The old GQ spongy brake feeling problem - HELP!!!!

[murcod]

Thanks for the tips guys, I'll be keeping an eye on all solutions.

I've got a whole list of things to try and I thought I'd be out trying to fix the brakes this weekend, but the decision has been made to leave it with Nissan until it is fixed. Probably the smartest decision given that it shouldn't be driven in it's current state.

Supposedly Nissan Australia don't even know what to do next, so it should be interesting! My father inlaw owns it and said the dealer sounded like they just wanted it out the door....

[GQ4.2]

I replaced my alternator as it was stuffed but it hasn't fixed up the brakes, before it happend the brakes were execlent so im suspecting the booster is faulty and I will be getting it looked at this week hopefully..

if anyone is after a upgraded alternator with a high volume pump on it for a TD42 (not sure if the same for the petrol series)

Bursons Part Number

65-3028 - Jaylec Alternator 90amp wih High Volume pump

Their price was $460

Just a few stats on this alternator

6000rpm = 108 amps
5000rpm = 107 amps
3500rpm = 101 amps
2400rpm = 88 amps
2000rpm = 74 amps
1600rpm = 51 amps

[love ke70]

is that engine RPM or alternator rpm?

[murcod]

I'd be guessing alternator revs given it's a diesel.

[GQ4.2]

I'd be guessing alternator revs given it's a diesel.

yep your right its alternator rpm

[ANDREWGQ 351]

To enter the discussion, i am confused, I assume that there is no fluid being used. It has been said a few times that alot of bits have been replaced with no result. However if the pedal goes to the floor then surely the booster is over boosting rather than not working at all.
my bet is the master is leaking air or fluid internally.
Check that there is correct clearance from the boster pushrod to the master piston cup and that the piston is not getting stuck in the booster rod or vise versa. Air in the lines will only come out at the wheels if the master is able to push it out. if there is air at the master because it was not bleed when it was fitted then it can be very hard to get out at the wheels, sometimes you will get none at the wheels at all.
Hope this might be of some help

[love ke70]

andrew gq, you would assume the brake shop or dealer centre bleed the master when they installed it, i learnt how important it is when i changed my own on a different car, you never know, they may not have, and yes, those symptoms do fit air in the master

[macneil]

i had this same problem with mine i rebled the barkes and it was fine have you tried to do that yourself? its simple to do.. took me all of 10 mins.. make sure all the bleed valves are done up tight other wise it can get air in it..

[danaz]

I had the same problem with the brake pedal slowly sinking, the piston in the master cylinder was damaged and letting oil past. You said you replaced yours but it may be worth checking again as it seems you've gone through everything else.

[murcod]

Latest news is the dealer has sent it off to the brake specialist again. Will be interesting to see what happens this time.

[MuddyTroll]

Just thought I would lend some experience.
Had the same problem with my Wagon. Turned out 2 B Air in the master cylinder and throughout the brake lines. Due to the twisting and turning of the brake lines I found it nearly impossable to get all the air out. Got a few fancy one way valves from a retic shop of all places and rigged them up to the port that the bleeding nipples screew into on the slave cylinders. Had it then draining into icecream containers. Pump the pedal like f#@k for a few seconds and recycle the drained fluid from the icecream containers. Repeat this a couple of times and hey presto!! assuming you can get the nipples back into the slave cylinders without allowing air back in, all is fixed. My brakes have never been better.

Also worth noting is if the master or slave cyinders were bought second hand or the vehicle is a bit long in the tooth, the cylinder wall can get worn much like an engine cylinder. When the rubber seal on the push rod gives up and is replaced, the seal no longer matches the cylinder wall and so the cylinder must be honed, just like an engine cylinder. If the cylinder is brand new, it should be OK.
I have an old Mazda ute that had this exact problem where the lines were fine and no leaks were found but the fluid passed around the seal and so, slowly released the clutch for me. Scary when it happens at a set of traffic lights. Honed Master and slave cylinders and OH YES!! Success!
Hope it helps
Dave

[MuddyTroll]

Yeah sorry
Of course I am talking about the clutch system and you have an issue with the brakes.
However I do believe the principle is still the same and the solution I found would still work on the brake system.
Again, sorry for the confusion

Dave

[Look'n 4 Mud]

Hi guys, just an add on to all this, no advice on the pedal though sorry.
I have hated the brakes on the GQ for ever. i come from a fast bike background and adopted some of the brake upgrades common to the sport.

Early on i replaced all six brake lines with snake racing braided lines. They work great.

Recently i have replaced my pads and rotors. I chased down on ebay a set of slotted rotors for the front!! Fantastic!!!

Slowing down a 3 ton GQ turning 35's hard and fast. Great upgrade.

I got the slotted rotors off ebay for only about $50 over Hobzee wanted for standard ones.

Dont hesitate. Go Hard, Brake hard. cheers guys

[murcod]

I heard yesterday that the brakes are "80% better". Something about adjusting the piston rod (?) length between the booster and master cylinder? ( I probably got that all wrong..... )

The brake pedal had been sitting too high (after some other brake work) and that had something to do with it. It's still at the dealer and I'll wait until the owner lets me know exactly how much better it is before saying it's fixed.

[murcod]

The final update for me:

The Patrol was picked up a couple of days ago. It turns out the adjustment I mentioned above was the problem the whole time so somebody early on in the repair process didn't refit the master cylinder/ power booster properly.

It was taken to the RAA and had a braking test completed, the only thing they picked up was a slight issue with front to rear balance which Nissan have adjusted.

Total bill? $3200, but it did include a full service and recored radiator.