soft brake pedal after bleeding

[red]

I replaced the front hard and soft lines and flushed new fluid through the system. The brakes are strong until the engine is running. I did a search and read about bleeding the master cylinder. I made hard lines to loop from the outlets back into each compartment. Pumped the brakes until no air came out, connected the master back to the prop block and bled all 4 points again (RR, RL, FR and FL).

 

I still have no brakes with the engine on. Did I miss a step or is there something else going on?

 

(BTW, I checked for fluid leaks all around and fixed one on the bottom side of the prop block and bled again)

 

 

Any ideas? :mad:

 

**edit**

We pulled the master cylinder while changing the lines because we could access some of the fittings. I reinstalled it just as it came off.

[Akula69]

I had a similar situation and worked with it for several weeks until I discovered one of the flares on the hardline on the prop valve had a crack in it that was leaking air.

[red]

I had a similar situation and worked with it for several weeks until I discovered one of the flares on the hardline on the prop valve had a crack in it that was leaking air.

 

Were your brakes soft with the engine off, on or both?

[TrailReadyMJ]

A few questions just to confirm your situation...

 

How did your brakes feel before you replaced the front lines?

Did you bleed everything (including rear) until new fluid came out?

Did you bleed them in the order you listed them? (RR, RL, FR and FL)

How firm does the pedal get with the engine off? If it just feels as it normally does when running, it's not enough. It should be stiff enough you can barely push it down with the engine off.

 

The only thing that happens when you start the engine is it provides vacuum to the booster. There really isn't anything else that changes other than the power assist from the booster. It is also a direct link between the pedal, through the booster, to the master cylinder.

 

Also, make sure one of your soft lines isn't defective and bloating under the pressure. This could explain a hard pedal when off, but soft when running due to the extra force provided by the booster. It may just be weak enough that it doesn't expand until it reaches high pressure.

[red]

A few questions just to confirm your situation...

 

The only thing that happens when you start the engine is it provides vacuum to the booster. There really isn't anything else that changes other than the power assist from the booster. It is also a direct link between the pedal, through the booster, to the master cylinder.

 

Also, make sure one of your soft lines isn't defective and bloating under the pressure. This could explain a hard pedal when off, but soft when running due to the extra force provided by the booster. It may just be weak enough that it doesn't expand until it reaches high pressure.

 

How did your brakes feel before you replaced the front lines? They were getting spongy (old soft lines and a pin hole leak in the FL hard line)

Did you bleed everything (including rear) until new fluid came out? Yup, the system was been flushed until clean.

Did you bleed them in the order you listed them? (RR, RL, FR and FL) Yes

How firm does the pedal get with the engine off? If it just feels as it normally does when running, it's not enough. It should be stiff enough you can barely push it down with the engine off. The pedal is firm when the engine is off but once it is running, the go to the floor pretty easily.

[Akula69]

I had a similar situation and worked with it for several weeks until I discovered one of the flares on the hardline on the prop valve had a crack in it that was leaking air.

 

Were your brakes soft with the engine off, on or both?

 

Firm with the engine off, but slowly sank to the floor when I started it.

[TrailReadyMJ]

Well, it appears you are doing everything right. It seems there is either a high pressure leak, or a line is soft and expanding. If you have a helper, get them to pump the brakes with the engine running while you reinspect the soft lines for expansion and check everywhere for leaks. Problems may show themselves under high pressure that you can't re-create without the booster.

 

Didn't pop in my head earlier, but have you checked the rear brakes? Is it possible your rear brakes are worn, or not self adjusting properly? Are the cylinders in good shape? Worn, or non adjusting shoes can cause over expansion of the wheel cylinders. I ran into this several years ago in my old XJ and experienced similar symptoms. The pedal would get pretty firm with it off, and almost to the floor when running. I replaced the cylinders, shoes, and springs and the problem was solved. Of course leaking cylinders would also cause issues, and may not be spotted right away without removing the drum.