Brake help needed

[xrunnr]

I just finished fixing a clutch problem and as always there is something else to fix. I have a '74 109 exmod that is almost finished with its frame off restoration but the brakes do not work. They didnt work when I started the restoration but I thought it would get worked out as I was replacing everything.

The problem: I believe there are two separate problems that could possibly be linked together.

First, no matter what speed you are going as soon as you push the brake pedal down it goes straight to the floor and nothing happens. I have gone around the truck 4 times on each wheel bleeding them and there is zero air in the lines.

Second, With the rover off you can push the brake pedal down and it will stop about half way with good pedal but once you turn the rover on and push the pedal down it will go straight to the floor and will not come back up. It is like the servo is sucking the pedal to the floor and wont let it go. I have added extra/ stronger springs to the pedal but that has not helped at all.

Already replaced the following parts: new brake lines, new shoes, I had the drums turned, new servo, new master cylinder and all new adjusters on each wheel as well as all new wheel cylinders.

I am about to pull my hair out because there is nothing left to replace and I am out of ideas.

[jac04]

3 things:
1) Do you have a brake failure valve in the system?
2) Do the rear brakes work at all?
3) 109" front brakes are notoriously difficult to bleed. Are you absolutely sure you have all the air out? I found that using a pressure bleeder along with the rapid pumping method was the only way to get all the air out of the front brakes.

[ignotus]

try isolating the components by clamping the flex lines. If they are all clamped off the pedal should be hard. If not then it is either the m/c or servo. If hard release the rear hose clamp, still hard?, release one of the front hose clamps, still hard?, release the other hose clamp.
If the pedal drops after releasing any one of the clamps there is your weak link.
Also make sure the adjusters are properly adjusted.

Hope this helps,
gene

[Apis Mellifera]

Also make sure the adjusters are properly adjusted.

Right here.

Unless you've done it before and have a feel for the amount of normal drag you need, it's easy to adjust drum brakes too loose. Since it's easy to adjust them, tighten all the adjusters all the way tight, then press the brake pedal. See if that does anything.

Also most MCs for drum brakes have a residual pressure valve inside that holds the pressure briefly after the pedal is released. If faulty they can hold the pressure longer.

I've never had a pedal get stuck down. Assuming the pedal moved freely prior to fitting the MC and servo, you can disable the servo by disconnecting the vacuum. Is it possible the operating rod of the servo and/or MC is adjusted too short?

[xrunnr]

Thanks for the suggestions.

Jac04 - I removed the brake failure valve and now have a simple connector for both the front and rear lines. None of the brakes work at all. I am using a pressure bleeder and rapid pumping but I am going to do it another few times for safe measure.

ignotus- That is a great suggestion and I will be trying that as well.

apis mellifera - I will also be trying out your suggestions as well. I didn't even think about the operating rod of the servo. that will be on my list as well.

Thanks guys