Hydroboost upgrade went haywire (brake gurus please help)

[Rox Crusher]

so back in 2010 I upgraded my 77 to hydroboost using the following components;

- astrovan booster, camaro master cylinder, saginaw dual return pump, stock power steering gear box, and h-block. When I put this system in it worked way better than I expected and was working flawlessly before I started my swap.

- I recently completed my 5.0 Explorer swap which means I now have a brand new Explorer pump, a single return remote reservoir, and I swapped out the camaro master cylinder for a new astrovan master cylinder with S10 reservoir

when I went to bleed the brake system I noticed that the h-block was leaking at the imbalance switch so I went and got one from the junk yard and it no longer leaks.

now to the problem, the rear brakes are working well but the front brakes don't seem to be working at all.

I ca't get the pedal to firm up even though I have bled the system several times. There is still a minute amount of small air bubbles coming from the front calipers but I'm not convinced that is the whole problem.

please send me in a direction that allows me to get this sucka back on the road

thanks in advance

 

[TAC71]

simple things first...did you bench bleed the master first? are you getting good flow when you open the bleeder on the frt cal.?

 

[Apogee]

My guess would be that the master cylinder wasn't adequately bench bleed. The quick take-up master cylinders can be a bit more difficult to fully and properly bleed than your typically straight bore units. I've included a link below to a Bendix procedure below.

www.remanbrakes.com/pdfs/benchbleedinggmquicktakeup.pdf

Just as a side note, I would also generally plug both outlet ports after bench bleeding and then confirm that there is no trapped air remaining in the MC by pushing the piston by hand. The piston should only move a small amount, maybe and 1/8" to 3/16", before hydraulically locking. If it feels spongy at all then you need to bleed more. Tapping on the MC body with a soft mallet while bleeding can help dislodge particularly stubborn air bubbles.

HTH,
Tobin

 

[Rox Crusher]

simple things first...did you bench bleed the master first? are you getting good flow when you open the bleeder on the frt cal.?

yes indeedy, but I am not opposed to doing it again

 

[Rox Crusher]

ok, stupid question time............

what about routing of lines from master cylinder to h-block ?

I have heard conflicting info. Most say that the line from the rear of the m/c always goes to the front brakes. I believe a different thread here (which I can't find) said it didn't matter ?

and yes, the reason I ask is that mine is plumbed with rear to rear and front to front

I think the lines are the same inside diameter and the h-block is stock unit

 

[ransil]

bigest reservoir goes to front brakes..

 

[Rox Crusher]

bigest reservoir goes to front brakes..

the S-10 reservoir I am using has two equally sized reservoirs. Essentially they are both the same size as the large reservoir on the astro van reservoir.

It is almost like one large reservoir as it has a short baffle in the middle that allows the fluid to be shared between the two chambers above a certain point.

I really like it but I am easily impressed

 

[Rustytruck]

Does the astrovan have rear drums? if not you no longer have a residual valve in the master cylinder to retain some brake pressure in the line without this pressure the rear drum brake springs collapse the rear cylinder. this makes the rear brakes take more fluid per stroke than the disks, which will give you uneven braking disks will lock up first. if your running a didk-disk mastercylinder you should add a residual valve to the drum brake side. you can buy them to adapt into the master cylinder port.
just one example.
http://www.speedwaymotors.com/Wilwood-Red-Drum-Brake-Residual-Valve-10-PSI,18908.html

 

[Apogee]

The Astro MC is front to rear and rear to front ASFAIK. I know the 1990-1993 are that way, but you haven't specified the year. After a quick check, it looks like the 96-03's are reversed as well.

 

[76Broncofromhell]

Typically the reservoir closest to the firewall goes to the front brakes - except in Toyotas which use an unusual rear brake metering system. But that's not pertinent to this conversation.

I would doubt this is a bench bleeding issue. My guess is the shuttle valve is tripped (you have to clip it in place when bleeding), or you have a leaking line. I've never bench bled a master when installing it, and also never had this sort of problem.

 

[Apogee]

...if not you no longer have a residual valve in the master cylinder to retain some brake pressure in the line without this pressure the rear drum brake springs collapse the rear cylinder.

