I just did this...it removes the factory mechanical parts but leaves the proportions valve. I can adjust if required. I got the idea from from a fellow mudder.
Write-up: Toss the LSPV and install a manual proportioning valve (1 Viewer)
- Thread starter jcardona1
- Start date
This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.
I'm dealing with some severe crotch rot on an FZJ80 I picked up, sight unseen, from a fellow IH8Mud member. The entire brake system needs work. I am looking at the cleanest fix possible. Is it as simple as swapping to a 93 non-ABS master cylinder and tying in the front and rear lines, then scrapping the LSPV and hardware, and the ABS module? Thanks in advance.
I have done this with both of my previous trucks. Never had a braking problem.
As an update, I still have awesome brakes after doing this.
alia176
SILVER Star
Oh good to hear, thanks for the feedback.
Hi All,
I've read everything I can find on the forum (links are welcome in case I missed something). I've got a 1996 with a leaking LSPBV, failed ABS, a terrible peddle feel, and poor braking performance. I'm trying to learn about how the system works before deleting. Honestly, I'm leaning toward putting it back in original working order. Note: the FSM calls the valve a "Load Sensing Proportioning and By-Pass Valve"
Has anyone seen a graph of brake pressure or brake pressure bias vs. vehicle load?
Any pictures of the stock bar from the axle to the valve? Mine has a bend in it and I'd like to be sure it wasn't bent in the course of some adventure.
From a physics standpoint, it seems that when the vehicle is loaded in the rear with cargo or the tongue weight of a trailer it would be best to INCREASE the proportion to the rear. I've seen postings that make claims both ways.
Given my last question, does the valve bypass a fixed proportioning valve and send a higher ratio of the pressure to the rear in a loaded condition? In other words, does the decreased space between the axle and the body cause the proportioning valve to be bypassed?
thanks!
I've read everything I can find on the forum (links are welcome in case I missed something). I've got a 1996 with a leaking LSPBV, failed ABS, a terrible peddle feel, and poor braking performance. I'm trying to learn about how the system works before deleting. Honestly, I'm leaning toward putting it back in original working order. Note: the FSM calls the valve a "Load Sensing Proportioning and By-Pass Valve"
Has anyone seen a graph of brake pressure or brake pressure bias vs. vehicle load?
Any pictures of the stock bar from the axle to the valve? Mine has a bend in it and I'd like to be sure it wasn't bent in the course of some adventure.
From a physics standpoint, it seems that when the vehicle is loaded in the rear with cargo or the tongue weight of a trailer it would be best to INCREASE the proportion to the rear. I've seen postings that make claims both ways.
Given my last question, does the valve bypass a fixed proportioning valve and send a higher ratio of the pressure to the rear in a loaded condition? In other words, does the decreased space between the axle and the body cause the proportioning valve to be bypassed?
thanks!
alia176
SILVER Star
Please conduct a search on this forum about the LSPV and associated pics. I believe the info on load bias % has been discussed in the past. The LSPV is common in Toyota trucks and this model landcruiser to accommodate additional cargo load so your assumption is somewhat correct.
Last edited:
SmokingRocks
hopelessly addicted to Cruisers
This is correct and is what the valve senses through the "bent" rod that attaches to the axle.
No, the LSPV is a physical sensor and valve in one. When the LSPV senses that the axle is closer to the frame (through the "bent" rod) it's usually because of extra cargo/tongue weight. The position of the bar physically changes the opening of the orifice inside the valve which regulates how much brake line pressure is seen by the rear brakes.
In a factory setup under a panic braking scenario, the front brakes should reach and exceed the grip coefficient of the tires at the same time the rears do. This is to improve the efficiency of the ABS system which ultimately provides more control to the driver as they attempt to navigate around whatever the hazard is. The reason behind this objective is that locking up rear tires in a panic situation is undesirable and can cause oversteer (rear to swing around aka fishtailing). Vehicle dynamic engineers don't want oversteer as it would result in thousands of "faulty vehicle" claims when inexperienced drivers panic brake in a corner, fishtail, and wreck.
It's not bad to have the LSPV but it's a pain because it is an area for air to become trapped in the system, which if not bled properly will result in poor braking performance. Many of us just eliminate the valve or replace it with a manual proportioning valve.
I can appreciate your desire to unpack the physics on this conundrum but think it would be an exercise in futility. Ultimately you would land at the answers we already know.
Last edited:
Rivman1243
SILVER Star
Have a look at this thread For Sale - 40, 50, 60, and 80 series FSM for a hell of a price.
Download the FSM. It does a decent job with explaining how it works. It has pictures and all the specs about how to properly adjust it.
Download the FSM. It does a decent job with explaining how it works. It has pictures and all the specs about how to properly adjust it.
Last edited:
So, bigger orifice (equating to more rear brake pressure) when the rear is loaded?
