Hi, I know there have been many posts regarding brake bleeding but really struggling to find the cause of my particular problem.
I have a 1967 camper with totally new (every single part!) braking system including dual circuit master cylinder and VW Jim servo. The van is still running drums up front.
After months of messing around, bleeding and re-bleeding I have still not managing to get a solid brake pedal I have however managed to trace the problem to the front brakes.
Basically I have bled each component individually and get a solid pedal with just the m/c connected, the m/c and servo connected and the m/c, servo and rear brakes connected. As soon as I connect either or both front brakes, the pedal travels right to the floor. There are no leaks anywhere and I have bled with an easibleed and hydraulic bleeder and the manual method.
Totally at a loss now as all slave cylinders are new and seems coincidental that both front brakes cause the fault and not just one side. Could it be a compatibility (capacity) issue between the m/c and slave cylinders? Anyone have any suggestions?
Many thanks

Something I've not asked you before, are you using normal brake hoses or braided hoses?

A bit of a faff, but curious if you the reverse the m/c plumbing, I wonder the fault goes to the rear wheels and the fronts become good

Hi Jim
I'm using normal brake hoses (all new along with the brake pipes).
I must admit I haven't tried that, I'm not sure if my pipe work will reach but I'll have a go although I won't be able to try for a couple of weeks. Just to confirm, I assume you mean the master cylinder to servo pipe work?
Many thanks

Do you get fluid out of the front drums?
You do have shoes fitted? Have the drums been skimmed?

Sent from my ONEPLUS A5000 using Tapatalk

Karmann wrote: ↑Sun Sep 17, 2017 7:54 pm Hi Jim
I'm using normal brake hoses (all new along with the brake pipes).
I must admit I haven't tried that, I'm not sure if my pipe work will reach but I'll have a go although I won't be able to try for a couple of weeks. Just to confirm, I assume you mean the master cylinder to servo pipe work?
Many thanks

Yep, thinking swap the two ports over on the m/c Everything else the same. If the fault moves to the rear circuit then maybe the m/c has a fault in the internal machining that means it can't push enough fluid.

ie you've tested and proved it does move some fluid and not leak air anywhere in the circuit. But maybe it's not moving enough fluid? It should, but something is not working.

Hi paul_f, fluid comes through front drums bubble free when bleeding. I've taken drums off to double check inside and no leaks. Shoes fitted and adjusted up so just rubbing slightly. Drums haven't been skimmed as far as I know.
VW Jim, yes sounds like a good test as will eliminate any problems with the front brakes. It does seem as if it doesn't push enough fluid on the front circuit as pedal goes right to the floor as soon as either front brakes is connected.
Many thanks for the help really frustrated that I haven't been able to sort this!

I found my brake light switch was the problem letting in air, that and making sure you bleed the servo master cylinder completely before doing the rest of the brakes.

Take a look at page 3 of my thread here:-

viewtopic.php?f=6&t=108903

I had exactly the same issue, ended up buying a different master cylinder which works fine. I spent a bit of time with the Technical guy at TRW and he said it is to do with the bore of the MC not being big enough, however loads of those MCs are sold every year to people doing exactly the same thing as you and I, it's wierd and extremely frustrating. I must have had the single circuit in and out 10 or more times, it's in a glass box with "break in case of emergency" in my garage now!

8 8US wrote: ↑Mon Sep 18, 2017 7:58 am Take a look at page 3 of my thread here:-

viewtopic.php?f=6&t=108903

I had exactly the same issue, ended up buying a different master cylinder which works fine. I spent a bit of time with the Technical guy at TRW and he said it is to do with the bore of the MC not being big enough, however loads of those MCs are sold every year to people doing exactly the same thing as you and I, it's wierd and extremely frustrating. I must have had the single circuit in and out 10 or more times, it's in a glass box with "break in case of emergency" in my garage now!

I remember you having that issue. I would be nice if a larger bore m/c could be found, to push more fluid and get shorter pedal travel.

Kurt on the Samba used a VW Fox MC. Info on stroke and bore in this and the following few posts. Not sure if this gives the desired effect...
Funky Truck VW Fox master cylinder

Thanks for that 8 8us. I had seen your postings previously but wasn't sure if you fixed it. I'm going to try VW Jim's suggestion of swapping the circuits around first just to eliminate and problems with my front brakes but if that fails as I suspect it will then I guess I will have to try a different m/c. It is weird though that most vans seem to work fine! Just to confirm, was it the Golf (Rabbit) m/c that you detail on page 3 that worked for you in the end and did the fluid reservoir fit this m/c?
Cheers
P.s. Definitely no leaks around the brake switch now as already had this problem!!

Thanks Who.me. I'll have s good read of that but from a quick skim wondering if it is because my van is a 1967 which it says has a larger bore m/c.
Why do I get the feeling this is going to get even more frustrating!

Karmann wrote: ↑Mon Sep 18, 2017 3:14 pm Thanks for that 8 8us. I had seen your postings previously but wasn't sure if you fixed it. I'm going to try VW Jim's suggestion of swapping the circuits around first just to eliminate and problems with my front brakes but if that fails as I suspect it will then I guess I will have to try a different m/c. It is weird though that most vans seem to work fine! Just to confirm, was it the Golf (Rabbit) m/c that you detail on page 3 that worked for you in the end and did the fluid reservoir fit this m/c?
Cheers
P.s. Definitely no leaks around the brake switch now as already had this problem!!

It was the Golf/Rabbit mc I fitted some time ago, all good so far. And the reservoir fitted okay.

I had problems with trying to get my brakes to be any good despite having R9 with discs front and rear and a VWJim servo.

Turned out I'd fitted the non return valve the wrong way round even though I'm sure I double checked before fitting

Brakes work great now