Anybody using a 15/16" bore master cylinder

[hunt2elk]

See post #21.

Sorry, trying to get around on the site on my phone and got you mixed up with somebody else.
By the way, I love your video.

 

[not so famous bob]

Which MC are you using? I have the aluminum dual from Cass for my 4 wheel manual discs.

If I remember right , its an 87 dodge diplomat , alum. , 2 reservoir , on an offset adapt block.

 

[not so famous bob]

You can forward to around the middle of the video for my lock up with 15/16 master.

Power brakes no doubt ! Mine are manual----------

 

[Billccm]

Power brakes no doubt ! Mine are manual----------

No sir! Manual Dr Diff disc brakes with 15/16 master.

 

[not so famous bob]

No sir! Manual Dr Diff disc brakes with 15/16 master.

How hard do u have to stomp them to get them to lock up?
Have u had it on the dragstrip yet , and how hi could u stall it w/ the discs ?
I found that mine dont hold as well as drums do when trying to hold it on the line .--------???

 

[mopar jack]

I have an E body with disc front drum rear manual 15/16 master and I raced it that way a couple years. I had to double pump the brake then set the line lock and and run rpms up to the stall speed around 3500 rpm. If I hit it any harder it would push the car even with locked wheels.

 

[Billccm]

In that video i was just a tick below 40mph and one stomp to the pedal.

 

[hunt2elk]

In that video i was just a tick below 40mph and one stomp to the pedal.

I may have missed it, but do you have the aluminum or iron master cylinder?

 

[Billccm]

I may have missed it, but do you have the aluminum or iron master cylinder?

Dr Diff master cylinder. I assume aluminum. It looks like a modern mopar master cylinder.

 

[hunt2elk]

Dr Diff master cylinder. I assume aluminum. It looks like a modern mopar master cylinder.

Yes, that is the aluminum version.

 

[Glenwood]

Like this Bill?

 

[hunt2elk]

@CK70, you will have to explain what warrants the big red X.

 

[68 Sport Satellite]

@hunt2elk did you ever get your brakes sorted with good pedal travel and stopping power?

 

[hunt2elk]

@hunt2elk did you ever get your brakes sorted with good pedal travel and stopping power?

Yes. Cass sent me another distribution block and that took care of the dash warning light staying on. I adjusted the rear shoes a tad tighter and bled the system a few more times. Everything seems to be fine now.

 

[Kern Dog]

Add me to the list of guys that can’t lock up the brakes.
I have tried numerous combinations too.
I started off with 12” front disc with 2.6” calipers and 10” drums, power booster and iron 15/16” master cylinder. Braking was good but I don’t recall ever locking them up. 2006, I added the Dr Diff 11.7” rear disc kit. Braking did not get better or worse.
In 2012, I went down a rabbit hole of multiple changes. My goal was to change to a manual setup for simplicity and a cleaner appearance.
I tried several MCs with different bore sizes and they all resulted in hard pedal, extremely high effort and brakes that wouldn’t even skid on dirt. I changed to larger 2.75” front calipers and that made no difference.
I tucked my tail between my legs, admitting defeat… and put the power booster back in.
Later I realized that I had a disc/drum proportioning valve in place which is wrong for a 4 wheel disc arrangement. I put in a 4 wheel drum distribution block and maybe it was a “placebo effect” but the brakes felt a little better. I pulled the brake pedal and drilled a hole up 3/8” higher to give the push rod more leverage. The brakes felt a little better. Lastly, I adjusted the little nub in the booster that makes contact with the master cylinder piston. All these things made tiny incremental improvements but still…. No lockup.
Last year I upgraded to the 13” Cobra brakes with 2 piston calipers. After reading the brake section of Andy Finkbeiners book, I learned that engineers aim for a 2 to 1 bias for brakes. The front caliper surface area should be approximately double that of the rear in a 4 wheel disc car. With the Cordoba 11.75 rotor, 2.75” piston front brake and 11.7 (1.5” single piston) rear setup, I was at 3.37 to 1. Way too much front bias. With this current setup, I am at 2.1 to 1.
I covered the troubles that I had with the hydroboost installation in another thread.
I tried manual brakes again late last year and had similar results… hard pedal, poor braking.
Even now with the car reasonably sorted out, I can barely lock the fronts. Braking is great but I’m still chasing that “Wow” feeling.

