Here's a new one! Firm pedal when booster not connected; no pedal when hooked up?!?!?

[BanditDave]

Hey Guys,

I finally got my brakes completely bled out on my '78 TA LS1 Swap project.

When I do not have the DSE booster hooked up to the motor and the vacuum line (again from a '99 Camaro LS1) plugged appropriately, I get a perfect pedal and the wheels stop turning. Once I hook up the vacuum line to booster (DSE Master Cylinder Booster Combo) the pedal drops to the floor...ALL THE WAY to the floor!!! Unplug it, cap it off and hard pedal again.

Does anyone have any ideas??? This is new to me...

Thanks,
Dave

[Payton King]

You have air in the lines. Re-bleed and try again.

Pedal feel good not hooked up because you are compressing the air. With the it hooked up the assist is really compressing the air in the lines...why you pedal is going to the floor. Did you bench bleed the master first?

[BanditDave]

Hey there,

Thanks for the tip...I am talking with Detroit Speed currently and they are talking with the vendor of the booster. On Lateral-g all I am hearing is that it is a bad booster.

I tend to agree with that at this point because I am getting a firm pedal that goes nowhere wiith out the booster hooked up. As soon as I hook the booster up it literally drops to the floor like a rock...zero effort and takes forever to come back up.

I will most definitely give it another try with the bleeding if at least one person...you in this case...still feels bleeding is necessary.

Thanks,
Dave

[JRouche]

A bad booster presents its problems usually in the same way, HARD pedal. A bad booster wont make the pedal go to the floor. There is a solid connection from the pedal to the booster and they have a solid rod that goes to the MC. There is nothing that can fail in the booster to allow the pedal to go to the floor. Its a safety measure, if the booster were to fail it becomes a non-boosted system.

Now, a bad MC will bleed through its internal ports and allow the pedal to dive to the floor. Air in the system would give a spongy feeling with the engine off. The sinking of the pedal is a bad master cylinder.. JR

[WS6]

Can you build pressure if you pump the pedal or does the pedal not even come back up?

This isn't a booster problem. It's an MC problem for sure. Question is if there's air in the system hiding somewhere or is the MC itself bad.

[Moose]

Just want to verify one thing.

on the master cylinder itself, (I have wilwood manual master cylinder) The port closet to firewall goes to back. The Other port goes to front.. Correct?

[BanditDave]

Moose, you need to check that with others on the forum for sure...I know that there are some that are reversed. The one on the DSE set-up is definitely the front port to the front and back to back as like factory.

I am going to try and rebleed tonight again. I will say DSE is bending over backwards to help me out though...they sent me another booster just in case.

Dave

[ProTouring442]

A bad booster presents its problems usually in the same way, HARD pedal. A bad booster wont make the pedal go to the floor. There is a solid connection from the pedal to the booster and they have a solid rod that goes to the MC. There is nothing that can fail in the booster to allow the pedal to go to the floor. Its a safety measure, if the booster were to fail it becomes a non-boosted system.

Now, a bad MC will bleed through its internal ports and allow the pedal to dive to the floor. Air in the system would give a spongy feeling with the engine off. The sinking of the pedal is a bad master cylinder.. JR

Not exactly. If, upon connecting the vacuum line, the pedal sinks WITHOUT putting pressure on the brake pedal, then the booster is bad as the valving inside is stuck, or you have the pedal rod adjusted so that it is pushing on the booster all the time. But, if you have to apply the brakes by pushing on the brake pedal, and then they go to the floor, it is most likely air in the system.

Shiny Side Up!
Bill

[BanditDave]

ProTour,

I bled the brakes yet again last night and here's how it went...

Without booster connected, pedal gets hard after about an inch of depression...

When Booster is connected you barely put pressure on the pedal, lightly tap it even, it will go all the way to the floor, even if your foot is not on it. Then it will very slowly make its way back up.

I am beginning to still feel there is air in the system. I am going to go through the system one more time and check all the fittings. I am also going to replace all the bleeders and teflon tape the threads to make sure no air is getting around the threads.

I will keep everyone posted.

Dave

[ProTouring442]

ProTour,

I bled the brakes yet again last night and here's how it went...

Without booster connected, pedal gets hard after about an inch of depression...

When Booster is connected you barely put pressure on the pedal, lightly tap it even, it will go all the way to the floor, even if your foot is not on it. Then it will very slowly make its way back up.

I am beginning to still feel there is air in the system. I am going to go through the system one more time and check all the fittings. I am also going to replace all the bleeders and teflon tape the threads to make sure no air is getting around the threads.

I will keep everyone posted.

Dave

So all you do is smack the brake pedal and it goes all the way to the floor, even though you are no longer pushing on the pedal? You have a bad booster. There is no way air in the system will cause the pedal to draw down on its own, thus the problem has to be in the booster.

Shiny Side Up!
Bill