LSPV Rear brake woes, MOT failure game

On tuesday a local guy called me wanting an LSPV for a Hijet,

I agree'd to deliver it on Wednesday as I would be in Northwich anyway.

I told him to get his knackard one off before I got there as I would show him a thing or two about it.


He was told by the MOT station that it was seized thus why it had failed the MOT on lack of rear brake efficiency.

His LSPV valve was not seized, the plunger moved freely (they pull outwards not push inwards, just like every LSPV does I've come across  )

Anyway, told him that he can have the new one I've brought, but personally I would strip and clean his old one and refit that as there is nothing wrong with it.

So I spoke to him yesterday, where he had failed the MOT retest  

So today after going shooting I went back up to see him, being a helpful sort of fool.

On his van, the bracket that mounts the LSPV was bent upwards, so the lever never had enough motion to actually contact the rubber "button" on the LSPV.

So I pulled(bent) the bracket back down to where it should be, helped him bleed his brakes as he'd changed a rear slave cylinder too, and now his back brakes work perfect.


Rear brake failure is very common on Hijets, and is always blamed on the greatly misunderstood LSPV - now I'm not doing myself any favours here, but I'm going to have to write some form of information article about them and their common system failure points. Although I quite like selling things, what I really like to do is get people back on the road properly and not chasing dead ends.

So here we go - Understand the misunderstood LSPV

LSPV valves rarely seize as the piston is constantly moving due to brake pressure every time you press the pedal.

The system stops working because:-

The LSPV actuation arm spring goes weak.
The upper bracket bends upwards due to overloading and poor build quality.
The LSPV actuation arm stops moving properly due to corrosion on the pivot.
The seals can fail in them, but then it would be actually leaking.
And finally yes, they can seize up inside.

The LSPV is fully rebuild-able. The inner is held in via 2 circlips underneath the rubber dust cap.
After these are removed the inners pull out.
You will find a spring, a couple of seals, a long shaft and that's it pretty much.

The spring keeps the "button" all the way in - so it never can be pressed.
Brake fluid pressure pushes it back out - touch the lever against the button and press the brakes - you will feel it push back at you.


I had someone try to collect an LSPV, but claimed the one I was offering was knackard as they couldn't press the button inwards. I showed them another one in bits to show them how it worked but they did not understand or want to understand.


What is the purpose of this post?

I'm sure you'll find out sooner or later    

Another monologue rant by HighlyJetted.

You're gonna like my new toy I bought for the shed

Tell me you've bought a motorbike rolling road ????

nice article. I had problems with mine as the M.O.T recorded the rear brakes as having 49% efficiency and either 50 or 51% was the minimum. I ended up stripping and resealing mine but this would have been helpful to me at the time. Its good of you to take the time to write these articles for people HJ.

and im pretty sure I ordered a spare from the isle of wight as a backup!  

HighlyJetted wrote:Tell me you've bought a motorbike rolling road ????

Not yet, but I did buy an ultrasonic cleaning bath  

Nice, that had them at aldi a little while back.

Is it big enough to fit a cylinder head in?!

HighlyJetted wrote:Nice, that had them at aldi a little while back.

Is it big enough to fit a cylinder head in?!

Yes.























































Off my latest purchase  

Blimey thats a little rarity see plenty of cub 90's not so many 70's or 50's plus a few town mates but I don't think I have ever seen the Suzuki version I don't even know what it's called.

HJ I just wanted you to know that your posts are very much appreciated. The post above gave me some pointers to check before pulling my valve apart. As it happened I did have to strip my valve as it was seized solid and it really took some effort to sort it but it moves great now. The only question I would have is that because the manual gives you a setup procedure that involves hydraulic pressure measurement, is there an easy way to set up the valve?

Yeah fuck all that.

Just adjust it to the max on the axle.

Ok cheers

Cheers HighlyJetted for the pictures and info.

I am digging this up because I am trying to understand how it works and want to get th info all in one thread. So I have been bleeding my rear brakes and and made some conclusions. But I dont know if my one is fully ok so can someone verify this please?

There are two break lines (139, 210) going from tandem master brake cylinder to load sensing propotioning valve.
The idle position would be: Piston pulled in by the spring inside the lspv so that both break lines are open.
With breaks applied the piston gets pushed out.
If there is no load in the back the piston can move out and closes the second break line 139. So only the 210 will be allowing fluid to the rear brake cylinders then.
If there is enough load on the rear axle the indicator leaver will prevent the piston from coming out and both break lines can deliver pressure to the rear brake cylinders then. Is that right?

Hi All - sorry to drag this one out again? Can anyone tell me how much you'd expect the button at the end of the plunger, at the bottom of the LSPV valve on a 1994 pickup, to move when you depress the brake pedal. I have movement on mine but only about 1mm?

Cheers

Hi Miniman. When you press the brake pedal or with the rubber seal removed you should be able to pull it down with a pair of Mole grips only 4-5 mm.

If yours only moves 1mm then you have a seizure problem by the sound of things. A strip down and clean up sounds like the order of the day.