The purpose of the residual pressure valve in a drum system is to maintain a very small amount of pressure to the rear brakes to inflate the cup seals so they do not leak, not to oppose the drum retraction spring. If you run the numbers, 10 psi residual pressure in a 15/16" bore wheel cylinder with .69 square inches of piston area exerts less than 7 pounds of force whereas the retraction spring is typically much higher by at least a factor of 10.

By keeping the seals inflated with a residual pressure valve when the retraction springs collapse the wheel cylinder, it keeps them from folding a lip and burping fluid out and air into the system, which can create a spongy pedal over time and reduce your rear brake effectiveness.

Tobin

 

[Rox Crusher]

so I will find the appropriate adapters and swap the lines and give it another whirl

 

[Ranchtruck]

The purpose of the residual pressure valve in a drum system is to maintain a very small amount of pressure to the rear brakes to inflate the cup seals so they do not leak, not to oppose the drum retraction spring.

Adding on to this, the valve that helps compensate for overcoming the springs on the rear drums is the metering valve. It holds off pressure to the front disk brakes until the system pressure has gotten high enough for the rear drums to start applying. It's the part of a combination valve block with the pin sticking out. You pull/push the pin to override the metering valve for brake bleeding.

If the truck has an H-block instead of a proportioning valve, it doesn't have a metering valve either.

 

[addicted]

Adding on to this, the valve that helps compensate for overcoming the springs on the rear drums is the metering valve. It holds off pressure to the front disk brakes until the system pressure has gotten high enough for the rear drums to start applying. It's the part of a combination valve block with the pin sticking out. You pull/push the pin to override the metering valve for brake bleeding.

If the truck has an H-block instead of a proportioning valve, it doesn't have a metering valve either.

I learned about this after dumping alot of time and money trying to get firm front brakes on my 79 Bronco. Easy way to check if this is the issue is to clamp off the rear break hose with some vice grips and see how the brakes feel. Ofcourse you want to wrap something around the hose so you dont damage it with the vice grips. At least it worked for me that is. After I wore a hole in the rear axle hard line I clamped the hose to get back home. My truck actually stopped better and I had a firm peddal with the rear drums blocked off. That led me to investigate the prop valve. You pull the pin out when you bleed the brakes. They make a tool supposedly that hold the pin out while you do it since its spring loaded. But small vise grips will do the trick in a pinch

 

[addicted]

Wait. you said "H block" Its a 77 right? Came stock with front disks and rear drums? You should definitly have a proportioning valve and not an H block unless someone swapped it.

 

[Rox Crusher]

It is a 77 so whatever came stock on it.

I called it an h-block because I have seen other guys call it a proportioning valve only to be told it was an h-block.

So I guess I have a proportioning valve then ?

 

[garberz]

Yes, the 76'-77' had a proportioning valve. I held the pin out with a small Vise-Grip and got a lot more air out of the fronts, while bleeding. I needed an adjustable proportioning valve for the rear, to keep them from locking prematurely. Where is your valve leaking from?

 

[Rox Crusher]

Yes, the 76'-77' had a proportioning valve. I held the pin out with a small Vise-Grip and got a lot more air out of the fronts, while bleeding. I needed an adjustable proportioning valve for the rear, to keep them from locking prematurely. Where is your valve leaking from?

the valve was leaking at the imbalance switch but I went to the junkyard and got another prop valve and all is good...........no more leaking.

the one from the jy didn't have the pin but rather a plunger in the same spot so I have to figure out how to push it in while bleeding the front

 

[garberz]

Take the cap off the plunger, I think once the cap is removed, you pull on the pin.

 

[Rox Crusher]

Well I swapped the lines and bled it again to no avail.

Then a friend of mine suggested tryng to get any air out of the power steering system by raising the front end and cycling the steering lock to lock.

While we did get a couple good burps of air out and the steering is much smoother......the brakes still suck.

I am guessing that the prop valve I got from the junkyard may be bad so I am going to hunt for another one or get an aftermarket adjustable one. Any recommendations on a brand, etc ?

Also, considering the new info.....any other ideas or input ?

Thanks again guys !