74 Fj40 Brake Troubles

[Igotmearedone]

I hope I explain things okay and I'm wondering if I could get some help here with my brake troubles. I have front discs and rear drums that worked OK in the past, but I did an overhaul because of extensive rust with a new CityRacer Brake Booster, a refurbished (by me, an amateur, with a kit) 75-80 brake master cylinder, a refurbished proportioning valve, and new brake lines. When I put everything together, bled them, and started the car, the brake felt very firm then suddenly gave way with a "pop" and is now very soft. It does not stop the car and I don't see the front discs even engaging when the brakes are pressed.

I tried bench bleeding and the rear reservoir kept getting air bubbles. There seemed to be a small leak at the proportioning valve, so I tightened up all the bolts/screws around there and the bubbles are less but still there. Front reservoir bench bleed went fine. Then I bled the brakes again, which was OK overall but the rear right seemed to also get bubbles more than the rest. Still soft brakes with 0 braking power. Also to note, I may have a vacuum leak because whenever I press the brakes it revs the engine slightly, but I couldn't find the leak with a smoke test.

My next step is just keep on bleeding the brakes, but anyone have any other thoughts on it? Could I have destroyed something in the booster when it popped? Or maybe one of the seals in the brake master cylinder?

 

[DeskJock]

If it were my rig. I’d get a new master cylinder. Sounds like you’ve bleed the system twice and from what you saying - sounds to me like something catastrophic happened to your master.

 

[Pighead]

Or maybe one of the seals in the brake master cylinder?

that was my first thought. Take it apart and see if maybe one tore or folded during assembly

 

[Flatlanderfj40]

IIRC, on my ‘74 (aftermarket front discs) I removed the residual value on the oe master. I didn’t have a prop valve. Now running rear disc setup with city racer booster and nonabs 80 master AND prop valve.

 

[45Dougal]

Isn't there a thing where the front and rear chambers of the master cylinder can leak into each other if you pressed it in too far during install??

Sounds like the master needs opening up for a look.
Are the rears adjusted?

 

[dazerb]

Another vote for MC here.
I have 74 with very similar setup. I bought the Booster/Prop valve/and MC from a93 Landcruiser all from city racer. Everything matched up real nice - worth the $. The knuckles/discs were pulled from an 83 fj60.
I did NOT have to fiddle with booster length at all - you didn't mention any adjustment there but i know it's important.
I did a full bench bleed on MC before dropping it in and used the gravity method to bleed farthest to closest wheel.
Adjusted the original rear drums and i am stopping on a dime!

 

[Igotmearedone]

The rears were adjusted before and if I remember correctly they were OK. This was a project I had started almost a year ago - i had put in the new booster and master in place, other stuff took over for a while, and now finally got back around to replacing/bending new lines. I'm pretty sure I adjusted the booster length back then when I first put it in. I must have set it too long and maybe I destroyed the master and hopefully not the booster. I'll take it apart this weekend to have a peak. Thanks for the tips everyone