LSPV Bypass

[codyrobinson]

I have a '91 FJ80, and experienced squishy weak brakes after replacing my knuckle.

I bled the brakes to death, then replaced the master cylinder, got shot in the eyes with brake fluid, bled for a few more hours... all to find out that my LSVP needs to be replaced.

I see that you can bypass the LSVP, if anyone can help explain or show me pictures, I would appreciate it!

Cody

 

[alkaline747trio]

Ok, there are two lines exiting your master cylinder. One leads to a Tee then to the front brakes and the proportioning valve (this is actually coming from the valve). The other leads directly to the proportioning valve.

What you need to do is remove the line running from the valve to the Tee in the front brake line, and remove the valve from the rear brake line.

Having done this will yield one line running from each port on the master cylinder to each axle without any connection between them other than the master cylinder.

 

[codyrobinson]

Correct if I am wrong. But it appears their are two lines going in to the LSPV and two lines going out. What you're saying is to take out the LSPV and just have a continuous line system?

How do I know which back line to connect to the correct line coming from the master cylinder?

What all do I need to buy for this procedure? 1 brake line and a T ?

I'm trying to picture the T in the front brake system, are there 2 "T" valves in the front brake lines?

 

[codyrobinson]

I got under my FJ80 and the first picture is what I perceived to be the brake system. Please tell me if this is wrong.


The next diagram is what I was picturing for a bypass. Once again, I am posting this for help and critique, so please let me know!

 

[Ebag333]

That looks right to me.

Instead of a straight T you may want to consider something like this:
http://www.summitracing.com/parts/RSD-PV71/
(Note: That's probably the wrong size, but you get the idea.)

That would at least give you some control over it in case you figure out that the rear brakes are kicking in too much. IMHO I wouldn't worry too much about going with an open T (drum brakes shouldn't be able to overpower disk anyway), but I'd like the ability to have some measure of control over it if I wanted to dial it back.

 

[codyrobinson]

OR do you just cut out that extra line from the front T to the LSPV completely? And have just two lines from master cylinder, 1 straight to front axle and 1 straight to back axle ?

 

[Ebag333]

OR do you just cut out that extra line from the front T to the LSPV completely? And have just two lines from master cylinder, 1 straight to front axle and 1 straight to back axle ?

You are making it too complex. Just go with a T or a manual proportining valve (with dual inlets and a single outlet) in the back.

 

[breathed]

I believe Beno replaced his LSPV with a manual valve that had the proper metric threads. Maybe he'll be so kind as to post the info for it.

 

[codyrobinson]

Thank y'all for the responses. A few more questions

1. How do I figure out the size of my brake line and nipples on the flared ends that would go into a manual proportioning valve or a T?

2. The angles with a T don't seem to work would this set up be best?





3. Has anyone ever taken a brass or aluminum block, bored and tapped out the needed holes and used that as an "open valve" in place of a proportioning valve?

Thanks again for the help!

Cody

 

[Cancruiser]

Cody,
I am experiencing similar symptoms with my brakes. I have rebuilt all 4 calipers and still feel mushy. I was wondering how did you come up to the conclusion that your LSPV is the culprit? Maybe it is the same in my case too. Is there a way to diagnose it?
Cheers,

 

[alkaline747trio]

OR do you just cut out that extra line from the front T to the LSPV completely? And have just two lines from master cylinder, 1 straight to front axle and 1 straight to back axle ?


View attachment 367189

Yes, this is EXACTLY how to do it. Ebag, not at all too complex....look at his diagram, that is the SIMPLEST system possible. And best at that. The extra line is only to bleed the extra pressure released from the LSPV to the front brakes.

Without the LSPV but still having the extra line you are making the system very vulnerable to total failure when only one axle has an issue.