HJ75 Load Sensing Proportioning Valve

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HJ75 Load Sensing Proportioning Valve

Unread post by Cervantes » April 1st, 2012, 10:48 am

Hi there,

I'm new to the forum and thought that I'd launch straight in with a technical question.

I've just bought a 1989 HJ75 Ute with a view to turning it into a bit of a project.

Some of the work such as suspension lift has already been done.

It would appear that the previous owner when lifting the suspension has just cut the load sensing spring for the Load Sensing Proportioning Valve.

My question is can I just bypass this valve and have a constant set amount of pressure to my rear breaks regardless of load?

If so how would I best do this?

It sounds like a real work up having to re-calibrate the set up for the increased suspension travel etc.



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Re: HJ75 Load Sensing Proportioning Valve

Unread post by mydmax » April 1st, 2012, 5:53 pm

G'day Cervantes
If you can find out the position and spring length of an originl system you should be able to recreate the same valve operation by just having and extender plate or rod.
This will make the valve run as close to OE as possible. The idea of the valve is to reduce the braking pressure to the rer brakes as the load shift forward with heavy braking, this has the benefit of trying not to lock the rear wheels and therefore preventing the uncontrollable 360 you may experience, particularly beneficial in high traffic situations on smooth bitumen on a wet day or night.

Seeing a very high percentage of braking effort is done by the front wheels of a vehicle around 80%, the rears are made to add as much braking effort as they can within the grip they have.

With the valve just left as it is, you may find the situation with full braking all the time to the rear wheels your skills at driving and fancy steering while using the rear vision mirrors, may have to be upgraded.


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Re: HJ75 Load Sensing Proportioning Valve

Unread post by wombats80 » May 12th, 2017, 9:39 pm

Old thread but i chanced upon it when researching for what feels like the hundredth time over my crappy brakes in my '91 80ser. This thread appeared after a google search today but what i was looking for specifically, was not what a lspv does but what happens internally for it to achieve what everybody says it does. This new search today come about from having my 80 in at Pedders for a shock absorber test & their gadjet machine performed a brake test as well. Old mate tells me my rear brakes are woeful & he'd not like to be out on the road with me. I cant quite remember the scale recorded but i had rear brake score just a tad over 1000 when it should've been in excess of 3500.
He suggested i look at my LSPV but i know i put a new one in about 4yrs ago and spec'd up a new boot kit as the new valve doesn't come with new seals. In the tropics here I flush my brake fluid annually and always include the LSPV in the flush procedure. So i decided to head straight for it but drop the rod away and take the boot off then dummy fit the rod to get a scope on contact between it and the LSPV piston. Guess what. To the contrary of what i expected to see, it was seized in the fully laden position and moving the rod up n down did nothing but float the rod inside the guide.
I always had the wrong impression that a lspv merely restricted brake force under panic braking & thought of it as an orifice much like a TX valve which orifice size is regulated by a needle valve meaning after a few seconds pressure equalises. Oh so wrong.
Not sure if this link paste works but it explained what i was asking for with how a lspv works;
http://www.winbrake.com/index.php/downl ... ing-valves
With this i looked a bit further and found a well known forum, discussing how people are getting rid of their lspv's AND failing abs systems. Touches on a significant area of concern doing these things but after suffering sub-optimal braking for a very long time, i decided to go the challenge. It was dead easy to bypass the lspv. Took it back to old mate and recorded 3500 on one side and 4000+ on the other. I know my shoe linings are nearly out which would mean glazed drums. Yep, got drums on the 91, they disappeared for rotors from '92 on.
I let the rego lapse a couple weeks ago, got other mods on the go but am keen to get a proper road feel for this mod in later weeks. Pedal feel from the short distance i moved the car didn't seem any better but crikey, brake response from a decent push is the 200% improvement recorded on their machine. Thumbs up at this early stage.

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