Brake pedal softens while braking.

[iamfine2]

Ok guys,
Here is my latest. The brakes on my 1981 work well, but the brake pedal goes soft during braking and sinks until the brake warning light comes on.
In park I can pump up the pedal again to a firm feel and the brake warning light goes out.
Master cylinder or power booster?

 

[TMPJoe]

Ok guys,
Here is my latest. The brakes on my 1981 work well, but the brake pedal goes soft during braking and sinks until the brake warning light comes on.
In park I can pump up the pedal again to a firm feel and the brake warning light goes out.
Master cylinder or power booster?

air in the brake lines... bleeding is a temp fix

Look for leaks around the pistons in the calipers.. tell tale signs around the wheels .... if you still have stock calipers its a good bet they are now sucking air in as you use them.... you can rebuild them or just get rebuilts with the stainless steel O Rings...

I just did mine .. went through the flintstone brake thing last season!

 

[fine69]

Ok guys,
Here is my latest. The brakes on my 1981 work well, but the brake pedal goes soft during braking and sinks until the brake warning light comes on.
In park I can pump up the pedal again to a firm feel and the brake warning light goes out.
Master cylinder or power booster?

Sounds like a master cylinder problem. They're an easy replacement.

 

[TMPJoe]

if its not the calipers then check the cylinder.. though usually when that goes it just goes and its not gradual

 

[6880 Mike]

Almost certainly not the booster; they seldom fail. Check calipers, mastery cylinder, and hoses.

Regardless of the cause, you have a brake system problem. Be careful driving the car.

 

[TMPJoe]

Almost certainly not the booster; they seldom fail. Check calipers, mastery cylinder, and hoses.

Regardless of the cause, you have a brake system problem. Be careful driving the car.

i see you and I agree mike!

the seals in the calipers are notorius.. about time too based upon age

 

[Brooklinite]

I had a soft pedal on my '72, no leaks anywhere. Bled the system and it was good for a couple of hours then gradually got soft again. Turned out the master cylinder was bad.