Soft brakes

[artpeck]

Some weekends working this truck are certainly more rewarding than others...

From an earlier post I noted that my brakes went soft after finishing installing new front parabolics and shocks. Theory is that I compromised the flex lines with the axle travel. New lines on order (thanks RN) but I did bleed the front brakes today and get a continuous stream of bubbles. Having said that I cannot find a leak anywhere. Additionally I clamped the two front lines and the pedal is very firm.

Given that I have been all over the brakes earlier replacing the master and all wheel cylinders as one of the first steps I thought I had a pretty good idea of what could go wrong but this is eluding me.

My question is whether it is possible to have air continue to get in the circuit without an obvious leak. I guess it obviously is but how? The flex lines needed replacement anyway but I have this nagging feeling that I am going to do that and still have the same problem.

Last I just want to thank all of you for always chiming in on all the questions that get posted here. I really enjoy bringing this truck back to life and use and really appreciate being able to take advantage of everyone's experience.

[jac04]

What bleeding method did you use? Pumping the pedal, vacuum bleeder, pressure bleeder? Only asking because it is very common to get a steady stream of bubbles when using a vacuum bleeder (air gets pulled in around the bleed screw threads). Also, did you try clamping off the front hoses one at a time? If so, what happened?

[artpeck]

The basic pedal pumping. Driving fluid from the master down.

[jac04]

Did you have someone filling the reservoir while you pumped? Lots of short strokes in a row or the one pump at a time method? My preferred method now is a combination of a pressure bleeder and pedal pumping.
Any results from clamping individual front hoses?

[artpeck]

Reservoir was kept full. Clamping only one side or the other yielded maybe some improvement but not much. Stark change from clamping both.

I have bleed these brakes several times due to all the work I have done to essentially replace everything but the hard lines and the flex lines and never had this issue. Can't figure where the air is coming from and again no fluid leaking from anywhere I can find. Basically says that the reverse stroke of the master is pulling air in a hole that fluid can't go out of. Or probably I am missing something.

[solihull109]

Check the rubber plunger on the brake master rod. $100 bucks says it's letting in on the pull stroke.

[jac04]

^^Good point. The only feasible way to get air into the system without keaking fluid is if air is being pulled in past a piston seal. The piston seals are a cup shape - designed to take high fluid side pressure. When the brake pedal is released, the piston in the master cylinder tries to return to its original position and the fluid side could see negative pressure and pull in some air around the piston seal.

[artpeck]

I hope not. But I will check. It is literally brand new and this happened immediatey after I changed the springs. Additionally the rear circuit is fine. And bleeds without air. The plot thickens.

[solihull109]

I hope not. But I will check. It is literally brand new and this happened immediatey after I changed the springs. Additionally the rear circuit is fine. And bleeds without air. The plot thickens.


I'm putting my money on the seal. I have replaced brand new units that would allow air to come in. Case in point, there was a forum member here who sent his truck to me, a lla 109. You may remember because he had several posts about the exact same thing you're describing. He probably bled 10 gallons of fluid, no bubbles, but still had a soft pedal.

After it left the shop he had firm pedal on the first push every time.

I don't care if that seal is brand new, it leaks.


Do you know how many geniune factory Land Rover parts I've pulled from their box and they were junk? Good Luck, and post up when you find it.:thumb-up:

[artpeck]

I will will let you know when I nail it down. Always appreciate the help. First thing to do is change the flex lines and then work it back from there.