Outer Limits 4x4 Board

Hi all,

Ok so ive overhauled my brake system, braided lines all round, new rear slave cylinders and pads, seal kit in both front calipers and pads, bleed lines extensively - Brakes still have a really crap feel - With engine running I pump the brake and it goes hard - Hold foot on brake is soft and sinks to floor...

Now ive searched the threads and read a lot but there isn't much consenses on what solves this problem, from what I can gather its:

1) Air in the master cylinder
2) The master cylinder itself
3) Air still trapped somewhere in the lines calipers etc - Though I doubt this

Any help with this would be great as im sure after doing all this it shouldnt be this bad!!!

Thanks,

Paul

Sounds like your booster has a leak

That sounds like a leak or you master cylinder is gone.

If the rubber piston inside the master cylinder has a leak and when you hold your foot on it for a long time the oil passes the piston and thats why it feels like its leaking.

Short sharp pumps will get good presure becasue the oil dosent have time to pass the piston.

Hope it make sense casue its confussing me.

Cheers Nick

Just a thought is it diesel or a petrol ?

Its a diesel - Does that make a difference??

Also, in regard to the comment about the booster leaking - what is the exact problem and how does this cause that spongy feeling??

Thanks heaps,

Paul

pauluow wrote:Its a diesel - Does that make a difference??

Also, in regard to the comment about the booster leaking - what is the exact problem and how does this cause that spongy feeling??

Thanks heaps,

Paul

booster faults will not make it feel spongy and will make it stay further away from the floor (like pressing the brake without the motor running)

cheers bru

as diesel engines don't have a manifold vacuum they normally run a vac pump off the back of the alternator to run the brake booster so like i said just a thought it may be worth checking the vac pump as this could the problem.

I'm just hoping someone will have the magical fix for GQ's shite brakes. Some poor blokes Camry has a GQ imprint in the back of it because of mine not pulling up. I'm not spending a cent until someone can point in the right direction. I always use "standard" pads, which will give a spongy pedal, but I'd rather change pads than rotors. The 4.8 GU's do have the biggest brakes, maybe I should get one of them instead?

gqtrol wrote:as diesel engines don't have a manifold vacuum they normally run a vac pump off the back of the alternator to run the brake booster so like i said just a thought it may be worth checking the vac pump as this could the problem.

If not the booster, a leak somewhere. Mine was leaking in the clutch booster or something like that???? and was doing exactly as you describe until I ended up losing all breaks. A mate put a bolt in the end of the vacuum line leading to it and fixed it. He told me to get the culprit overhauled (pictured) but I haven't got around to it yet.

my brakes were really spongey and shite i ended up putting in new pads and in the process i removed the anti squeel shims as they were bent an thin an out of shape i also removed all the anti squeel silicone that the last person had put on to excess and now my brakes pull up very well and a nice firm feel to the pedal not spongey as it was before and going to the floor

my experiance anyway

make sure ur proportioning valve in the rear end is working

and if u can get a power bleed done ...

Any other thoughts on possible solutions for this spongy brake issue?

A relation has a GQ 4.2 diesel with after market turbo and is currently spending a bucket load of $$$ trying to fix the brakes. Basically it's almost lost all braking power from what he's said.

From memory so far it's had a new master cylinder, reconditioned booster, new rear cylinders, been bleed a gazillion times and the rear proportioning valve has been checked (or replaced?) The front pads/ rotors checked out OK and the rear (drums?) were machined IIRC?

I'm suggesting for the clutch to be checked for causing vacuum leaks as per an above post, but is there anything else that should be checked? A couple of different brake places have looked at it without fixing it and its been at a Nissan dealer for a long stint and still no solution.

air in master cylinder or leak in master cylinder or fluid side of booster, bleed the master cylinder and see how it goes.
if thats no help, master cylinders arnt too expensive and its probably due a replacement by now, and if that doesnt help, try the booster.
when all else fails, update your insurance policy and torch it

love ke70 wrote:when all else fails, update your insurance policy and torch it

well that's all that's left out of your list that hasn't been done!

The master cylinder is new and the booster reco'ed with no difference. I'm assuming it's been bled correctly given that professionals have done all the work?

Seems like a bit of a common problem given a number of posts complaining about the same issue when I searched?

