air and the fluid is bleeding with no bubbles its the mc seals that are trashed.

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I think one of your servos is leaking but Id bleed out one mire time just incase. I just took my two servos out and they were practicly full off fluid.

However the bleeding of the rhd system is a bit of an art. I generaly use a pressure bleeder. The cheap gunson one using tyre pressure. At times ive had to bleed at the master cylinder first with no pressure applied. Then oressure bleed the two servos. Then the rear. When doing the front bleed the top bleed screw first then the inner screw then the lower outer. Be prepaired to bleed out a good 2 litres overall possibly more.

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 i have been using. volvo caliper has 3 bleed nipples but. Im only using the highest one. Should i also be using the ones on either side half way down?

 

Dave--Yes, you want to bleed all three front caliper bleed nipples on each side in the sequence given above. That RHD system sounds like a bear to bleed! --Fred

--Fred

'74tii (Colorado) track car

'69ti (Black/Red/Yellow) rolling resto track car

'73tii (Fjord....RIP)

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+1.  gotta bleed all three on each caliper.  upper, inner, outer.

 

Unless the RHD cars have multiple masters you don't have to do LR first, the RR, then LF, etc.  the direction to do "furthest" corner first is an old wive's tale.  hydraulically, each corner has its own brake line.  even the rears are exactly the same distance from the master as they share a common line that runs to a T in the middle of the car and then splits to the same distance to each wheel.  it makes no difference at all which of the four corners you bleed first or last.  the hydraulic system does not care.

 

if it is easier to remember which one you have done by using the "furthest away first" sequence, go for it.  

2xM3

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Unfortunately the RHDs have essential a master and two slave cylinders thus the 10 bleed nipples!! . A dual circuit into two single circuits, ive found the hard way sequence is everything with them as the lines flow up and down and trap air in u-bends that can feed back into the upper parts of the system. Front calpers need all nipples bleed, top, inner outer. I do RH first because its further from the servos but servos first back and then front. The RHD system was very much an after thought and the routing very poor, on the plus side the twin servos provide great assistance when working properly. Although its a bit on/off in terms of feel. It you want to try out servo less, a volvo 240 brake union valve should sort you out if you not mind hard brakes, NOS servos from what I've seen don't work predictably but if go onto 02forum.co.uk there is a chap rebulding RHD servos or you could try the Chinese Lockheed servos. It seems the RHD servos are suseptable to salt as the Irish ones seem to last longer dude to Irish councils using grit rather than salt but even at that they have almost run out and weve change to pure salt in the last couple of years.

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