hydraboost revisited

After reading the excellent article by Full Monte and doing a search on the subject, one question. Has anyone ever tried the hydraboost unit from GMC or +99 SD since the F450s are hard to find in the salvage yards?

Some of the old Lincolns had hydroboost too, I had a 79 Lincoln Mark something that had it.

JPR said:

After reading the excellent article by Full Monte and doing a search on the subject, one question. Has anyone ever tried the hydraboost unit from GMC or +99 SD since the F450s are hard to find in the salvage yards?

Click to expand...

Gary(icanfixall) has went that route and wasn't sucessful. Something about full metric fittings.

I guess that means I will be paying out some cash then. The truck is technically down, power brakes went out today, appears to be the booster this time.

Update, I purchased a Cardone rebuilt hydro-booster, new lines and inline filter. Can't wait to get them installed.

Dammit, I hope the 20 dollar "mystery" Ford hydroboost unit I bought on Ebay is gonna be alright.

Is there anyway to check for semi-proper operation of these things on the bench? I dread buying 100 bucks worth of hoses to find out my unit is junk...

Full metric fittings though...although it's not as elegant, I was told my by local hydrualic hose shop that if I can bring them the strange power-steering like fittings that the hydrobost unit needs, they can attach hose onto it, and I'd be golden. Provided enough of the steel line hangs off the fittings.

And provided I can find the stupid fitting it needs...

See my post about parting out the F-600.

What I found out about the 99 and up boosters is they have a larger base mounting bracket bolting pattern and.... The threads on all the bolts are metric. Now probably the hose fittings are too but I have not checked that out yet. Also the link from the peddle to the booster is longer on the later model units and thats about all I have found. I did find an F450 (1991) in a wrecking yard. I bought the new master cylinder (1 5/16 inch) on it and the booster each for $16.00. I also bought the brake peddle because the pin on it is 2 3/4 inch down from the bushing that the peddle rides on. The stock F250 & 350 length is 3 1/2 inch in the same area. The overall length of the peddles are the same. The numbers stamped on the 450 peddle is E7TA-2455-AA and #4TA-2455-CB on the 250 and 350. So when I'm done I'll have more braking power going to the 350 brakes. Thats more leverage.... More fluid so thats way better brakes for me.... Remember, vacuum suxs.....

icanfixall said:

What I found out about the 99 and up boosters is they have a larger base mounting bracket bolting pattern and.... The threads on all the bolts are metric. Now probably the hose fittings are too but I have not checked that out yet. Also the link from the peddle to the booster is longer on the later model units and thats about all I have found. I did find an F450 (1991) in a wrecking yard. I bought the new master cylinder (1 5/16 inch) on it and the booster each for $16.00. I also bought the brake peddle because the pin on it is 2 3/4 inch down from the bushing that the peddle rides on. The stock F250 & 350 length is 3 1/2 inch in the same area. The overall length of the peddles are the same. The numbers stamped on the 450 peddle is E7TA-2455-AA and #4TA-2455-CB on the 250 and 350. So when I'm done I'll have more braking power going to the 350 brakes. Thats more leverage.... More fluid so thats way better brakes for me.... Remember, vacuum suxs.....

Click to expand...

Fixall,
You have obviously had to contend with more than I did on my install. I'm not sure about your last statement about more fluid equalling more braking. It's actually brake fluid pressure that increases braking power, not volume. The hydroboost raises the pressure from about 1000psi in the lines to 2000psi. Foot pedal lever arm length might make it easier to approach the pressure by the light feel in your foot, but the linkage rod only acts as a valve opener that turns on the hydoboost. Additional leverage won't increase the line pressure.
I hope I understood your post correctly.

This is what I'm trying to say. With the rear brake auto adjusters not working like they are designed to we need more volume to fill the rear cylinders. With the F450 1 5/16 master cylinder I can push more fluid to fill the reara. Now with the hfdroboost and the differant brake peddle combined my brakes should be similar to air brakes in the amount of effort I need to start the braking process. I do understand why our brakes really don't work so well. It took me some time and I cracked several front rotors and wore out plenty of front pads. Thats how you know the rears are way out of adjustment. That and by setting the parking brake. If it sets more than half way to the floor the rears are way out of adjustment. Now I should have pelnty of volume plus better pressure for stopping. I hope this clears up some questions.

If brakes are out of adjustment, they are likely not to work with any delivery system. The amount of fluid required to make the brake system work should be very low, as the amount of travel of a properly adjusted set of shoes/calipers is very small. This makes the issue of stopping power one primarily of line pressure. If my logic makes sense, a larger diameter master cylinder shouldn't improve stopping power. In fact, the power assist you get from the hydroboost is additional "push" on the master cylinder piston. The amount of pushing force is the same, no matter the size of the piston diameter. If this pushing force is distributed over the larger area of a bigger diameter piston, the brake line pressure should drop proportionate to the inverse of the square of the diameter.
Therefore, a larger piston should decrease available line pressure and decrease stopping power. What this means is that there is no free lunch. You trade off brake fluid volume pumped against line pressure at the brakes. If you want large volume, you get less pressure. The ideal master cylinder diameter should be the one that has just enough volume displacement to make the shoes/calipers work, not the one that has the largest diameter.

What Ihave done is make an F450 brake system fit an F350 system so now you might see what I have done. Larger more powerful system coupled to a smaller system. I now have more pressure, leverage and volume working on a smaller system.

I think I understand what you've done, since I wrote the tech article on this subject.

I'd like to add one comment to what Full Monte said:

"Therefore, a larger piston should decrease available line pressure and decrease stopping power. What this means is that there is no free lunch. You trade off brake fluid volume pumped against line pressure at the brakes. If you want large volume, you get less pressure. The ideal master cylinder diameter should be the one that has just enough volume displacement to make the shoes/calipers work, not the one that has the largest diameter."

Which is the other variable is pedal effort. I don't think anyone is complaining about their brake pedals being to stiff. i.e. the effort to push the pedal down being to high with the stock vacuum system. You only realize how much power assist the vacuum booster supplies when the belt breaks! I think that the reason many people are happy with a larger diameter master cylinder with either hydro or vacuum is that they are more than willing to increase pedal effort for increased breaking force. It seems ford may have agreed since the have that TSB about sinking pedals and the fix is a larger diameter master cylinder ( although not as large as the f450 one, I believe).

My truck is an 89 F350. I replaced the original master cylinder with one that is 1 1/8 inch bore. I really don't remember what size I had to begin with, maybe 1 or 1 1/16th. Anyway my brake peddle effort was never a problem till I lost the vacuum pump or belt. Now I wont have that to deal with anymore. If I loose vacuum I loose the cruise control and the ac-heater vents. No more brake loss for me. It only happened twice and each time it was a real mess. If its never happened to you then good but its really hard stopping a 6500 lb truck pulling a load of horses on the freeway. Steady HARD pressure on the brake peddle pays off but its slow happening.......

The no assist brake failure only happened to me once. My friend (with ones like this...) returned the truck to me stating " I'm not sure what's wrong with the brakes?!?"
I only started up the truck and drove in reverse a little way. It was frightening at 5mph, I can only imagine what it would be like at speed with a load!
It does make me think that the vacuum assist does work better than most people credit it for. But the hydroboost system seems to have a better relibility record.