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Brakes: Load Sensing Proportional Valve LSPV and LSPBV


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Glad that helped Mark. No I just got a much younger person to show me how to move cell phone pictures into the computer... My phone did NOT automatically recognize itself to the computer so he "introduced" my phone to the computer with some wizardry that only younger people seem to possess. Let us know how you like your new brakes.

PS did you see my new tail lights in the electric forum

 

Edited by Lee & Joan
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I did Lee WOW! Nice fabrication! I got the old Reflect-O-Lights tail lights which aren't made anymore. If they ever fail I could try and copy your setup unless you have a Patent LOL! Thanks again for the pictures. I now know what to do!

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  • 1 year later...

Just did something similar on mine while i had the axle out.  I simply cut the rod about 2 inches past the valve and zip tied the rod to the valve.  Tossed the rest in the scrap bin.  There, 4 pounds lighter, no holes or brackets to make.  

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  • 3 weeks later...

After reading through this thread am I correct that I can simply completely remove my LSPBV and install a T?  Currently running break lines for the Odyssey 

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10 hours ago, Odyssey 4x4 said:

After reading through this thread am I correct that I can simply completely remove my LSPBV and install a T?  Currently running break lines for the Odyssey 

When I finally get back to working on  my Nissan Sunrader that is exactly what I will do. Those valves on Nissan's are not adjustable and with the camper weight can be dangerous. On a V6 D21 chassis. Don't know if the earlier ones were set up the same way

Linda S

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The valve was put on the pickups to keep the rear brakes from locking up with no load it was controlled by ride height there is no such a thing as a toy home being too light in the back. If everything is working properly the valve would be in the fully loaded position anyway. Pickups dive on hard braking lifting the rear end because of the weight transfer  the toy homes don't. Bottom line if the valve is by passed it will have no effect on the breaking provided the system was working properly in the first place. Same goes for removing it it will not hurt a thing. 

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Thought so, considered putting a hand adjustable valve but as previously mentioned, basically useless on these rigs.  

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  • 2 months later...

Well, I'm late to the discussion as usual, but after doing a significant amount of research above + beyond, I have a few questions that I'd like to pose to members who have tackled the LSPV valve or "un-balanced braking" issue, or those who may be in the process of modifying their system.

But first, my situation is this: I have an ‘84 4x4 SunRader. The current LSPV is one with 3 ports. See Below.

About 8K mi. ago the vehicle underwent a brake system inspection and subsequent stock rebuild.  

This included new stock rotors and calipers in the front (next time I’ll replace them with vented LandCruiser units), new master cylinder and turning drums and new rear shoes.

Prior to this, I had wired the LSPV valve all the way up, after reading related posts and data ad nauseaum. It appeared to had little to no effect. I have always noticed front-heavy braking and lots of brake dust accumulating on the front rims, but no side-to-side pulling on an even road crown. Most recently, I have felt some slight pulsing in the pedal, feeling suspiciously like rotor warp possibly caused from over-heating.

 In an effort to arrive at a better understanding of WTH is going on, I recently took the rig down a very steep local grade on a very chilly day, using only brakes and no downshifting to slow down. At the bottom, I slid underneath and checked the temperature of the brakes of all four wheels. Both fronts were 175 degrees (even side to side) and both of the rear drums were 65 degrees (even side to side). According to my wheel and brake guys, this seals the too-much-front brake diagnosis and I now want to deal with it. It seems clear that the valve is faulty.

My question is this: Is there any performance difference between replacing the stock LSPV valve (retrofit at about $165.00) and wiring it open / up, and/or plumbing in a “T” ? (swaging tool needed and possibility of acquiring the ability to swage steel brake line x 3 ?).

For some reason, local shops seem to think this "T" modification is worth about $600.00 and claim it’s not as easy as it seems. The rumor is, bleeding the system is an absolute pain, even with a vacuum bleeder.

I know Maineah replaced his, but I don’t know if the unit was functional, but lacking when he did, and if it improved any with the addition of a T, or if his valve wasn’t functional, like mine, and that was his motivation.

As always, thanks for any useful input..

BR, TG

LSPValve Small.JPG

Edited by ToyoGuy
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Hey Toyo! I don’t have a 4x4. Just my luck I wired up the LSPV and realized the valve was stuck! Couldn’t figure out a way to loosen it up so I’m stuck LoL!