 

[hunt2elk]

Add me to the list of guys that can’t lock up the brakes.
I have tried numerous combinations too.
I started off with 12” front disc with 2.6” calipers and 10” drums, power booster and iron 15/16” master cylinder. Braking was good but I don’t recall ever locking them up. 2006, I added the Dr Diff 11.7” rear disc kit. Braking did not get better or worse.
In 2012, I went down a rabbit hole of multiple changes. My goal was to change to a manual setup for simplicity and a cleaner appearance.
I tried several MCs with different bore sizes and they all resulted in hard pedal, extremely high effort and brakes that wouldn’t even skid on dirt. I changed to larger 2.75” front calipers and that made no difference.
I tucked my tail between my legs, admitting defeat… and put the power booster back in.
Later I realized that I had a disc/drum proportioning valve in place which is wrong for a 4 wheel disc arrangement. I put in a 4 wheel drum distribution block and maybe it was a “placebo effect” but the brakes felt a little better. I pulled the brake pedal and drilled a hole up 3/8” higher to give the push rod more leverage. The brakes felt a little better. Lastly, I adjusted the little nub in the booster that makes contact with the master cylinder piston. All these things made tiny incremental improvements but still…. No lockup.
Last year I upgraded to the 13” Cobra brakes with 2 piston calipers. After reading the brake section of Andy Finkbeiners book, I learned that engineers aim for a 2 to 1 bias for brakes. The front caliper surface area should be approximately double that of the rear in a 4 wheel disc car. With the Cordoba 11.75 rotor, 2.75” piston front brake and 11.7 (1.5” single piston) rear setup, I was at 3.37 to 1. Way too much front bias. With this current setup, I am at 2.1 to 1.
I covered the troubles that I had with the hydroboost installation in another thread.
I tried manual brakes again late last year and had similar results… hard pedal, poor braking.
Even now with the car reasonably sorted out, I can barely lock the fronts. Braking is great but I’m still chasing that “Wow” feeling.

I'll have to wait a few more months until I try to lock up the wheels on this car and my RR. At the time, I was just happy to get everything else sorted. I have this same setup on my Duster, and I got that car to lock up the brakes evenly if I want to. Had to add an adjustable valve in the rear line however.

 

[68 Sport Satellite]

I run front 11.75" disc, rear drum with a Raybestos blue iron MC, currently 1-1/8" and previously 15/16". The 1-1/8" got the pedal off the floor when braking hard. Neither MC setup provided lockup. I don't have an inline prop valve as the one I used to have had no effect. I've since bought a Wilwood prop valve but haven't installed (supposed to have more range of adjust). I also self-biased the brakes by installing new smaller Rear drum cylinders per recommendation from Rick Ehrenberg. I too have not yet had the WOW factor with brakes on this car.

I used to think I just need larger front calipers and wanted to increase my wheels from 15" to 17" to try that, but KD is having the same issues as me and he's running bigger wheels.

I'll look into adjustment of the rear shoes. I'm confused on how that would impact front clamping force.

 

[hunt2elk]

I also use one size smaller than stock rear wheel cylinders on all 3 of my cars. My Duster is the only car I have really experimented with to get the wheels to lock up. I first tried the standard rear prop valve that everyone is selling. Couldn't get the results I needed, so then tried the Wilwood valve. That did indeed give more adjustment.

 

[1STMP]

I realize this is an old thread.
To get firm pedal the bleed ports on
your front discs need to be at the
highest point possible to get the
air out of the system.
For mine I used a piece of wood the
exact thickness of the rotor and removed the caliper from its' mounting
rotating the bleed port to its'
highest point. Bleed the brakes from
there.
Also, your proportioning valve does
not need to be installed in the same
location as existing. You can move it
to a location under your booster for
easier access.