Proportioning valves

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Spook50

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Everyone says to install a proportioning valve when doing a rear disc conversion. I'm curious as to why this would be needed in addition to the LSPV? Has anyone tried adjusting the LSPV to accomodate for the pressure necessary to work the calipers? I would expect that like a regular prop. valve, the LSPV would simply reduce the initial pressure to what would be best for the rear brakes (based on what it's adjusted to). I would've thought that another prop. valve inaddition to the LSPV would bugger up the works, unless the LSPV is eliminated completely from the system. IIRC, the LSPV is connected only to the rear brakes, right? The front brakes receive pressure directly from the master cylinder?
 
The LSPV is calibrated for the weak drum brakes. Once rear discs are installed w/ more braking force than the stock front discs, all bets are off.

You could try changing the springs inside the LSPV, but that's a lot of trial & error hassle for something that may or may not work right, eventually.

Seems easier to install a Wilwood PV, adjust it for 4 wheel lock up, and call it as good as most other stock vehicles.
 
FJ40Jim said:
The LSPV is calibrated for the weak drum brakes. Once rear discs are installed w/ more braking force than the stock front discs, all bets are off.

You could try changing the springs inside the LSPV, but that's a lot of trial & error hassle for something that may or may not work right, eventually.

Seems easier to install a Wilwood PV, adjust it for 4 wheel lock up, and call it as good as most other stock vehicles.

Well what I'm thinking is, since you can adjust the positioning of the LSPV where it connects to the axle, if it was adjusted to a "more weight in the back" position, would you be able to adjust it far enough to send the right pressure to the discs?

I'm thinking I'll go ahead and order the Wilwood valve in case my theory is wrong, but when I do the install, I'm going to at least attempt to mess with the LSPV. The valve allows for a lot of travel of the rod connected to the axle, so I would think it could go far enough to send the MC's full pressure to the rear brakes. At least that's my theory. But if the internals of the valve reduce the pressure a great deal for the drums, then installing the Wilwood valve forward of the LSPV would do no good either, unless the LSPV is eliminated from the system.

I'm probably sounding confusing as all hell, but I'm just pondering out loud at this point. I really should get a junker LSPV and break into it so see if I can figure out how it works. What other Toyota vehicles used this same LSPV?
 
Adjusting the angle (load) of the rod varies the rear brake pressure a little. But if the GM rear discs go on, then the rear brakes are much more effective, requiring much less brake pressure. When I do rear disc on a 76-newer fj40, I add the Wilwood adjustable PV to the stock PV. The 2 together in series provide enough pressure reduction to keep the rears from locking. The wilwood by itself will also do it, but requires turning the knob much further. You might consider using both PV as well, to provide the general pressure range needed (wilwood) and to retain the minor load sensing feature (stock PV).
 
FJ40Jim said:
Adjusting the angle (load) of the rod varies the rear brake pressure a little. But if the GM rear discs go on, then the rear brakes are much more effective, requiring much less brake pressure. When I do rear disc on a 76-newer fj40, I add the Wilwood adjustable PV to the stock PV. The 2 together in series provide enough pressure reduction to keep the rears from locking. The wilwood by itself will also do it, but requires turning the knob much further. You might consider using both PV as well, to provide the general pressure range needed (wilwood) and to retain the minor load sensing feature (stock PV).

I was under the impression that more pressure was needed for discs as opposed to drum brakes because of a smaller friction surface, but if the Eldo calipers I'm using require less pressure than the stock wheel cylinders, that answers alot of questions I had. In that case I could see why the LSPV might not be able to be adjusted far enough to properly set the pressure at the rear calipers...
 
Don't for get that Eldo & Monte carlo calipers have different piston sizes so the y require differnt pressuree (The eldo's are smaller so require more pressure) I would install the calipers with the LSPV installed and see if the eldo's will even lock at all (I don't think they will) then pull the LSVP & see if they will lock first. if they do then install the wilwood valve and adjust them right. just remeber you want them to lock after the front & it should be pretty straight forward waht to do.

I had MC's & they worked great with WW prop valve, then went to Eldo's & they won't lock at all. Now I need to pull the FJ60 Prop valve and see if that will give me enough pressure to lock the eldo's.

There's a million combo's out there just find the one that works for you.
 
Never understood why you want the fronts to lock 1st: you couldn't steer & you've reduced braking on the heavier end. And when you have a load in the back it's a more dramatic difference.

And to explain what's really going on check out http://www.teamscr.com/grmbrakes.htm
 
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Ok .. my experience ..

When I go with reard disk brakes I thought " I need a PV " so I await to get all in place and test it. Yes my actually setup rebuild front calipers, new pads ( Toyota ) new master ( 80 series ) and rear disk brakes very very well ..

With 37" MTR and unloaded .. means block the rear tires ..

Ususally I use my TLC only for long trips .. ( are not my DD ) usually with more than 400 lbs in toolboxes, spares, hi lift, chains, coolers etc .. with this load awesome braking performance ..
 
If you lock the rears first you will slide sideways into intersections..

It is a bit of a headache..
 
Mace said:
If you lock the rears first you will slide sideways into intersections..

It is a bit of a headache..

I try to do that .. but I can't .. ! :D
 
I can ;)


It gets creepy..


40 with 39.5's, 80 series master, D60 front and 14 bolt rear with discs...

I need to turn the proportioning valve down some more.
 

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