SmokingRocks
hopelessly addicted to Cruisers
alia176
SILVER Star
For those of us who has a phat arse, the load ain't changing. Elimination of the LSPV sounds beneficial or leave the adjusting rod in the extreme position at one end.
SmokingRocks
hopelessly addicted to Cruisers
Or if you know how to control a skid (oversteer or understeer) and don't want the headache of having air getting stuck in the LSPV then dump it.
alia176
SILVER Star
Yeah, I'm going to the route of dumping the LSPV & ABS because locking up my tires is non existent in my reality.
jjdeneen918
SILVER Star
Yup, I’ve never been able to get my ABS to activate.
I’m going to delete my ABS & LSPV.
I am going to install a manual proportioning valve Incase I do need to do some fine tuning of the bias.
The hassle with the manual proportioning valves (Wildwood, ect.) is they are different brake line fittings, which require you to cut & reflare brake lines with new fittings.
I did some research & found a Miata site that sells a Willwood PV with their own custom adapters which should be compatable with our brake lines.
So no more having to cut & re-flare. I couldn’t believe how impossible it was to find such a fitting adapter.
www.flyinmiata.com
I’m going to delete my ABS & LSPV.
I am going to install a manual proportioning valve Incase I do need to do some fine tuning of the bias.
The hassle with the manual proportioning valves (Wildwood, ect.) is they are different brake line fittings, which require you to cut & reflare brake lines with new fittings.
I did some research & found a Miata site that sells a Willwood PV with their own custom adapters which should be compatable with our brake lines.
So no more having to cut & re-flare. I couldn’t believe how impossible it was to find such a fitting adapter.
Complete adjustable brake proportioning kit
Everything you need to install an adjustable brake proportioning valve on your Miata!
www.flyinmiata.com
alia176
SILVER Star
Yup, I’ve never been able to get my ABS to activate.
I’m going to delete my ABS & LSPV.
I am going to install a manual proportioning valve Incase I do need to do some fine tuning of the bias.
The hassle with the manual proportioning valves (Wildwood, ect.) is they are different brake line fittings, which require you to cut & reflare brake lines with new fittings.
I did some research & found a Miata site that sells a Willwood PV with their own custom adapters which should be compatable with our brake lines.
So no more having to cut & re-flare. I couldn’t believe how impossible it was to find such a fitting adapter.
Complete adjustable brake proportioning kit
Everything you need to install an adjustable brake proportioning valve on your Miata!
Regarding the manual prop valve, the consensus point to not needing one due to the weight of our rigs. Perhaps try it w/o the manual valve and see? The folks who have installed this valve has them wide open. This is the path I'll be going.
In all vehicles regular four-wheeled road vehicles, front brakes do basically all (90 pct) of braking when going forward. Only time rear brakes do the majority of braking is when reversing.
My 80 doesn't have ABS, but it does have a proportioning valve. The purpose of the LSPV is, as I understand it, to regulate how much brake pedal pressure goes to the front calipers based on how much the rear raises when braking (99.9 percent of the time while going forward) as 'sensed' via the bent rod joined to the rear axle housing.
Remember that to make a vehicle move forward or backward, the driveline lifts the vehicle against it's own gravitational downforce and the weight reaction combined with the angle of rotation of the wheels makes it 'move' forward or backward with respect to the surface it's sitting on.
The braking effect is the reverse of this. So as weight naturally transfers load forward due to inertia when going forward, the vehicle is attempting to 'roll' itself (ie. flip) around the leading axle centreline (front if going forward, back if going backward) and the brakes attempt to control that by converting kinetic energy in the form of directional inertia into heat by acting against the 'roll' in a regulated way. The LSPV will 'limit' the braking force transferred to the front brakes when the rear rises up (due to the 'roll' effect).
Most vehicles without ABS have 'matched' 50/50 braking normally, which is probably ok. 4wd's have a far higher centre of gravity so the 'roll' effect is a lot more due to both high CoG and weight.
My 80 doesn't have ABS, but it does have a proportioning valve. The purpose of the LSPV is, as I understand it, to regulate how much brake pedal pressure goes to the front calipers based on how much the rear raises when braking (99.9 percent of the time while going forward) as 'sensed' via the bent rod joined to the rear axle housing.
Remember that to make a vehicle move forward or backward, the driveline lifts the vehicle against it's own gravitational downforce and the weight reaction combined with the angle of rotation of the wheels makes it 'move' forward or backward with respect to the surface it's sitting on.
The braking effect is the reverse of this. So as weight naturally transfers load forward due to inertia when going forward, the vehicle is attempting to 'roll' itself (ie. flip) around the leading axle centreline (front if going forward, back if going backward) and the brakes attempt to control that by converting kinetic energy in the form of directional inertia into heat by acting against the 'roll' in a regulated way. The LSPV will 'limit' the braking force transferred to the front brakes when the rear rises up (due to the 'roll' effect).
