Mopar Hydroboost problem

Hey folks!

I am working on a hydroboost instal on my 74 cuda.

I am using a HB unit from a fullsize chev van, sourced from the wrecking yard.

Running -6 PTFE hoses with rubber return lines.

I have drilled out the return fitting on the HB unit and added a separate -6 return fitting on the PS pump!

PS pump is a rebuilt factory Saginaw unit.

THe MC is a mopar aluminum unit of unknown bore size.

I ran all new brake lines and added a line lock. All pressure bleed and no air in the lines.

I tried to bleed the HB system several times.

NOW the problem, the brakes do not seem to work very well. I have only tried it on jack stands at this point. Drop it in gear and the pedal is pretty spongey and the rear wheels do not stop spinning.

The other issue is the pedal does not return. I have to lift it up with my foot to turn off the brake lights.

At this point I am not sure what the issue is.

I thought of going to a new MC, Wilwood suggested a 1 1/8th bore, but will that help the pedal return.

Any thoughts before I throw kore money at it would be appreciated.

thanks,

jason

Digging back in my h-boost brain from way back, I remember Paul from Hydratech telling me that the pedal return issue is often due to a blockage in the low pressure return line. You mentioned drilling out the return line on the booster unit. Did you drill out something on the low pressure return?

What brakes do you current have on the car? If they're the OEM brakes, I think a 1.125" bore master would definitely be recommended.

Todd Z.

I drilled out the low pressure return line.

I am running stock front discs and rear drums.


Jason

Are your rear drums adjusted properly that they were working before the HB install?

How old are the brake lines? Could one of the hoses collapsed causing fluid blockage?

I would also highly recommend a 1 1/8" master cylinder bore. I'm running an HB off a 05 tahoe w/ 1980 corvette master cylinder, it's been working great.

Did you block off the distribution valve when you were bleeding the brakes?

Did you check the master cylinder's pin clearance to be sure the HB unit would engage properly?

I was running standard brakes before, and all was working fine.

the rear drums are adjusted properly.

the rubber lines are a few years old and the only parts I did not replace on the brake system. I suppose that could be the issue?

i am running a new wilwood adjustable dist valve.

i was thinking that the hb unit is not engaging the MC properly. I will
measure that when I blow it apart and compare to the new MC.