Need help with 80series brakes

[Diorama]

I rebuilt all my brakes last year. All wheel calipers new master cylinder new rotors all round. They were working really well until recently when I noticed that it was getting really hard to pull the cruiser up. When inspecting the rotors most of them are rusty (Keep in mind the vehicle does get used to launch a boat)with just a small amount of contact on a small area. They were fine when I rebuilt them. I have checked all the calipers and none are seized. The brake pedal does not hold pressure. I have to pump it but even when pumped up it only pulls the vehicle up slowly and it sinks to the floor when held down. I have done a full fluid flush and there is definatly no air in the system and there is no sign of any leaks. Its as if there is only a small amount of pressure getting to the calipers. I thought that maybe the master cylinder had failed so I put my old one back in which wasn't that bad when I renewed it but still no difference. Anyone got any ideas what it could be.

[nztimr33]

clamp off the the brake hoses and check the pedal each time you clamp one off to see if there is a difference (if there is and the pedal goes hard you know thats where the problem is) if not i'd be picking master cylinder or somewhere between brake hoses and m/cylinder , sometimes if it has a load sensing proportioning valve on the back they can get air trapped in them , some of them have bleed nipples on them if not you could crack the pipe nut off on the wheel side of the valve and bleed it out there , Hope this helps

[Diorama]

The proportioning valve has a bleed screw. I had already bleed it but still no good. The one thing I did do to check the master cylinder was disconnect the outlet pipes from it and plug the master cylinder outlets. Thought this might prove if the master cylinder seals were passing. The pedal was rock hard. Couldn't move it at all. Not sure whether it proves the master cylinder is good or not. Its like very little pressure is making it to the calipers. Everything is pointing to the master cylinder but I'm doubting that I have 2 stuffed master cylinders but maybe I do. The thing is do I go and get another one to try or is there something else I may be missing.

[Diorama]

Now I'm really stumped.
All my brakes were rebuilt last year and were working well. Things that were done. New master cylinder, All four calipers rebuilt with new pistons and seals. New rotors all around.
The brake pedal now sinks to the floor. It will pump up but feels as though there is air in the system. I have had the master cylinder tested by Apex and they tell me they had it on the test rig for 4 hours and it didn't loose any pressure. I peeled back the dust boots on the calipers last week and found fluid in them. I have now replaced the whole calipers with new ones. I have bleed and bleed the system but still no good. There is no longer any leaks in the calipers but the pedal still sinks to the floor and I can't lock the front wheels. The rear wheels will lock if I really stand on the pedal which tells me the proportioning valve is working as it should.
Also the fluid level is not going down so I'm convinced there is no leak. Anyone got any ideas where to start looking.

[Mattman]

Did you bench bleed the MC before installing it?

Is the bleed nipple on the calipers at the top?

Matt.

[bob_or_jim]

Would take a guess that your not getting the vacuum booster working. From memory there is a small canister on the pass side under the bonnet that stores the vacuum made from you vac pump. Check ya hoses running from the brake booster to the canister then if no joy check that your getting vacuum from your pump. (Not sure if its on the back of the alt or steering pump like the 1kz's) if its petrol then it will come off the intake manifold between the throttle body and head. Something to look at anyway.

[Diorama]

Did you bench bleed the MC before installing it?

Is the bleed nipple on the calipers at the top?

Matt.

Yea it was bench bleed and had been working fine in the truck since June last year and yes bleed nipple is at the top.

[Diorama]

Would take a guess that your not getting the vacuum booster working. From memory there is a small canister on the pass side under the bonnet that stores the vacuum made from you vac pump. Check ya hoses running from the brake booster to the canister then if no joy check that your getting vacuum from your pump. (Not sure if its on the back of the alt or steering pump like the 1kz's) if its petrol then it will come off the intake manifold between the throttle body and head. Something to look at anyway.

I was wondering about the booster but I don't think so. When the truck is off the pedal is hard. With foot on the brake pedal it sinks when I start the truck which indicates its pulling vacuum. Pumping the pedal it does come up hard and the brake warning light comes on which would be expected if the vacuum pump can't keep up (yes it is a diesel). If I let the truck idle the warning light goes out. I can then turn the truck off leave it for 10min and turn the ignition on and that warning light has still not come back on which to me indicates its holding vacuum. If I then depress the brake pedal before starting the truck the warning light comes on as one would expect when the vacuum is released.
Also correct me if I'm wrong but I thought the booster just assists the pushing of the pedal. The first time I push the brake pedal it goes almost to the floor and the back wheels just lock. If I pump the pedal just before planting my foot down hard on the brakes it comes up relatively hard but when I slam my foot down hard its still the back wheels that lock. (this is also being tested on my gravel drive so should lock up easily) Its as if the pressure is not building in the front brake line. If I then hold my foot down on the pedal it sinks to the floor. When the pedal is hard it feels as though there is air in the line and I'm trying to compress it.

[Mattman]

What's the condition of the front flexible lines?

[Diorama]

What's the condition of the front flexible lines?

Lines seem good
I can crimp off the lines as close to the calipers as possible and the pedal is good. Indicates that its not the lines bulging but something to do with the calipers but there is no difference between the old and new calipers. Looking at putting braided lines on anyway.

[derk]

I can crimp off the lines as close to the calipers as possible and the pedal is good. Indicates that its not the lines bulging but something to do with the calipers but there is no difference between the old and new calipers.

