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Re: swapped the 11 inch discs in and now brakes are worse. [Re: RapidRobert] #1733338 01/21/15 10:31 PM 01/21/15 10:31 PM
Joined: Feb 2003 Posts: 4,793 Castlegar, BC, Canada That AMC Guy master
That AMC Guy master Joined: Feb 2003 Posts: 4,793 Castlegar, BC, Canada	Quote: no proportioning valve on this car. was a single pot master, and all I did was run dual lines. (I know, I know, I should add one, just never got around to it). Well there's your problem! You need a proportioning valve for a disc/drum system to work properly. Without one (and a dual circuit master) all you're doing is ahem pushing rope. Last edited by RamblerMan; 01/21/15 10:34 PM. Bloody Mary, Full of Vodka, Blessed art thou among cocktails....

Re: swapped the 11 inch discs in and now brakes are worse. [Re: That AMC Guy] #1733339 01/21/15 11:59 PM 01/21/15 11:59 PM
Joined: Feb 2003 Posts: 8,670 A Andrewh OP master
Andrewh OP master A Joined: Feb 2003 Posts: 8,670	the rears never locked up. and I was going to switch to disc in the back too. got the kit, but waiting on a sure grip before I rip the rear apart for the kit. so I figured I could wait and see if I needed it after that. plus I have one from a 68 sitting in the garage, but the mix of chevy master cylinder and such seemed to screw me up, so I would need new lines. it just kept snowballing, so I never got around to it.

Re: swapped the 11 inch discs in and now brakes are worse. [Re: Andrewh] #1733340 01/22/15 03:36 AM 01/22/15 03:36 AM
Joined: Feb 2003 Posts: 4,793 Castlegar, BC, Canada That AMC Guy master
That AMC Guy master Joined: Feb 2003 Posts: 4,793 Castlegar, BC, Canada	The rears not locking up is irrelevant. Dissimilar brake systems require a proportioning valve as disc brakes need higher pressure to function than drum brakes. That's why I used the 'pushing rope' analogy - your trying to move something that requires 1000 lbs. of force with only 1 lb of pressure. It simply won't work. A Proportioning valve and proper Dual Circuit master cylinder will give your car brakes. You could always get an adjustable proportioning valve. That way, you can adjust it now for your disc/drum combo, but then later when you go four-wheel disc, have the added luxury of being able to adjust your front/rear brake bias. Bloody Mary, Full of Vodka, Blessed art thou among cocktails....

Re: swapped the 11 inch discs in and now brakes are worse. [Re: That AMC Guy] #1733341 01/22/15 11:22 AM 01/22/15 11:22 AM
Joined: Feb 2003 Posts: 8,670 A Andrewh OP master
Andrewh OP master A Joined: Feb 2003 Posts: 8,670	perhaps I don't understand what a proportioning valve is supposed to do. are you saying bad front brakes are because I don't have one? my understanding is that all it does is limit the force applied to the rear's over the fronts. AND it has that block off if I lose one circuit. it doesn't bleed pressure over from one circuit to the other. Would defeat the purpose of having a dual circuit system.

Re: swapped the 11 inch discs in and now brakes are worse. [Re: Andrewh] #1733342 01/22/15 12:54 PM 01/22/15 12:54 PM
Joined: Oct 2005 Posts: 8,862 Ontario, Canada S Stanton Don't question me!
Stanton Don't question me! S Joined: Oct 2005 Posts: 8,862 Ontario, Canada	No prop valve ... here's how I see it ... You apply the brakes, the rear cylinders fill and subsequently the m/c won't travel any further. Meanwhile the fronts haven't got enough fluid in them to do squat.

Re: swapped the 11 inch discs in and now brakes are worse. [Re: Stanton] #1733343 01/22/15 01:53 PM 01/22/15 01:53 PM
Joined: Feb 2003 Posts: 8,670 A Andrewh OP master
Andrewh OP master A Joined: Feb 2003 Posts: 8,670	http://stoptech.com/technical-support/technical-white-papers/proportioning-valves this article says, it isn't doing that. it just helps prevent rear lockup's or over bias.

Re: swapped the 11 inch discs in and now brakes are worse. [Re: Andrewh] #1733344 01/22/15 03:13 PM 01/22/15 03:13 PM
Joined: Sep 2007 Posts: 14,889 up yours Supercuda About to go away
Supercuda About to go away Joined: Sep 2007 Posts: 14,889 up yours	Quote: http://stoptech.com/technical-support/technical-white-papers/proportioning-valves this article says, it isn't doing that. it just helps prevent rear lockup's or over bias. Too many people without a clue about how a disc/drum brake system works give poor advice. The factory combination valve incorporates the functions in your link and more. Lack of a combo valve will not keep your discs from working. You could plumb the M/C direct to the front and rear brakes and they would work after a fashion. But they would not work properly do to the inherent differences in how drums and discs operate. The rears would tend to lock up first. If you have a FSM from the drum/disc pre-ABS era there is a pretty good write up in there on how they work and why. They say there are no such thing as a stupid question. They say there is always the exception that proves the rule. Don't be the exception.

