Brakes Problem

[10G]

Just replaced the master cylinder after 2 mechanics & myself tested the pedal and found that if we keep our foot on the pedal, it will eventually go to the floor.

Well, with a new master cylinder fitted, I have exactly the same problem. Push hard on the brake pedal and leave your foot on it, your foot eventually goes to the floor.

I've got new extended rubber brake lines as I have a 3" lift.

There's no loss of brake fluid.

Is this a Patrol 'thing'? I wouldn't have thought so.

Thanks for any help.

[threedogs]

Try teflon braided lines they cant expand like rubber will

[10G]

Yeah, I'm thinking that TD.

[Turtle_au]

How old is brake fluid? Is engine running (vacuum for booster)? Drum or disc brakes? Rear proportioning valve (load sense)?

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[10G]

Fluid is new as all hoses were replaced in the last 6 months. discs all round. Doesn't have rear prop valve.

[BillsGU]

Bleed / test the LPV. Every mechanic (even brake specialists) miss that.

[dom14]

Just replaced the master cylinder after 2 mechanics & myself tested the pedal and found that if we keep our foot on the pedal, it will eventually go to the floor.

Well, with a new master cylinder fitted, I have exactly the same problem. Push hard on the brake pedal and leave your foot on it, your foot eventually goes to the floor.

I've got new extended rubber brake lines as I have a 3" lift.

There's no loss of brake fluid.

Is this a Patrol 'thing'? I wouldn't have thought so.

Thanks for any help.

You can sometime end up damaging the master pump by manual depressing of the brake pedal to bleed the system(pressing it all the way to the bottom), but that usually happens with a used master pump, where the seals are already weaker.

How did you bleed the master pump, etc?

[10G]

Bleed / test the LPV. Every mechanic (even brake specialists) miss that.

I don't know if the wagons have LPVs?


You can sometime end up damaging the master pump by manual depressing of the brake pedal to bleed the system(pressing it all the way to the bottom), but that usually happens with a used master pump, where the seals are already weaker.

How did you bleed the master pump, etc?

I let the mechanic do it.

[mudski]

Its a Patrol thing. I have changed to braided line, new cylinders and rebuilt calipers and it still does it. I wouldn't be concerned about it.

[10G]

Its a Patrol thing. I have changed to braided line, new cylinders and rebuilt calipers and it still does it. I wouldn't be concerned about it.

Bloody hell, that's not too brilliant.

The other week I was travelling home, a guy towing a Dunny door on a trailer got into trouble coming down hill (this is 100kmh both ways, country road), I was going up hill. He fishtailed until the trailer began to steer the car, he crossed both sides of the road and a bit more, I planted my foot on the brakes and the damn pedal just kept going to the floor and I was getting closer and closer to this guy.

Anyway, I'm still here.

[garett]

i've never had that problem. but i'm dealing with 2 inch lift most of the time. it ain't right. what size tyres are you running?. will it happen from cold stationary ? the fluid level stays the same... which rating fluid.
don't think it would be air unless there is lots of air. my wag has a load valve for the rear. (it's a gq) by all means try bleeding it. (i upgraded the rear from drums to disc didn't have any issues bleeding it)(but then again i did the slave on my clutch and never had issues bleeding it)

[mudski]

Bloody hell, that's not too brilliant.

The other week I was travelling home, a guy towing a Dunny door on a trailer got into trouble coming down hill (this is 100kmh both ways, country road), I was going up hill. He fishtailed until the trailer began to steer the car, he crossed both sides of the road and a bit more, I planted my foot on the brakes and the damn pedal just kept going to the floor and I was getting closer and closer to this guy.

Anyway, I'm still here.

Jesus! Well maybe mines not as bad as yours as my Patrol stops really well, in the dry. But if I am sitting at the lights and push hard on the pedal it does slowly sink in. I can't say I have experienced it whilst on the move. Rubber brake lines are known to expand when old, yours should be ok still. But having said that, braided lines are worth every penny in my opinion. Im not sure if a vacuum leak would exasperate the issue or not.

[10G]

Im not sure if a vacuum leak would exasperate the issue or not.

Funny you should mention that. When bigguwesty was helping me with the Dawse install, he wondered if I may have a vacuum leak at one stage.

How do you look for a vacuum leak?

[BigRAWesty]

A vacuum leak makes the pedals feel heavy, it won't make it bypass.
Id be maybe looking at the abs unit.
Pretty sure they have a bleed off so the can take full control of each wheel / axle.
But they can only supply the pressure recived by the master..

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[JME_GU]

Bleed / test the LPV. Every mechanic (even brake specialists) miss that.

