Need thoughts on braking issues

[Gecko17]

Hi all,

Over the last couple of months, I have had an issue with the braking ability on my patrol and am my wits end as to the cause. I have a 06 GU IV wagon with a 6.5l ICTD V8 with a chevy auto as well. I am currently running 33in tires. When I brake, the patrol pulls up eventually but nowhere near where it should. It slows up a lot quicker under 60km/h.

This is what has been done so far...
Replaced all brake lines with braided brake lines (for ABS)
Replaced all pads
Replaced master cylinder with OEM
Replaced all brake fluid and bled lines
I haven't replaced the rotors as they are in good condition
Calipers are working correctly

I took it in the the local Nissan dealer and they had a look at it and then said that, in order to analyse it, it would cost a lot due to the amount of time need to find the problem, so I should take it to a brake specialist. (to be fair to Nissan, they looked at it for a couple of days and didn't charge me for it)

Potential problems:
Air lock in the ABS unit
ABS unit not working
O-rings on calipers rolled in
Vacuum pump not working properly (it is not a constant vacuum, more like an intermittent vacuum)

My mechanic spoke to a brake specialist, who made the comment that patrols have craps brakes! Is this the case? I am pretty sure that my 98 GU stopped pretty damn well.

I have heard that I can upgrade to the brakes on the 4.8l but then also have to change rim size to 17in and really don't want to do this unless absolutely have to.

Is there something I am missing?

[the evil twin]

Hmmm... the 60 KPH comment is interesting.
The vacuum comment even more so.

The booster should hold steady vacuum so maybe the check valve is faulty
That can be a tad hard to sort out without test gear
You could find somewhere safe and see how many brake applications you have with the engine turned off

Long shot but a faulty ABS bypassing some pressure maybe?

[Gecko17]

Thanks ET. I was hoping that you would see this as wondered if it was a conversion thing, with the vac pump...

[threedogs]

Which pads did you fit??

[Gecko17]

Same as before 3D. Does it make that much of a difference?

[threedogs]

It did with BA made a huge difference,
DBA are a sponor here with a post on this forum 1st page maybe send them a PM
a softer pad may be better than say a black/green pad.
My mate with the extended GU has kevlar pads and swears by them bit smelly at first
but stops on a dime now.
Rotors are cheap enough these days to change every two years or so

[mudski]

From what i have found using tb48 calipers and discs you can still use 16inch rims. They are 10mm larger in diameter. Not much. But all lot in braking terms.
I dont know about the rears though, as the tb48s had the hand brake in the caliper, not on the tailshaft. Whether they still could be fitted, im not sure.

[threedogs]

@ GKO if your select the right components for your brake,
bleed it correctly using the correct fluid it should stop.
You would only be a bit heavier than a standard patrol with mods
wouldnt you say 200kg plus heavier

[billyj]

as long as the caliper pistons are moving freely and the slides are well lubed and moving freely then my first thought is keep bleeding, patrols are a complete bitch to get bled properly, you can have what feels like a nice hard pedal but still have air in the system, i think it took about 2-3 hours to get my gq fully bled after a caliper reco and new front lines.

[the evil twin]

Thanks ET. I was hoping that you would see this as wondered if it was a conversion thing, with the vac pump...

Dunno, maybe, maybe not... other posts about the things being a turd to bleed are 100% correct as well.

Maybe find a nice safe bit of road/car park and;
Pull the ABS fuse... (good tip for off roading as well, non ABS braking stops heaps quicker in the weeds using "brush and bury" technique).
Do some emergency braking runs and see how much and what lock up your getting and how much pedal effort.

That will start to help isolate it down to poor vacuum, unbalanced pressures, dodgy bias valve, cold pads etc

[Rumcajs]

Incorrectly set or dodgy load sensing valve can have an effect on braking performance.
Insufficient or intermittent vacuum will definitely have the effect on braking pressure application as pressure loss/assist will affect the outcome.
Incorrect master cylinder will affect braking pressures. I wonder if you have correct one!

Finally standard Y61 brakes except on 4.8L engined ones are chit! Generally softer pads will improve braking performance but wear out quicker.
4.8 L brake pads (Nissan OEM) will fit to ZD30/TD42 brake calipers and they're an improvement.

Regards

[Gecko17]

We bled the brakes, putting about 3 litres through and then Nissan did the same. Having said that, we could only bleed one port on the ABS unit so there is still a chance that there is an airlock in that.

The vacuum sounds more like a air pump than a steady vacuum and that could well be the culprit....

I will remove the ABS fuse and see what that does....


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[Gecko17]

I replaced the master cylinder with an OEM one.

What is the load sensing valve and where is it?


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[billyj]

with the poor braking, hows the pedal, firm? soft? high or low? will it lock wheels or at least trigger the abs if you nail the brakes suddenly? maybe remove the abs fuse and do a little test to see if it will actually lock the fronts if you slam on the brakes

[the evil twin]

I replaced the master cylinder with an OEM one.

What is the load sensing valve and where is it?


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Rear diff where the brake line tees off for the rear wheels... it senses the vehicle load and proportions the amount of braking pressure between front to rear axles

[BillsGU]

Went through the same thing some time ago. Ended up being the LPV. Most brake "specialists" don't even know it is there. When I eventually bled it the brakes were much better but because it had not been bled since the Patrol was built the LPV was stuffed. I repleced it and the brakes are now perfect.

[nipagu7]

if you have raised suspension the lsv may not be portioning enough of the braking effort to the rear wheels . some suspension mobs make a plate that they sell as apart of their kits that lowers the valve to the correct position depending on the height of the lift ( I think arb-ome ) .

[Rumcajs]

What is the load sensing valve and where is it?



From "Nissan Patrol Reference document" page 56

WHAT IS I T – A TECHNICAL EXPLANATION
A load sensing proportioning valve system for the hydraulic brake system of passenger cars and
the like for varying the amount of brake fluid pressure and thus the braking torque at the rear
brakes of a passenger car.



It is located on the RHS above rear axle.....
Regards