Re: swapped the 11 inch discs in and now brakes are worse. [Re: Supercuda] #1733345 01/22/15 05:26 PM 01/22/15 05:26 PM
Joined: Jan 2003 Posts: 10,538 Freeport IL USA poorboy I Live Here
poorboy I Live Here Joined: Jan 2003 Posts: 10,538 Freeport IL USA	Just to add to the confusion, i had a car i put one of those booster/corvette master cylinder kits on, with a combo valve, and the brakes still sucked. Throwing the master/booster in the trash and installing good parts solved my problem. In my case, the master didn't have enough travel. Loosen the lines and see if the pedal will go to the floor. I'm betting it won't. Gene

Re: swapped the 11 inch discs in and now brakes are worse. [Re: Stanton] #1733346 01/22/15 06:41 PM 01/22/15 06:41 PM
Joined: Feb 2003 Posts: 4,793 Castlegar, BC, Canada That AMC Guy master
That AMC Guy master Joined: Feb 2003 Posts: 4,793 Castlegar, BC, Canada	Quote: No prop valve ... here's how I see it ... You apply the brakes, the rear cylinders fill and subsequently the m/c won't travel any further. Meanwhile the fronts haven't got enough fluid in them to do squat. I'd be willing to bet that's exactly what's going on. With no proportioning valve, front/rear pressure is equal, but the discs require much higher pressures to operate correctly. He's probably getting some brake action, but not enough to do squat. To figure exactly what's going on, I'd need to actually crunch some numbers. I'd need cylinder diameters, caliper piston sizes, master cylinder size.... the numbers wouldn't lie. He could also have a grossly undersized master. I must've missed the part where he said he had an aftermarket master. Bloody Mary, Full of Vodka, Blessed art thou among cocktails....

Re: swapped the 11 inch discs in and now brakes are worse. [Re: That AMC Guy] #1733347 01/22/15 07:47 PM 01/22/15 07:47 PM
Joined: Sep 2007 Posts: 14,889 up yours Supercuda About to go away
Supercuda About to go away Joined: Sep 2007 Posts: 14,889 up yours	Quote: I'd be willing to bet that's exactly what's going on. With no proportioning valve, front/rear pressure is equal, but the discs require much higher pressures to operate correctly. Don't bet alot on it. The pressure differential is handled by the diameter of the piston in the caliper and the diameter of the wheel cylinder piston. Do the math http://www.school-for-champions.com/science/pressure.htm They say there are no such thing as a stupid question. They say there is always the exception that proves the rule. Don't be the exception.

Re: swapped the 11 inch discs in and now brakes are worse. [Re: Supercuda] #1733348 01/22/15 10:26 PM 01/22/15 10:26 PM
Joined: Oct 2005 Posts: 8,862 Ontario, Canada S Stanton Don't question me!
Stanton Don't question me! S Joined: Oct 2005 Posts: 8,862 Ontario, Canada	If I understand the OP, there are no valves of any sort in his system, the front m/c line feeds the front brakes, the rear feeds the rear. The rear cylinders are smaller and fill before the fronts. With nowhere for more fluid to go, the master can no longer move and subsequently the fronts get no more pressure.

Re: swapped the 11 inch discs in and now brakes are worse. [Re: Supercuda] #1733349 01/22/15 10:30 PM 01/22/15 10:30 PM
Joined: Feb 2003 Posts: 8,670 A Andrewh OP master
Andrewh OP master A Joined: Feb 2003 Posts: 8,670	corvette 1974 master cylinder. stock 10 inch drum rear's for a 65 coronet stock mbody calipers up front.

Re: swapped the 11 inch discs in and now brakes are worse. [Re: Stanton] #1733350 01/22/15 11:04 PM 01/22/15 11:04 PM
Joined: Sep 2007 Posts: 14,889 up yours Supercuda About to go away
Supercuda About to go away Joined: Sep 2007 Posts: 14,889 up yours	Quote: If I understand the OP, there are no valves of any sort in his system, the front m/c line feeds the front brakes, the rear feeds the rear. The rear cylinders are smaller and fill before the fronts. With nowhere for more fluid to go, the master can no longer move and subsequently the fronts get no more pressure. Please stop, you have no idea how hydraulics work. They say there are no such thing as a stupid question. They say there is always the exception that proves the rule. Don't be the exception.

Re: swapped the 11 inch discs in and now brakes are worse. [Re: Supercuda] #1733351 01/23/15 12:15 AM 01/23/15 12:15 AM
Joined: Jun 2005 Posts: 5,102 Western Md. skicker "The Champ"
skicker "The Champ" Joined: Jun 2005 Posts: 5,102 Western Md.	Whats to say the pedal ratio is correct for the GM master cylinder? I know from building my own set-up years ago to put the master cylinder behind and under the floor that ratio was a huge driving factor in the performance. ...FAFO...

