bad brake booster? - JeepForum.com
 
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post #1 of 8 Old 03-27-2006, 10:02 AM Thread Starter
JOKER4INK
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bad brake booster?

Tell me if this could be the brake booster: If you have a bad power brake booster could it suck air into the master cylinder reservoir? Ive been trying to bleed my new master cylinder but a ton of air is coming out of the reservoir when i press the brake pedal. I cant get the air out of the lines because I think the power brake booster is pushing air back into the reservoir. What do you think? Or how could I test the brake booster?


88 YJ...kinda. Clayton Hard Arms, V8, 1 tons running gear, twin sticked, Irok's, fuel cell, multi-colored
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post #2 of 8 Old 03-27-2006, 10:35 AM
JJorda
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Nah, I don't think a bad booster could suck air into the master cylinder. Have you bench bled the master cylinder before hooking up the lines? If not, just take some tubing and go from the outlet ports of the master up around to the top of the reservoir, then pump until the air bubbles stop. Then you can hook up your lines to the wheels and continue bleeding, checking the fluid level in the master cylinder as you go.

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post #3 of 8 Old 03-27-2006, 06:52 PM Thread Starter
JOKER4INK
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I replaced the power brake booster now too because I could hear air leaking out of it where it met the master cylinder. So it now has a new power brake booster, a new master cylinder, and new calipers. Still air in the system. I get decent brake pressure when the motor is off, but as soon as I start it the pedal goes to the floor. Does the system need to be pressure bled?

88 YJ...kinda. Clayton Hard Arms, V8, 1 tons running gear, twin sticked, Irok's, fuel cell, multi-colored
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post #4 of 8 Old 03-27-2006, 07:14 PM
barry1me
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Quote:
Originally Posted by JOKER4INK
I replaced the power brake booster now too because I could hear air leaking out of it where it met the master cylinder. So it now has a new power brake booster, a new master cylinder, and new calipers. Still air in the system. I get decent brake pressure when the motor is off, but as soon as I start it the pedal goes to the floor. Does the system need to be pressure bled?

Well the way that a brake booster works 'brake actuation' is the booster has two sealed halfes that have an input shaft and an output shaft. The input shaft connects to the brake pedal and is pressurized to ~ 1 ATM, while the other side of the booster pushes into the master cylinder piston this side has a vacum line connected to the engine. This creates a mechanical advantage when the engine is on. when you say you get pressure when the motor is off do you mean the pedal is harder...that is normal, and if you have air in you systemwhen you turn on your jeep when you touch the brakes your pedal will go to the floor...still normal. Im sure you know how to bleed brakes, so all I can tell you is make sure all your lines are tightened down and have a friend sit in the seat and pump the brakes.
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post #5 of 8 Old 03-27-2006, 07:19 PM Thread Starter
JOKER4INK
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I bled each side for quite a while. Do Jeeps need to be pressure bled you think?

88 YJ...kinda. Clayton Hard Arms, V8, 1 tons running gear, twin sticked, Irok's, fuel cell, multi-colored
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post #6 of 8 Old 03-27-2006, 08:04 PM
sentinal02
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Quote:
Originally Posted by JOKER4INK
I bled each side for quite a while. Do Jeeps need to be pressure bled you think?
i never had a problem bleeding mine normally and i've done it several times between bad lines and replacement parts. can't hurt to try it though. like J said though, you did bench bleed the new master right?

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post #7 of 8 Old 03-27-2006, 08:44 PM Thread Starter
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This is how I bled it. I filled the reservoirs, put the fittings and hoses on the ports, ran the lines back into the reservoir. Pumped the acuator a few times til no air bubbles were present. took the hoses and fittings off, hooked up the brake lines and attempted bleeding the brakes at the calipers. Is that right? Do I need to hold the plunger for the master cylinder in while I hook up the lines or something? what did I do wrong?

88 YJ...kinda. Clayton Hard Arms, V8, 1 tons running gear, twin sticked, Irok's, fuel cell, multi-colored
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post #8 of 8 Old 03-27-2006, 08:48 PM
sjrider
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you could try gravity bleeding it.....or... you doint think that they have a cup reversed in the master cylinder?
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