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Think about it. Draining fluid from a complicated pressure system or draining fluid from a clear line all the way from your master cylinder to your brake cylinder. Which sounds harder to do. My vote is for the clear line. Look at this simple LSPV delete. 

https://www.youtube.com/watch?v=Cs56YzyP3mc

Lots of people experience spongy brakes after replacing the fluid. That is often caused by the LSPV. Interior pistons get gummy and are no longer responsive. As far as cost. That mostly has to do with where you live. 

One other thing. Are you sure your rear brakes are adjusted properly

Linda S

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Thanks jjrbus, I used a Harvard Freight infared heat-sensing gun, I think it was about $25 on sale. It was one of those "oh, what the hell, this looks like it may be useful" purchases, and it has become invaluable for troubleshooting cooling system, brakes, over-worked alternator, plus checking the fridge-alcove, inside of the floor of the cab and walls of the coach after installing insulation etc.  I also use it for checking cooking temperature on the BBQ and oven temp when I'm baking cookies. :)

My wife uses it to check the tub-temp for baby baths, go figure.

Thanks Markwilliam1, I'm leaning toward just replacing the valve assembly and wiring the valve all the way up. No one seems to have experienced a massive performance leap after eliminating the stock valve altogether, bending brake lines, re-flaring and refitting to a generic "T" fitting, so why pay for, or do all that? 

I'll give it a couple of days to let anyone else chime in, then invoke my usual SWAG (Scientific Wild-behind Guess, for you non-military types) process and swap it out.

BR,

TG

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Hey Linda, Thanks for your thoughts on this. Yeah, after a go-back, I held the grumbling brake shop's feet to the fire on the rear adjusters, and I think it was you that finally told me there are Ford brake parts that would retrofit for missing Toyota stuff. At any rate the rear adjusters work now.

On hydraulic flow, in principle, I agree with you, but when I ask people to make a definitive statement about what's most cost effective, safe and functional, everyone kinda goes squishy on me.

On the youtube video, I'm confused about a couple of notes the guy makes in his initial disclaimer, and then 2 years later...

In a portion of the initial heading/disclaimer:

"  do not delete the LSPV. There are mixed opinions on this topic but I stand behind mine. The LSPV system is a constantly variable proportioning valve. No manual proportioning valve can claim to work as well. Also, when I removed the LSPV the rear brakes never worked as well. For reasons unknown, the automatic brake shoe adjustment system ceased to work after this mod. I dealt with this for less than a year before installing a functioning LSPV from the junkyard. "

Then 2 yrs later, same video he has added:

 

If you remove the LSPV then you must cap off the third line from the junction at the front brakes and install a proportioning valve for the rear brakes. I will also add this: I didn't leave it like this for even a year. Removing the LSPV caused the rear brakes to suck and the auto adjustment for the drums stopped working correctly. I get fed up with it and installed a working LSPV from the junkyard. I recommend refurbishing your OEM system rather than doing what I did with the LSPV.
 
Not sure what to draw from this ummm, ...."ambiguity"? Sure like his front brakes though.
TG
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Guess I should have watched the vid closer. What he says makes no sense. The LSPV takes pressure from the rear brakes and redirects it back to the front. Removing it leaves full pressure in the back which means more brake, not less. Also brake adjusters are mechanical, not hydraulic. No way they would be effected. He did install a manual LSPV in the engine compartment but I was more interested in his clean simple 90 degree fitting job. No one with a truck is going to have the same results as us unless they use it to haul bricks 24/7

Linda S

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When I got my Toy, the first summer project was brakes. I was fortunate in that some in the RV's life the front brakes had been redone. The generic no-name pads were almost worn out. BUT the fluid had been flushed. Installed new HD pads, turned the rotors and new calipers. With that done I pulled the rear brakes and discovered almost unworn brake shoes with one leaking cylinder. Installed new cylinders and degreased the shoes. Put it all back together. Guess what? poor braking. So I started to research the LSPV and how it worked. With that understood the simple answer was just to crawl under the RV and bend the  arm up so that the LSPV was maxed up. Now great brakes.

I was lucky in that some time in its life the brake system was flushed. The LSPV still worked. Most Toys have the OEM brake fluid resulting it a gunked up nonworking LSPV. Adjusting the arm does nothing with a gunked up valve.

I was lucky... If I had to start with a messed up system this is what I would do.

