Topic: How to bleed lspv

[bigyotad]

Having some issues with my brakes 85 4runner on 35s. New dual piston front calipers, existing rotors that came on truck, new MC, booster, rear disc conversion. No matter how much I bleed brakes the pedal feels soft, not too bad but feels like air still in the system. Wondering how to bleed the lisp. Mine is not hooked up at the moment the arm that mounts to the axle was removed by previous owner. I still want to bleed it to make sure there is no air in the system. Thanks

[gnob]

If its not hooked up just remove it.  Brakes have hit almost 100% better on all trucks ive removed the valve on.

[Gnarly4X]

The Toyota LSPV (Load Sensing Proportioning Valve) is in the brake bleed sequence, typically rotating from closest to furthest hydraulic line from the master cylinder.  I bleed the LSPV first.

The factory lever system is designed to open the valve more when the bed or rear of the vehicle is weighted down, to increase hydraulic pressure to the two rear brake cylinders.

On my trucks I adjusted the lever, or modified it so I added braking the rear wheels. This is because when 4-wheeling and climbing the front tires lose traction, so the front brakes have very affect, leaving the two rear wheels to do the braking.  I’ve seen, and there are documented cases where tragic accidents have occurred because the vehicle did not have adequate braking when climbing, especially when needing to hold or back down from a steep incline.

Because my trucks have always been daily drivers as well as active and serious rockcrawlers, I adjusted my LSPV so on the street it would lock up the rear wheels under heavy braking. This was a trade-off because sometimes when the rear tires locked up the back end wanted to come around, especially when the street was wet.  Also I occasionally slid to a stop with the locked up rear tires howling because I had hit the brakes hard.  I’m sure the person driving the vehicle in front me when that happen crapped their pants thinking I was going to rear end them… big tires make big noise when sliding!

If it were me and I’m going off-road, I’d adjust the LSPV to provide more braking to rear wheels and experiment with the adjustment until I got it where I needed it.  If you do not want to connect the valve to the lever system, I would adjust it so the valve is full open.

If hydraulic proportioning becomes an issue for safe adjustment, you can contact Wilwood for advice:

http://www.wilwood.com/MasterCylinders/MasterCylinderValves.aspx
 
Assuming you have no hydraulic fluid leaks, if you have a spongy feeling brake pedal, it is typically caused by air in the lines, but it can be other things.  If the front wheel bearings are too loose the calipers will push against the rotor and the rotor moves and so will your brake pedal as you push it.  Another is the master cylinder is bad, but you have a new one.

Oh by the way... some LSPVs apparently have a hex head bolt instead of the typical bleed screw.

That’s just my opinion – it may be worthless.

Gnarls. 

[OVRAROK]

Having some issues with my brakes 85 4runner on 35s. New dual piston front calipers, existing rotors that came on truck, new MC, booster, rear disc conversion. No matter how much I bleed brakes the pedal feels soft, not too bad but feels like air still in the system. Wondering how to bleed the lisp. Mine is not hooked up at the moment the arm that mounts to the axle was removed by previous owner. I still want to bleed it to make sure there is no air in the system. Thanks

Bleed like any other system, farthest from master, to nearest. Then bleed LPSV. This is per the FSM

[Gnarly4X]

So I can see the color of the fluid and any air bubbles as I bleed the brake cylinders, I made a bleeder bottle from a plastic peanut butter jar.

Gnarls.

[bigyotad [OP]]

My

[bigyotad [OP]]

My

Is this the hex bolt you were speaking off? That was my question was how to bleed without a bleeder nipple. Im assuming I can crack it open a little push the brakes and see what comes out. Can I put a bleeder nipple in there? Bolt looks a little bigger in diameter than the bleeder nipples on my calipers.

[OVRAROK]

Right above bolt looks like a rubber cap, pull it off

[Gnarly4X]

Is this the hex bolt you were speaking off? That was my question was how to bleed without a bleeder nipple. Im assuming I can crack it open a little push the brakes and see what comes out. Can I put a bleeder nipple in there? Bolt looks a little bigger in diameter than the bleeder nipples on my calipers.

All four of my Toy trucks the bleeder valve looks the same.

I have not seen an LSPV on a Toyota that had the hex head bolt as bleed screw.

Gnarls.

[Gnarly4X]

Right above bolt looks like a rubber cap, pull it off

OVRAROK beat me to it.... that little rubber cap is what typically covers the end of the bleeder valve.

Gnarls.

[bigyotad [OP]]

Thank you both found the nipple under the rubber boot but it's fixed, no bolt section to turn like a caliper has. I'm assuming loosening the bolt beneath it, is what is going to allow fluid to come out of the nipple. Ill give it a shot and see what happens. I'll re-post when I get it bled. Looks like it hadn't been bled in quite a while! 

