You should be able to buy a test gauge kit that will let you check pressures at the master cylinder and also at the bleeder valves with the correct adapters. with only one gauge you can check the MC first then compare that at the calipers. I'm curious at what pressure the pedal goes to the floor.

 

With the new porportion valve does the brake light come on when the brake pedal goes to the floor? I would consider rebuilding the new master cylinder and see if that makes a difference. I'm highly suspicious of the way it's operating.

 

Thomas

Interesting question, no the brake light no longer comes on. I double checked the electrical connection to make sure its making contact. Given that, today i decided to drive it in my cul de sac, and the brakes are working but still feel mushy. I noted a very slight leak in the input side of the prop valve (embarrassing as this is first part I replaced) on the back brake side. I since further tighten that connection. Now I'm wondering if the brakes were always soft. My wife says yes....and she's always right even when shes.....

Odd thing, the engine is running rough, as opposed to running smooth before this brake episode, I'm thinking bad gas from sitting so long?

 

You could try disconnecting vacuum lines one at a time and plug them to see if the idle smooths out. Junk in the carburator maybe. Mushy brakes are interesting, Have the brake pads been replaced recently? Sometimes new pads don't fit completly flush against the rotors and have a little spring in them that can cause soft brakes. It was common on older drum brakes to do that until then broke in, pads can do that to a point until they break in. No brake light is good but you would think it would come on if the brakes were out of balance.

 

Would it be possible to remove the brake lines from the master cylinder and plug the master cylinder? If possible and the pedal still goes to the floor with the engine running then that pretty much points to the master cylinder. This conclusion is based on my new found knowledge of power brake operation recently provided by Thomas. Any chance the master cylinder came from China? I put a master cylinder on a friend's '66 Corvette , which turned out to be faulty and from China. Have also heard on the interweb of other people. Getting bad brake components from China.

I agree with your wife. I always felt that power brakes of that era and earlier felt a lot softer than manual brakes.

 

That would be a very good test, plug the lines and see if the pedal still goes to the floor. I'm thinking it's bypassing internally under pressure. But why would a new (or rebuilt unit) do excarly the same thing the original unit is doing? Thats odd. When power brakes first came out the brake pedals had two holes on the pedal atachment, the holes were about 1in or 1,5in apart that the MC clevis was plinned to the pedal. The top hole was used for manual brakes and the lower hole was used when a booster was used. I will look that up and see if the older pedal assemblys had two holes for use. I don't think manual brakes are an option on anything anymore. One hole in the pedal assembly only. I replaced my 77 MC years back with a Orilies unit, I'm sure it was probably china but the original had to many pitts to rebuild. No issues with the new unit faily stiff pedal. Has not touched the floor since it was bled. I would almost like to go back to manual brakes where they are more responsive. Manual brakes use an 1in bore where the PB system uses a 1 1/8 in bore. Or go hydrulic with the PS. I haven't decided yet.

 

68 to 79 brake pedals have two holes depending on you brake option. There was point in early 70s where PBs became standard and not an option.

 

I specifically ordered my '73 without the power brake option. I just did a quick search and power brakes became standard in '76

 

Ok, I was thinking it was before that year. Thanks for looking. Early 70s it was considered a Luxury to have power steering, power brakes, power windows and A/C if you had that you had a fancy car. My brother bought a 68 roadster in 69 with no power anything 327 4 speed and it drove nice.

 

Bleed, Bleed, Bleed...