Brake proportion valve question

clhman

clhman

Member
Curiousity question. I have an '80 Scout II, 304, 727, 44's. I am cleaning up all the extra useless wiring in the engine bay and I'm perplexed about something. The master cylinder goes directly into another valve beneath it and then on to the brakes. I assume it is some sort of propotioning valve. My question is there is a green wire that comes out of the top of it. What is that? Ground? Do I need it? The brake light switch is behind the pedal so I know it can't be that. I haven't bought a shop manual yet, so sorry if this is an obvious question. Thanks.
 
Its a disc/drum proportioning valve. The wire is for the brake warning light in case of a fluid pressure issue.
 
Yep. If the light comes on and stays while the e-brake is cancelled, it is either a problem with the e-brake switch (common) or a hydraulic system issue.
 
This has come back to haunt me. During my conversion I changed to hydroboost brakes and changed axles, etc. When I installed everything and went to bleed the system, somehow I tripped the stupid thing. I cannot for the life of me get the dumb thing to recenter. I've looked online and there are several people that give directions on how to fix it and it just doesn't seem to want to reset. Anyone have any suggestions on how to handle it? Maybe a link to your favorite directions? I'm almost at the point of just replacing it. Thanks for the ideas.
 
Still having problems with brakes

I am ready to throw the towel in. Someone must have had the same problems as me. I have thrown the book at this issue and I am super perplexed.

I swapped in a hydroboost from a breadvan to start this issue. This is the history of it...

Swapped in Dana 44's from an earlier Scout.
Rebuilt all brakes.
Changed proportioning valve.(new)
changed master cylinder.(new)
changed almost all brake lines.(new)
bled system multiple times.
No leaks.

Somehow the proportion valve is still tripping. I am stopping right now on just the rears. The only thing that isn't new is the hydroboost. Could that be an issue? Why is my valve tripping? What am I missing?

I could use any ideas anyone has.

Thanks
 
You have changed two things that could be your issue.
The mc and the prop valve should be identical to the ones you had originally. If not, there will be problems.
Assuming the Scout is still disc/drums, you'll need a disc/drum mc. If you are using the parts that came with the hb off the bread truck, it might be a drum/drum setup. Your truck wants a m/c that has a large reservoir located in the front. This is for the drum brakes. Its bigger because the wheel cylinders need more fluid to apply the brakes. The fact it is in front makes it confusing. Don't attach it to the front brakes (discs).
The same is true of the prop valve. It has to have the correct lines run to the correct ports. Since most of the braking is done via the front axle, the ports to the rear of the vehicle get diminished pressure to keep the rear axle from locking up first. Full pressure always goes to the front.
Make sure all of that is correct and you'll have brakes that put you through the windshield. Best mod I did to my truck was that hydroboost.
 
Thanks for the reply. I think I 'might' have it figured out. I reused the Scout mc (disc/drum) and installed a new Scout proportion valve. The only thing that is from the breadvan is the hydro. I think the root of my problems is the distance the hydro is from the firewall and the distance the pedal is from the hydro. I don't think the mc is fully reseting. I have never gotten a hard pedal since the swap. I'm going to start over from scratch. I'll report back with my results next week.

Fwiw, I did hook up the brakes the way they were before as per the service manual. It says big reservoir to the front discs and small rear to the drums.
 
Uhh yeah, my dyslexia gets the better of me sometimes...
Good catch on the m/c. Hope you get it going. You won't be disappointed!
 
I finally have brakes only to now be down due to a leaky tank. Ugh.

I ended up with a different hydroboost unit and a different mc out of a late 70's Chevy. I needed one with a 'shallow' pocket to work with my hydro as opposed to the deep pocket that IH used. Anyway, on to different problems now!
 
I have a Scout 800 that has a Scout II master cylinder, proportioning valve, front disc brakes and rear drum. What is the process of adding a hydroboost.

I am very interested in that. Currently I practically have to stand on the pedal to get this thing stopped properly and power brakes seems the way to go.

Thanks.
 
hsv_scout said:
I have a Scout 800 that has a Scout II master cylinder, proportioning valve, front disc brakes and rear drum. What is the process of adding a hydroboost.

I am very interested in that. Currently I practically have to stand on the pedal to get this thing stopped properly and power brakes seems the way to go.

Thanks.
Click to expand...

Do you already have power steering?
 
clhman said:
do you already have power steering?
Click to expand...

No I don't currently have power steering but that is on my to do list. My current steering is very sloppy and I figure if I am going to need to rebuild/replace the steering box I might as well go the power steering route.

I currently have a 266 v8 in it.
 
hsv_scout said:
no I don't currently have power steering but that is on my to do list. My current steering is very sloppy and I figure if I am going to need to rebuild/replace the steering box I might as well go the power steering route.

I currently have a 266 v8 in it.
Click to expand...

Okay, then you have quite a bit of work then. It'll be totally worth it. Your shopping list will include:

power steering pump with two returns
power steering gear box
new hydraulic lines
hydroboost unit
pos. New master cylinder
return lines
 
clhman said:
okay, then you have quite a bit of work then. It'll be totally worth it. Your shopping list will include:

power steering pump with two returns
power steering gear box
new hydraulic lines
hydroboost unit
pos. New master cylinder
return lines
Click to expand...

Do you have any recommendations on what to use for the power steering pump, gear box hydroboost unit etc...? I have noticed several different models that have been mentioned but not sure which is the most popular or easiest upgrade.
 
hsv_scout said:
do you have any recommendations on what to use for the power steering pump, gear box hydroboost unit etc...? I have noticed several different models that have been mentioned but not sure which is the most popular or easiest upgrade.
Click to expand...

The saginaw power steering pump for a Scout II would work fine. It will need a cover though that has two returns. Several choices are out there. Dodge cummins one works or a GM 6.5 diesel version.

Most hydroboosts are the same. The Chevy astrovan seems to be the simplest/easiest.
 
If there is room for it, and yes it does run off manifold vacuum. Be aware there are two varieties, one for power drum/drum, and one for power disc/drum. The one in your picture is for power disc/drum, for I believe 75 and newer scouts. The hydro boost takes a little more digging to find all the parts, but takes up less space, as well as really stopping. I had them on an 84 diesel suburban - it was a slug but it stopped on a dime.
 
If you go with the hydro boost, add power steering pump mounting brackets and pulleys, to you shopping list.
 
This sounds like an excellent upgrade. Need to start collecting the parts.

So as I understand it I would need a power steering pump and box from a Scout II and the hydroboost unit from an astrovan. Should be lots of those I the junkyard... Lol

what about a proportioning valve? Does the Scout II one work?

Does anyone have any pictures of how this all looks piped up?
 
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