Soft brake pedal - 1983 Land Rover Discover Series III (88" wheel base)

Background Info:
- 1983 Land Rover Discover Series III (88 inch wheel base) with a 2.25L diesel engine came into shop with soft brake pedal
- braking system on this 1983 Land Rover is hydraulic with drum brakes at the front as well as drum at the rear (see attached pic)
- customer has installed a new aftermarket vacuum brake booster as well as a new aftermarket brake master cylinder

What our shop has done:
- replaced the shuttle valve (as Land Rover calls it) / see attached picture / not sure if the shuttle valve also has a metering valve too???
- bled the braking system with DOT 4 even though the factory manual in 1983 calls for DOT 3
- test drove the vehicle with no change in pedal
- re-bled the braking system
- check for external leaks - none found
- tested brake master cylinder for internal leaks
- as per the ASE-A5 Test Prep Manual for brakes (i.e. press down slowly on the brake pedal looking for a rise in the fluid level within the brake master
cylinder and release the pedal slowly looking for the fluid level to fall); passed the test
- tested brake booster - failed
- additional notes for the status of the brake booster: 1)check valve on exterior of brake booster housing will not seat proper = no vacuum in brake booster when engine is not running 2) engine off and no vacuum in brake booster (because the check valve does not seat properly) - the brake pedal goes right to the floor 3) turn engine on and after 4-5 pumps of the brake pedal you will get some brake pedal feel

What we are still having a problem with:
- there is no brake pedal - it basically goes to the floor

What I don't understand:
- we bled the braking system and checked the master cylinder for external leaks as well as internal leaks; none found
- if the brake booster lost its vacuum, we should have a hard pedal - no?

I am guessing that both the brake master cylinder and brake booster are no good. However, I am not sure if I am missing obvious. Thoughts appreciated. Thanks.

Has the brake shoe adjustment been checked yet?

No, it has not. Guess I had target fixation - hydraulics....hydraulics...hydraulics... Zooming in on a new target - drum adjustment !! Will keep you guys posted - thanks Matt.

Did you bench bleed master cylinder before installing it in the car? Not bleeding it before install will prevent it from building pressure as air would be trapped inside the master cylinder. Otherwise the rear seal on the master cylinder is bad preventing proper brake operation.

With low vacuum due to the vac leak you would develope a hard pedal after pumping it up with car off does this happen? It's normal if it does but you will want to fix the vac leak.

Also what Matt said 100 percent.

Put me down for shoe adjustment
+1
Good luck!

Haven't re-bleed the master cylinder on the 1983 Land Rover (as this vehicle has won the award of "recovery room status" and thus sits to the side of the shop at the moment) . Thinking more about this issue, couldn't I see if the master cylinder is providing pressure or not by isolating the master cylinder and connect a cheap brake pressure test kit (e.g. www.amazon.com/SSBC-A1704-Brake-Pressure...+%2Caps%2C157&sr=8-6 ) right to the master cylinder so that I can see the pressure output of the master cylinder right at the cylinder?

As always - thoughts appreciated.

That could work looks like it connects at bleeder screws at wheels though. So it won't without modifications work on the master cylinder itself.

Agreed. Will have to do some modifications at the master cylinder to get that cheap test kit working.