LSPV confusion (1 Viewer)

[jblueridge]

While mounting a new LSPV and spring (arm) to the old painted bracket, I discovered that I don't understand the FSM.
Can anyone help me understand? see pics.

On page BR-59, Step 3 says to install spring to valve using a clip.

I used a clip on the rubber boot but also ran the bolt through the spring and mounting bracket. see below

Later, the manual says Confirm the valve piston moves down smoothly. How do I do that with the rubber boot in place?
Also, inside the LSPV is a spring that keeps the piston/pin up regardless of the position of the spring (arm). see 3 pics below.

I seems to me that the instructions don't match the operation of this LSPV setup.
Can anyone confirm?
Thanks.

 

[AcroSteve]

Tagging along, as I'll be bleeding and adjusting one soon...

Figure it's the same on 80s

 

[TreadingLight]

Why did you decide to replace vs remove? Asking as I just replaced my suspension, lifting the body a bit, and am assuming my very old lspv is out of adjustment and in need of attention.

It is probably original and may be worn out as well.

I'm on the fence about keeping it.

 

[RHINO]

i think you answered your Q about step 3, they are calling the "arm" a load sensing spring, not sure about the other part

 

[jblueridge]

Why did you decide to replace vs remove?

My brakes were behaving strangely so I am replacing most everything.
A new LSPV and spring were available and not too expensive.

i think you answered your Q about step 3, they are calling the "arm" a load sensing spring

Yes, the long arm is officially named the "spring".
It is some very unyielding steel, like piano wire.

Still hoping someone can clarify the FSM instructions.

 

[TreadingLight]

My brakes were behaving strangely so I am replacing most everything.
A new LSPV and spring were available and not too expensive.

I am in a similar boat but still deciding how to proceed. Good luck. Following the thread with interest.

 

[Felde]

I was into that just yesterday...

I used a clip on the rubber boot but also ran the bolt through the spring and mounting bracket

Thats correct. That round clip is what the manual refers to. (Well, to be picky: It doesn't say that is the only way the assembly is attached to the LSPV.

Later, the manual says Confirm the valve piston moves down smoothly. How do I do that with the rubber boot in place?

Not at all. The sequence of the manual is odd here. I removed the clip and pulled down the boot yesterday in order to check on the pin as a regular maintenance. A real PITA to do with the LSPV in place and lying under the car with no lift...

Also, inside the LSPV is a spring that keeps the piston/pin up regardless of the position of the spring (arm). see 3 pics below.

The pin is moved out (down) once any brakeforce is applied. The spring from the axle (loaded with the trucks rear weight) is acting against it, pushing it up (in). Only if the trucks rear comes up while braking more intense, the spring from the axle moves down a bit (giving some room and actually not applying any significant force to the pin any more), the force of the inner spring then overweights and pushes the pin out as far as the room the axle spring gave way allows. This actuates the distribution of brakeforce to the front; actually the pin moving out, not in (as one might think at first).
And this is how you check the pin movement with no brake power applied / on the workbench: Pull ! on the pin (overweighting the spring inside).

All correct on your end.
Probably you should look into a career at Toyota to write manuals. (But you are 30 years too late to improve thisone)
Cheers Ralf

 

[Felde]

And because I know what's coming next...

Mounting the LSPV to the frame and attaching the spring to the axle...
Goal is to mount LSPV and axle-spring (the long arm) in a way that the end of the axle-spring inside the rubber boot on the LSPV barely touches the pin.
First do the axle side. There are some default figures in the manual on how to dial in the adjusting screw. Do not put nuts and cotterpin yet.
Then do the LSPV to the frame. The bracket has long holes, so it can be moved up and down a bit. Move it cautiously and you can feel ! the spring touching the pin. Mount it accordingly.
Go back to the axle side, pull off the spring from the pivot and check. If the LSPV sits correctly, you won't have much deviation. If not good, you can fine tune with the adjusting screw.

Bleeding the LSPV
Put the axle spring on its pivot (still no nut and cotterpin yet) and bleed your brakes / rear brake normally.
Follow the instruction in the manual and bleed front first, then bleed the LSPV using the bleeding nipple on it. Then bleed the sections LSPV to rear axle ( rear brakes).
If you had the LSPV out, your long line from the front might be empty, and also your line from the LSPV to the opposite side is quite long. Be patient. Use a bleeding device (don't ruin your master cylinder by pumping it) and pull trough quite a cup of brake fluid on each nipple.

