GQ Brakes pedal - take up point changing

[bogged]

Weird shit happening

GQ Auto Diesel 4 wheel discs.

When Im driving and go to hit the anchors, the pedal appears to have sunk and takes up later (or lower)... Not when you apply it that the pedal slowly sinks, but sometimes when you hit the brakes, the pedal feels liike the brakes are working in the normal place, then others it feels as though it takes up lower - quite low . Pumping them makes no difference.

I know the front pads will need replacing soon, they are at about 10% of meat left, but its the fact sometimes it goes down further to start working worries me. Dont want them to not work one time...

I have replaced the fluid and master cyl recently and it has been fine since then, just seemed to be different this weekend. I shit molten steel the first time it took up lower down...

All lines and calipers appear to have no leaks that I can see. At all times the brakes are working fine, they lockup the JT's no probs with loaded truck.

Although I think the rear calipers which were replaced 18mths ago with reco ones have siezed up

Anyone got ideas?

If it was an airleak, it wouldnt feel ok anytime of the day would it..

Thanks

[Tiny]

Weird shit happening

GQ Auto Diesel 4 wheel discs.

When Im driving and go to hit the anchors, the pedal appears to have sunk and takes up later (or lower)... Not when you apply it that the pedal slowly sinks, but sometimes when you hit the brakes, the pedal feels liike the brakes are working in the normal place, then others it feels as though it takes up lower - quite low . Pumping them makes no difference.

I know the front pads will need replacing soon, they are at about 10% of meat left, but its the fact sometimes it goes down further to start working worries me. Dont want them to not work one time...

I have replaced the fluid and master cyl recently and it has been fine since then, just seemed to be different this weekend. I shit molten steel the first time it took up lower down...

All lines and calipers appear to have no leaks that I can see. At all times the brakes are working fine, they lockup the JT's no probs with loaded truck.

Although I think the rear calipers which were replaced 18mths ago with reco ones have siezed up

Anyone got ideas?

If it was an airleak, it wouldnt feel ok anytime of the day would it..

Thanks

a leak in the line? I had a leak in the joiner block from the braided line to the steel line that goes to the calipers.....did exactly that, noticed when paint stripped off the pumpkin

[meiamaro]

Try clamping front and rear brake line's(rubber one to diff's).
if you pedal still feels wrong it will be in the master cylinder
or direct line's.
Or if ok (nice and hard) release each clamp one at a time and
check the pedal as you go.
When you undo a clamp and get a poor pedal that is the
direction of the problem.
then you can do the samething on the caliper's hose's,
if need be.

hope this helps.

cheers Ian.

[+dj_hansen+]

Could it be a vacumm booster problem?

[bru21]

disconnect the booster and try driving it slowely on a quiet road and see if it is still low. it should feel higher with no vaccum. chech all the hoses ar ein good nick with no cracks etc, check vac pump is working on the back of the alt

on mine i will be fitting a vac reservoir to make the clutch consistant. it will work for the brakes too. old cruisers had them or amke one outta stlle tube with endcaps ans a one way valve prob 500ml

cheer sbru

[bogged]

Could it be a vacumm booster problem?

Im thinking this....

Bru, how do you check the vacuum pump is actually workin? remove hose off booster, and see if it sticks to ya finger?


The clamping brake line thing wont work, as it doesnt always happen... itds sort of intermittant...

[InSanE]

check your wheelbearings for play sometimes when the wheel bearings are loose it causes play in the hub witch is connected to the rotor witch can move the calaper piston in and can give you a shit pedal every now and then.

You can check a brake booster by turning the car off and pumping the pedal untill it goes hard releasing all the vacuum from it then holding your foot firm on the brake start the car and after a seccond or two your brake pedal should drop telling you booster is operating properly if it doesnt drop you know you have a booster/vacuum fault.

[GutSquisher Media]

If your pads wear down to below a certain thickness there is not enough clamping pressure.

Depending on the load been carried at the time the performance of the brakes will be affected, the heavier the vehicle the more bias is directed to the rear.

[InSanE]

pad wear will not affect your brake pedal tho because it is hydraulic and as the pad wears it compensates for it by applying more fluid to take up slack as the pad wears it is not noticible to you when you drive.

[bru21]

the way described is good for checking the whole system. i have never had a vac pump always had pettys. i would assume putting the tip of your finger not completly across the end would be a good start. check for leaks with soapy water on all the fittings. warped discs or shot wheel bearings will do this too if my moto experiance is anything to go by. try and see if its rpm dependant or wheel speed dependant to seperate these two fields.

interestingly on another note you can buy an eletric vac pump for $300 so if ya motor dies on a hill you can walk the truck down under vac breaks.

also check the bush on the break pedal, they are fiddely to get out so be careful as they have a plastic barb fitting and an r clip from memory

[+dj_hansen+]

pad wear will not affect your brake pedal tho because it is hydraulic and as the pad wears it compensates for it by applying more fluid to take up slack as the pad wears it is not noticible to you when you drive.

The last person who replaced my front pads (before i bought the car) did not put the anti squeel plates back in, so i had zero brakes, but pads were only half worn....

Maybe check this aswell?

[meiamaro]

warped discs or shot wheel bearings
Correct! Land cruisers are know for this,as the
loose/warped rotor turns it knock's the pad/caliper piston
back a bit. So when you take a first stab at the brake's it feels
long and spongy,you then do it again thinking what the???
and the pads are back out and you get a good pedal.

