View Full Version : Hydraboost - ? about getting it going...

04-24-2006, 04:51 AM
Anybody here put a hydraboost off a heavy duty truck on their hot rod?

(Not a hydratech unit, just a unit off a 83 Chevy truck)

I installed one on my 69 Vette. I made sure it mated up to the correct depth piston master cylinder.

So far the brakes don't seem to work. The pedal goes to the floor then kind of kicks back while it is running.

Any special air/bleeding issues with one of these units?

I have had them on 1 ton trucks, motor homes, etc, but never had one off and on before.

04-24-2006, 05:56 AM
run the engine for some time and keep adding fluid to the reservoir/checking the fluid level. There's air in the syhstem and it'll take a short while for it all to get pumped out. You have a power rack installed right?? Is it giving assist or not (probably not)???

04-24-2006, 06:04 AM
The rack appears to be working fine at this point. The air purged out of it pretty fast. However, I manuall ran the rack left and right many times while adding fluid before lowering the car to the ground.

When I apply the brake I can see the pressure lines on the booster jerk as if they are getting a surge of pressure through them, just no assist taking place.

I have only run the whole set up for a few minutes at this time, but have spent 1/2 hour or so bleeding the brakes as I had them open for a bit. I bench bled the m/c and even ran a bench bleed line on it after it was in the car to make sure there was no air in that part of the system.

04-24-2006, 07:44 AM
They bleed very quickly and easily. I suspesct you have a base brake issue rather than a hydroboost issue. Bleed, bleed, then bleed some more.

04-25-2006, 09:09 AM
I can't rule out a regular brake issue, so will continue to bleed.

Here is what I found doing some research. I found a bronco group doing this swap and they ran into problems with the return line being "T'ed" into the power steering return line. It can create a restriction sensation to the unit.

The solution is to plug a second line into the resevior (like the actual Chevy trucks do).

The test is to run the return line into a catch can. Start the car up and test the brake. If the pedal comes right up and it works, then I have to re-route the return. If no change...then I am going to consider again issues with the brake fluid/air and or a bad hydroboost unit (bought it used from the j/y).

04-25-2006, 04:32 PM
It sounds like you may have the high pressure lines hooked up backwards. With the pressure lines reversed, you will have proper PS functions, though will have no brake assist until you crank the steering wheel up against a steering stop = try that real fast and see what happens. Also, note that these systems will provide a true manual brake interface with the engine off = if you can't get a good pedal with the engine off, you certainly will not have a good pedal with the engine running (assist unit powered up).

Here are the port ID's:


Also, the whole return line T fitting issue IS actually just fine, though most all plumb it in incorrectly - click here for the facts: http://www.hydratechbraking.com/forums/viewtopic.php?t=38

Depending on various factors, you may also be misinterpreting what you are feeling in the brake pedal. The best answer here would be to securely raise the rear wheels off the ground, then see if you can stop the wheels from turning against engine power by applying the brakes.

Let us know what you find :P

04-25-2006, 04:48 PM
Wow! Paul, I am blown away that you would take time to respond considering this is a homemade system. It means a whole lot to me.

I am actually taking Wednesday off work to spend with this rascal to get it and some other issues ironed out quick.

I will post what I find.

A bit more info though. The unit is from an 83 truck and may very well be from 1983! I picked it up cheap and made the mods to it for my application. I spent the better part of a day. If time was money, I am already WAY behind on just having bought one from you ready to go.

Its funny because I do the headlight conversion on the Vettes. I frequently field questions from people that are taking my pictures off the web and duplicating their own brackets. Nine times out of ten they get it wrong and I have to straighten them out...so that is why I really know how much it means that you took the time to respond.

We will let you know!

04-25-2006, 06:22 PM
I just confirmed I have the hoses in the correct location.

When I shut the car off I get about three pumps where there is zero pressure against the pedal, then on about the 4th push it gets hard at the VERY bottom of the stroke.

When I start it up, the pedal wants to stick down and doesn't actuate the brakes until the very bottom.

Now, when I open a brake bleeder I get fluid pumping out of each caliper all the way through the stroke of the pedal.


