Hydroboost Prop valve Question

[72tutone]

Guys,
I scored a hydroboost off a 93 astro van over the weekend. I have a question within regards to the prop valve and master cylinder hookup

Which port on the master cylinder serves as the front brakes? I plan on using my original prop valve and I need to know which port goes to the port on the master cylinder. I would think the larger of the two reservoir would go to the front brakes and the smaller to the rear. Whats odd though it looks like the front of the master cylinder users 1/4 and the rear uses 3/16. So from that perspective I would think the larger would go to the rear as well. But its also using the front port which is the smaller of the two reservoir's

My setup is disc/drum factory.

Thanks all

[Valarius_Starchaser]

I looked on my catalog and found on the original prop valve set up the front port on the prop valve goes to the front (smaller) reservoir on the master cylinder.

That being said I do not see where the brake line run to the wheels from the prop valve so I do not know if it infact goes to the front wheels from there on the original setup. I would go back and take a look at the van you got it from to be certain.

[72tutone]

Originally Posted by Valarius_Starchaser

I looked on my catalog and found on the original prop valve set up the front port on the prop valve goes to the front (smaller) reservoir on the master cylinder.

That being said I do not see where the brake line run to the wheels from the prop valve so I do not know if it infact goes to the front wheels from there on the original setup. I would go back and take a look at the van you got it from to be certain.

Thanks Valarius. So I went out and looked at my truck again and did confirm the front of the prop valve 3/16 is for the front disc setup and the larger 1/4 is for the rear brakes.

So looking at the hydro master cylinder I would believe that the larger of the two reservoirs would server as the front brake connection and the smaller the rear.

The more I'm thinking about it, it makes sense. As the line coming out of the hydroboost master cylinder large reservoir is also a 3/16 line and the smaller is the larger 1/4 line.

I guess they have the larger line for the amount of length it takes to get the fluid all the way to the back of the truck?

I dont know, I'm taking an educated guess. If someone knows for certain can you please chime in?

This is place is the best for information. Quite invaluable!

[Andy4639]

Factory front disc line works on pressure more than volume so the smaller line is correct.

Rear drums work off volume instead of pressure so the 1/4" lines are correct.

[72tutone]

Awesome Andy.

So it looks like the front of my prop valve 3/16 will hook to the rear of the MC <large reservoir>, and the 1/4 is self explanatory from there.

Excellent information. Best community around. Cheers!!!

[cleszkie]

All the above info is correct if you have a 1/2 truck. If you have a 3/4ton truck, then the front and rear reservoirs are reversed on the master cylinder.

[Keith Seymore]

Originally Posted by 72tutone

Which port on the master cylinder serves as the front brakes?

The large reservoir and corresponding port go to the front brakes. This is because of the volume of fluid required to backfill the movement of the front pistons, compared to the size of the rear wheel cylinders. (Visualize the piston diameter vs the wheel cylinder diameter and I think you'll agree).

It should be as you have it marked in the first photo.

K

[Keith Seymore]

As far as the prop valve - I'm being told that it should be marked ("in" and "out"). Take a good look at it and let us know if that is not the case.

I think we collectively have decided it would be the opposite of what you show in your second picture.

K

[72tutone]

Originally Posted by Keith Seymore

As far as the prop valve - I'm being told that it should be marked ("in" and "out"). Take a good look at it and let us know if that is not the case.

I think we collectively have decided it would be the opposite of what you show in your second picture.

K

Ill take a look at the prop valve when I get a free moment and let you all know.

Thank you all again