1965 4 wheel disc brakes

[zach_carver]

I wanna see if you guys have ever heard anything like the situation I am currently having. Ill try and sum it up. My truck has front and rear disc brakes with new master/booster and disc/disc prop valve. I have no brake fluid leaks! My truck has a perfect brake pedal until I hook up my vacuum to my brake booster. When I plug in my vacuum my pedal goes all the way to the floor with slight resistance. However Ive been driving the truck with it unhooked and it does fine. It all started after i replaced booster/master and installed rear disc. Anyone ever seen such??

[chevy_mike]

Likely a bad booster. My buddy has done his '72 Nova and '68 C10 with CPP boosters and in both cases, they were bad right out of the box. Had them replaced under warranty and the replacements worked perfect.

[zach_carver]

Originally Posted by chevy_mike

Likely a bad booster. My buddy has done his '72 Nova and '68 C10 with CPP boosters and in both cases, they were bad right out of the box. Had them replaced under warranty and the replacements worked perfect.

My booster is a MBM booster off ebay. But they already sent me another one and it changed nothing. Does changing booster size (diameter) matter any? I have a smaller booster than I did before.

[PGSigns]

I would say there is still some air. The added brake line pressure from the booster is able to better compress it over the manual brakes.
Jimmy

[zach_carver]

Originally Posted by PGSigns

I would say there is still some air. The added brake line pressure from the booster is able to better compress it over the manual brakes.
Jimmy

I have bled probably 3 pints of brake fluid through. I was getting solid fluid through it at the end. But Idk maybe I should try it again. It's crazy though because the pedals fine until I hook booster up. Then goes to the floor.

[PGSigns]

So there are two ways a master cylinder will go to the floor, air or its bad.
Jimmy

[zach_carver]

Originally Posted by PGSigns

So there are two ways a master cylinder will go to the floor, air or its bad.
Jimmy

Could my bore size being too big or too small have any effect? I guess I need to get another master cylinder.

[jweb]

Have you tried adjusting the push rod on your booster?
Here's a link to the CPP trouble shooting guide. There's a tool they recommend for checking the length
http://www.classicperform.com/TechBo...ot.htm#pushrod

[zach_carver]

Originally Posted by jweb

Have you tried adjusting the push rod on your booster?
Here's a link to the CPP trouble shooting guide. There's a tool they recommend for checking the length
http://www.classicperform.com/TechBo...ot.htm#pushrod

Yea my booster and master are correct. Im unfamiliar with the tool though? My master is deep and I had to add a piece between my booster because it was shallow. I added a piece that was included with booster/master. Ive seen some people talking about drilling the hole 1" lower in pedal but I havent tried that yet. I wasnt sure it would cure the issue I am having.

[zach_carver]

Does brake booster size have any affect? My old booster was HUGE compared to this 8 or 9" I have now..

[jweb]

Originally Posted by zach_carver

Does brake booster size have any affect? My old booster was HUGE compared to this 8 or 9" I have now..

Most Disc/Disc set ups I have seen use an 8" dual booster and 1 1/8 bore master cylinder. Do you know what size your master cylinder is?

Here's a helpful article about Booster/Master cylinder combos:
http://www.mpbrakes.com/techtalk/boo...ur-classic-car

[zach_carver]

Originally Posted by jweb

Most Disc/Disc set ups I have seen use an 8" dual booster and 1 1/8 bore master cylinder. Do you know what size your master cylinder is?

Here's a helpful article about Booster/Master cylinder combos:
http://www.mpbrakes.com/techtalk/boo...ur-classic-car

No I dont know my bore size.. The guy I brought from off ebay is not much help. He wont even respond to me now. I cant seem to find mine even in 1 1/8 bore for sale anywhere so idk if they even make it in that bore. Im about to the point to just order a new different master cylinder and try that. Im lost lol

[jweb]

I would just go to your local parts store and buy a master cylinder for a late 60s or early 70s Corvette with power brakes. Those years of Corvette have 4 wheel disc and a 1 1/8 master. Only about $35 but I think they are shallow so your booster pin may need to be changed

[zach_carver]

Originally Posted by jweb

I would just go to your local parts store and buy a master cylinder for a late 60s or early 70s Corvette with power brakes. Those years of Corvette have 4 wheel disc and a 1 1/8 master. Only about $35 but I think they are shallow so your booster pin may need to be changed

I think ill try this. Thanks man! Ive got the different adapters for shallow and deep pocket masters. Thanks will report back

[jweb]

Don't forget to bench bleed the master before installing.

I hope this helps, good luck.

[zach_carver]

Originally Posted by jweb

Don't forget to bench bleed the master before installing.

I hope this helps, good luck.

Thanks man, will do!