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6.5 Power brake booster

matuva

matuva

Tropical 6.5er
Messages
1,996
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Location
New Caledonia. An island in south west pacific, cl
Today, I changed the leaky Hydoboost (Power Brake booster) on my Blazer.

The old one is leaking, but do assist brakes almost well.

Changed to a reman ACDelco, start engine, pump brake pedal several time, and had the bad surprise of finding a "rock hard" brake pedal, and almost no brakes!!!:eek:

The brake pedal is hard and brakes are not working, it's the same than when you are cruising and engine stalls cause of PMD. Very few brakes, but steering is perfect!

Is there something I did miss somewhere, or should this reman unit failed ? :mad2:
 
Did the pin in the HB bore mate up the the MC correctly? There are a couple different lengths of pins.
 
Done!

Pulled out the return line on the unit, plug in a hose on it to a can, ran the engine and press/depress 2 times the brake pedal.

First press, nothing, still rock hard a pedal.
2nd press, the pedal start hard, then goes down suddenly. Hoorray! the bleeding is successfull.

Press and depress the pedal 4-5 times to get sure, at each depress we had a nice spread of oil.

Put back the return lines, add fluid, and went for a road test.100% strong brakes now...

So, the lesson is : make sure it is well bleeded. Starting the engine, pressing/depressing the brake pedal is not enough.
 
matuva said:
Done!

Pulled out the return line on the unit, plug in a hose on it to a can, ran the engine and press/depress 2 times the brake pedal.

First press, nothing, still rock hard a pedal.
2nd press, the pedal start hard, then goes down suddenly. Hoorray! the bleeding is successfull.

Press and depress the pedal 4-5 times to get sure, at each depress we had a nice spread of oil.

Put back the return lines, add fluid, and went for a road test.100% strong brakes now...

So, the lesson is : make sure it is well bleeded. Starting the engine, pressing/depressing the brake pedal is not enough.
Click to expand...

Not clear on your Islander speak. What are the return lines? Where do they return to?
 
2 hoses come on the top of the unit : the one on the firewall side is the high pressure one coming from the power steering pump.
The other one, on the master cylinder side is the "return line", low pressure. This is the one you have to disconnect for bleeding.
 
What's the unit? Power steering or brake master cylinder? I'm really not clear on this and how it affects the brakes.
 
I guess I was confused by the hoses. Here's a pic of mine:

1336069470.jpg


All hard lines. Does this Hydro Boost share fluid with the brake system? Why would I need to bleed it? My pedal has been historically spongy and I've bled the crap out of the system numerous times.
 
With the exception of 1 line has a rubber portion going into the brake booster.

That rubber line is removable, once it is moved, hook a tube to the main unit (Brake Booster).
Route that tube to a container somewhere outside.
Start the engine and it will start flowing PS fluid through it to bleed.
It can also be used to flush the PS fluid, not a bad idea for old truck like mine.

If the pedal is spongy, you may want to change/flush the brake fluid.
May be some brake hoses are worn out, somebody can chime in.
 
I've completely replaced the brake lines with stainless. Brake hoses have been replaced, LF is braided stainless, RF is OEM rubber after one stainless rubbed through on the tire.

Installing the stainless hard lines and hoses has been the biggest mistake I've made with this truck. It was merely preventative as the OEM brake system was working, but the truck came from Illinois and I was concerned about rust. I've been tormented with leaks on the lines ever since installation. Most at the ABS pump and recently at the union nut on the RF line. The flares on the stainless lines are very difficult to achieve a seal and if you don't get it right,they screw up the flare on the opposing fitting. Where I thought I had them sealed, they'd start leaking months later. So in the course of addressing these leaks, I've probably flushed the brake system several times.

I am running on brake lines and fittings from a bone yard while I'm waiting for a new line from the manufacturer. This has gone on for over 2 months now. I cannot recommend the manufacturer as they errantly sold me the wrong flaring tool and once I used it, they would not take it back. I used it twice before realizing something was wrong. By then, the fitting at the ABS pump was destroyed and I needed a new line.
 
The hyd brake system and the power assist are two seperate systems and fluids. Power assist uses the power steering fluid, the brakes obviously use brake fluid.
 
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