Outer Limits 4x4 Board

Help! have replaced front calipers on Disco S1 with defender calipers (bolt right in) and re-run the brake lines to remove original second lines from front. Now have primary MC circuit running rears and secondary MC circuit running fronts.
BUT now have no brake pressure at all front or back.

Have bled it 100 times and can only get peddle pressure if I clamp front hoses, but lose all pressure front and back circuits when clamps are released.

Has the MC has shit itself allowing primary and secondary circuits to mix? Or are the Def calipers too big to run faulty?

I remember a thread (probably on another rover forum) where this symptom was diagnosed as something which can happen in the valve that proportions the braking force between front and rear.

It can happen in some situations when working on the brakes, when lines have been disconnected. My memory is a bit dull on this as it is not something that has happened to me.

From memory, you have to re-set the spool in the proportioning valve.

Hopefully someone else can add more sense/knowledge to this.

The other possibility is that the piston in the master cylinder normally works over a small distance and corrosion can occur on the part of the bore beyond where the piston normally stops (brake fluid absorbs moisture, which is why it should be changed from time to time).

But when you have lost a lot of fluid from the system and bleeding the brakes, the piston travels all the way and the piston seals can be damaged by the corrosion. Sometimes the damage manifests at some later stage, after the brakes are bled, other time the damage prevents bleeding.

I don't know how different the S1 is to the S2 Disco as far as brake setups go but on the S2 Disco is very very hard to bleed the brakes. I ended up having to get the local LR specialist to do it.

Why would you remove the 2nd circuit ? Will defender calipers make any real difference ?

Little more info for by post above.

The dual circuit is designed to allow some braking if a line fails. There is a shuttle valve that is offset when pressure is lost in one of the circuits.

It is possible for this to happen when you are bleeding the brakes. The brake warning light is supposed to come on when this happens, but it does not always come on.

If it does, you can pull the valve apart and put the shuttle back in the centre position.

There is a brake bleeding technique for resetting the shuttle if it gets offset, but I am not clear on this.

If it happens when you are bleeding, then close the nipple that you are working on and go and bleed fluid from a nipple in the other circuit (even if it does not need bleeding).

So try bleeding the rear calipers, while the clamps are on the front lines. This may centre the shuttle for you.

If this centres the shuttle, then leave the clamp on one front while you bleed the other.

If bleeding the rear doesn't centre the shuttle, you may have to pull the valve apart and re-centre to centre it.

I am not sure with disco's, but the valve is usually located on the inner guard, below the master cylinder. You will see all of the brake lines going in/out of the valve, and possibly electrical wires for the brake warning lamp.

Many thanks guy

pulled the MC to pieced and it had some issues/blocked inlet on PCircuit. Also found one of the caliper pistons was RS leaking in air. So, its off to find some parts.....more money

Reddo,

Might have some caliper pistons /seals etc if you're interested. Im In Hobart. 6229 1102 BH

Yes thanks Justin, will see you soon....

reason for upgrade is that the Defender front calipers are 25% more brake surface area, and with vented rotors will greatly assist stopping and pad wear with the bigger wheels (currently 33" and going to be 35's soon).

Pistons locally cost way too much, can get a full set of 4 and seals from UK for the same price as two piston (no seals) locally, including air frieght!

I thought Discos and Defenders had the same disc size???

All that matters is swept area for braking ability.

I believe he means that the pads have a 25% larger area, which would mean better heat transfer, and therefore more effective braking for longer.....

...yes thanks, that's what was meant....anyhow, reports are that pad wear and braking performance are greatly improved, so worth the PITA effort - 8 hours so far and counting......just as well Sunday was raining all day and perfect for playing with cars in the shed!

Will source pistons/seals (all 8 are rooted) and give it another go sometime. Thanks again

Brake up date

got the new pistons in the Defender calipers, changed over rotors to Defender vented version. Calipers bolted straight in but needed to re-routed the brake lines, bled them endlessly and bingo, brakes that now put you head thru the screen. Much much better than the original calipers and pads! A huge improvement.

Got the pistons from the UK on Ebay - original parts. Cost $ 156 for Royal mail, 8 pistons and all seals etc. Took 5 days to get them. Local quote was over $500!

Cost of up grade was $350 (200 for s/hand calipers and rotors plus $150 for new pistons, seals etc). Also now got 2 sets of bearings/seals and Defender spindles as spares.