04-25-2006, 07:09 PM
I also have verified my T is in the correct location relative to the hoses. I had not read this prior but while I was installing it, it just made sense to flow it out of the rack into the pump and "T" the brakes into the side.

One other item. The m/c that was on the booster from the j/y had the piston in the same depth as the one that was on the Vette. I reused the power brake application m/c that was on the Vette already. So, I am fairly confident I don't have a mismatch of the inner rod of the booster reaching into the m/c.

I will run these tests on Wed.

1. Disconnect the return line and run it into a catch tank to see if there is any change in the pedal. If it does, I will yank the pump and figure out how I can plump a nipple in the housing. Or, I was thinking about putting a second resevior up under the fender to run from the booster to the 2nd resevior, then down to the T. Don't know if that would solve anything or not. The other idea is to put a one way checkvalve in the line. I was thinking an import style PCV valve would work great.

2. Check for air in the system (m/c, lines, calipers) by re-bleeding.
I suppose it is possible that there is air at the proportioning valve since I pulled the lines loose there for the removal and install.

3. I will pull the m/c off the booster and just make sure there is nothing strange between them.

4. Hook it all back up, be patient and try to run it some more and see if it kicks off (air gas bubbles in the new fluid theory).

5. If all else fails, I will replace the booster.

04-26-2006, 12:31 PM
It sounds to me like you still have some brake bleeding issues or possible MC pushrod mismatch issues (most likely bleeding issues though). One of the best methods of determining where the problem could be is to buy some appropriate port plugs for the MC. Yank the brake lines loose and cap them with vac caps, then plug the ports on the MC. Now go apply the brakes with the engine off and see what you get. If the MC is bled properly and you have the MC pushrod interface setup properly, you should have very little pedal travel before being met with a brick hard pedal (as the fluid simply has nowhere to go with the MC ports plugged). If you cannot get a hard pedal with the MC plugged, then the MC in play has obvious issues. You will most likely find that it passes the MC port plug test, and the next move would be to only connect the front brake line. Since you have only the front brakes hooked up, you will be able to clearly see if the fronts are pressurizing up correctly during brake apply - if they aren't, bleed them as needed. Once you have the fronts situated, then connect the rear line and see what happens. Typically the rear circuit is where most find the culprit...

We have thousands of customers succesfully running the T fitting return line arrangement, and it works just fine unless you have a super mega flow pump (like some offroad apps). The best answer is to run twin low pressure return line nipples though. Note that in most GM applications running a Saginaw P series, that a simple housing swap to a factory hydroboost specific reservoir is reasonably simple, though the housings can be tough to locate. Spanking the housing off and introducing a second return nipple is also a reasonable proposition, though you have to watch the heat you apply to the thin sheetmetal to make sure you don't warp it. If introducing a second nipple, run the steering return line to the factory nipple, as it has been engineered / carefully targetted in the reservoir to prevent the pump from possibly sucking in any air circulating though the PS system. Since the return line from the brake assist unit will only flow when you release the brake (about a tablespoon of fluid will exhaust during brake release), you may target a second nipple anywhere you like in the housing. We have tested some various types of directional flow check valves in experimental exercises to find no merit, and actually found them to be too ratchety in their operations (which can cause more trouble than good). PCV valves are never a full shut off device - more so a variable flow device based upon vac levels = don't bother even trying this...

04-26-2006, 03:07 PM
Well...I am a friggin idiot sometimes.

My problem was a mismatched pushrod. I swear I looked at it and compared it to the 1 ton truck m/c that the booster came with. I matched up the depth of the face of the piston, not looking at the CENTER OF IT!

Picked up another m/c today and slapped it on there.

Let me just say...this is the most AMAZING brakes I have ever experienced on a C3 in my life. WOW!

Just ran the car about 10 miles. The steering (Grand Am rack conversion), brakes, new clutch, etc. etc. worked fantastic.

04-27-2006, 01:13 PM
Doh! A sharp guy like yourself missed that !? (and admitted it too!)

I can't seem to find that forest with all of these darn trees in the way! :unibrow:

I'm glad to hear that you've got it all straightened out, and are now experiencing some of the best darn brakes in town. The C3 conversions are indeed amazing, as those factory discs REALLY shine when hit with higher line pressures - as you said, actually downright amazing!