Manky's Pop.

[snafu]

[/quote]
Iain they release when you crack open the bleed nipple on the front
[/quote]

with the calipers stuck on start releasing the line joints on the presure side of the components starting at the master cylinder, when the caliper frees the problem will be with the component preceeding it.

hope that makes sense

[hunter]

Andy,I can't help with this problem all i can say is,
Try to chill,If you have other things to do get on with them,
Don't wast brainpower on the brakes,
I'm sure this problem will be resolved pretty soon.
Enjoy the sun today,

[kapri]

M/c is correct size for system ,increased from previous bore as supplied with wrong info re rear axle /front brake source initially. Convinced the excessive travel is down to trapped air .

Me too.....either in the servo unit or the master cylinder. Bleed the servo has to be first on the list.

Just spoken with Terry and can understand his logic if the master cylinder is just a duel outlet and not a duel circuit.

Master cylinder is dual circuit, not dual outlet. Completely seperate circuits to front and rear lines .

[ByzMax]

Iain they release when you crack open the bleed nipple on the front
[/quote]

with the calipers stuck on start releasing the line joints on the presure side of the components starting at the master cylinder, when the caliper frees the problem will be with the component preceeding it.

hope that makes sense
[/quote]

Yep thats the solution

M/c is correct size for system ,increased from previous bore as supplied with wrong info re rear axle /front brake source initially. Convinced the excessive travel is down to trapped air .

Me too.....either in the servo unit or the master cylinder. Bleed the servo has to be first on the list.

Just spoken with Terry and can understand his logic if the master cylinder is just a duel outlet and not a duel circuit.

Master cylinder is dual circuit, not dual outlet. Completely seperate circuits to front and rear lines .

Ah right.

As snafu said clear/isolate the cause of the callipers not releasing and bleed the servo. One may be related to the other in some way.

[tbone]

As Terry has said, no one is setting out to pick at anyones work, both Kev and Terry have been superstars, going above and beyond.
We all have the same goal here, and I realise that we have gone over old ground, but I think it`s been worthwhile to clarify and double check things.
For what it`s worth, everyone that has had a hands on roll has my full admiration, particularly you Mr Field, the rest of us can turn our computers off and walk away, you cant do that when it`s your project.
Keep up the great work fella`s, it`ll come right soon.

[kapri]

I knew there may be a problem with the m/c . What happens on a Beetle is that the m/c has a rearward brake bias due to the light front end. I am presuming that this is exactly the same on the Bus  m/c .

Now we already had a problem with too much braking on the rear due to the lightness of the pick up and also that the servo was piped  ( we later found out by using pressure gauges ) incorrectly .

The servo piping has been corrected to place the 150psi 'lead in' on the front brakes as theSVA requires visual confirmation that front wheels lock before the rear.

To that end the m/c is currently piped with the (presumed) 150 psi lead in also to the front.


This may mean that ( if fitted internally) the OEM residual valve MAY be holding on line pressure. However I can't find any info on whether it has a residual(s) internally .

However the m/c we are currently using was destined for a disc drum ( with servo )Bus set up.

The other m/c that was available to fit the chassis member was larger ,would have required a greater pedal ratio than was available from teh space.

[Manky Monkey]

Anyone wanna buy a truck -& 3 or 4 years of my life  Believe me I regularly feel like walking away from it Tim.
O.K fellas, so what's the plan of attack then?
Bleed the servo, (does it make any difference which side we start with? -front or rear brakes?).
Bleed the 4 corners again.
Jack up the front of the truck & check the front brakes for binding.

Then what? If they are, make up a bridging pipe to by-pass the front residual valve & bleed the system again?
The pushrod from brake pedal to master cylinder was too long last time around, meaning the brakes were permanently slightly "on". I'm pretty sure there's some slack there now though, but the pedal's dropping right to the floor on the first push -further than I expected it to be able to travel, (our old friend, pedal ratios again). That suggests a lot of air in the system somewhere to me. Excuse my ignorance, but wouldn't that prevent the brakes from locking up, rather than locking them on?

[terry t]

how about this then.
the air is trapped in the master cylinder.
the residual valves are holding the fluid in the brake circuit.as the front brakes are locked on.
pump the peddle to build up pressure in the cylinder.

[Manky Monkey]

Solution?

[steve brock]

Seek higher plane of existence to physically solve..

[ByzMax]

Terry is on the right track

The solution is.............

Bleed the servo.

Find the source of the front brakes binding, probably the residual pressure valve in the master cylinder as  I think Kapri stated.

If it has one in the master cylinder then it's probably for drum brakes which holds 10-12 psi in the system.

You have disks on the front and they only  2 psi in the system which is why you have problems.

Either that or the residual pressure valve you have fitted for the front brakes is the wrong one. Either it's been ordered wrong or badged wrong so check it and cure this problem.


Check the system to see if the problems have gone.

Only make one change at a time and check the results. Soon you'll solve the problem.

Simples.

Don't get fed up with it Andy. You'll get it sorted.

[poprodder]

excellent advice there.

[Manky Monkey]

Ta-daa!!
Problem solved ...maybe.
I finished work late today then had to mind the workshop while Loony delivered a car to a customer, so we didn't have a lot of time to play with the Pop.
Started by bleeding the servo -yup, should've done it last time but Terry & I were both tired & it was his fault -joking Tel!! 
Jacked the front wheels off the ground & sure enough, they were binding.
So I followed Kev's advice & loosened the 2 master cylinder mounting bolts, allowing the cylinder to drop back from the pedal pushrod a centimetere or so.
Tried the wheels. They spun! Hurrah!
We made the pushrod between the pedal & the master cylinder adjustable, using a short rod with a threaded end that screws into the main rod, with a locknut on it, though I believe we have to weld it in one fixed position for the test. So I wound it in 5mm & refitted it.
Lots of freeplay at the pedal, but more importantly, the wheels still span free. I spent half an hour gradually winding the rod back out, checking the wheels each time, reducing the pedal freeplay. I swear it's back where it started now, but the wheels are still free. Maybe I'll back it off a touch to give a little play in the pedal to make sure the cylinder piston's definitely disengaged. The system still needs another proper bleed at all points, but the pedal doesn't seem to drop to the floor on the first push like it did before. We may have cracked it chaps.   

[Manky Monkey]

Had a pressie in the post the other day from Steve Brock, over there in Ireland land.
He recently lazer cut a mild steel bonnet badge for me, using a pencil sketch I drew, scanned & emailed to him.
He's sent me a larger, stainless steel version of the design. I don't want to add any more badges to the truck as it's supposed to be a bit industrial/agricultural, but this looks great! I was thinking maybe a belt buckle. Loony suggested a club plaque, hung under the back of the truck from 2 short chains, like the Latino lowrider guys do. Who knows. Like it though.
Thanks Steve. 

[Manky Monkey]

Loony also had a pressie. One of his customers is a young lad who works in an office. Loony's de badging & smoothing his Saxo hatchback. All the office staff were recently given new chairs by one of their clients & he donated his to Loony's office. A bit chavvy maybe, but incredibly comfy.