ayoung101

so would it be a HORRIBLE idea to completely bypass the LSPV? i have a major brake line leak in 1 of the lines (not sure which one) that run to the rear. unfortunately my brake lines are rusted solid to the LSPV, there's no way they are coming off, so i can't just simply R&R the lines and be done with it. i tried heat, i tried PB blaster, and with either an open end wrench OR a vise grips, the edges just round off. i gotta get this thing fixed. is it possible to just omit the LSPV altogether, and instead have 1 brake line split to the front, and 1 brake line split to the rears, and be done with it?

CJM

No, you will have brake problems. you need some kinda proportioning valve there. Summit sells them afaik, but adding one would be more trouble than its worth. You are using a flare wrench to remove them right???

Cut the lines, and put a connector, then flare the ends, then connect the two. Flare tool is super easy to use and only costs about 25 dollars, lines are really cheap.

Tofer

i removed mine when i did the SAS/rear leaf. i have a T where the 2 breaklines come in and then the 1 drops down to the axle. I have had zero breaking issues.

ayoung101

do you have pictures?

bigt

my 4runner bypassed this when i got it...it drove fine...for a saftey i had to hook the lspv back up..works good too...


on my trail rig i didnt bleed the lsv and the breakes were crappy....but they it works good..

Tofer

i'll try to grab some pics when i'm at the shop today.

Swansen

There was a thread on Pirate, and a guy took off his LSPV for his SAS swap, and his rear drums went to crap.

Tofer

like i said i have had no issues. i can lock up the rears if i really stand on the brakes and there is plenty of bite with out locking up.

Swansen

um? i don't think you want to lock up the rears, and on that, i would think it would be a lot easier for the drums to lock up. Ether way, its not a good idea to remove the LSPV for daily driven use, for a trail rig, i'm sure its ok. The LSPV is a part of the Toyota brakes, they were engineered that way,

Tofer

it take alot to lock them up, but i can which tells me the brakes are working.


the 2 lines from the LSPV used to be to 1 line (with arb line) down to the brakes.

dirtoyboy

really? how do you adjust your brake bias? Have you tested your bias to see which end locks up first? This does not seem safe at all to me....

abecedarian

so you're saying you have the two lines from the MC tee'd together and dropping to the axle with one flex line and tee'd out to the wheels?
hope you don't blow a rear wheel cylinder, caliper or a line 'cause you'll loose all your brakes.

dirtoyboy

one line is a return line and one is a pressure line....

abecedarian

return to where?
you might wanna trace those lines and figure where they go.
one comes from the rear circuit on the mc, the other tee's into the passenger front line.

dirtoyboy

The return line reroutes excessive line pressure back into the front brake-lines. The tee fitting where the return comes in is rerouted. When you use a brake prop valve the "return" line is completely eliminated...thats what makes it so nice...it completely seperates the front and rear brake systems...

drew303

=)

You can remove the LSPV, but you'll want to hook up a Manual LSPV. Running without one means equal pressure is exerted on the front and rear brakes simulataneously which will cause rear-brake lock up if you ever STEP on it. Which... will cause a complete loss of directional control. And it'll probably happen in the rain.

I redid my entire braking system about a year ago when I did my rear-disc brake conversion and I've tried all the combinations mentioned above.

You can trick your LSPV into being wide open (no resistance) (tie the bar as high up as it'll go). Go for a drive and hit the brakes HARD and see what happens. =) Done it, it's not safe.

My Manual LSPV (from Summit)



I'd reccomend a more permanent mounting solution but having said that I've had no problems with the zip tie solution =)

I run a manual LSPV and the stock LSPV (under the bed) with my disc brakes. Most folk who do the disc conversion don't use their rigs as a daily.. Without both LSPV's the rear will lockup before the front (unsafe).

drew303

For more information, you can browse my Disc Brake Conversion thread here:

https://www.yotatech.com/forums/f116.../#post50586263

and Elvotas (for part numbers and further details... ie the manual lspv)

https://www.yotatech.com/forums/f116...c-swap-107749/

SwampThing

Yeah, I did the t-mod on my 89 4rnr. Had no braking issues. Could lock up the rear just fine when I needed to, but still had control over when it did it. Though the welded rear and great rear brakes made for great spin outs in the rain!

abecedarian

I get how the valve works.
The original post I replied to concerning this was a "TEE", not a proportioning valve, fitting installed in place of the LPSV between what you are calling 'pressure' and 'return' lines.
The error is in assuming that one can tee the rear circuit into that so-called return line which is connected to the front brakes, in essence making it an extension of the front circuit, and not realizing that the loss of pressure from a failed caliper, cylinder or hose or hard line will cause complete brake failure, except for the parking brake.
You can completely eliminate the LPSV and the line from the front circuit then tee the rear circuit to the two rear wheels, and optionally install an adjustable proportioning valve anywhere on the rear circuit hard line.
And the LPSV uses the front brake pressure to help modulate the rear pressure depending on the position of the load sensing spring/vehicle load. There is no bleeding of excess pressure from the rear to the front since the front brake pressure is higher than the rear at all times except when the LPSV determines the truck to be fully loaded at which time the front and rear pressures are equal. Check the FSM pages BR-34 and BR-35.

Anyways, I'm done. Cheers!

tc

First, the front/rear isolation of the Toyota braking systems SUCK. I had a line fail and lost all the brakes in my '89.

Anyways, with my new suspension, the LSPV is going to be a major headache. Any ideas how removing it will affect things with the rear ABS?