Help with brakes

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Sep 17, 2006
Santa Rosa, CA
I'm sorry - this is not about anything stock. I need to some help diagnosing brake issue.

A local guy help me redoing the brakes on my 40 after a dana 60/14 bolt axle swap. He replaced all the brake lines with new hard lines and a new chevy master cylinder with adapter. And, it worked great when we took delivery.

But, after sitting for about 4 weeks, I took it out for a drive and the brakes were awful. Not just loss of power boost awful, but unable to bring the 40 to a stop even on a slight hill.

When I got home, I tested the booster key on (pedal should drop) and key off (pedal should not come up). It failed the key off test, but then I realized there's no check valve, so that makes sense. So, it doesn't appear to be the booster. So, I can't figure out what it might be. It's not like some of the brakes are bad, they are equally bad. So, it's not one of the circuits or some of the calipers, otherwise you'd feel it braking unevenly. It's still braking evenly. that made me think that maybe there's something obstructing the pedal from going all the way down, but I couldn't find anything.

What else can I look at?

IMG_6381 annotated.jpg


Any leaks ?
No, dry as a bone all over. I should add, reservoir is still full up - not losing any fluid.
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Does pumping them help? Still air in lines, improperly sized master cylinder for caliper piston volume, incorrect pushrod adjustment (pedal to booster/booster to master). Is the larger line going to the rear (front port to rear brakes). Why so large of a line from that port?
Brakes can be tough to bleed. I worked for a week on mine. Takes two people…,
I even had full recirculating tubes back to master cycl. And just kept seeing bubbles.

Ultimate it was bad fittings.

Keep punching
But it was fine until it sat for 4 weeks. What can happen to chevy brakes when sitting so long?
Install an inline check valve. I am dubious about a booster running prop without one.
Okay, I'm back to looking at this again. Driving it again, I'm thinking that I'm only getting either the front or the back circuit. However, everything is dry and both reservoirs are full, so it's not a leak. So, what could it be? And I remembered that I've got a line lock on one of the brake circuits. I checked it, the ground had been torn off, but that would not cause it to close. I reconnected the ground and took it out again, no change. So, I'm trying to think if the line lock could have failed somehow - and how I can check it to see if it is working.

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