What's an LPV?

[Touses]

What's an LPV?

Load Proportioning Valve. It regulates the amount of "braking" in the rear of the vehicle, depending on load.

[BigRAWesty]

Yes wagons have the LPV unless you have a later model with all 4 wheels seperate threw abs system.

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[Turtle_au]

Load Proportioning Valve. It regulates the amount of "braking" in the rear of the vehicle, depending on load.
It has a lever arm that changes the rear brake pressure depending on the height of the rear suspension. That should be adjusted when a suspension lift is done, otherwise it will always think there is no weight on the rear and your rear brakes will be doing nothing.

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[10G]

Yes wagons have the LPV unless you have a later model with all 4 wheels seperate threw abs system.

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When I replaced my brake hoses post lift, I had to get 4 due to ABS. What's your brake pedal like Kallen??

[BigRAWesty]

When I replaced my brake hoses post lift, I had to get 4 due to ABS. What's your brake pedal like Kallen??
Mine is good. Have no faults with it.
My rear axle is off one line still threw a LPV, only front axle is split.

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[Rayala]

It is a Patrol thing. Because the booster on them is so big and effective, it gives the symptoms of a bypassing master cylinder.

[BillsGU]

I had the same symtoms as you have and had it to many mechanics (and brake specialists) to fix with no improvement. I heard about the LPV problem and bled it myself. A whole lot of brown muck came out of it. The brakes did improve a bit so I took the valve off the Patrol and when I had a close look at it I noticed it was partially stuck. I went to a wrecker and picked up one off a recent Patrol, fitted it and the brakes are now good as new.

[10G]

I had the same symtoms as you have and had it to many mechanics (and brake specialists) to fix with no improvement. I heard about the LPV problem and bled it myself. A whole lot of brown muck came out of it. The brakes did improve a bit so I took the valve off the Patrol and when I had a close look at it I noticed it was partially stuck. I went to a wrecker and picked up one off a recent Patrol, fitted it and the brakes are now good as new.

What year is your GU Bill??

[Throbbinhood]

Small hijack, but is there a '2nd stage' to the pedal? Ie, when I depress the pedal far enough under extreme heavy braking, does the pedal get to a point and then hit another rod or something to increase braking pressure? Or is it all in my head.

[dom14]

Small hijack, but is there a '2nd stage' to the pedal? Ie, when I depress the pedal far enough under extreme heavy braking, does the pedal get to a point and then hit another rod or something to increase braking pressure? Or is it all in my head.

There's only one rod on the master pump. May be you're feeling the LPV kicking in??!!

[Throbbinhood]

There's only one rod on the master pump. May be you're feeling the LPV kicking in??!!

Quite possibly. All I know is I can feel some sort of feedback in the pedal and then the thing just stops haha!

Hey mudski I think it was you, you were mentioning the pedal slowly going down, how do you find it on long steep downhills, say out in the high country? Ever run out of vacuum and subsequently out of brakes?

[Turtle_au]

LPV will give the feeling of 2 stages under heavy braking.
Initial braking causes weight transfer to front, LPV senses this and reduces pressure and fluid to rear brakes.
As you slow down more weight transfers back to the rear and the LPV will then start increasing the pressure and fluid to rear brakes.

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[BillsGU]

What year is your GU Bill??

It is a 2000 GUII.

[Col.T]

G'day 10G man.
Seems to me, a brake system is fairly simple.
Bang your foot down,,,master cylinder shoves pressure down the tube,,,,,,
slave cylinder slams pressure into the pads. All 4 wheels.
You've got a few points at which there could be a weakness/leak/failure.
4 wheel acting points. Got leakage???
The balancing point at the ars*nd of the system?? I've never seen leakage there but?.
I think (although I'm usually wrong), that if there's visibly no leak at any of those points, the only problem can only be the master cylinder with some bypass system involved.
Can't remember how those bypass/safetypass/whatthehellpass systems work but if , as said, there's no leak elsewhere I'd be looking for a new master cylinder.
Good luck,
Col.

[billyj]

keep bleeding, when i did new master, lines and reco calipers on my gq it must have taken about 3 litres of fluid before all the damn bubbles were out and i had a good solid pedal

[dom14]

keep bleeding, when i did new master, lines and reco calipers on my gq it must have taken about 3 litres of fluid before all the damn bubbles were out and i had a good solid pedal

Good to know that. Thanx mate.

