Write-up: Toss the LSPV and install a manual proportioning valve (2 Viewers)

[landtoy80]

I had a code stored when my abs kicked in for no reason. Checked again later and got different code. Gave up when i checked again (different code again) after I about rear ended a car. Pulled the abs fuse and removed abs bulb. 285/75-16 tyres, stock gears. Later removed the ABS and LSPV and got a adjustable valve.

As long as all tires are the same diameter,size shouldn't matter. When the computer reads one wheel is locked, the computer triggers the brakes to reduce braking while pulsating.


I dont think the 95+ Fzj80 have traction control TRC and or vehicle stability, do they?
My son's 2004 Rav4 is having the traction control triggered for no reason.
Possible causes from Toyota are:
hard tires (they said to use softer tires)
worn shocks (dont use stiff shocks)
worn bushing in the rack and pinion

My thought is the abs system back in the 90's was new technology and they didn't have all the bugs worked out. After so many miles or years the system starts to fail, then it gets thrown into the recycle bin.

 

[half k cruiser]

Does anybody have a link to the manual valve they are using ???????

 

[SmokingRocks]

Does anyone have a part number for just a T? or will anyone from Napa fit??

 

[Dirty Koala]

Does anybody have a link to the manual valve they are using ???????

http://www.summitracing.com/parts/wil-260-12627/overview/

Does anyone have a part number for just a T? or will anyone from Napa fit??

Why don't you use the OEM one under the brake booster? If you need a new one, you can use any Tee, as long as you match the fittings on the lines appropriately.

Having a hard time finding a Tee that has M10 x 1.0 Inverted (double) flare in all three ports. This ones has 2 M10 x 1.o ports and the 3rd ports is SAE 3/8 -24
http://www.summitracing.com/parts/ear-972056erl/overview/

 

[SmokingRocks]

I was unsure if people were using a manifold like T in order to not have to bend brake lines.

 

[Dirty Koala]

I was unsure if people were using a manifold like T in order to not have to bend brake lines.

You will need to bend some lines regardless. You can see how I did it here: ABS & LSPV Delete

 

[jcardona1]

Does anyone have a part number for just a T? or will anyone from Napa fit??

Having a hard time finding a Tee that has M10 x 1.0 Inverted (double) flare in all three ports. This ones has 2 M10 x 1.o ports and the 3rd ports is SAE 3/8 -24
http://www.summitracing.com/parts/ear-972056erl/overview/

Replacement tee if you need one: Universal Brake Line Tees

 

[Dirty Koala]

That is a good one. There is also this option on the same site: Brake Line Tee (3 - 10mm x 1.0 female fittings)

 

[sunrk]

Dunno when Aussie 80's got ABS - probably 8/92 onwards? Mine (3/92 build) does not have ABS. The stock proportioning valve is mounted under the back near the rear axle housing and has the bendy rod going to it off a bracket mounted onto the rear diff part of the axle housing.

I used to have a 4" (I still reckon it was more like 5") lift on HD springs and the brakes were ok but not great. Now it's down to a 3" lift on MD springs and the brakes are better, but still not great. I moved the LSPV down about 5 mm on it's bracket. But it's old/original and probably doesn't work very well after 24 yrs of exposure to reality.

 

[cartercd]

I was considering this mod, but want a better understanding of how Mr. T engineered the LSPV vs. what happens with no proportioning or the aftermarket manual proportioning valve. We have a few data points from the FSM ('97):

- At 2,932 lb rear axle load and front pressure of 1,138 psi, rear pressure should be 869 +/- 86 psi. This is 57/43 bias
- With LSPV adjusted to uppermost position (no load sensing adjustment)

- At 498 front psi, rear should be 498 psi, so 50/50 bias
- At 783 front psi, rear should be between 527-612 psi. So 58/42 bias
- At 1,424 front psi, rear should be between 655-797 psi. So 64/36 bias​

And we also know:
- With no valve we have 50/50 bias
- The Wilwood valve pressure adjustments range from 100-1000 psi and provides for a maximum decrease of 57% in line pressure (which mathematically is 70/30 bias). I contacted Wilwood tech support and they clarified the 1000 psi spec. This is not the max operating pressure, this is the maximum amount that the inlet pressure can be reduced.

So if we plot a few scenarios:

OEM: This is likely designed to provide 50/50 bias up until a "knee" point of around 500 psi, and then the vehicle load dictates whether the valve stays at 50/50 or proportions to a lower rear bias for light loads. We can assume that a properly bled system and functioning LSPV should provide the best performance and front/rear bias for varying loads . The light blue area represents my estimate of the LSPV operating range (graph cut off at 1,800 psi, but pressures can exceed this)

No valve: This seems more appropriate for a heavily loaded truck. An empty truck would have significantly more rear pressure than Mr. T designed, which could result in dangerous rear lockup before front

Wilwood valve: I plotted a sample 25% pressure reduction which would mimic the spec at 2,932 lb rear axle load, but obviously this could be adjusted to best suit vehicle load. For a lightly loaded vehicle this seems a better option than no valve. It's still a compromise though, because even if you adjust the valve every time you change load, it will not mimic the proportioning curve of the LSPV.

I am inclined to keep the LSPV as in theory that should provide the best braking performance. I think the trick is getting the system (particularly ABS unit) completely bled to eliminate those pesky air pockets that are causing spongy pedals. If you eliminate LSPV, I'd pay careful attention to dialing in a pressure bias that works for your load.