Do all GQ's have vacuum assistance on the clutch as mentioned a few posts back? I was chatting to the owner today and he seems to think it doesn't have a vacuum line running to the hydraulic clutch?

i,ve had the exact same problem for the last 6 monthes. i've had a new master cylinder fitted, new rubber lines to the calipers, booster tested , calipers rebuilt, new rotors & pads fitted and another proportioning valve.
i've had a mechanic mate do all the work and another mechanic look at it and although all this fixed it a bit we sent it into a clutch and brake place and they blocked off one of the lines from the prop. valve to the "t" piece at the front of the car and this improved the barakes about 70%.
it now holds pedal idling but as soon as i rev it, it goes to the floor. so they tested the vacuum pump on the back of the alt. and found it wasn't generating enough vacuum. now i have to chase up another alt. to see if this finally fixes it.
i can take some pics of the line the brake blokes blocked off tomorrow and post up if anyone is interested (apparently they had another one in a few weeks previously that did the same thing).

deano

Deano, thanks for the info.

Please post up a pic when you get a chance and I'll pass on the info to the Nissan dealer. It's my father inlaw's car and he can't really afford to go replacing parts in an experimental fashion to try and fix it (which is whats been happening.)

heres some pics of the line clutch and brake blocked off at thr prop. valve. hope it helps.

deano

Thanks for the pics.

I've pointed the dealer at this thread to hopefully give them some ideas on further fault finding.

hi mate,

just had a gq in the shop with the same problem and we replaced the master cylinder and brake booster.
this fixed only 50% of the problem and fouind the rear calipers slides were sticking and one was siezed. replaced the caliper slides and bingo problem fixed.
hope that helps
Baxy

Hi Baxy, I was under the impression that the relation's GQ has drum brakes at the rear? If you had the "calliper slides" sticking then that would indicate you've got rear discs?

Was there an update or something (or am I just confused?)

when my alternator died so did the brakes, I went to bursons to get a new one (hitachi) and there is 3 alternators you can get

1 - 70amp standard volume pump
2 - 70amp High Volume pump
3 - 90amp High Volume pump

I got a 90amp and will be fitting it this week I will post up if it improved the brakes etc...

Latest I've heard is they machined the front rotors and replaced the pads with no change. I don't see the logic in them doing that given the severity of the problem?

gq 4.2, when you said they died, did they go to the floor or just really bloody hard work for not much work done? as in the booster wasnt doing diddly squat?

cheers, andrew

just a thought i recently replaced my front pads in my D40 navara and i also had a sinking pedal i was hororfied. But i went and bedded them in PROPERLY and the pedal came back to its former hard self. oh i also had the same problem with my gq and a different brand of pads when i put my GU front diff in. So maybe try bedding them in properly as per manufacturers specs and all may be good if you havent already done this

just my 2 cents

Brad

I'm in the same boat with this problem.
I've just picked up my '93 TD42 LWB from the local brake shop, where I asked the guys to have a look at the brake system in general, but have a close look at the booster and the vacuum pump, as I've never thoroughly checked them.

The guys told me that calipers, pads, brake lines, master cylinder and prop valve are fine and that there is no air in the system whatsoever (which is what I thought when I checked it myself).
Also, the vacuum pump is up to spec and the booster has no leaks.
The guys rang two other brake specialists for feedback and were told that the booster is under dimensioned for this vehicle (this makes sense to me).

They recommended either of these two solutions:

- get the master cylinder resleeved so that it can create more pressure in the hydraulic system.
- get a better booster. Apparently there are some GQ models equipped with twin diaphragm boosters which perform much better (I suspect, it's the EFI models with the four piston calipers). I also heard that the GUs don't have this problem and that the GU boosters bolt straight in the GQs.

My question is, have people done any of this and what was their success?

Cheers
Joachim

be careful swapping boosters, i gave a petrol one to a mate who had a diesel and the brakes locked up. i checked my diesel one against a petrol one i had laying around and although they look the same they have different part numbers.
deano

What about boosters out of a GU TD42?

Cheers
Joachim

An update on the GQ I mentioned. It's being picked up from the Nissan dealer tomorrow with lots of new/ reconditioned brake components, but the pedal still slowly sinks to the floor.....

They even rebuilt the front callipers from what I heard today.

i picked up another vacuum pump for mine during the week. will put it on over the weekend and give you an update.
deano

Could be getting air down the thread of the bleeder screw. I have had 2 cylinders do this on the rear of my MQ, one old and one new. Put a bit of clear hose on the screw and leave it open for about 30 seconds and see if there is any air coming through after giving it a few pumps.
Johno.