Series III, only one brake working after full replacement

Hi all, coming to the end of my Series III rebuild and unsurprisingly, the brakes are the hardest bit! Replaced almost the entire system (pipes, flexi, slave cylinders, pads, springs, adjusters) and cleaned the shuttle valve. It's a late dual circuit system with servo.

I've run about 10 litres of fluid through the system with an Eezibleed, and the pedal doesn't pump up at all so I'm confident all the air is out. No leaks either.

However, only the left rear brake is coming on with force - it easily locks the wheel up. I thought it could be the front section in the master cylinder as it was left empty for a while, so I replaced the master cylinder and reservoir with a TRW part. Bled it again with even more fluid, and still the same result.

All the adjusters are dialled in so the pads just rub a little, and I've pulled all the wheels off to check the cylinders move, which they do. Also done the ratchet straps on the shoes trick to get all the air out...same result, just the one brake coming on.

Did think it was the shuttle valve as that's the only original part in the system, but if that had jammed then the entire rear axle would come on. Also, as far as I know, the valve's only purpose is to indicate with the dashboard light when the plunger moves over.

Thanks for your help on this. Going mad, I'm going to take it into a garage soon and let them pull their hair out instead!

What sort of a brake pedal have you got, is it high and firm or low and spongy? If low, does it come up firm if you pump it a few times?

It’s high and pretty firm, pumps once just a little barely perceptible bit. Thanks.

Best thing you can do is remove shuttle valve and bin it. Only function it gives is the warning light which you can replace with defender fluid level switch.

I agree with Blackburn about the shuttle valve, a very expensive and virtually worthless gadget. Your brake problem as you have described it doesn't seem connected to the shuttle valve though... Are you certain that you have fitted all the various parts of the brake system properly: shoes on the right way round, likewise wheel cylinders? When you bled the system, did the fluid come out at the same rate from each bleed nipple, or did you notice that some seemed a little feeble? Can you be sure that you have adjusted the brakes properly? It is possible to turn the adjusters the wrong way, the wheel seems to lock and when you back the adjuster off the wheel becomes free again but in actual fact is the opposite of being properly adjusted.
Some close-up pictures of each wheel with drums off might provide a clue. You haven't mentioned what LR you have.

Agree re shuttle valve; its a dead-end technology that causes more problems than it fixes. Als agree re adjusters, they all tighten clockwise like doing up a bolt., very easy to get mixed up and turn one side the wrong way as the feel is very similar. I suspect you have 2 faults; a stuck shuttle valve and a wrong way adjuster.

Beat the bejesus out of each hub as a pressganged youth jumps up and down on the pedal.
Or take the cylinders out and lubricate them with a smear of pink stuff like your ment to

Thanks all. I replaced all the adjusters and checked them with the drums off before adjusting with just the drums on, so I'm confident they're all working properly.

When assembling I also greased the cylinders with Brembo grease, and the front cylinders are moving correctly, I've checked by getting someone to gently press the pedal with the drums off.

The shuttle valve's piston is moving smoothly, I can easily pop it back and forth with a screwdriver with the switch removed. However, it moves into the front fail position when the pedal is pressed, so the pressure differential is enough to trigger it between back and front circuits. This doesn't affect the flow of fluid though, as the pressure bleeder can still push fluid out.

Fluid comes out at the same rate from all bleed nipples, and I'm sure that it's all assembled correctly. I'll double check today though, and pop a photo up. It's a 1982 Series III with the 11" twin leading shoe front and 9" rear.

In the title you say "full replacement" does this include the master cylinder? If so and the old MC is still servicable, I'd try swapping it back to see if this has any affect.

Col

I don't know how an easy bleed works, never used one, but it's it interfering with the shuttle valve?
Open each bleed nipple in turn to make sure there's no pressure build up anywhere

I replaced everything except the shuttle valve and master cylinder due to multiple stuck/leaking slave cylinders, and the problem with no front brakes was occurring then.

Thinking it was the front section in the master cylinder that was leaking, I replaced the master cylinder but the problem stayed. Stripping down the old cylinder, the seals and bore looked fine though.

The easy bleed forces fluid at low pressure through the system from the reservoir through to the wheel cylinders, and fluid flows freely (and with no air) from each wheel.

The shuttle valve doesn't actually cut off fluid to any part of the system, it's just there as an indicator of failure to trip the little switch on the side of it and illuminate the dash light. It can however be a pain to bleed as air gets stuck in it.

I thought the shuttle value was there to provide a dual circuit, if a leak develops, that circuit cuts off and the dash light comes on, the other half of the system remains active

The master cylinder has two sections to the piston, one for the front and one for the back. The reservoir is also divided in two internally, so if the rear develops a leak for example, that section of the reservoir will drain but the front will remain full and operational.

The shuttle valve's piston will move across if there's a pressure difference between the front and rear sections, but it doesn't actually cut off fluid to the low pressure section of the system. You can demonstrate this by manually moving its piston across and then bleeding the brakes - fluid still flows out the bleed nipple.

On the 109 i had, the valve definitely shut off the low pressure side if there was a leak

So, the left rear is working the best; do the others work at all? I'm suspecting that they do but the NSR is a bit keen and beating the others to the punch... Did you replace the drums and if so what make of drum? (Britpart drums are notoriously inconsistent in quality). Have you tried swapping the rear drums and/or the shoes over to see if the problem swaps sides?

The rear axle is definitely coming on strong, I can lock up both rear brakes with touch of the pedal. NSR comes on first but with a bit of adjustment I've got both rear ones working at roughly the same strength.

Drums are original but in good condition with no scoring, and the new pads are TRW. The fronts are definitely doing a little bit and the shoes are contacting the drums - there's marks on the new pads. An emergency stop locks the rear up and brings the car to a relatively gentle halt, nothing like what it should be.

Can you pump fluid out of bleed nipple with pedal,thinking master clyinder not being allowed to open recuperating valve fully in cylinder to allow fluid to refill it.[easy bleed uses pressure normal operation only atmospheric pressure]
The servo has some adjustment of the operating rod between it an master cylinder.
Is pedal return spring fitted in cab?

Pedal return spring is fitted, and the master cylinder is fully returning to its home position. Conventional bleeding also works fine, fluid flowing easily from all bleed nipples.

Double checked the front shoes and springs this morning, springs are all definitely in the right place.

Thanks for all your help!

How are your front cylinders connected? Does the feed go into the upper cylinder, such that you're trying to flush the bubbles downhill to the bleed nipple?

I saw some comments on a different thread that this can leave bubbles in the upper cylinder that don't get flushed out. A better approach is to replumb the system to feed into the lower cylinder and bleed from the upper one.

I thought the MC was responsible for the dual brake system, it sounds like it thinks there is a leak in the front system and pumping all the pressure to the rear

Col