If that statement means your brake pedal comes right when you clamp off the hose(s) your problem is in the callipers you've just isolated

[Diorama]

I can crimp off the lines as close to the calipers as possible and the pedal is good. Indicates that its not the lines bulging but something to do with the calipers but there is no difference between the old and new calipers.

If that statement means your brake pedal comes right when you clamp off the hose(s) your problem is in the callipers you've just isolated

Totally agree and that's where I have been trying to locate a problem. One would think that brand new calipers would do the trick but they are no better than the old ones. Everything points to air in the calipers but I have put about 4L of juice through them and still no better.

[smurf182]

OK this may sound basic but do you have the right pads? Check there is not excessive clearance between the pad and rotor.

Also I believe the 80 went to bigger brakes in 1995, did you get the right callipers for your year?

[Diorama]

OK this may sound basic but do you have the right pads? Check there is not excessive clearance between the pad and rotor.

Also I believe the 80 went to bigger brakes in 1995, did you get the right callipers for your year?

Yep right pads
Yep right calipers.
The problem has been solved and yes it was basic but would never have thought of it.
Who wants to know?

[catalystracing]

oooo pick me, pick me

[smurf182]

Go on, don't leave us hanging..

[redz driver]

Go on, don't leave us hanging..

X2 do tell

[Diorama]

Over the last few weeks I have been researching different forums for the solution to my braking problem. I have found a lot with the same problem but no real solutions.
It appears that the 80 series cruiser is well known for its braking issues.
My brakes are now unreal and can lock up my wheels with 35" tyres on tarseal with ease.
The solution that solved my problem. The thin shims that go between the brake pads and the caliper pistons. Simply take them out and throw them away. Mine were slightly deformed and acting like a spring pushing the pistons into the caliper further than they should. This meant I had to push the pedal in further to activate the brakes. I found it hard to believe but when you think about the volume displaced in the master cylinder compared to the volume needed to move 8x42mm pistons. The pads wouldn't need to be moved out from the rotors by much to cause the brake pedal to sink to the floor. Pressing the pedal a couple of times would take that up but then sink again. Due to this extra distance the caliper pistons needed to move the front was not building pressure before the front brake sensing line to the proportioning valve was not sensing pressure and activating the back brakes which is what it is designed to do. I guess that's why loose wheel bearings also have such an effect on braking as well.
The braking force on the front was 260 and rear 360 before removing the shims. It is now 390 on the front and still 360 on the rear.
Hopefully this will help others with 80 series cruisers that have brake issues.

[redz driver]

Cheers for the reply. I increased the size of my master cylinder in my 70 series to remedy the same problem

[Smurf]

Interesting info.
I have had a similar but not as severe issue with my brakes in my LJ78. Still able to pass WOF but way more pedal travel than I have had in any other 4wd (or car for that matter).
I'm going to remove the shims this weekend and see if it makes a difference.

[Diorama]

Interesting info.
I have had a similar but not as severe issue with my brakes in my LJ78. Still able to pass WOF but way more pedal travel than I have had in any other 4wd (or car for that matter).
I'm going to remove the shims this weekend and see if it makes a difference.

Let us no what difference it makes

[Diorama]

Check there is not excessive clearance between the pad and rotor.

You were on the right track when you mentioned excessive clearance between pads and rotor

[crazyclark31]

Thanks for that. Dad has had similar issues in his 80 and just lives with it. Will take the shims out and see what happens.
Thanks for posting your solution

[Diorama]

Thanks for that. Dad has had similar issues in his 80 and just lives with it. Will take the shims out and see what happens.
Thanks for posting your solution

Not saying it will cure everyones braking problems as there are a lot of other components that can cause similar symptoms. I was convinced it was my master cylinder until I clamped off the front brake lines. After replacing just about everything that probably didn't need doing too such a simple solution was hard to believe.
Also my calipers had 2 shims behind each pad which would have made it worse. Not sure whether 2 is normal but that's what was there when I rebuilt the calipers so just put the same back again.

[wopass]

2 is normal. Cheap to replace as well.

[Diorama]

2 is normal. Cheap to replace as well.

What use are they and are they needed.

[wopass]

All vehicle manufactures use them, and they spend a lot of time getting them right, like the double layer in the cruiser and many other heavy vehicles as they are there for a vibration barrier between the piston and the pad and yes, in a road going bus you should have them. Off road bus not so important as they don't see the same mileage.

[Petemcc]

Hi all.

I'm running an 80series master in my hilux with larger surf front callipers and mr2 rears. I have the creepy pedal too. Just read this and took out my shims in the front and it helped a lot but still not perfect. Will try taking out the shims in the rear too.

Brakes were fine for a while and have been slowly getting worse. Not too sure I have solved it with taking out the shins but I certainly seems to have helped.

Has this come on quite suddenly for anyone else that has had the same problem? My brakes were never rock hard in the truck since doing the conversion and would sometimes seems to go soft randomly the get better then a few weeks ago after a long down hill (off road) felt like they were fading heaps and never got better. Weird

[mudlva]

Something to consider is the true running of the discs.
If they have a slight amount of wobble then that movemdnt will also push the pistons in. Meaning that more peddle travel will be required to achieve braking

[Petemcc]

I was wrong.... Removing shims didn't help.

Gave it a better bleed which did help a bit. Used a 10m hose from the calliper back to the master and pumped for about 10min per calliper got a few bubbles out but still not getting full force....