Rear Brake Proportional Valve

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01 Nov 2012 06:08 #1 by dandjcr
dandjcr created the topic: Rear Brake Proportional Valve
Forum Home > OKA Maintenance > Rear Brake Proportional Valve

Alister McBride
Member
Posts: 97
Hi all,

My brake proportional valve has siezed (apparently pretty common), Paul Nott told me of a couple of alternatives being the falcon ute one with different sized ports and another one (i can't remember the brand/model etc, it was a while ago now) which was manually adjustable. Apparently we can't get a straight replacement anymore...

The other oprion is obviously to pull my one off and free it up, possibly requiring O-rings etc... I don't want to pull it apart without a solution ready as i need it running regularly.

Any thoughts/experience?

Cheers,
Alister
September 25, 2010 at 8:32 PM Flag Quote & Reply

John and Linda OKA 42
Member
Posts: 4
Hi Alister i had a similar problem withmy prop valve and i ended up removing it although not recomended it was causing one of the rear calipers to stick on .
This fault caused some very annoying episodes before i had realized that it was the prop valve .
Apparently a rebuild kit is available for the valve .

Regards John
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September 25, 2010 at 9:16 PM Flag Quote & Reply

Alister McBride
Member
Posts: 97
Thanks John.
Yes, i can just remove it but i've changed my vehicle from a bus body to soon-to-be dual cab and it's light on the back end, when i brake hard it locks the rear wheels and steps out sideways (even worse with a 4T trailer behind you too!!). I'd prefer to have it working if possible...
Can anybody help with the actual PBR part number? All i can find is the OKA part number in my manuals...
Cheers,
Alister
September 28, 2010 at 3:46 PM Flag Quote & Reply

joseph baz
Member
Posts: 331
Alister,there is two proportional valves,one by the master cyl and the load sensing proportional attached to the chassis,i don't know the part number but it looks a lot like the Holden HZ 1 tonne ute,you maybe able to matched at the local brake shop???,
Cheers
Joe
September 28, 2010 at 9:48 PM Flag Quote & Reply

dingo
Member
Posts: 14
Hi Alister,
Got the same problem but worse cause of rear air suspension. My rear end doesn't sink when loaded so the standard valve just can't work. Plus its not up to the big load changes you get with a dual cab (mainly empty).
The factory proportioning valve is to easy to unseize and fix, just make sure you note all washer and seal positions and directions. I have even tried manually adjusting, helps but not good enough.
But here's the solution I was about to do before having to sell my truck (stopped working on it). Years ago we put a ford 9" disc rear end in an HQ Monaro and had big rear over braking problems. we found that the Hot rodders and race cars all use a cabin adjustable rear brake bias valve. Fitted it up and we were go, so go in fact that we were adjusting it for wet/dry roads, bloody impressive fine tuning that was real easy and very accurate once we got to know how many clicks of adjustment.
I was going to install one below the front seat where I could reach down with my left hand and adjust but not bump it. It's a simple plumbing job and I would strip the guts out of the factory valve and leave in place for roadworthies. You might have hassles getting a blue plate!!!!!
Below is where to buy, cheep and easy but would be perfect and very safe. I have had some serious close calls trying to pull up unloaded in the wet quickly. I have to focus on the back sliding while getting the fronts to do the hard stopping then brake off straighten up then brake hard again, bloody scary.

Brake Proportioning Valve

thanks,
Tim
September 30, 2010 at 10:37 AM Flag Quote & Reply

Alister McBride
Member
Posts: 97
Gday Tim,

That's something i hadn't thought about, i was thinking that down the track i would install airbag rear suspension and hadn't really thought about the effects on the prop valve!

I didn't think of racing equipment but that's a great idea! I might even contact Repco to see if there's a generic (non-wilwood) brand valve available...

