Adjustable proportioning valve question

[blazerbones]

Hi everyone.

I'm removing the rear adjustable proportioning valve off of my M1008 for various reasons... it's the same setup as any factory 80's chevy 1 ton pickup as far as I know... with the prop valve linkage actuated by the weight in the pickup bed.

Anyway, I fixed the linkage in the open position so that I could evaluate if the brakes would be OK after just bypassing the valve with a straight line.

WAY to much rear braking. Spinout waiting to happen.

Got an adjustable valve off of a friends shelf, but it came with 1/8npt to 3/16" tube adapter. The rear brakes are 1/4" line.

I'd like to know if it would be OK to use the smaller ID type proportioning valve, or if that would act as a restrictor to fluid flow to the big rear brakes (14BFF drums).

Also, what type of adjustable valve I should use, or where to find a 1/8"npt to 1/4" tube adapter? No dice at the local auto parts stores.

Thanks for any help in advance.

 

[4X4HIGH]

Just remove the complete valve and use a union to connect the two lines together (if the lines aren't long enough to make this happen then add a new piece of line inbetween the existing lines). The valve you're talking about is called a load sensing proportioning valve. There is still a standard front/rear proportioning valve on the front crossmember.

 

[blazerbones]

Thanks for the input Scott.

When I turned up the load sensing prop valve manually and kept it there (I'm assuming that's 100% pressure transfer across the factory valve) the truck had scary rear brakes. On wet pavement the truck was dangerous in my opinion.

I believe the load sensing valve had the pressure to the rear turned way down during unloaded conditions.

Maybe there's something else wrong.

 

[4X4HIGH]

I don't know which way does what but many people have removed them with no issues. They were also installed on some Burbs. The Burb i pulled my 14ff from had it but someone just disconnected the lines and did what i described. Don't worry about it, just bypass it as i said and you should be good.

 

[blazerbones]

I just thought I'd let everyone know that removing the valve didn't work for me. Rear tires were way too easy to lock up... with little stock tires and 35's.

Everything in the entire braking system seems to be functioning 100%, and I bled out and replaced the silicone based fluid in its entirety.

So I found the needed fittings and it's working good with the new manual prop valve adjusted all the way down (60% pressure to rear).

This is an M1028, thought some others might find this useful.

 

[MontanaJohn]

Anybody know where new stock replacement rear proport. valves are available? Mine is leaking on my '82 GMC dually, and I'd just like to replace it. Or possibly a rebuild kit? Tired of bleeding the rear brakes every time the fluid drains out of the master cyl.

 

[tRustyK5]

Old thread, but my old K5 when I installed the 14 bolt with the big drum brakes would lock up so easy it was retarded. I swapped to rear discs (3/4 ton front stuff) and braking was amazing after that. I could lock up all 4 39.5's, but never got rear only locking. The braking was awesome, but much more balanced and this was without any adjustable prop valve to fine tune it. IMO the huge 13" x 3.5" brakes are just too much brake unless you have 4000lbs in the bed.

Rene