Ian.

[GutSquisher Media]

Incorrect insane, you forget that the calipers can only extend so far, as the rotors wear down the pads contact pressure needed to stop the vehicule needs to increase. The problem is the calipers are close to the max extension when the pads are worn down as much as he said any wear in the rotors will cause soft brake feel.

As I also stated if the problem is mainly when the car is lighty loaded and when you load the car up the braking preformance changes its due to the rear brake bias doing its job.

[360 scout]

Incorrect insane, you forget that the calipers can only extend so far, as the rotors wear down the pads contact pressure needed to stop the vehicule needs to increase. The problem is the calipers are close to the max extension when the pads are worn down as much as he said any wear in the rotors will cause soft brake feel.

WTF!!!
does anyone else have trouble with this explaination?
the pistons in the calipers do the extending & they will exert the exact force on the rotors no matter where they are in their travel.
they have no travel limits. if you remove the pads they will actually fall out if you keep pumping the brake pedal!!
Any rotor wear will NOT cause soft brake feel!! worn rotors are not replaced because of lack of brakes ,they are replaced as they can get that thin they may crack warp & maybe disintergrate.

Anyway my feeling is if you're having to use varying pedal pressure to stop or slow down ,I'd be looking a either crook bypass valve in your booster or sticking valve on primary or secondary piston in the master cylinder. that would be my educated guess!

[GutSquisher Media]

Pull a GQ apart and you what I mean, yes the piston will fall out if you keep pumping with no pads in place but you will not have any pressure in the brake system as piston has moved past its sealing ring.

As I said once you get to this point you have no brakes the the piston has been pushed to its limit. Now if the rotor is warn the pads will not have the required pressure to clamp onto the rotor. For confermation on this talk to Guts we had this problem occure to us on last years Gembrook Campfire Weekend it was the reason I did not drive on the Sunday.

I had the same feel in the brakes as was first highlight in the post funny feel to the brakes worked some times not at all at others, when Gut's and I packed up and started for home the brakes where not to bad, stopped in Gembrook to change tyres for trip home and found the front pads where shot inside ones down to about 3mm outside down to around 8mm. Ask an mate who is an brake expert (sets up brakes on race and rally cars) what the go was, His explantion is what I posted.

[bogged]

I have seen this in the past, once the pads wear and the disc's wear beyond their limit you do lose braking power.

but thats not my issue

discs are 2yrs old, pads are rooted. Master cyl is weeks old.. brakes went south on weekend.


the thing that gets me is they only suck occasionally.. not every 3rd time, but when they suck, they suck for say the next 5 times u use em. then all of a sudden the pedal is back at where 'it should be'...

Pumping them makes no difference. weird shit...
will ook more on monday

[GutSquisher Media]

That’s some weird shit happening, it sounds almost like the pads are been pushed back away from the rotor and when you need to apply them they have to travel a greater distance than they should but pumping them should take up the gap (so rule this out).

Just a though came to me. I was on a trip when one of the group ran out of brakes, pedal went to floor then came back but didn't feel right keep doing this for the rest of trip. He also had the master cylinder done not long before the trip, turned out to be the rubber cup in the master cylinder inverted itself so under normal braking the car stopped but hit the brakes hard they failed to work right. Could be worth a look.

[bogged]

That’s some weird shit happening, it sounds almost like the pads are been pushed back away from the rotor and when you need to apply them they have to travel a greater distance than they should but pumping them should take up the gap (so rule this out)..

This is almost what it sounds like.. but the discs arent warped, although I do have the JTs on and the shake factor is happening. will put the BF"s back on tomorrow and see what happens.

Its weird that its so random.. Today I drove out, as I backed out the brakes were fucked .. drove up the road turned a few corners, and they were fine again.. they were good for 20 odd mins and then sucked again

Might be a job for ABS or better brakes.. dont wanna get this one wrong.

[tuf045]

That’s some weird shit happening, it sounds almost like the pads are been pushed back away from the rotor and when you need to apply them they have to travel a greater distance than they should but pumping them should take up the gap (so rule this out)..

This is almost what it sounds like.. but the discs arent warped, although I do have the JTs on and the shake factor is happening. will put the BF"s back on tomorrow and see what happens.

Its weird that its so random.. Today I drove out, as I backed out the brakes were ***** .. drove up the road turned a few corners, and they were fine again.. they were good for 20 odd mins and then sucked again

Might be a job for ABS or better brakes.. dont wanna get this one wrong.

my call would be lose wheel bearings or master cylinder bypassing.

[V8 Middy]

the way described is good for checking the whole system. i have never had a vac pump always had pettys. i would assume putting the tip of your finger not completly across the end would be a good start. check for leaks with soapy water on all the fittings. warped discs or shot wheel bearings will do this too if my moto experiance is anything to go by. try and see if its rpm dependant or wheel speed dependant to seperate these two fields.

interestingly on another note you can buy an eletric vac pump for $300 so if ya motor dies on a hill you can walk the truck down under vac breaks.

also check the bush on the break pedal, they are fiddely to get out so be careful as they have a plastic barb fitting and an r clip from memory

Where can you get a vac pump for $300? I was quotes $800!!!! It could be the answer to my woes in another thread!!