OKA's have the brakelines running down the passenger side of the vehicle where instead we could run the brake lines down the drivers side and install the prop valve directly inline with the adjustment knob sticking through into the cab beside the drivers left leg... I have to replace my brake lines anyway because of the common 'rusting-from-sitting-on-top-of-the-sheet-metal-infront-of-the-radiator-problem' so i may aswell do all of that at once!

Thanks for the help everyone!

Cheers,
Alister
September 30, 2010 at 1:30 PM Flag Quote & Reply

Paul & Sue Crompton
Member
Posts: 44
Hi folks, just chasing a little bit of information on rear proportioning valves. Am I right in thinking that if you are fully loaded (bus camper) all the time then the proportioning valve should be fully open? I have always felt my rear brakes have not been working enough and had them serviced recently which certainly made a big difference to the height of the brake pedal. I am still not real happy with the rear brakes. I was thinking perhaps that because I have 2 extra leaves in each set of springs all the way around, that the proportioning valve may need adjusting. If I adjust a couple of links in the chain, this may compensate for the extra height of the leaf springs. Any comments would be appreciated.
--
Paul & Sue Crompton

October 4, 2010 at 5:22 PM Flag Quote & Reply

Alister McBride
Member
Posts: 97
Hi Paul/Sue,


I'd say at the recent service they bled the brake system and/or replaced the brake fluid which would both help get a firmer pedal.


As far as brake performance is concerned it all depends on your situation. The rear prop valve is calibrated to the standard spring and brake system. If you beef up the springs the ride height is affected and therefore the brake proportion to the rear is affected as the ride height to braking relationship is changed. Yes you can make adjustments by changing the length of the chain to the diff but if you then lighten the load you will probably start locking the rear wheels (in your case you may never lighten the load being a camper...).


In my humble opinion, it's better to have less braking than you need at the rear than more because you have more control in emergencies that way...


When you have a tray you can have a range of GVM's from about 3.5T to 5.5T so it's important to have the rear brake proportioning working properly...


Also, it's important to know, why do you think the rear brakes aren't working hard enough? Are the front wheels locking under hard braking?


Cheers,
Alister
October 4, 2010 at 7:44 PM Flag Quote & Reply

Aussie Bight Expeditions
Member
Posts: 109
Interesting note Alister on your comment that you are thinking of air bag suspension. My second OKA I bought did not have the air bags on it when I bought it, my original OKA did. Interesting thing here is that I actually run the suspension on the First OKA about 75 mm higher than the second and I have not changed any thing else and I have not had it step out yet except when one rear brake caliper stopped working.
With the second OKA I had problems with rear breaking and then I put the air bags on all 4 corners and run the suspension off a measurement for the front and a separate one for the rear. That keeps me the same height backwards and forwards and side to side and since I have done that in the past 4 years have had no problems with the braking mode at all. I can change numbers of passengers and the amount of weight up to well above legal and it still performs fine with out it being a problem.
I run the height appox 25 mm off the springs. That way the bags do the work and the axles just line up the diffs. Works well for me, gives a great ride and better traction in sand I have found out too.

That my pennies worth for tonight

Regards
ABE TONY
--
October 4, 2010 at 11:54 PM Flag Quote & Reply

Aussie Bight Expeditions
Member
Posts: 109
Should not do things early in the am.
The last part should read. "That way the bags do the work and the springs just line up the axle assembly".
My thought was this, if you run the air bags on all 4 corners as I do, then does this stop the affect of the rear stepping out under heavy breaking as I maintain the original stance of the manufacturing specs, although it is higher than originally built.
Question Dingo do you run front air bags? Because I can run 3T different in weight and I do not have the problem.
Maybe I am just lucky

Regards
ABE TONY
Esperance
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October 5, 2010 at 1:48 PM Flag Quote & Reply

Alister McBride
Member
Posts: 97
That sounds exactly what you should expect... When you jack the rear up with airbag suspension the prop valve closes and you get less braking than you need on the rear brakes as the brakes effectively 'think' you have no load even though you may have a large load and would probably benefit from much more braking on the rear...

