Re:Re:Jimny Front Brakes Seizing

CCBaxter - As you've had the same problem then it looks like changing the master cylinder has definite potential, although I would have expected the rear brakes to either seize/get hot/wear prematurely as well. I'd already ordered a replacement pressure differential valve/splitter/compensator (I've seen it described as all 3) because when I took it to my local garage and it had seized, we talked it over for a while, then gave this valve a good whack and the brakes had released, HOWEVER - it had been stood a while so could have released itself, and the next time it seized I whacked it and it didn't release. I've not driven it since whilst awaiting delivery as not only am I limited to 40-50mph, but it also shakes violently at this speed when the brakes are seizing (OK rest of time). It's due tomorrow, but if it looks like it's just a connector with no valves inside, I can't see the point in fitting it and will look at changing the master cylinder next. Here is the webpage with the braking diagram - Item 3 is what I've got ordered.
suzuki.7zap.com/en/jimny/51483-2003/128179-0-0/1460-0-0-0/

Witzend, item 3 looks like what used to be called a brake bias valve (front to rear) if this is the case there is every chance a new one will fix the problem. I certainly hope so. As the master is only a two pipe ( flow & return) front/rear balance is likely to be handled by said valve. Failing that, go back to the master cylinder scenario.
Chris

All - thebias valve arrived yesterday and new pads (old ones worn down after <2,000miles). I set off for the garage to fit it this morning with all four brakes running free. After RainerK's question, I managed to get onto the dual carriageway without using footbrake or handbrake. After about 5miles, the brakes started seizing by themselves and within a mile I was down to 40mph flat out and slowing. Got to garage, still without having applied any brake (foot or hand), got it on ramp and both front were hot and seized. Rear had also started to get warm. Following Jimx5's suggestion, we also checked for clearance/free-play/lock nut between the pedal and master cylinder and it is fine.
We took off n/s calliper and they couldn't push it back. Cracked nut on ABS pump(which has always released the pressure previously) but it didn't release enough to push it back (although calliper was off so pipe could have been twisted) - however, the o/s released. Cracked nut on n/s calliper and it completely freed off and could easily be pushed back.
As I'd applied no brake pressure, we didn't see the point of fitting the bias valve. As the pressure didn't release until we cracked the calliper nut, they are convinced replacing the flexipipes is the next step, but cannot explain to me why a kinked n/s flexipipe would seize the o/s as well, or why the rear started getting warm. For me, something is causing a build-up of pressure, whether or not I apply any.
We have decided to work back from the callipers, so flexipipes are on order, failing that, matercylinder is probably next unless today's events give anyone any other ideas.

So the fact that also the rear brakes engage means that there is a pressure build up in the braking system as it should be.

Therefore my guess would be that the problem is the master cylinder or the booster or the mechanical arrangement. The last item that could be defect and influences all breaks would be the ABS block, but then I would expect an error code.

As all breakes engage, I would not see any indication to start with the calipers - I think this might be a waste of time.

After inspecting the mechanical arrangement thoroughly, I would go for the master cylinder first, next would be the booster.

If your braking pads and disks are worn, I would of course also change them, but only after the problem with the unwanted self-breaking is solved.

Sorry to hear you're still having trouble with this.
It seems to me you're doing all the right things but not necessarily in the right order (to paraphrase Eric Morcambe). If you've paid for the bias valve, fit it anyway. If you can return said item for a refund then don't fit it, bypass it. Get a couple of of double ended female unions and join the lines without the bias valve in place. That might give an indication where the pressure lock is happening. Try to avoid throwing money at this fault. Slow and deliberate diagnosis is the key to such problems. It's clear from your description that this vehicle does not belong on the road in it's present state.
You are getting plenty of good advice from this forum but of course it won't all apply to your situation, none of us are looking over your shoulder.
As a footnote - have you bled the brakes fully (both Calipers both cylinders) working from the farthest corner from the master to the nearest. Bleedin can often reveal faults in the master cylinder and associated valves, fluid is cheap. Stop buying parts on the off chance of a quick fix.
Chris

Thanks, RainerK. It does appear that pressure is building up somehow. I'd already tried disconnecting the servo vacuum before starting this thread, but it still seized, so we ruled that out early on. I also ran it with all three ABS fuses removed in case this was to blame, but again it still did it.

As for the calipers, I didn't mean I was changing them, I meant we are starting at that end and ruling things out one by one.The calipers are free and working OK, so they've suggested changing the flexipipes next - they think that was why they couldn't push back the piston. I've only noticed the rear brakes getting warm twice, and once was when using the handbrake only to see if it still seized without footbrake (every time it seizes I check all four for temperature), so up until recently it appeared to be a front brake problem.

I've got new pads awaiting a solution, but as you say, it's pointless fitting them until it's sorted.