Make the system NEW, new pads shoes, cylinders, calipers and rotors. If the LSPV was questionable I would just remove it. No t fitting. hard line from the MC to the rear brake line flex hose. A simple plug in the  bypass line on the front caliper.

Brake in the new pads carefully and then try a medium brake test on low traction surface (dirt road) and see if everything locks up at the same time. If the rears lock first then a simple Wilwood manual valve.

YMMV

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           

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I'll chime in here because I just had to deal with my rear brakes and the LSPV played a significant role in the process.  

I had a rear brake issue a few weeks ago (failure of the auto-adjust mechanism that was eventually traced down to a broken parking brake cable).  I normally have my LSPV on "full up".  I was about to leave on a 300+ mile trip when I noticed after a test drive that one rear hub was very hot and the other was cold.  Heated hub had lots of brake dust and the cold one had basically none.  I checked the pad to hub distance by removing the round rubber plug on the brake plate and the hot one was tight and the cold one was loose.   I had to either leave in <30 minutes or abandon the trip.  I didn't have time to properly fix the brakes so I decided to move the LSPV lever from "full up" to "full down" in order to make the fronts to more work and ease up on the rears.  Before at full up the one hot wheel would lock up on gravel.  At full down it would not lock up but the fronts did now.  To me this is a simple test that demonstrates that the LSPV valve was working.  So I decided to do the trip on the "full down" (front favored) mode.   I checked temps (by hand, not a fancy meter :), at 50 and 100 miles and both rear hubs were cool and the fronts were warm.  I could feel the front brakes working because the nose dipped more on braking.  I was very careful about braking the whole trip but it did work to just use the fronts.   To me I see a lot of difference in my LSPV full up vs full down.  I did remove and flush the LSPV with isopropanol about 5k miles ago during a big brake overhaul.  Maybe this helped, may not.  But I do feel like my LSPV works and I can tell the difference between full up and full down.   Find yourself a spot with loose gravel and try the full up vs. full down hard braking test.  If you see no difference then perhaps your LSPV is not doing it's job.

Last week I replaced all of the parts in the rear brakes (if I'm going to open the axle everything is getting serviced...).  This is when I noticed the broken housing on the failing side of the rear brakes.  Once everything was fixed, cleaned up and bled  I again tested the LSPV at full up and full down.  Full up and the rear wheels would lock up on a loose gravel driveway and full down the front would lock up but not the backs.  I leave it set at full up.  As long as the rears are adjusted tight (~1mm gap of shoe to hub through the sight hole on the rear of the brake plate) then I get the rears to lock up on a hard pedal with LSPV full up on my loose gravel.  I'm going to monitor the brakes to make sure the self-adjusting mechanism is working properly (I don't trust it now).

I looked into replacing the LSPV with something that I could adjust with more precision but I never got to the confidence level with how to properly plumb the system and which specific valve to throw money at.  When I found that I could get a decent "rear favored" bias with the lever full up after a complete brake system overhaul I decided to just leave it.  I am using an 'upgraded' dual diaphragm booster but otherwise everything is stock.  

 

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I remember back in the 60's -70's large dual axle dump trucks had no front breaks! Basically they didn't need them all the breaking was where the weight was. This to some extent is the issue with a toy home the weight is the rear frame and a house on it's back. Bottom line they do not need the proposing it already is at max weight unlike a standard pickup truck. Let me put it this way I defy anyone to be able to lock the rear wheels on a toy home. The brake systems are separated there is no hydraulic coupling between the two the reasoning is if one system fails you will still have one working one, some thing is better than nothing.

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2 minutes ago, Maineah said:

I defy anyone to be able to lock the rear wheels on a toy home.

I can lock the rears up on very loose gravel with the lever full up.  It would never lock up on pavement of course.  

I think the dual diaphragm brake booster plays a significant role because it gives me a lot more power under the pedal.  Almost too much.  I had to get used to braking with a light foot after I installed it.  But if/when I need to really lay on the binders I've got a lot of power in the pedal (probably more than the stock master cylinder can handle).  This photo shows the new (painted/left) and stock brake booster:

1.jpg.95bb1527ee214a2afa2d13d76c311366.jpg 

 

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2 hours ago, WME said:

If I had to start with a messed up system this is what I would do.

Make the system NEW, new pads shoes, cylinders, calipers and rotors. If the LSPV was questionable I would just remove it. No t fitting. hard line from the MC to the rear brake line flex hose. A simple plug in the  bypass line on the front caliper.