Most vehicles without ABS have 'matched' 50/50 braking normally, which is probably ok. 4wd's have a far higher centre of gravity so the 'roll' effect is a lot more due to both high CoG and weight.
SmokingRocks
hopelessly addicted to Cruisers
I hate to be the one to poke holes here but this is incorrect. The rear brakes can provide up to and in some cases more than 40% of the braking force. The fronts can provide up to and in some cases more than 75% of the force.
Actually, the LSPV does not affect the pressure going to the front brakes at all, it only regulates the pressure applied to the rear calipers. And while it will reduce the amount of brake pressure to the rear in a panic brake situation (when the nose dives and the rear lifts) it does this to prevent the rears from locking up. Locking up the rear in an emergency stop situation could cause oversteer which can result in a rollover.
Kind of, but not really. The torque that is applied through the rotational force of the tires applied to the ground creates a vector, that vector flows through the suspension links into the frame which propels the vehicle forward. The torque over I believe you are referring to is a product of the rotational force of the driveline against the frame. Yes, it loosely ties into this whole theory but it's not the primary moment that results in acceleration.
100% Well said
The LSPV has no affect on the brake force applied from the MC to the front calipers, it only regulates the pressure to the rear brakes.
This is not true, most vehicles have some type of proportioning system. Many economy passenger cars in the last few decades had a fixed proportion. Usually, fixed proportioning is done in the master cylinder.
The vehicle will not 'flip' over the front axle if the brakes are applied at a theoretical 100%. The grip coefficient of the tire on any surface will be reached far before the moment of inertia has moved the COG past the front axle. Even if hypothetically the front tires had infinite grip, then the drag coefficient of the brake pads on the rotors would be reached and surpassed, the vehicle would not front flip. This is not the purpose of the LSPV.
The LSPV regulates the pressure to the rear brakes based on the position of the axle in relation to the frame. The closer it is to the frame the more pressure the rear brake calipers will receive, this makes sense because obviously there is more weight on the rear which increases traction which would allow the rear tires to better aid the fronts when braking. (This is why rear engine Porsche 911's routinely set 100-0 brake distance records, all of the weight is behind the rear axle so the rear tires can provide huge amounts of brake force)
Now the farther the frame is from the axle means the LSPV will reduce the brake pressure the rear receives so that in a panic situation the rear will not lock before the front. Imagine a driver coming around a mountain corner at 60mph to see a moose in the middle of the road. He slams on his brakes and tries to swerve around it, these are the two possible outcomes in a stock vehicle configuration:
- With the LSPV is functioning correctly
- He applies the brakes fully, is able to swerve around the moose, maintain control while braking with the full force designed by Mr. T. The LSPV did the job and prevented the rear tires from locking up.
- Without the LSPV
- He applies the brakes fully, the vehicle transfers its inertia forward taking the weight off the rear tires which reduces their traction coefficient. The rear tires lock up just as he is turning to avoid the moose. The front tires traction coefficient has dramatically increased due to the weight transfer and therefore do not lock up yet if at all. This means he is able to steer (as the front tires are rotating) while the rear is locked up and if you've ever yanked your e-brake while going around a corner you understand this will result in oversteer. So now the vehicle slides sideways as the rear comes around. Too often than not this results in a vehicle rollover.
And in stock form it does exactly what it should, it's just that many of us are at the limit of the brakes capabilities anyway so the LSPV isn't really needed to prevent us from locking up the rears.
Last edited:
@SmokingRocks Thanks for the video and explanation of the LSPV. I was confused as to its function. Given the complete name of the valve according to the FSM is "Load Sensing Proportioning & Bypass Valve" I had assumed that the purpose of the bypass was to apply more braking to the rear wheels when loaded and/or towing (i.e., more weight on the rear due to trailer tongue weight).
My assumption might be forgiven because I race a 1970 911. I was consistently locking the 911's rear wheels on the track so I installed a manual proportioning valve in the FRONT braking line to allow me to increase the braking provided by the rear wheels.
I'm comfortable with threshold breaking and managing a lockup. But, my wife and kids drive the LC occasionally. So, I don't want to second guess the Toyota engineers and remove the ABS or the LSP(&B)V. I'm simply trying to address a leaking and possibly non-functional LSP(&B)V.
How do I get in touch with Mr. T?
My assumption might be forgiven because I race a 1970 911. I was consistently locking the 911's rear wheels on the track so I installed a manual proportioning valve in the FRONT braking line to allow me to increase the braking provided by the rear wheels.
I'm comfortable with threshold breaking and managing a lockup. But, my wife and kids drive the LC occasionally. So, I don't want to second guess the Toyota engineers and remove the ABS or the LSP(&B)V. I'm simply trying to address a leaking and possibly non-functional LSP(&B)V.
How do I get in touch with Mr. T?