Re: swapped the 11 inch discs in and now brakes are worse. [Re: skicker] #1733352 01/23/15 08:18 AM 01/23/15 08:18 AM
Joined: Dec 2014 Posts: 5,777 ohio R ruderunner master
ruderunner master R Joined: Dec 2014 Posts: 5,777 ohio	I beiee some here are unsure how a dual circuit master cylinder works. They are under the impression that both pistons are connected to the pushrod. Only one piston is actually connected to the pushrod,the other is activated by hydraulic pressure and is free floating in the bore. The only time the pistons actually contact each other is when there is a failure of one circuit(pimar circuit, closest to the pushrod). This allowed the hydraulic cushion between pistons to fail and they then stack solid

Re: swapped the 11 inch discs in and now brakes are worse. [Re: Andrewh] #1733353 01/23/15 11:31 PM 01/23/15 11:31 PM
Joined: Jan 2003 Posts: 28,067 Irving, TX feets Senior Management
feets Senior Management Joined: Jan 2003 Posts: 28,067 Irving, TX	Quote: corvette 1974 master cylinder. stock 10 inch drum rear's for a 65 coronet stock mbody calipers up front. Andy, why didn't you tell me about it when we were on the phone this week? What size is that MC? 1" or 1.125"? I bet it's the 1.125" power MC. If the bore is the wrong size for the calipers you will never get the car to stop. Grab my brake math spreadsheet and run the numbers. When I had the big MC and the slider calipers I could have both feet on the pedal, my butt out of the seat, and still not be able to stop the car. It magically fell in line when I put the AMG brakes on the car. The MC was perfectly sized for those calipers. I bet the proper sized MC would make the problem go away. Those calipers were likely paired with a 1.031" master cylinder. If I have the MC sizes correct you are down 16% on your brake pressure. We are brothers and sisters doing time on the planet for better or worse. I'll take the better, if you don't mind. - Stu Harmon

Re: swapped the 11 inch discs in and now brakes are worse. [Re: feets] #1733354 01/24/15 01:03 AM 01/24/15 01:03 AM
Joined: Feb 2003 Posts: 8,670 A Andrewh OP master
Andrewh OP master A Joined: Feb 2003 Posts: 8,670	says it is 1-1/8" Bore Dual Reservoir Master Cylinder problem is this is a gm master cylinder. not sure on the interchange to get a 1 inch bore. searches show some aftermarket stuff that might work. but I want to steer clear of that if I can. I decided to pick up the corvette booster and master combo from autozone. So I don't have to go out again, if I find it is the problem. if it isn't I will just return it instead. I would really like to find a more "factory" solution but not sure it is out there with how cobbled together this is. I did mention it the other day, just got around to playing with it last weekend.

Re: swapped the 11 inch discs in and now brakes are worse. [Re: Andrewh] #1733355 01/24/15 03:11 AM 01/24/15 03:11 AM
Joined: Jan 2003 Posts: 10,538 Freeport IL USA poorboy I Live Here
poorboy I Live Here Joined: Jan 2003 Posts: 10,538 Freeport IL USA	If you have room for a Volare booster and master cylinder, I'm betting your brakes will be much better. If you used a pedal assembly from the same company you got the booster/master from, your pedal ratio is no where near correct either. That company sells a lot of junk under several names. Someday it will catch up with them. Gene

Re: swapped the 11 inch discs in and now brakes are worse. [Re: poorboy] #1733356 01/24/15 02:22 PM 01/24/15 02:22 PM
Joined: Feb 2003 Posts: 8,670 A Andrewh OP master
Andrewh OP master A Joined: Feb 2003 Posts: 8,670	so to the person that guessed no pedal left. you win. I cracked open the bleeder screws and it still didn't go down any further than if they were closed. I know the pedal and booster have more movement because I disconnected the master and I can put the pedal to the floor. looking at the corvette booster and master combo, there is no way to make that work with this bracket setup. the rod on the back of the booster is too long. it would be engaging the booster when I bolted it up. not sure if replace just the master is the answer. maybe as someone above said, internal bleed by so it isn't giving enough force, and that might solve it. going to a smaller bore doesn't seem to be a good idea, if I am maxed out on distance already. the volare one is too big in diameter. I did find that the a body ones are 7 inch boosters and would bolt in, but not sure about braking force.

Re: swapped the 11 inch discs in and now brakes are FIXED [Re: Andrewh] #1733357 01/25/15 02:26 AM 01/25/15 02:26 AM
Joined: Feb 2003 Posts: 8,670 A Andrewh OP master
Andrewh OP master A Joined: Feb 2003 Posts: 8,670	just finished. update in the original post.

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