Master Cylinder -updated you are NOT going to know this

[dubdubz]

Trying to bleed the brakes on my 68 which has 72 servo brakes.......

the fronts bled through fine, small bubbles but as the system was part drained as I've been removing pipes etc - I thought I'd do the rears get the majority out and then go around again!!

but the rears just would not move fluid with the bleed nipples opened??

If the MC was faulty - I thought the pedal would go to the floor eventually - leaking past the seals??

it doesn't do this the pedal pressure is firm.........

If I crack the union on the MC for the rear cct it has fluid there, I also removed pipe before it went into the brake proportioning valve [late brakes , disc front drums rear] and got the missus to press the pedal and it squirted out fine.

Attach the b p valve and it won't pass through this - I just wanted to rule the MC out first??? IE the MC broke and not producing enough pressure? to get through the b p valve??

confused.........please help

 

[dubdubz]

the bit you are not going to know

So the brake bias valve on a 71? on bus

has a bleed screw in it - mine has sheared off whilst trying to bleed brakes

what size is this screw as in what size thread tap do I need to buy tomorrow?

I seriously cannot see anyone knowing this...........


and or if you know of anyone that has one for sale in case this one is broked for ever!! bias valve that is.....

 

[Nick-Rackham]

Try just cracking off one of the front bleed nipples and opening a rear one at the same time, and get the missus to pump the pedal hard! Sounds like the valve is limiting flow. Seem to remember having this problem on a mini 20+ years ago!

EDIT:- Just read your second post!

 

[dubdubz]

the problem - fairly urgent too tbh - is the bias valve is in bits in my shed, it was dirty inside and the bleed screw needed drilling out, as these need bleeding to aid getting the system back to normal on a partial to full drain.

I hope the bleed screw is an M7 x 1.0 one, as I can get that fairly easily get the valve together.

wish I knew where the problem was? I might even try temp joining the 2 ends where the bias valve went and see if I can at least get fluid out of the rears then......

do these valves go wrong?

wish I had a spare as I could drill the 'valve' part out and try it then....what do they do?

 

[froggy]

If you can get a new bleed screw then take this with you and goto a small engineering company and ask them for a tap to suit, i'd imagine (and this is only a guess) but most pipe fitting are not metric so the chances are its 1/4 BSP (british standard pipe).
Try looking on VW heritage to see if they stock the bias valve as they might also stock the bleed nipple and might give a screw / thread size.

 

[dubdubz]

If you can get a new bleed screw then take this with you and goto a small engineering company and ask them for a tap to suit, i'd imagine (and this is only a guess) but most pipe fitting are not metric so the chances are its 1/4 BSP (british standard pipe).
Try looking on VW heritage to see if they stock the bias valve as they might also stock the bleed nipple and might give a screw / thread size.

good thoughts I'd already gone that way in my thinking the bias valve is £180!! no mention of the bleed screw [ mainly because the later ones didn't have a bleed screw and I guess that's what they have got hold of ]

 

[CHR]

now i have maybe a stiupid question, or i dident understand it when it was writen somwhere...
do you still use '68 MC or do you have a newer one?
just because, the '68 can not be used together with discs how i had to learn when i updateed my '68 with the csp-discs. you need a newer one that is for discs i think. or is it another thing with '72 discs? i'm not realy the expert for that.

 

[dubdubz]

now i have maybe a stiupid question, or i dident understand it when it was writen somwhere...
do you still use '68 MC or do you have a newer one?
just because, the '68 can not be used together with discs how i had to learn when i updateed my '68 with the csp-discs. you need a newer one that is for discs i think. or is it another thing with '72 discs? i'm not realy the expert for that.

it's not a stupid Q - I have late braking parts throughout, apart from the rear drum are early bay.

so the MC is a dual cct strapped to a servo, I'm sure it's the bias valve not being at the correct angle.........

 

[ground hugger]

now i have maybe a stiupid question, or i dident understand it when it was writen somwhere...
do you still use '68 MC or do you have a newer one?
just because, the '68 can not be used together with discs how i had to learn when i updateed my '68 with the csp-discs. you need a newer one that is for discs i think. or is it another thing with '72 discs? i'm not realy the expert for that.

it's not a stupid Q - I have late braking parts throughout, apart from the rear drum are early bay.

so the MC is a dual cct strapped to a servo, I'm sure it's the bias valve not being at the correct angle.........

Have you try'd removing the bias valve from the chassis and tilting it.
When bleeding the brakes on my 72 I had the same problem and it worked.

 

[dubdubz]

All fixed now

I'll post some pics in a bit - it was epic.......the valve was indeed installed at 0 deg as opposed to the correct 30 degrees tilt rearwards.

so the valve has been dismantled /cleaned, the bleed screw that sheared off has been drilled out and retapped and replaced [it was m7 x 1.0mm for reference]

I need to bleed again but there's fluid and only a few minor bubbles at the bleed screws now....so all good.

overall exploded pic [well kind of!]

the pesky bleed screw

the odd valve on the outlet of the bias valve - the gunk in the end was cleaning fluid just before Mr compressor

and this is the angle it should be at [pic of my 72!] it was almost perfectly horizontal on the 68!