Either way it's much better/safer than my situation where my prop valve is siezed open so with no load (probably the same height as yours) the rear locks up as the brake system still 'thinks' it has a heavy load...

I do expect to have airbags at some stage like what you've done or similar so i can either fix the prop valve and run the system the way you do or get a manually adjustable prop valve and have 100% braking effect at all times (with the draw back of having to adjust it depending on the load). Hmmmm, my partly scottish heritage is coming out here, fixing the prop valve and not doing airbags is A LOT cheaper!! lol

cheers
October 5, 2010 at 3:00 PM Flag Quote & Reply

Paul & Sue Crompton
Member
Posts: 44
Thanks for the input guys.

Alister - I did the service which included replacing the brake fluid and putting new rear pads on the back. The rear brakes did not work at all when I first purchased the vehicle. I found this out the hard way as one of my front brake pipes blew and I pumped like hell and the back brakes did not work at all. Lucky I was in first gear with no traffic and even the handbrake, even though it works well, didn't make any difference in slowing me down. The reason why the back brakes did not work at all is because the rear bleeder nipples were fully seized and the system was full of air. Anyway, that part of it seems to be sorted out.

As to your question, driving on the highway, the front wheels do not lock up and I assume that if I am in first gear on a gravel road and hit the brakes hard, all wheels should lock up but at the moment only the front ones lock up.
--
Paul & Sue Crompton

October 5, 2010 at 5:52 PM Flag Quote & Reply

Alister McBride
Member
Posts: 97
Gday Paul,
Sorry, when you said 'you had it serviced' i assumed you got it serviced by someone...
I'm no expert but it might be an idea to try releasing the prop valve lever from the diff just to try it out then you could post the results so we all know what full braking is with a heavy load... (ie locked rear brakes or not etc) Is the weight pretty much 50/50 front to rear?
I'd definitely be interested in the results! Also, obviously if there's no difference to your braking you know the valve is seized like mine, apparently a common problem (you could see the valve moving either way when you're under there).
cheers
October 5, 2010 at 10:17 PM Flag Quote & Reply

Paul & Sue Crompton
Member
Posts: 44
Hi Alister - the truck is reasonably balanced and I have already adjusted a couple of links on the chain which controls the rear proportioning valve. I have not had a chance to take the Oka out but I will be going away in the next few days and will see what difference it makes. If it doesn't make any difference, then I will have a closer look at the proportioning valve. Will let you know either way in about 2 weeks as I won't have access to a computer. Thanks for your help.
--
Paul & Sue Crompton

October 6, 2010 at 5:29 PM Flag Quote & Reply

Paul & Sue Crompton
Member
Posts: 44
Hi Alister - I tried the truck out in relation to the rear brakes. As mentioned, I adjusted the rear proportional valve (a couple of links more). It seemed to make a difference, so I may even go one more link. We went away in heavy rain and the rear brakes did not appear to be locking and the braking felt much better.

PS: If anybody else is reading this, this is not a suggestion or recommendation as my Oka body sits slightly higher due to the extra leaves all around. So if you want to play around with your brakes, I would strongly recommend taking it to a brake specialist. It is just that my brakes never seemed to perform well.
--
Paul & Sue Crompton

October 23, 2010 at 4:47 PM Flag Quote & Reply

OKA4WD.com
Administrator
Posts: 412
From Peter K (Oka 334):

Could any one help fitting a new brake portional valve and i need the the size of the plate that is fixed to the diff ,the longest side centre of hole to bend ,centre of hole on the short side to bend and if they are 90degrees thanks peter
December 12, 2010 at 10:31 AM Flag Quote & Reply

deedy
Member
Posts: 18
I removed mine just make sure you keep some weight in the rear otherwise you will lock up th rear brakes in the wet/gravel
February 27, 2011 at 10:40 PM

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