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Brake Booster


oceanrunner
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I have a LS 400 90 model. Just recently, the brake pedal just went to the flood. Remind you, I havent driven the car in a while(garage kept). I start it up periodically. I replaced the master cyclinder and bleed brakes. I have a hard pedal after bleeding, but when I start it up, the pedal rides to the flood again. What are the chances it may be the brake booster? If so, how do I check to see if working properly. Perhaps, any other suggestions.

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I have a LS 400 90 model. Just recently, the brake pedal just went to the flood. Remind you, I havent driven the car in a while(garage kept). I start it up periodically. I replaced the master cyclinder and bleed brakes. I have a hard pedal after bleeding, but when I start it up, the pedal rides to the flood again. What are the chances it may be the brake booster? If so, how do I check to see if working properly. Perhaps, any other suggestions.
pump brakes a few times to get a hard pedal with motor off. Push brake and start car, brake should sink a little, not go to floor. Stop car and wait about 30 seconds. push brakes again, you should feel the assist, ie. it should go down a few like you were idling. If it doesnt, you have a leak somewhewre, it could be as simple as the vacuum one way valve thats pushed into the brake booster, a cheap part to fix. It could be an air pocket somewhere but if you bled them that is not likely. Sometimes you can hear a brake booster hissing when you put the brakes on. a booster is not that hard to replace, just getting it in and out may be a hassle. I did my Suburbans for less than 120 bucks but that was a truck...with a large engine compartment. Hardest part was getting the nuts loose behind the dash.
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  • 2 months later...
I have a LS 400 90 model. Just recently, the brake pedal just went to the flood. Remind you, I havent driven the car in a while(garage kept). I start it up periodically. I replaced the master cyclinder and bleed brakes. I have a hard pedal after bleeding, but when I start it up, the pedal rides to the flood again. What are the chances it may be the brake booster? If so, how do I check to see if working properly. Perhaps, any other suggestions.
pump brakes a few times to get a hard pedal with motor off. Push brake and start car, brake should sink a little, not go to floor. Stop car and wait about 30 seconds. push brakes again, you should feel the assist, ie. it should go down a few like you were idling. If it doesnt, you have a leak somewhewre, it could be as simple as the vacuum one way valve thats pushed into the brake booster, a cheap part to fix. It could be an air pocket somewhere but if you bled them that is not likely. Sometimes you can hear a brake booster hissing when you put the brakes on. a booster is not that hard to replace, just getting it in and out may be a hassle. I did my Suburbans for less than 120 bucks but that was a truck...with a large engine compartment. Hardest part was getting the nuts loose behind the dash.

Hi,

What is that part called exactly? I believe I need that part, but have heard different names. Thanks.

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I have a LS 400 90 model. Just recently, the brake pedal just went to the flood. Remind you, I havent driven the car in a while(garage kept). I start it up periodically. I replaced the master cyclinder and bleed brakes. I have a hard pedal after bleeding, but when I start it up, the pedal rides to the flood again. What are the chances it may be the brake booster? If so, how do I check to see if working properly. Perhaps, any other suggestions.

First thing check for a leakin the system. I do not think that is the problem. @nd rebleed the brakes you more than likly have a air bubble in the line somewhere. If you do not have a pressure bleeder then fill the master cylinder then remove the bleeder screw from each caliper one at a time and pump the brakes (engine off) and run a bowl of fluid to each caliper. Just opening the bleeder will not always move a air bubble since not alot of fluid come from the bleeder. Take your time. The booster does not sound like the problem. air in the lines sounds like a problem. If there is a local parts store that rents pressure bleeders that would work also. Rich

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