Brake in the new pads carefully and then try a medium brake test on low traction surface (dirt road) and see if everything locks up at the same time. If the rears lock first then a simple Wilwood manual valve.

This is the path I would follow if I came to the point where I had lost confidence in my LSPV.  I'd try a no valve approach and if that doesn't work figure out how to plumb a manual valve.  

2 hours ago, WME said:

try a medium brake test on low traction surface (dirt road) and see if everything locks up

I'm going to stick with loose gravel rather than a dirt road though 🙂

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Thanks to all for checking in on this meaningful topic. In the picture below, it seems like the top port (A) should be the main pressure into the valve from the master cylinder, right?

 So, If I get this right, Line A gets connected to line C by whatever means possible.. brass block, or L-shaped steel manifold,( hopefully without having to cut or modify it), and Line B, the re-direct or return line gets plugged / terminated (somewhere) up front and is eliminated altogether from the rear brakes. Or, do I have Line A and Line B labeled bass-ackwards?

 

image.jpeg.48a4b7cacca80cb515dc63a17ed4fd13.jpeg

 

 

Edited by ToyoGuy
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4 hours ago, ToyoGuy said:

Thanks to all for checking in on this meaningful topic. In the picture below, it seems like the top port (A) should be the main pressure into the valve from the master cylinder, right?

 So, If I get this right, Line A gets connected to line C by whatever means possible.. brass block, or L-shaped steel manifold,( hopefully without having to cut or modify it), and Line B, the re-direct or return line gets plugged / terminated (somewhere) up front and is eliminated altogether from the rear brakes. Or, do I have Line A and Line B labeled bass-ackwards?

 

 

 

3

Sounds right

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Here is a diagram of my system and perhaps we all have the same thing.

1532780028_LSPVbrakelinediagram.JPG.48c6625be7705f1f7251b8d5c1c3ef92.JPG

This is a picture of the connections near the passenger front wheel where the return from the LSPV is routed back into the fronts:

1510165499_LSPVsplits.JPG.a02c7eae2c51e048525c7b5bb7311aac.JPG

You would connect A and C with a union of some sort and then insert a plug in the "T" in the front where the B line is connected to the front brake lines (the "from LSPV" spot in the second picture).  

The master cylinder has two ports and I suspect this means it has two separate pistons that each generate an independent pressure.  Can anyone confirm or clarify this?  In theory each of these two exit ports on the master makes an equal but isolated/independent pressure.  One port is sent directly to the front brakes and the other port is sent back to the LSPV input.  This second master port is split between the rears and the return to the fronts.  Any 'extra' pressure not being used by the rears from master port 2 is combined with the pressure from master port  1 at the "T" near the passenger right front wheel.  

With the LSPV lever "full down" there is a small amount of pressure delivered to the rears and the fronts experience the combined pressure of both master cylinder ports/pistons.   With the lever "full up" the rears experience full pressure from master port/cylinder 2 and the fronts get full pressure from master port/cylinder 1.   Removing the LSPV and plugging the return to the fronts would send the second master port only to the rears and the first master port dedicated to the fronts. Common experience based on running with LSPV "full up" suggests that this equal balance between front and rears is functional.  The temperature of all four hubs after working the brakes hard is roughly the same in my experience in the arm 'full up' mode, suggesting to me that the one piston to the fronts and the second piston to the rears is a simple and functional approach achieved by doing the A to C union with B plugged.

If we really wanted to make the rear drum brakes pull their weight we would put in a proportioning valve, but do it the reverse of the existing system design.  The existing system is set up to deliver more to the fronts than the rears.  The rears can never get more than "one cylinder" of pressure while the fronts can get both cylinder pressures combined (with lever 'full down').  There is likely a valve available that would allow us to dedicate one cylinder to the rears and then split the second master cylinder between fronts and rears.  The rears would receive the combination of one dedicated cylinder plus whatever is re-directed from the second cylinder away from the fronts.  Would there be any clear advantage in putting more brake power to the rear drums than we would get by simply removing the LSPV and connecting A to C and plugging B?  I would be concerned about brake fade on the rear drums if we asked too much from them.  People who do more climbing than me might have better insight on what might be the 'best' brake proportioning setup.

 

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The Toys have a split brake system. It's a safety thing that dates to the late '60s. The MC is split so that if there is a broken brake line at least 1/2 the brakes work. In the old days, there was a single line to all the brakes and if a line failed ALL the brakes quit.

