Replace brake booster

[dkmcgowan]

Can I replace brake booster in my 89 4.0l without removing brake lines from master cylinder? I just bled that thing forever when I did brake lines and I hate bleeding brakes.

 

I'm not sure if there is any slack really to pull it back and remove from those mounting bolts on booster.

 

My booster is hissing with pedal down, can hear it in cab. Stops hissing when you let off brake.

 

Not looking to upgrade now like I know many do.

[shelbyluvv]

You can but you will have to be very careful not to kink the lines. It is a very tight fit between the two.

[dkmcgowan]

Plan to try tomorrow. I've always thought bad booster meant hard pedal. My pedal is soft, but the vehicle isn't stopping and you have to push really hard, but pedal seems soft, and a constant hissing if your foot is on pedal.

 

I know booster works somewhat because it's rock hard with engine off, crank engine, pedal goes down, but starts hissing.

 

I guess somehow it's possibly to have soft pedal with bad booster?

[HOrnbrod]

Test Power Brake Booster

If the pedal feels "hard" while the engine is running, the booster isn't operating correctly. If you suspect the booster is defective, do not attempt to disassemble or repair the power booster. Doing so is unsafe and will void your warranty.

Test 1

1. With the engine off, pump the brake pedal to remove any residual vacuum in the booster.
2. Hold pressure on the pedal while you start the engine. When the engine starts, the pedal should drop about a 1/4", this indicates that the booster is working properly.

Test 2

1. Run the engine a couple of minutes.
2. Turn the engine off and press the pedal several times slowly. The first pump should be fairly low. The second and third should become slightly firmer. This indicates an airtight booster.

Test 3

1. Start the engine and press the brake pedal, then stop the engine with the pedal still pressed. If the pedal does not drop after holding the pressure on the pedal for 30 seconds, the booster is airtight.

Inspect the Check Valve

1. Disconnect the vacuum hose where it connects to the intake manifold. Do not disconnect the vacuum line from the booster. Air should not flow when pressure is applied, but should flow when suction is applied. If air flows in both directions or there is no air flow, the valve needs to be replaced.

Verify Enough Vacuum

1. Check the operating vacuum pressure when the engine is at normal operating temperature. There should be a minimum of 18 in. of vacuum. Vacuum may be increased by properly tuning the engine, checking for vacuum leaks and blockages in vacuum lines.

[dkmcgowan]

I think my booster was working, but probably going out. It was hissing constantly when pedal was depressed.

 

For others that try, I do not believe on a renix 4.0l it's in anyway possible to remove the brake booster without the master cylinder.

 

I tried and bent up some brake lines a litte, but was able to get them back in place I think.

 

So I ended up just getting a new master cylinder as well just because I was already doing it.

 

Got it all put together and bled all the brakes, think I got them good.

 

Brakes worked better, but still a little soft.

 

I then discovered that the rear brakes were pretty far out of adustment.

 

I tightened them up until if I spun the wheel off the ground hard it only made one full rotation.

 

Brakes are better now.

 

I then read that I have to do some other special bleeding process again with the front caliper open to open the rear valve. I have not done this yet. I feel I need a 3rd person to just watch fluid to get this done.

 

I hate bleeding brakes.

[sloride]

I hate bleeding brakes as well. That's why I replace bleeder valves with speed bleeders, one way bleeder valves you can pick up at parts store like NAPA, oreilly, autozone. They come two to a pack.. With those installed, I bleed alone.

[1989 Eliminator]

If you ever want to do the brake booster upgrade (which I highly recommend), look in my signature for the link.

[dkmcgowan]

I probably should have done it this time around but stuck with stock.

 

Drove well this morning, I also adjusted the rear brakes, twisted the star things up until when I spun the tires hard they did one full rotation.

 

I did over tighten them once and forced them to loosen up, it worked but was hard, later realized I should have been pushing that tab forward to allow it to go the other direction, hope I didn't damage anything, might take drum off and check.

 

Also seems like I need to bleed again with thag front wheel open and brake light on, but that seems like a pain and I would need 3 people. Also seems like front caliper would sucks in so much air while waiting on me to bleed the rear again.

 

Progress though.

[1989 Eliminator]

Yeah having two people to bleed the brakes is definatly much easier. But... you could also buy a vacuum gun to suck the brake fluid out too. I tried that before and seemed to work pretty well.

[cruiser54]

Make sure the check valve on the booster only flows air one way.........