Help please! 110 Brake seize mystery

Hello all, I'm looking for a bit of advice with fixing my brakes. Another chance for a bit of remote problem solving!
I've got a 110 200tdi 1991. Front discs and rear drums.
The problem is that after about 10 minutes of driving the brakes become stuck on, with the pedal becoming pretty much solid. And then obviously if I continue the brakes get very hot! So I have to stop, let them cool down and then I'm on my way again after about 15 mins..... Driving my landy really is slow! :doh:
A few facts:

It has a new master cylinder.
Today I bled all the brakes, which definitely needed doing but didnt fix it.
Brakes are much faster to lock on if traveling in 4th or 5th and going quickish.
More frequent braking seems to prolong the inevitable for a short while.
I recently bought the truck and beforehand I think it had sat around for a while.


So there you go! Sorry for the long post, but I might as well get as much info in as poss?!

Please fire away with your suggestions of what to do next!!

Cheers

it may be that rod in servo needs adjusting for new master cylinder

It sounds like you're boiling your fluid. That makes the pedal go rock hard. Something might be catching or the pads might be rubbing on the discs when you're driving along. Mine did it once and when I took the back drum off the pad had come away from the shoe and ground a deep groove into the drum.

Sounds like the brake fluid isnt fully returning back to the resovoir , so its building up in the system . Like JM said check the rod free play and make sure there is some .

Another thing to check is make sure that none of your pipes are crimped .

Thanks very much for all replies so far - I'm going to look into the servo rod as suggested. I don't know what one looks like yet, but I think I'm sensible enough to work it out?!
I did check the brake pads yesterday and one of the front ones had come away from the back plate a little - so perhaps it could be that? Would that boil the fluid sufficiently to make all wheels lock up and get hot??

Adam

If the brake fluid was excessively dirty it could be causing the calipers to seize, even after you change the fluid the crud sticks to the seals, I would suggest checking the seals in your calipers, also check for bluing of the disks, if this has happened they will also need to be changed as they have been over heated.

if rod is poorly adjusted it lets servo gradually pull rakes on ,you can rule it out by removing vac feed to it ,if fluid cant return to reservoir cracking bleed nipple or pipe will indicate it if pressure is relieved,check pistons arent seizing

Thanks again guys. Jamesmartin... Would you mind just breaking down that little test run into even more obvious steps please?! Embarrassingly, I don't quite know what you mean. I'd like to test the pushrod theory though. Does the engine need to be running?

Well, just to be clearer - what outcome am I looking for? If i take the vac pipe off and fluid won't return, what does that mean? If I crack a nipple and it relieves pressure, what does that mean? Thank you!

yes engine needs to be running and brakes pulling on ,you remove vac pipe if rod is too long and pushing against servo it willl release brakes

Thanks again

Today's update. I've fitted new pads on the front, it really needed doing. The pistons were a bit awkward to push back in but weren't too worrying.
Took the truck for a drive and I've got about 4 times further than I normally would, braking much better as well, BUT - they have eventually stuck on again.

James - I tried removing the vac pipe once the brakes had seized on, but it didn't release them. So I'm guessing it's not the push rod. Have I understood that properly?

The mystery continues...

It sounds like the pistons could be seizing in the wheel cylinders. Pop them out, grease them, and re-fit. Also make sure the any dust seals on the wheel cylinders are intact too.

Wheel cylinders - as in the rear drums? Would this cause all four wheels to lock up?? The front brakes/wheels get locked up and heat up the most.

Really appreciate all of this...

martin1512 said:

It sounds like the pistons could be seizing in the wheel cylinders. Pop them out, grease them, and re-fit. Also make sure the any dust seals on the wheel cylinders are intact too.

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why would you grease them ,you should only use rake fluid to luricate seals

have you checked to see if theres pressure in system by undoing a bleed nipple,quickly closing it when rakes pull on ,have you other symptoms ?

jamesmartin said:

have you checked to see if theres pressure in system by undoing a bleed nipple,quickly closing it when rakes pull on ,have you other symptoms ?

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That's a good idea! No, I haven't tried it yet - not driven with the spanner in the landy, so I shall do that.
Other symptoms... The brake pedal 'builds up' as I'm pressing it - with a bit of a hiss. Pedal travel gets less and less as I go along - that's how I know its about to get locked up. I can smell the brakes, but that's just cos they get hot. And in 'normal' braking, the pedal requires a lot of effort. But I know it's a landrover - so im not sure how much to judge by that!

sounds like you do have a problem with servo/master cylinder,if pedal free play reduces during driving ,if you press pedal with engine off you should have a little freeplay and stiff pedal ,holding foot hard on pedal start engine ,servo should allow pedal to sink further as vacuum from servo helps

jamesmartin said:

sounds like you do have a problem with servo/master cylinder,if pedal free play reduces during driving ,if you press pedal with engine off you should have a little freeplay and stiff pedal ,holding foot hard on pedal start engine ,servo should allow pedal to sink further as vacuum from servo helps

Click to expand...

Well, I've had a go at adjusting the rod in the servo - it was a bit fiddly and vague to adjust - but it seems to have done the job for now!! I need to drive it round some more before I'm convinced...but fingers crossed... !