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Old 10-30-2017, 12:03 PM   #1
atotalnincompoop
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Hydro boost swap

I have swapped a hydro boost system from a 99 gmc 2500 van into my 55 gmc pickup (4w disc setup). I purchased a disc/disc proportioning valve to run on the truck. I'm having issues with bleeding the brakes.
From what I've read the mastercylinder does not require a proportioning valve as the abs system handles that. however, since I am not using the abs system, I installed the proportioning valve.
Should I be running the prop valve on the original 99 gmc mc or should I swap in a different style nd and then run the prop valve?
Thnx☺
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Old 10-30-2017, 02:21 PM   #2
Custom 68
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Re: Hydro boost swap

when I swapped mine I used the original style disk/drum proportioning valve. I would think either should work.
Just make sure you bench bleed the master cylinder (if new). I always start on right rear and do the left rear, them right front... I had heard to start the furthest from the cylinder.

Different method but did you get the air out of the hydro boost as well?
Dave
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Old 10-30-2017, 10:02 PM   #3
68c10airstream
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Re: Hydro boost swap

A couple suggestions that almost always help is this;
Jack the front or rear of the truck to level out the master cylinder. as an example gm cars in the 80's had a master cylinder that was pointed uphill in the front and would get air bound up in the front chamber and was impossible to bleed. i did many for friends that couldn't get fluid to move through the lines. I would remove the master cylinder lid and watch the fluid as someone else jacked up the rear to level the master out. About when level air bubbles would come up through the brake fluid, and then you could proceed to bleed.

The last suggestion is to NOT pump the brakes up frantically in between each bleeding cycle. What happens is air will be introduced from the back side of the master cylinder. The plunger that moves back and forth with your pedal effort has lip seals that are pointed forward (towards the fluid) and when you repeatedly pump the pedal the return motion can only seal against the bore by the residual tension of the lip. When you push down on the brake pedal the lip is forced against the bore and seals tight, but the return motion isn't forcing the lip to the bore, it's just dragging along for the ride. So pump slowly and also don't bottom the pedal out because you are going into a portion of the bore that typically isn't used. I've seen them stick to the floor a couple of times.
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Old 10-31-2017, 10:10 AM   #4
atotalnincompoop
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Re: Hydro boost swap

Quote:
Originally Posted by Custom 68 View Post

Different method but did you get the air out of the hydro boost as well?
Dave
I haven't even got to that yet. Hopefully will get this all sorted out today thnx
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Old 10-31-2017, 10:13 AM   #5
atotalnincompoop
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Re: Hydro boost swap

Quote:
Originally Posted by 68c10airstream View Post
A couple suggestions that almost always help is this;
Jack the front or rear of the truck to level out the master cylinder. as an example gm cars in the 80's had a master cylinder that was pointed uphill in the front and would get air bound up in the front chamber and was impossible to bleed. i did many for friends that couldn't get fluid to move through the lines. I would remove the master cylinder lid and watch the fluid as someone else jacked up the rear to level the master out. About when level air bubbles would come up through the brake fluid, and then you could proceed to bleed.

The last suggestion is to NOT pump the brakes up frantically in between each bleeding cycle. What happens is air will be introduced from the back side of the master cylinder. The plunger that moves back and forth with your pedal effort has lip seals that are pointed forward (towards the fluid) and when you repeatedly pump the pedal the return motion can only seal against the bore by the residual tension of the lip. When you push down on the brake pedal the lip is forced against the bore and seals tight, but the return motion isn't forcing the lip to the bore, it's just dragging along for the ride. So pump slowly and also don't bottom the pedal out because you are going into a portion of the bore that typically isn't used. I've seen them stick to the floor a couple of times.
I try to take it slow, one of these days I'm going to invest in one of those reverse bleed pumps. I'll make sure the nd is level before I start today, good point thnx
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Old 10-31-2017, 11:03 AM   #6
BR3W CITY
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Re: Hydro boost swap

Hydroboosted cars need to be power bled, or bled while the truck is running since the reserve pressure cannistor only holds 2-3 "pumps" when the truck is off. Bleed the HB unit itself after install (bleeding the p/s side) with the wheels off the ground. Then bleed the actual brake system with the prop all the way open. After no air remains, set the prop.
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