The LSPV has a 2nd line that runs back to the T on the front and feeds into the front brake circuit. When active, the LSPV sends brakeforce from the rear to the front trough this return line.
When stationary, the LSPV is blocking this line. It is then part of the front brakes pressure system and air in it causes poor braking in the front. This line is however not easily been bled. As the LSPV blocks it, there is no fluid flow in it. To bleed it, one must indeed undo and lower the LSPV spring arm! So, off the pivot it goes again.
The issue is this: You can't only use the bleeder nipple on the LSPV for bleeding the return line. With that bleeder nippel open, you actually have two parallel lines from the front sending fluid to the back. The fluid may take the main line only.
Nevertheless start with bleeding on the LSPV, with the spring arm down, unless running clear of bubbles. But usually that's not sufficient for the return line.
So, to eventually bleed the return line, I made the fluid go the intended direction and bled it from the front ! (wheel next to the T), with spring arm down and LSPV bleeder nipple closed. Again: The line is very long and probably empty. Be patient and pull trough a lot of fluid.
Also note that the air passes the T in front and may also get into the line to the other front wheel a bit. Once you lower the spring arm and free the return line, air might also get backwards into the section LSPV-rear axle a bit.
So: after bleeding the return line, you are due floor another full cycle of bleeding front - LSPV -rear.
The secret really is: Pull trough a lot of fluid!

Adjusting the LSPV
Check here (featuring additional bonus video)

What did you do on your 70 series today?

Those look great! They are so much comfier than the factory seats too, granted the drivers side one had seen better days

forum.ih8mud.com

It's a mission, but you can do it!
Good luck Ralf

 

[jblueridge]

After 2 months of almost no rain, we are supposed to get it all day tomorrow.
I'll spend some of that time reading Felde's authoritative treatise above and painting some small LSPV-related parts.
I skimmed it just now and it made me realize I have been thinking of the LSPV system as static, as if the truck was parked.
It makes more sense to think of jamming on the brakes and the truck pitching forward on it nose.
Also it seems likely that the FSM is not describing the LSPV on our trucks (or doing it very badly).
Here's the new LSPV and spring back on the truck.
I considered trashing the metal clip that holds the boot on and just using a small zip tie: huge hassle getting the clip and rubber into place.

 

[Felde]

Looks good
Yes, that clip is a pain. But it's very important that boot is sealed well.
The LSPV sits in a spot where it is exposed to all dirt, water and mudd. And the boot is like a cup. Would be terrible to have it filling up over time.
I wonder whether a Zip would be thight enough. The rubber boot and clamp actually sit in a groove. Would need a really tiny zip to fit in there.
And when cutting the zip later in that grovve to remove it , you might damage the rubber boot.
Cheers Ralf

 

[jblueridge]

I got the damned clip on while the stuff was clamp to a table. I bet you went insane trying to do that while it was on your truck.
I took the old LSPV apart to see what's up. I am still not sure how fluid moves around in there as the piston slides up or down.

 

[Felde]

Very nice writeup. Thank you

 

[Rigster]

I got the damned clip on while the stuff was clamp to a table. I bet you went insane trying to do that while it was on your truck.
I took the old LSPV apart to see what's up. I am still not sure how fluid moves around in there as the piston slides up or down.
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Thanks for the breakdown of some of the engineering wizardry they created here in this proportioning valve.

I had to replace one hard line on this unit when I did my lift, but a good rule of thumb to follow is to measure before and after lift; then, I just created a bracket to raise that "spring arm" the same amount as the lift. Worked like a charm. But of course, this is supposing that the LSPV is functioning correctly and within spec to begin with...

 

[jblueridge]

I was able to get an Aisin part number off a rubber component.
It led me to a Russian LandCruiser forum.
From Russia Useful pics and info. Hopefully no spyware there.

 

[desmocruiser]

Nice detail! My goal was to stop the leak, goal accomplished!

I did have to get one brake line remade. Separating the valve from the bracket was an issue that was solved with a cut off wheel and a hammer and punch, fortunately I had also purchased Toyota 47937-60010 Plate, Load Sensing Valve Set (the U shaped piece that holds the valve to the bracket) as it would have been impossible to reuse.

I didn’t install the spring on the rubber boot, seemed like a solid fit and the original was missing a long time ago, now you have me wondering if I should go back in a install, I have another bolt to install after I chase the threads.

 

[jblueridge]

I’d use a zip tie or try to find a narrow hose clamp.
The Toyota clip would require you to take everything apart.

 

[LDRF]

You could twist on some stainless wire to secure it. You could back it with a peice of zip tie, plastic or thin steel strip to lower chances of cutting the rubber boot.