hey guys last night i drove about 5 blocks and as im braking down a hill( i live in san francisco) my brake pedal just went straight to the ground and didnt even slow down. i got it back in my garage easily because it was uphill but still sketchy. i noticed that if i pumped them i got a little resistanced and could slow down barely. i checked the fluid and both reserviors were full. im not much of a mechanic yet but my buddy is and he had put a disc conversion kit on the front a couple weeks ago. If any of you guys have any suggestions on a cause i would appreciate it, thanks.

 

Bad master cly or system not properly bled when installed. Ask you freind if he bench bled it before installing. If he does not know what that means then find a new mechanic.

 

lol thats some good advice thanks

 

+1.

Full m/c and no brakes usually = bad master.
Most are about $20 at the local parts store.

- Eric

 

Hope you did not loose them on Crooked St...

Most likely a bad master cyl.

 

disc brakes front and drums still in the rear? did he install a proportioning valve ?

 

i couldnt afford to convert both, no he didnt install a proportioning valve.

 

i didnt, but wouldnt that have been fun.

 

i figured out what the problem was,i think, i completely lost my rear drums. i jacked up the cutty and had my buddy press the brakes while i tried to spin the wheels, front wheels wouldnt turn but tried the back and they spun no problem while the brake was pressed. what he told me was that all the fluid was going to the rear trying to make them press in so the front wasnt getting any fluid. that sound correct to you guys?

 

The Kit should have come with a Hold off valve that mounts near the Master before the distribution valve which mounts to the drivers side frame

Since disc brakes were new in 1967, the valve was still being worked out for the next few years. The 1967-70 valves could consist of as many as three elements and the valves would not work properly without all the pieces. Both 1967-70 factory drum and factory disc cars have (or had) a distribution block which is identical whether the car was drum or disc. Although very similar in appearance to a proportioning valve, the distribution block does not alter brake line pressure. The distribution block keeps front and rear systems separate, splits the left and right front lines and houses the sending unit for the brake failure warning light. The 1967-1970 factory disc vehicles employed an additional valve, referred to as a hold-off valve, mounted at the master cylinder. The final component in the 1967-70 factory disc brake systems was a correction valve typically located in the front to rear brake line for the rear brakes. This valve was not used in every factory disc brake car, but would make the front to rear line two pieces with the valve usually found mounted near the floor pan of the car. An original 1967-70 disc car can be factory correct without the correction valve, but not without the hold-off valve at the master cylinder.


Source was Inline tube http://www.inlinetube.com/

 

So i was right ? cause OP said there was no proportioning valve installed and he said the rear was getting all the fluid and the front discs werent getting any.

So he needs to do like we said and block off the discs from the drums with that part

 

This makes no sense.
This car uses a dual master cylinder - the fluid cannot go from one circuit to another unless the master is bad.
The hold-off valve is designed to place a delay between the application of the rear and front circuits (drums first, then disks, I think) because drums and disks have different delay times between the increase in fluid pressure and the application of the brakes.

A bad master cylinder can do exactly this sort of thing, shunting fluid from one circuit to another, and reducing pressure in one, so that you've only got the other, which gives you a soft, low pedal which does work somewhat when you really push into it, or when you pump it.

- Eric

 

Yes.
The front disc has no springs to pull the pads away from the rotor, we all know they have a certain amount of drag all the time and therefore take little pressure to begin stopping the car, the rear do have springs to pull the shoes away from the drums. The hold off valve keeps the front disc from getting fluid pressure so the rear shoes can get close to the drums. The shoes getting to the point they are touching builds up some resistance/pressure in the fluid system. When this gets to a certain pressure the hold off valve is overcome with pressure and turns loose allowing the front and rear brakes to engage at about the same time. The hold off valve has a spring and plunger inside it and can be rebuilt, as with most mechanical pressure stuff. So a disc/drum system needs something to equal out the pressure so to speak even though the front and rear systems are completely separate as far as the fluid path is concerned.

Mike

 

The brakes should of worked anyway.
I say bad master or something to do with it too.
You can still use a drum master cylinder and the smaller diameter power drum brake booster without a hold-off or combination valve and the brakes will work fine.
I put front discs on my '68 GTO and drove it for ten years like that and never had a problem.
It's all correct now, should of left it alone because it stopped better before.

 

I agree The Master isn't that expensive to change and if it is the original a new or rebuilt one couldn't hurt ....