The Toy PUs had to have enough brakes to stop a loaded PU, but most of the PU spent their life with an empty bed. So in the pre-ABS days, the answer was a mechanical system to keep from locking the rear wheels when empty. We are never "empty". We have 4000 lbs on the rear axle and we have dual rear tires for even more traction. We obsess over the RV being level and that confuses the LSPV... the answer is to remove the bugger and run full pressure to the rear brakes. In all the posts about adjusting/defeating/removing the LSPV, I remember only 1 person who had to add a manual proportioning valve.

I went the defeat route because my LSPV still worked. My Toy had worn out 2 sets of front brake pads in 50,000 mi and my rear shoes looked almost new so I knew something was off. After defeating the LSPV I was MUCH happier with the braking action and never looked back.

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I read somewhere that the LSPV has a mechanism to still keep the fronts isolated from the rears in the event of a failure of one of the two master cylinder pistons.  If it gets gummed up so often and can't even do the proportioning correctly, how can we assume it will function correctly in a partial master cylinder failure?  The procedure of removing/bypassing the LSPV is also a good safety move from this perspective because it  completely isolates the fronts on one cylinder and the rears on the other.   

If someone is wondering if the LSPV is working after you have wired it 'full up' (defeat mode), you should feel the rear hubs get warm after a decent amount of braking.  In addition you should see brake dust accumulate on the inner wheel surface.  I had a similar experience as WME with fronts wearing and rear pads no wearing.  When I first got my Toy the lever was full down and the rear pads looked practically new, the hubs ran cold and the inside faces of the wheels were clean.  By simply wiring the lever 'full up' I get good rear brake response, warm (not hot) hubs and I see brake dust on the inside rims.  If I ever have a whiff of trouble from the LSPV I'm simply going to remove it and plug the return line.  Simple, effective.  

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So have you ever taken one of these master cylinders apart? I have. There is only 1 piston. The 2 holes in the reservoir are separate for front and back but that's just where the fluid goes. The master cylinder goes out and you have no brakes anywhere except your trusty emergency brake. If a brake line fails you do have a little extra time to stop before your sucking air, but that's about it.

Linda S

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20 minutes ago, linda s said:

So have you ever taken one of these master cylinders apart?

I did about 2 years ago, but I wasn't paying enough attention to remember if it was a single or double piston.  I had purchased a Centric master and it failed right out of the box.  It bypassed so it had something wrong during the "re-manufacture".  I opened it up before I returned it but wasn't able to repair it.  Then I ordered a Beck Arnley 072-8522 and it has given me no trouble.  Linda, I recall a post recently about Centric brake pads and your comment there plus this master cylinder experience means I'll likely never order another Centric part again. 

I wonder if the single piston version you took apart was for a different year?  The picture Derek posted looks more accurate and corresponds to the image in the FSM that shows 2 pistons.

589712084_mastercylinder.JPG.568f30a3474f7a916ebcb96f0809231f.JPG

25 minutes ago, linda s said:

The master cylinder goes out and you have no brakes anywhere except your trusty emergency brake.

I was actually thinking about this earlier today and I was wondering about what kind of backup plan I have in case something like a rear cylinder goes bad.   My assumption is that if, for example, a rear cylinder goes out and leaks like a sieve then the proportional valve safety mechanism would keep the fronts working and separate and I'd be able to stop until I ran out of fluid. Supposedly there is some mechanism in there that keep the front and rear systems separated through the LSPV but I've not been able to actually verify that.  Seems like another good reason to do the LSPV delete as it would absolutely keep front/rear separated.  In theory I'd also have some advance warning from the brake indicator in the dash due to low fluid, but I just checked my brake fluid cap and the sensor doesn't seem to do anything.  Maybe mine is bad.  I figured the dash would light up with some indicator if that sensor went low, but I get nothing.  I'll have to look into that and see if I can figure out how to get my low brake fluid indicator to light up.  Gee, I'm glad I have my emergency brake system working properly again.  That cable I had to splice together with clips to mod the new replacement brake cable is doing very well and I actually tested it for it's ability to stop the camper without using the brake pedal.  E-brake worked well and did stop the rig.

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1 hour ago, AtlantaCamper said:

I just checked my brake fluid cap and the sensor doesn't seem to do anything.  Maybe mine is bad.  I figured the dash would light up with some indicator if that sensor went low, but I get nothing.  I'll have to look into that and see if I can figure out how to get my low brake fluid indicator to light up.