[Gnarly4X]

Thank you both found the nipple under the rubber boot but it's fixed, no bolt section to turn like a caliper has. I'm assuming loosening the bolt beneath it, is what is going to allow fluid to come out of the nipple. Ill give it a shot and see what happens. I'll re-post when I get it bled. Looks like it hadn't been bled in quite a while! 

Yes... I think you are correct.  If it is just a nipple, then it makes sense that the hex head bolt will allow the fluid to flow out the nipple... as it should.

A word of caution.... those valves and the head hex bolt do NOT need to be highly torqued.  Lightly snug them up, BUT be careful NOT to over tighten them.  The Toyota FSM says 8 ft lbs for the bleeder valve... that, for me, is a little too much torque... but who the hell am I to know anything!

EDIT:  I tried my clicker torque wrench at its lowest setting of 10 lbs.  I did seem to be OK judging from my "right-hand torque-o-meter"... so 8 ft-lbs is probably OK.

If you have not tried to loosen them, I would spray a little liquid wrench on them and let them sit for a few minutes.


Good job!

Gnarls.

[Snowtoy]

Did you bench bleed it the new MC, is it the larger 1" bore or stock replacement?

If bleeding the LSVP doesn't fix the symptoms, I would rebleed the entire system.

[bigyotad [OP]]

ell it looks like I need to re bleed the entire system. Bled the lspv and the fluid was very discolored I have a picture. Thanks for all the help gnarls. The bolt loosened up very easy like a caliper bleed screw and I didn't close it with any more pressure than I felt it took to loosen it. Super easy once I found the bleeder nipple.

However the problem still exists. First press of the brake pedal is mushy, it doesn't fall to the floor but it feels like air in the system. 2nd press on the pedal the truck stops pretty good, I can't lock up the fronts even on a dirt road but maybe I need to press harder on the pedal to get them to lock up. At this point I am contemplating removing the lspv from the system because I don't think its doing anything to help me.

Snowtoy The MC was a brand new 1 inch bore FJ 80 master cylinder from Trail Gear, the one they recommend with the disc conversion. It was bench bled before going into the truck. I have a friend who did the same disc conversion on his truck using the exact same parts I did and he has the same problem. Im going to re-bleed everything including the MC. I have already checked the vacuum on the booster and the one way valve but I'm going to double check everything and see what I can find. Thanks for all the help
 

[OOPS]

"...This is from the FSM and it works great..."
1. Drivers side rear
2. Passenger side rear
3. Passenger side front
4. Drivers side front
5. LSPV (Load sensing proportioning valve)

[johnny_boy02]

Off the top of my head is your booster working? I picked up pneumatic bleeder from harbor freight and bled the hell out of my brakes last weekend. It improved a lot. Still not great, but much better.

If you decide to get rid of the LSPV I have a part number somewhere I can dig up for a plug that works perfect on the front block that the line comes out of..... I am drawing a blank on the real name of that part.

[OOPS]

I just read your original post again and see you have a rear disc brake conversion. Are the calipers on the rear solid mounted or are the floating calipers? If the are solid mounted that could be your problem. When I did mine they worked fine on the street but as soon as I went off-road I would have to pump them. The tiny amount of flexing in the axles caused the rotors to open up the calipers a bit more hence having to pump the brakes. Did a re-do on the brake set-up with floating calipers, problem gone. Can you post up a picture of your rear brake set-up?

[Ritchie]

OP,
Ditch the LSPV and go with a Wilwood unit or similar.
When I installed my rear Diamond w/ discs, I installed the Wilwood at the same time. I still have the OEM MC and booster and my brakes are friggin' awesome.
For around $60.00, this unit will cure your headaches.  Tylenol gets pricey after a while. If you need pics, let me know.

Good luck.

[bigyotad [OP]]

Still having brake issues but moving in the right direction. Lspv has NOT been removed but I do have the proper bracket got 2 at pick n pull cut and welded them together to delete return line as shown. Ive been running tests where Ill drive the truck with lspv arm zip tied high up as possible, then as low as possible. Then I'll adjust the summit portioning valve I have off my master cylinder in both configurations to see what is best. Obviously my brakes are best when the arm is high as possible and the portioning valve all the way open to rear brakes. My confusion is in the fact that it feels like the front brakes are a lot better with that valve open directing more braking to the rears. I hit the brakes hard on a dirt road expecting to slide and fish tail but the way the front suspension compressed it seems like my fronts are doing majority of the work, this was 1st time I opened the valve all the way max to rear brakes. I know i have a problem somewhere but not yet sure where it is. The valve is on the rear line not the front one that Ts under the master and goes to the front brakes. My pedal seems stiffer as well. Any ideas?

[Gnarly4X]

Still having brake issues but moving in the right direction.... Obviously my brakes are best when the arm is high as possible and the portioning valve all the way open to rear brakes.

After 6 months you are still having an issue? 

What is “best” mean?  Is this a daily driver or do you wheel it? 

