Author Topic: Factory adjustable proportioning valve? Check it out...  (Read 3377 times)

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H8PVMNT

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Factory adjustable proportioning valve? Check it out...
« on: Oct 05, 2016, 09:01:04 AM »
I am currently peeling down a parts truck.  It was a 1980 2WD SR5.  I was taking the back end apart and I found it odd it did not have a LSPV, but when we got to the engine bay I found what I think is a brake proportioning valve bolted to the brake booster directly below the master cylinder.

The front brakes are straight through and the rear fluid seems to be metered through something that you can take out and adjust. I haven't taken it apart yet so I'm not sure it's adjustable.  Anyone ever seen one of these?

I might use it next time I want to eliminate the LSPV instead of the zip tie up the rod or all thread adjuster method.  Might be a super cheapo or free alternative to the aftermarket pieces.
« Last Edit: Oct 05, 2016, 03:49:59 PM by H8PVMNT »
“I would rather wake up in the middle of nowhere than in any city on earth.”
– Steve McQueen

"Except for maybe Seattle."  -H8PVMNT

"I plan to hit 300k in this truck"  :)bestgen4runner

 "I'm jealous of your shop. It has concrete and doesn't smell like pickles like the old shop  "  300K

H8PVMNT [OP]

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I took the guts out at lunch.  The rear brake bias is restricted by a rubber seal that opens and closes in a bore and is modulated by a coil spring.  So this is not really adjustable unless you changed the spring pressure.  This would be pretty easy to do though.  I am guessing it will be "just right" front to rear bias on a pickup with rear drums.  I think I'll try it when I re-do my 1980 4WD and just change the spring out for lighter or stiffer ones if it needs a change.

I know this is gloriously boring since we have slick adjustable valves with knobs for $40, but I usually have little or no budget, especially on my pickup, so these kinds of possible junkyard find tricks always get me excited. 

It all adds up :).

You figure if you can use recycled chevy rears and rears up front for springs, yank 13" stroke shocks off the back wrecked super-duties and this proportioning valve instead of a new one,  you already paid for your dual adapter.  See my line of thinking here?
“I would rather wake up in the middle of nowhere than in any city on earth.”
– Steve McQueen

"Except for maybe Seattle."  -H8PVMNT

"I plan to hit 300k in this truck"  :)bestgen4runner

 "I'm jealous of your shop. It has concrete and doesn't smell like pickles like the old shop  "  300K

Gnarly4X

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....  See my line of thinking here?

Yes... it's called FRUGAL!!... I've been in frugal mode since 2008.

Gnarls.

« Last Edit: Oct 05, 2016, 09:52:20 PM by Gnarly4X »
1986 XtraCab SR5 22RE 5speed W56B, ~16,000 MI after break-in, DIM (Did It Myself) rebuilt engine - .020" over, engnbldr RV head, OS valves, 261C cam, DT Header. https://imgur.com/oACTHTR

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Gnarly4X

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Experience is the best teacher.

Experiencing “no brakes” while rockcrawling and trails where I was steep climbing, is a real attention-getter!  :yikes:  I have seen several times a vehicle losing control while their vehicle has no brakes and starts backing downhill!  This can be very scary to very tragic. 

On my ’85 and ’86 I adjusted the stock prop valve - designed to increase hydraulic pressure to the rear wheels when the bed of the truck is lower, presumably when loaded.  I adjusted and tested it so that it would actually lock up the rear wheels under heavy braking on the street.  This was to provide more braking to the rear wheels when wheeling…. which was very noticeable.  When you are climbing a rock, hill, or ledge the weight of the vehicle is shifted to the rear wheels so your front brakes are practically worthless – now you have less than half of your normal braking power, right.

The funny thing about changing the proportioning valve like I did is that while driving on the street, I had to be extra careful with braking too hard. If I did, the rear wheels would lock up and with the big tires it sounded like a very loud tire screeching and sometimes I’d slide for 10 or 15 feet.  This happened once in awhile and it was funny to see the reaction of the vehicle in front of me as they are looking in their rearview mirror as my lifted truck with 33” tires comes barreling down on them with screeching tires!  When they locked up and the street was wet, the back end wanted to come around, so I was always on “alert” when driving on wet roads.

Gnarls.  :D
« Last Edit: Nov 03, 2016, 05:06:12 AM by Gnarly4X »
1986 XtraCab SR5 22RE 5speed W56B, ~16,000 MI after break-in, DIM (Did It Myself) rebuilt engine - .020" over, engnbldr RV head, OS valves, 261C cam, DT Header. https://imgur.com/oACTHTR

God Bless Our Troops... Especially Our Snipers. The 2nd defends the 1st
MEMBER: WWP, T2T, VFW, NRA, GOA, SAF, Mammoth Nation, C2 Tactical, Hillsdale College, Humane Society of the U.S. - "We cannot solve our problems with the same thinking we used to create them." ~ Albert Einstein

Ritchie

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H8PVMNT,
Are you trying for a 50/50 set-up with the valve?

I have my Wilwood set at 50/50 and it works awesome... just curious.
'03 Step side Pre-runner, F/R 4WU 3 linked, F/R Diamond axles, F/R ARB's w/5.29's, F/R Fox 12" CO's, ShrockWorks front bumper, self made rear bumper, WARN M8000S w/ remote, 4.7 Inchworm Lefty, MC sliders that hold air & a bunch of other stuff.

H8PVMNT [OP]

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H8PVMNT,
Are you trying for a 50/50 set-up with the valve?

I have my Wilwood set at 50/50 and it works awesome... just curious.

I'm thinking like 55/45 but not completely sure.  We have ice on the roads here probably 5 months out of the year so you really don't want your rears coming in too soon.  I made an adjuster from all thread to raise and lower the cut off stub of the arm on my LSPV for my 4runner and messed with it until the fronts lock just before the rears.  We had ice this morning and I did a good 45 mph brake check and it was still just perfect.  Rears came in just after the fronts and I locked but tracked straight.

So I want to have the same end result on my pickup when I do it.  I have no idea how this particular piece will work so I will just have to run it and see how it is, then tune it by changing springs.
“I would rather wake up in the middle of nowhere than in any city on earth.”
– Steve McQueen

"Except for maybe Seattle."  -H8PVMNT

"I plan to hit 300k in this truck"  :)bestgen4runner

 "I'm jealous of your shop. It has concrete and doesn't smell like pickles like the old shop  "  300K

 
 
 
 
 

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