brake ignorance question

psy9zach

Full Access Member
Joined
Aug 27, 2018
Posts
72
Reaction score
10
Location
keego harbor michigan
not sure where to start this question but my truck was originally a 460 gas auto 2wd, its now a 6.9idi it has a mount with a old proportioning valve on it thats bypassed with it going straight to a splitter to the drums, i know the 6.9 usually uses RABS and ive converted to hydroboost but would putting a proportioning valve in the truck get me more pressure to the front? im about to be replace all of brake lines(blew a line between front and read not sure if its related) and would like to get it to behave somewhat normally ive never had a vehicle with working abs so to me its not a loss not having it. just curious bc i saw another post where someone said our master cylinder(the old iron ones) have a built in proportioning valve but if it has one it sure dont look it to me but ive been wrong before and this is what it looks like

You must be registered for see images attach
 

Macrobb

Full Access Member
Joined
Jun 12, 2016
Posts
2,380
Reaction score
1,234
Location
North Idaho
I think the proportioning valve was only used on earlier models, to reduce the amount applied to the rear brakes when unloaded(to prevent locking up the rear tires). My 88s and later(with rear ABS) do not have the valve.

If you reinstalled it, you could probably get it to do what it was designed to do - prevent the rear tires from locking when unloaded, and have full force to them when loaded - but I've never worked with one myself. Looks simple enough though.
 

Randy Bush

Full Access Member
Joined
Jan 2, 2019
Posts
708
Reaction score
453
Location
Great Falls, Mt
You must be registered for see images attach
All of my trucks have this valve . 89-90-93 dually. It screws into the master cyl.
 

Macrobb

Full Access Member
Joined
Jun 12, 2016
Posts
2,380
Reaction score
1,234
Location
North Idaho
You must be registered for see images attach
All of my trucks have this valve . 89-90-93 dually. It screws into the master cyl.
That's not a proportioning valve, it's a residual pressure valve - basically, drum brakes need to have a little pressure even when your foot is off the pedal, so they don't collapse too far. Disc brakes don't need any pressure. So, a disc-drum setup will have a residual pressure valve on the drum side.
 

Randy Bush

Full Access Member
Joined
Jan 2, 2019
Posts
708
Reaction score
453
Location
Great Falls, Mt
That's not a proportioning valve, it's a residual pressure valve - basically, drum brakes need to have a little pressure even when your foot is off the pedal, so they don't collapse too far. Disc brakes don't need any pressure. So, a disc-drum setup will have a residual pressure valve on the drum side.
That may be , but it is still listed as a proportioning valve. Isn't the job of the brake adjuster to keep them from collapsing to far.
 

franklin2

Full Access Member
Joined
Feb 24, 2009
Posts
5,161
Reaction score
1,385
Location
Va
Don't worry about not having the ABS, that system is difficult to keep working and most people bypass it. The factory proportioning valves on the older trucks are starting to fail also with rust in the fluid. If I were worried about it, I would buy one of these adjustable valves and put it in the line to the rear. You could mount it beside the seat if you wanted to adjust it on the fly.

https://www.speedwaymotors.com/Speedway-Purple-Adjustable-Brake-Proportioning-Valve,23498.html
 

Forum statistics

Threads
91,217
Posts
1,128,495
Members
24,045
Latest member
Ramtough01
Top