Cheers

 

[Rivman1243]

I was considering this mod, but want a better understanding of how Mr. T engineered the LSPV vs. what happens with no proportioning or the aftermarket manual proportioning valve. We have a few data points from the FSM ('97):

- At 2,932 lb rear axle load and front pressure of 1,138 psi, rear pressure should be 869 +/- 86 psi. This is 57/43 bias
- With LSPV adjusted to uppermost position (no load sensing adjustment)
- At 498 front psi, rear should be 498 psi, so 50/50 bias
- At 783 front psi, rear should be between 527-612 psi. So 58/42 bias
- At 1,424 front psi, rear should be between 655-797 psi. So 64/36 bias

And we also know:
- With no valve we have 50/50 bias
- The Wilwood valve pressure adjustments range from 100-1000 psi and provides for a maximum decrease of 57% in line pressure (which mathematically is 70/30 bias). I contacted Wilwood tech support and they clarified the 1000 psi spec. This is not the max operating pressure, this is the maximum amount that the inlet pressure can be reduced.

So if we plot a few scenarios:

View attachment 1297204

OEM: This is likely designed to provide 50/50 bias up until a "knee" point of around 500 psi, and then the vehicle load dictates whether the valve stays at 50/50 or proportions to a lower rear bias for light loads. We can assume that a properly bled system and functioning LSPV should provide the best performance and front/rear bias for varying loads . The light blue area represents my estimate of the LSPV operating range (graph cut off at 1,800 psi, but pressures can exceed this)

No valve: This seems more appropriate for a heavily loaded truck. An empty truck would have significantly more rear pressure than Mr. T designed, which could result in dangerous rear lockup before front

Wilwood valve: I plotted a sample 25% pressure reduction which would mimic the spec at 2,932 lb rear axle load, but obviously this could be adjusted to best suit vehicle load. For a lightly loaded vehicle this seems a better option than no valve. It's still a compromise though, because even if you adjust the valve every time you change load, it will not mimic the proportioning curve of the LSPV.

I am inclined to keep the LSPV as in theory that should provide the best braking performance. I think the trick is getting the system (particularly ABS unit) completely bled to eliminate those pesky air pockets that are causing spongy pedals. If you eliminate LSPV, I'd pay careful attention to dialing in a pressure bias that works for your load.

Cheers

Thank you for the great post and time and effort.

 

[Tedward]

carterocd

I mean that in the nicest way.

 

[cartercd]

carterocd

Over-analyzing things is a hobby

 

[alia176]

excellent info, feel free to over analyze other aspects of the 80, always like to learn new things.

 

[warezdog]

used existing t, ditched the LSPV and ABS, installed 100 series pads up front and it brakes better than I could have ever hoped for, well over a year now, loaded down, empty, hauling trailer and never felt better. Less crap to fail and better brakes, a win win in my book.

 

[landtoy80]

One thing that needs to be added is that with the ABS module, the extra lines and LSPV removed, braking is improved do to whatever issue all ABS system has on braking. I am not sure if air gets into the ABS module and that affects braking or if the brakes work better was there is less brake line pluming in the system? I dont see the LSPV being the problem with braking on the 80, I believe its the ABS module. If the LSPV could be used when removing the ABS module, that might be the way to go but I am not sure if that can be done.

 

[JeepinPete]

The LSPV requires compression of the rear suspension to up the rear braking pressure. If you haul/tow enough weight often enough to squat the rear end of the truck, you will probably do something about that, like install heavy duty springs, or airbags like I did. Now you are trying to stop the heavy load without the increase in rear brake force.

The first time I towed my loaded M1102 trailer (about 5500lbs) after I installed airbags, the loss in braking was very noticable. Just to make sure I wasn't imagining things, I let the air out of the bags when I got close to home. Sure enough, the braking improved quite a bit.

IMO, Toyota made a very good system for a stock truck, used in the way they had in mind. Once you go about modifying the suspension and adding tires, those system no longer work very well. Just my experience.

 

[warezdog]

One of the deciding factors in the ditching the LSPV when doing the ABS delete was it that it had just started to leak, the cost of a new one wasn't realistic to my budget, I opted to skip the portioning valve only because others before me had done without just fine and I could always put one in later.

The best part about this is you need no parts to do it, they're all there just waiting to be reconfigured. I've successfully locked up all four to avoid T-boning and idiot that pulled out in front of me making a left had turn from my right side, 35" tires @ 45mph left a nice strip about 40 feet or so long. After that experience I never had any questions of whether this mod was worth it, ABS would have had me into that car without a doubt possibly killing the moron.

I'm weighed down quite a bit, haven't put it on the scales yet but I know I'm north of 7500 easy.

 

[alia176]

One of the deciding factors in the ditching the LSPV when doing the ABS delete was it that it had just started to leak, the cost of a new one wasn't realistic to my budget, I opted to skip the portioning valve only because others before me had done without just fine and I could always put one in later.

The best part about this is you need no parts to do it, they're all there just waiting to be reconfigured. I've successfully locked up all four to avoid T-boning and idiot that pulled out in front of me making a left had turn from my right side, 35" tires @ 45mph left a nice strip about 40 feet or so long. After that experience I never had any questions of whether this mod was worth it, ABS would have had me into that car without a doubt possibly killing the moron.

I'm weighed down quite a bit, haven't put it on the scales yet but I know I'm north of 7500 easy.

I'm weighed down quite a bit as well, around 7,000 lbs when fully loaded. Laying down a 40' black strip would be impossible in my 80 so this mod is on my to do list. My LSPV has been permanently adjusted with the arm pointing in one direction, can't recall which way at the moment. The weight in the cargo area doesn't change a whole bunch but it does have around 200#s of drawers and associated crap.

 

[silverhorse]

Great write-up and mod! I used the factory 3-way and mounted it where the LSPV bracket used to be... I cut part of the LSPV bracket off to make a bracket for the 3-way. I also went ahead and replaced the original brake line with the (longer) NAPA 38256. This hose can be used front and rear......

Toyota Part No.: 90413-10058