I determined that my sensor in the cap is working with a continuity test.  Since the e-brake is also not lighting up the brake warning light and it doesn't come on with the key in the first position it is pretty clear that the bulb is burned out.  Fiddlesticks, i guess next time I've got the instrument panel loose I can check and replace the bulbs...

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6 hours ago, AtlantaCamper said:

I read somewhere that the LSPV has a mechanism to still keep the fronts isolated from the rears in the event of a failure of one of the two master cylinder pistons.  If it gets gummed up so often and can't even do the proportioning correctly, how can we assume it will function correctly in a partial master cylinder failure?  The procedure of removing/bypassing the LSPV is also a good safety move from this perspective because it  completely isolates the fronts on one cylinder and the rears on the other.   

If someone is wondering if the LSPV is working after you have wired it 'full up' (defeat mode), you should feel the rear hubs get warm after a decent amount of braking.  In addition you should see brake dust accumulate on the inner wheel surface.  I had a similar experience as WME with fronts wearing and rear pads no wearing.  When I first got my Toy the lever was full down and the rear pads looked practically new, the hubs ran cold and the inside faces of the wheels were clean.  By simply wiring the lever 'full up' I get good rear brake response, warm (not hot) hubs and I see brake dust on the inside rims.  If I ever have a whiff of trouble from the LSPV I'm simply going to remove it and plug the return line.  Simple, effective.  

Generally when there is a failure in the master cylinder you end up with rear brakes.

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I may have been incorrect about the master cylinder workings but there is one thing I am absolutely sure of. When mine failed the front and back were equally affected. I could get a tiny bit of braking with a lot of pumping but mostly got home with emergency brake. No leaks were found in the lines. New master cylinder fixed it completely

Linda S

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7 hours ago, linda s said:

I may have been incorrect about the master cylinder workings but there is one thing I am absolutely sure of. When mine failed the front and back were equally affected. I could get a tiny bit of braking with a lot of pumping but mostly got home with emergency brake. No leaks were found in the lines. New master cylinder fixed it completely

Linda S

I have seen that when one of the internal springs break. 

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Well, whatta deal, just got home and checked in on this thread and was grateful to find data and pictures from more experienced folks on this hydraulic stuff. (That must be why you guys get paid the big bucks)

This proves particularly beneficial with regard to how to do the mechanical plumbing on this simple-sounding but somewhat mysterious mod I've heard discussed for some time, but never had explained mechanically, top-to-bottom.

I may be wrong, (imagine that ), but I think the time spent outlining the nuts and bolts of this commonly overlooked system's operation and the possible alternative solutions will help a lot of members stay safer.  (Not to mention the ability perform a very useful maneuver called stopping, when and where you want. well, .....as close as possible anyway)

Many thanks to AtlantaCamper for the very helpful photo and DerekUpNorth, Linda s and Maineah for the diagrams and experience.

BR, TG

 

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  • 2 years later...

I'd like to thank everyone who has participated in this awesome thread - very helpful.  I also have an issue I'd like some help with that may be relevant.

 

As I  posted here: https://toyotamotorhome.org/forums/index.php?/topic/12604-brake-booster-question/&tab=comments#comment-116439 , I had a hard brake pedal almost continuously and found that the booster was full of brake fluid.  So I replaced both the booster and the master cylinder.  The brakes work "way more better" than they dd.  However, when I press the brake pedal quickly I don't seem to have any assist and have to stand on it to stop.  But when I press the pedal more slowly, I have great power assist and the brakes are awesome. 

 

I asked someone about what it could be and he replied "The proportioning valve only operates when the brakes are depressed quickly, and it prevents the rear brakes from locking up first and sending the vehicle into a skid. When the brakes are depressed slowly the proportioning valve does not operate."

 

This seems consistent with what I read in the training manual pdf in the initial post of this thread, e.g. "The proportioning valve only operates when the brakes are depressed quickly, and it prevents the rear brakes from locking up first and sending the vehicle into a skid. When the brakes are depressed slowly the proportioning valve does not operate."

 

Makes sense to me, and the whole "no proportioning when pressed slowly" thing would seem to point to the LSPV.  However, I fail to understand how a faulty LSPV could make it seem like I have no power assist when the pedal is depressed quickly.

 

I'd really appreciate it if you kind folks can help me to better understand this issue.

 

 

 

 

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