Driving down the road about a month ago and the big pedal on the left went right to the floor. Not good but after a moment of complete panic, I got her shut down without an accident. I had been wanting to do a hydroboost conversion for quite some time, so it seemed like a perfect time to pull the trigger. So, I went to the local LKQ pull & pay and oddly enough I found a 96 F-Superduty so I grabbed the hydroboost, but someone had cut all the lines, so no joy there. I also wanted to get rid of the lousy ford power steering pump in favor of the Saginaw.

I scored all the factory 460 aluminum brackets from a van (factory saginaw) and the quasi-serpentine belt system. I got the GM dual return saginaw pump and hydroboost hoses from a 99 K2500 suburban. I also split the hydroboost, taking the front half so that the hoses would fit and mated it to the rear half so it would still be a direct bolt-on to my 78 F150 firewall.

The hodge-podge hydroboost system seems to be functioning fine, according to all I have read. The only hose I had to have reworked is the hydroboost to steering gearbox. bought a new ford hose since mine was a bit chewed up and had a shop mate the gearbox end to the GM hydroboost end, as well as adding 6 inches of rubber line.

Now that it is all back together, I still have the brake issues I had when it initially failed. Pedal will not build pressure, but it all bleeds out fine. I am sure that the vacuum booster was bad because I got about a pint of fluid out of it.

I had the 78 cantilever mounted booster, which gives me a pedal ratio of 6.5:1 (give or take). I had to space the hydroboost about 5/8" off the firewall because the center hole was too small.

Is it possible that that 5/8" enough to keep the hydroboost from its full travel and keeping it from building pressure? I replaced all of the wheel cylinders, calipers, master cylinder, and some of the lines.

My other thoughts were that the proportioning valve on the frame rail is bad, or getting too much fluid, given the 99 K2500 master cylinder piston size. there are no leaks in the system, so I don't think that's the problem. I'm about to pull my hair out.

Please help...

 

All I got for you, hope the answer is in here?

https://www.ford-trucks.com/forums/1...ht=hydra+boost

https://www.ford-trucks.com/forums/1...ht=hydra+boost

 

PM cracker289, he's your man.

 

Found this for you...https://www.ford-trucks.com/forums/8...sion-done.html

 

Thanks for the quick replies!

So, I was able to get some basic troubleshooting done today. The master cylinder was bad, though that didn't fix all of the issues. I took a couple of short pieces of 3/16 tubing, slid a tube nut on each of them and flattened the other end. I rolled the flat end over a few times and flattened again, then pulled a vacuum on them to make sure they were indeed sealed. once I installed the plugs, I realized that the K2500 master was blowing fluid from the primary port to the secondary, within the bore. So, I swapped back to the 81 F350 master, which did run full pressure to the plugs after extensive bleeding...

So, reconnected the lines and started the bleeding process. This is where it seems to fall apart, so to speak. I have been through a gallon and a half of DOT-3 and its only getting marginally better. It doesn't go all the way to the floor, but only about an inch from it, but now it holds firm.

When I had the master plugged off and holding firm, I was able to test the functionality of the hydroboost itself, which behaved as Bendix described...first bonus I've had in this whole process.

The floor comes up way to fast, so I'm thinking that I need a pedal ratio a bit better, maybe like 4:1 or 5:1. I also need that 5/8" or so back, so that spacer needs to be gone because I need more pedal travel.

I can't work on it for a couple of days now, so any thoughts on this would be greatly appreciated...

 

I don't know if your pedal ratio is the problem, I didn't change mine at all. When your brake pedal is all the way up, is it where it's supposed to be (right where the brake light switch engages)?

Your problem might be - how far down does the pedal go before the hydroboost unit starts to engage the master cylinder? If the rod is too short for example you might have a significant amount of travel before the master cylinder begins to push fluid.

What size bore is your master cylinder? A lot of the F100's up through 60's 70's and into the 80's had a 1 inch bore, you might want to step up a little bit to a 1-1/8 m/c or maybe even 1-1/4. I did 1-1/8 and the extra power from the hydro unit still makes it almost effortless.

Another symptom of low pedal (which then firmly engages once it does eventually get there) is rear drum brakes out of adjustment. Just a possibility, maybe they need a couple of clicks on the adjustment wheel.

 

So I got a few hours to work on it today. I pulled both back wheels off to check on the adjustment of the drums. I was sure that I had adjusted them but it never hurts to check. I found a problem in the right side. There are two short pins that allow the wheel cylinder to engage the brake shoes. I found that the front pin was not riding in the notch on the front shoe, it had popped out but was still sitting in the rubber cup on the wheel cylinder.

When I install drum brakes, I typically give the completed shoes a couple of good whacks with my deadblow hammer to make sure that everything is seated where it belongs and that nothing is going to come apart on me. I think that pin popped out of the notch when I did that.

So, with the bleeding issue resolved, I still didn't like how close the pedal was to the floor. I originally had that 5/8" spacer between the hydroboost and the firewall. I got to thinking that with a 6.5:1 pedal ratio, that 5/8" is far more than that at the end of the pedal. After I removed the spacer, I used a drum sander in the drill to enlarge the hole in the firewall and bolted it up tight to the firewall. That actually made it quite a bit more sturdy when pushing on the pedal and it brought my pedal back up where it belongs. Now when I push the pedal hard, it is about 2" off the floor.

I took it for a quick test drive around the neighborhood and it's quite impressive, to say the least. I need to get it out for an extended test drive this week, but I already figured out that the back locks up before the fronts. Looks like I need a proportioning valve, are there any tried and true gems to be had at the pick & pull? I've heard of a lot of people using the one on the Astro van, but maybe I didn't hear that right. Any suggestions?

And a big thanks to all of you that helped out or tried! Special thanks to cracker289 for your words of wisdom, that ultimately led me to the problem!

 

Get a Wilwood adjustable prop valve. Worked great on my hydro swap.

 

In stock and on the hook.

 

What's the damage ($)?

 

Well I'm glad you got some brakes now! I plumbed a wildwood prop valve into the rear brake line of mine too, no complaints.

<a href="http://s1020.photobucket.com/user/crazycracker289/media/F-100/69%20F100%20Brake%20Upgrade/IMG_0326_zpsze7n0ug7.jpg.html" target="_blank"><img src="http://i1020.photobucket.com/albums/af330/crazycracker289/F-100/69%20F100%20Brake%20Upgrade/IMG_0326_zpsze7n0ug7.jpg" border="0" alt="Adjustable proportioning valve photo IMG_0326_zpsze7n0ug7.jpg"/></a>