The P-valve is a simple lever valve. It is designed to open more hydraulic pressure to the rear wheel brake cylinders.  The lever is adjustable.  If the bed of the truck is lowered (like added weight from hauling something), the lever moves down and the valve is opened more, producing more braking power to the rear wheels. That should not significantly reduce the hydraulic pressure to the front wheel discs.

When wheeling off-road and climbing or backing off of an obstacle, the weight of the vehicle shifts to the rear brakes, the lack of traction on the front tires causes the front brakes to become practically useless.  I adjusted my p-valve by adding a longer lever bar made from aluminum bar stock.  I adjusted the p-valve until the truck would lock up the rear wheels on heavy braking, so I would have more braking power to the rear wheels when rock crawling. Since my 85 shortbed was a daily driver and week end crawler, on the street sometimes the rear wheels would lock up and the big tires would squawk loudly, and the back end wanted to come around.  I quickly got used to how much I could brake when stopping suddenly.  Once in awhile on wet pavement, I would have an adrenaline rush!! That was a trade-off I was willing to make. 

With the stock p-valve installed and Summit valve fully open, the stock p-valve will still be either open (all way down) or closed (all the way up) or somewhere in the middle.  If the Summit valve is proportioned to reduce the hydraulic fluid to the rear cylinders, it will simply reduce the pressure the p-valve can receive when it’s adjusted.

I’ve seen a number of drivers backing off a steep rock and the rear brakes cannot hold the vehicle from gravity and they lost control going backwards… that will get your attention! 

In all my years of wheeling two Toy trucks, after making my p-valve adjustments for crawling, I did not feel I needed any more braking power other than the Toyota stock brake system – of course everyone’s experience is different.

Gnarls. 

[bigyotad [OP]]

Thanks Gnarls. Truck is not a daily driver its a project that is almost "finished." The brakes have never been right since I bought the truck. I have to pump the pedal two or three times to build pressure in the brakes to get the 4runner to stop. I thought this issue was from air in the lines so I bled the system 5 times according to fsm and it didn't change much, even had a local shop bleed my brakes for me and I couldn't feel a difference. It was during the 1st bleeding process that I asked the question about how to bleed the lspv. I've been testing the brakes by making small adjustments between the lspv and the summit portioning valve, these adjustments were too small to notice and I got frusterated and opened the portioning valve 100% to rear brakes. This resulted in the best I ever got which was  almost locking up the front brakes on the dirt road I live on. At about 25 mph I stomped on the brake like a deer ran across the road in front of me and It almost locked up. My surprise was that most of the braking was done up front when I opened up a valve that is supposed to control the rear brakes.
I would like to get to where you were being able to lock up the rear brakes. Maybe if i try 45 mph I'll be able to lock em up.

[Gnarly4X]

bigyotad,

You probably know all this....

The brake system is closed. Assuming there are no leaks and the pads and shoes are not contaminated with oil or brake fluid and are within spec thickness, then there are only few issues than can affect the braking power.

A soft spongy pedal is typically air in lines, but you may not have to pump the pedal. If the system is bled properly and the brake fluid is coming out with no air bubbles, it’s good.  Sounds like you have no air in the system.

If the pedal goes to the floor or you have to pump the pedal to feel braking, there are several things that can cause this. Usually this is caused because the front discs are moving when the caliper pistons extend to clamp it.  This is usually because the wheel bearings are loose or badly worn.  CHECK THE WHEEL BEARINGS FOR PROPER ADJUSTMENT OR CONDITION.  You can jack up the front end to get tire off the ground. Grab the top and to bottom of tire, try to move it back and forth in parallel to the axle. There should be no movement.

The other thing than cause the brake pedal to go to the floor or require pumping is improper adjustment at rear brake shoes and drum. MAKE SURE THEY ARE ADJUSTED SO THE SHOES JUST BARELY TOUCHING THE BRAKE DRUM WHEN ROTATING THE REAR WHEELS.  You can drive the vehicle, then re-check if you are not sure of the adjustment using a screw driver on the star wheel through the slot on the back of the backing plate.

If the brake pedal goes to the floor when braking or goes to the floor slowly when holding the pedal down, usually the master brake cylinder piston seals are allowing brake fluid to pass over the piston, causing insufficient hydraulic pressure to the wheel cylinders.

Check to see that the p-valve lever is fully open, to allow the most brake fluid to pressurize the two rear wheel
brake cylinders.

Of course the type of front brake pads and rear brake shoes can affect the braking power.  I like the ceramic pads.  Semi metallic or ceramic brake shoes for the rear may be more scarce.  I would call Wagner and Raybestos technical guys and ask them for a recommendation for a higher friction rear shoe.

Larger tires and more vehicle weight often requires more braking power over factory stock.

I’m not a brake system expert, so there may be other considerations or factors that contribute to good or bad braking.

That's just my opinion - it may be worthless. 

Gnarls.