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Trying to determine if I have a bad booster. Just put a brand new master cylinder in and bled the rear. Pedal still goes to the floor. Has anyone had a bad booster? Can you tell me if this sounds like that to you?
pedal goes to the floor with engine running? or not? or both?
sounds more like you need to rebleed ALL 4 Calipers.
Did you bench bleed the master before installing??
Last edited by 4-vettes; May 30, 2021 at 05:31 PM.
It is nearly impossible to bleed the air out of the brake lines unless you First put the master cylinder in a vice and bleed the air out of it by pushing on the plunger with a large Philips screwdriver until no air is in the clear tubes (keep the master cyl. full of fluid at ALL times)...
Then...install the distribution valve or the proportioning valve and bleed the air out of it.....
Then...install the assembly onto the booster/reconnect the brake lines and bleed the system (many members use the Mighty Vac to make the system bleeding easier)
I don't think the engine needs to run when using the Mighty Vac.
Last edited by doorgunner; May 30, 2021 at 05:38 PM.
The Booster is strictly an assist to the brake pedal. It helps apply enough pressure that a little girl, barefoot, could lockup all four wheels with her pinky toe.
It has very little correlation with a pedal that goes to the floor. Look else where. Your issue is not the booster.
When everything is working as it should, you can stand on the brake pedal all day long regardless if the booster is activated or not.
See my profile. then click on photo albums > bench bleeding for some helpful tips.
pedal goes to the floor with engine running? or not? or both?
sounds more like you need to rebleed ALL 4 Calipers.
Did you bench bleed the master before installing??
pedal goes down running or not. But I rebuked the calipers and got some progress. The pedal is much more firm now. I think you were right. Thanks
It is nearly impossible to bleed the air out of the brake lines unless you First put the master cylinder in a vice and bleed the air out of it by pushing on the plunger with a large Philips screwdriver until no air is in the clear tubes (keep the master cyl. full of fluid at ALL times)...
Then...install the distribution valve or the proportioning valve and bleed the air out of it.....
Then...install the assembly onto the booster/reconnect the brake lines and bleed the system (many members use the Mighty Vac to make the system bleeding easier)
I don't think the engine needs to run when using the Mighty Vac.
thanks for the detail and pictures. Helps a lot. I don’t have the connections like that to put the hoses back into the master. First time I’ve heard of the proportioning valve in this process.
The Booster is strictly an assist to the brake pedal. It helps apply enough pressure that a little girl, barefoot, could lockup all four wheels with her pinky toe.
It has very little correlation with a pedal that goes to the floor. Look else where. Your issue is not the booster.
When everything is working as it should, you can stand on the brake pedal all day long regardless if the booster is activated or not.
See my profile. then click on photo albums > bench bleeding for some helpful tips.
this is really helpful. I don’t know how the heck air got in the system all the sudden. My theory is the master was indeed bad and the new one brought air into the system.
Be careful when shoving a screwdriver in the MC that you don't go beyond 1 3/8" or you will void any warranty and cause damage in the unit.
Later, when you hook-up your brake lines to the recently mounted MC there will always be a bubble at the line fittings. So a complete flush / bleed is in order again.
The less you touch the brake pedal during the entire process the less likely some other issues will pop up later.
Last edited by HeadsU.P.; May 31, 2021 at 08:56 AM.
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Brake Booster Question