[ugandasafari]

Brake and clutch servo share the same vacuum pump and accumulator. I have had days of brake head scratching only to find my clutch servo needed a kit. If you don't have a vacuum gauge you can stick your thumb over the end of each pipe in turn where it plugs onto the servo. If it doesn't hold vacuum check for pipe leaks back to the pump. Its usually the front clutch servo seal that goes. Always bleed your brake apportioning valve first. I'm under one of mine today with no rear brakes.

[dom14]

Brake and clutch servo share the same vacuum pump and accumulator. I have had days of brake head scratching only to find my clutch servo needed a kit. If you don't have a vacuum gauge you can stick your thumb over the end of each pipe in turn where it plugs onto the servo. If it doesn't hold vacuum check for pipe leaks back to the pump. Its usually the front clutch servo seal that goes. Always bleed your brake apportioning valve first. I'm under one of mine today with no rear brakes.

Welcome to the forum!

I've had no idea they both use the same booster.
It's apparently not the case with RB30, but I suspect TB42 & TD42 it is as above.

[Turtle_au]

Welcome to the forum!

I've had no idea they both use the same booster.
It's apparently not the case with RB30, but I suspect TB42 & TD42 it is as above.
Not same booster but a vacuum leak in one will effect the other.

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[garett]

wait you guys have a booster on the clutch ? i must be the lucky one without it.

but if the booster is leaking you should feel the pedal "push" back if you hold the brakes on then switch off the engine.

[dom14]

wait you guys have a booster on the clutch ? i must be the lucky one without it.

but if the booster is leaking you should feel the pedal "push" back if you hold the brakes on then switch off the engine.

Vacuum Assist is the booster, is it?!

Booster leak means a vacuum leak, isn't it?

[dom14]

Not same booster but a vacuum leak in one will effect the other.

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Yeah, I can understand. "Sharing the same booster" doesn't make any sense.

[garett]

Vacuum Assist is the booster, is it?!

Booster leak means a vacuum leak, isn't it?

yeah the booster uses vacuum to assist the work you do to push the pedal.
if the booster fails completely on a clutch makes the pedal like mine, booster fails on brake you have to push very hard on the pedal.
if i remember right the booster should hold a vacuum at rest. you push the pedal and you let air onto the diaphragm inside and the vacuum behind it sucks/pushes the diaphragm making it easier to apply pressure to the master. surely if you google it someone would have made a neat little animation

so yes it does mean a vacuum leak, but you could have other sources of leaks.

it should have a check valve as well so if the engine dies you still have a bit of vacuum left to stop.

[dom14]

yeah the booster uses vacuum to assist the work you do to push the pedal.
if the booster fails completely on a clutch makes the pedal like mine, booster fails on brake you have to push very hard on the pedal.
if i remember right the booster should hold a vacuum at rest. you push the pedal and you let air onto the diaphragm inside and the vacuum behind it sucks/pushes the diaphragm making it easier to apply pressure to the master. surely if you google it someone would have made a neat little animation

so yes it does mean a vacuum leak, but you could have other sources of leaks.

it should have a check valve as well so if the engine dies you still have a bit of vacuum left to stop.

I'm bit confused.
Does the clutch booster do the same thing as the brake booster?
Basically, making it easier to push the clutch pedal?
In other words, failing clutch booster means harder clutch pedal?

[garett]

yes dom they are the same just different sizes. ( not saying the are interchangeable just they work the same way)
but i would be surprised if a leaky clutch booster would affect the brake much. unless its a really big leak. never seen one i real life so speculating here.

[Turtle_au]

Maybe an ABS thing? Not sure on the intricacies of the unit but it does control pressure to wheels, maybe bypasses excess pressure?

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[garett]

Maybe an ABS thing? Not sure on the intricacies of the unit but it does control pressure to wheels, maybe bypasses excess pressure?

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yeah i agree it might even be a bit of air in the abs unit. or one of the valves/solenoids not closing properly

check the bleeding procedure for the abs (some cars are picky about this)

[dom14]

yes dom they are the same just different sizes. ( not saying the are interchangeable just they work the same way)
but i would be surprised if a leaky clutch booster would affect the brake much. unless its a really big leak. never seen one i real life so speculating here.

Cool, thanx mate. Mine's never had a clutch booster(afaics), so it's a totally new territory for me. :)

[billyj]

a leaky booster makes the pedal rock hard not soft, a soft sinking pedal is air or a leak no ifs buts or maybes

[BillsGU]

a leaky booster makes the pedal rock hard not soft, a soft sinking pedal is air or a leak no ifs buts or maybes

I agree. With mine the air was in the LPV and could not be bled out due to the piston not working correctly. The LPV is the highest point in the rear brake system and all air and moisture seems to accumulate there, especially if it is never bled - which seems to be the case in most Patrols.