Spongy brakes

[nlbyrne]

As the title suggests I have straight to the floor spongy brakes.
Now they were spongy when i bought the Cruiser and a DOE cert stating a brake imbalance in the rear.
After further investigating it was a sized near side caliper, that sorted showed up a warped disc. So new pads and discs (rotors) still the same.
Checked the front, all looked good. Still no difference, replaced front pads as they were 50% gone, to help as much as possible. Still no joy
Bleed the system numerous times since I got the truck, the last time a 1.5L flush.

So I got a lend of 4 clamps and clamped the rubber hoses just before the calipers.
All clamped up hard as a rock (tested with engine on and off)
Release near side rear good and hard.
Reclamp
Release offside side rear good and hard.
Reclamp
Release offside side front slight drop but hard.
Reclamp
Release near side front drops to the floor.

Any suggestions
Before I buy new calipers

 

[IRLGW]

could be air in the system possibly. Could be worth bleeding starting from the furthest brake. However I think there are two slave cylinders for controlling front and rear brakes so one of those could be dosey. I usually attach a piece of tubing to the bleed nipple and lead it up to a point above the reservoir. This way you can bleed on your own and all air goes clear of the system. I have a 93 12v and there was a letter from toyota in the handbook to say that it had the brake vacuum assist replaced as part of a recall basically. Could be that the owner of your jeep was never traced if it is a similar age

 

[frank rabbets]

Probably a faulty master cylinder sucking air past the seels and they don't always leak.
Try bleeding with engine running. This sometimes works if it is just an air problem.

Frank

 

[Chris]

Have you bled the LSV at the back? Bit of a long shot as you do have pedal pressure on three calipers. I can't see any need to be replacing the calipers at all.
It could well be the master. We have posted on this before and if the master has not been bled in a long time, the seals get 'ripped' if you bleed the brakes when the piston is pushed all the way down the cylinder of the master. This is an unused portion of the master which isn't as smooth and nice as the part which gets worked every day. If you have put over a litre through it then any more of the same is unlikely to make a difference. I would push the pistons back into the calipers to reduce the amount of fluid in the pots perhaps and see if that makes a difference. IE bleed each one (maybe just the troubled one) with the pistons held back. There is less space for any air to hide.

I went round and round on my brakes and then I heard about over extended MC issues. Yep, that cured it. You could also try bleeding the master cylinder of course. Undo the unions on there and push the pedal with finger of the outlet (gently, mind your eyes) then hold finger firmly in upstroke to suck fluid back into the cylinder from the reservoir.

Also got to suspect the seals on the front cal, I gues.

Chris

 

[nlbyrne]

Ye bled the LSV, It has been bled while running, not running, pressure bled, gravity bled, so bled to death. And in the specified order starting from furthest away to the master cylinder.
Surely with all hoses clamped its the master cylinder that is under pressure and the pedal stays hard, so I would of thought the master cylinder is good

 

[Justin_Elliott]

Are your brake hoses expanding more than they should? is this a feel rather than performance issue??

 

[nlbyrne]

The hoses look ok. Its both really, there is no real bite feel when you press the breaks.
It travels nearly to the floor before you start to slow, performance wise it stops you and it will lock up the ABS

 

[Cptsideways]

I've had this with a seized rear caliper slider bolt.

 

[Justin_Elliott]

So, if you have either side front hose clamped - do you get the same 'feel'?

Also, when 'hard' do you have any creep or does it pretty much lock solid...?

 

[nlbyrne]

With both front hoses clamped its locked solid no creep, with the engine running and not

 

[Justin_Elliott]

Assuming you can't find a mechanical cause (binding etc..) I'd suggest you consider changing your front brake hoses to braided... Relatively cheap/quick (been discussed before, so worth a search)

Can't see how it could be MC if you don't get any creep.


Sent from my BlackBerry 9800 using Tapatalk

 

[Andrew Prince]

Have you rebuilt the calipers with new seals, grease etc? I would do that before replacing a whole caliper as it will be much cheaper. That way you can be sure that the pistons are free and moving properly. On the brake hoses, it is possible that your hoses have delaminated internally so expand along much of the length when under pressure, so not obvious to the eye that there's a problem.
It sounds like it may well be an issue with the master-cylinder though.

I hope you get to the bottom of it soon!

 

[Chris]

Hang on a minute. All hoses clamped, the pedal is solid. Release and clamp each hose in turn and the the pedal is still solid until we come to one particular caliper.

Well call me Perry Mason, but doesn't that strike anyone else as being the probable cause. It's something to so with that corner. I know that hoses can fail but for the pedal to go straight to the floor, it would have to be filling up like a balloon. It's not may call but I would be focussing my attention there first, If the hose is clamped near the joint to the caliper and still the pedal is hard, then that has to pretty much rule out the hose too - yes?

These 4 pot calipers can take some bleeding, hence my suggestion to open the nipple and squash each piston back fully and clamp them there (easy done) and then bleed that corner. With the hose clamped you shouldn't drain the whole leg. Pushing the pistons back will show you that they are freed off and they will push any manky old fluid that has been sitting there out of the system. If none of that gives you pressure then do look under the truck as a massive lake of DOT 4 will be a clue!

If the seals have gone on the pistons, I would expect that to be pretty visible. The fact that you have some braking would indicate that the split circuit seems to be working.

I'd get a good fettle on the suspect corner if I were you. Do not try to spin the pistons in the cylinders at all, they will bind and you'll end up in a mess. I would clamp three off and work the fourth. Then clamp that one and work another in rotation. I really can feel you frustration, but it's a pedal, a pot, some tube and some metal bits on the ends. There isn't much in there to have to deal with. I think that you have done a good elimination job so far. Keep going!

Chris

 

[nlbyrne]

Thanks for the response lads

I'm goin to have to break down both front and check the sliders properly and fill with rubber greese like I did to the back. Just haven't had the time to go at them properly. Busy time of the year. I might get to them next week
Will do that trick of pushing back the caliper while bleeding, I'll let you know how i get on.

 

[DaveN]

There's no sliders on the front. Fixed calipers with 4 pistons.

 

[Chris]

An annoying factor (in my experience) of brake problems on the 80 is that it seems to be opposite pistons that seize up. This gives even braking, whilst reduced of course. Eventually this mismatched force applied across the disc does seem to result in distortion or warping of the disc. If you think about it, when braking very heavily, the forces applied to the disc are considerable plus of course the heat build up. Never really analysed the fluid flow through the caliper, but maybe it's a cause of these lazy pistons.

In truth, over the years, I have probably been less impressed with Toyota brakes than any other vehicle that I have worked on. I have never really found them to be durable in terms of surviving British conditions. They seem to want constant attention to keep them running. And I have never really felt that they'd put me through the windscreen if I stamped on them. I have had a LOT of Toyotas since I learned to drive. I wouldn't have many other marques frankly, but if I could nail some nice big brakes on there I'd be very happy.

Chris