Hard Pedal - Poor Brakes

[Damo]

Hi All

I've got a GQ patrol with terrible brakes. The pedal is very hard, but the braking performance is way below acceptable. It doesn't seem hydraulic as the pedal is nice and firm and doesnt sink to the floor if you keep your foot on it.

If I do press really hard, it will pull up, but the front left consistently locks. I do have to try hard to get that to happen.

I've tested the booster by pressing the pedal and than turning on the engine. I can feel the booster working and pulling the pedal down further. Aso if I turn it off and wait a minute I can feel the booster work and after a few pedal pumps the vacuum assist is gone.

So...any ideas what it could be. The discs and pads do need replacing, but I would of expected better brakes than that.

cheers
Damo

[dom14]

How do you know front left consistently locks?

I have trouble processing brake pedal being very hard and being nice and firm at the same time.

[PeeBee]

I am wondering about piston condition in the calipers - are these free to move? Maybe you have checked this, but you will need the calipers off and then slide the spools by hand - they could be nearing a seize condition, hence the excessive hydraulic force required to actually slow down. This would explain perhaps why one wheel locks before the others - it could simply not be as seized as the others.

[mudnut]

I recently had to clean the rear caliper slides and replace the pistons due to a rubber seal being ripped. Fairly simple to do. The search function is your friend. Here are some threads I found :

http://www.nissanpatrol.com.au/forums/showthread.php?38930-Brake-slides-are-stuck&highlight=brake+slides


http://www.nissanpatrol.com.au/forums/showthread.php?27855-GQ-Brake-caliper-seal-replacement&highlight=brake+caliper

[Turtle_au]

Diesel or petrol? Determines how the vacuum is generated.
Could also be glazed pads.

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[Damo]

How do you know front left consistently locks?

I have trouble processing brake pedal being very hard and being nice and firm at the same time.

Because when I brake hard, that wheel locks up.

The pedal is hard and wooden in use. I was making the point that is doesnt sink to the floor, so not leaking past seals in Master Cylinder.


I am wondering about piston condition in the calipers - are these free to move? Maybe you have checked this, but you will need the calipers off and then slide the spools by hand - they could be nearing a seize condition, hence the excessive hydraulic force required to actually slow down. This would explain perhaps why one wheel locks before the others - it could simply not be as seized as the others.

I do need to replace the disks and pads. I'll check that when I do it on the weekend. Just got the parts this week.


Diesel or petrol? Determines how the vacuum is generated.
Could also be glazed pads.



Petrol. I've just bought the GQ, and I'm thinking its been sat un-used for a while. I expect that glazed pads may be the case.

Thanks for all the comments. I have a feeling replacing the disks and pad will help a lot.

Greasing the caliper pins will probaly be a good thing too.

cheers
Damo

[dom14]

Because when I brake hard, that wheel locks up.

The pedal is hard and wooden in use. I was making the point that is doesnt sink to the floor, so not leaking past seals in Master Cylinder.


You obviously understand how the brake system works and the possible culprits.

I can suggest the slide pins from my experience. They do get jammed after losing the lubricant(copper or rubber grease)

I had fair bit trouble pulling out the jammed one(it was basically welded) and then spending a fair bit of time polishing the sliding pin hole and sliding pin using smooth sand paper and then smooth grinding paste.

[Damo]

You obviously understand how the brake system works and the possible culprits.

I can suggest the slide pins from my experience. They do get jammed after losing the lubricant(copper or rubber grease)

I had fair bit trouble pulling out the jammed one(it was basically welded) and then spending a fair bit of time polishing the sliding pin hole and sliding pin using smooth sand paper and then smooth grinding paste.
It was doing my head in because none of the expected problems were the problem. Also I'm used to toyotas where you can just pop the wheel off swap the disk and pop it back on. All 4 disks and pads in a couple of hours. The GQ looks to be a big pain in the @ss to get the whole hub off to swap disks.

[dom14]

It was doing my head in because none of the expected problems were the problem. Also I'm used to toyotas where you can just pop the wheel off swap the disk and pop it back on. All 4 disks and pads in a couple of hours. The GQ looks to be a big pain in the @ss to get the whole hub off to swap disks.

Front is bit of a PITA, rear is normal & can be done it 15 minutes.

[Damo]

So....I got the disks replaced on the front. Not so bad. But I couldn't find any pads in stock for the twin piston GQ calipers so will need to wait a couple of days for them to come in for a trial.

It looks like the problem was the disks have rusted pretty bad in the past and the pads and disks suffered for it. I've just bought the car and think its sat for quite a while before I bought it. The disk surface looks "wierd" so hoping that was the problem.

[Damo]

SOLVED

Certainly WAY better than it was. Not stopping like a sports car, but the new pads and disks did the trick. I think once they are bedded in properly it will stop great.

Luckily the pin and caliers were in great condition. Just a quick regrease and all working fine.

cheers
Damo