Master Cylinder Question

[Daytrepper]

That block has a built in proportioning valve I believe. Your rear line goes into the left side as pictured, then out to the rear drum. The front go into the right side, with two lines out?

Plumbed just like the diagram below. There are no markings on the MC for front or rear though.

 

[Dragon Slayer]

Fine print tells you, the front outlet (small chamber) goes to rear. The Aft (large) chamber goes to front. 2 reasons. The larger chamber for the disc because more volume of fluid needed as piston pushes out. Second, the first piston to move and be directly connected to pedal is the primary piston, for the primary front brakes.

 

[Daytrepper]

Fine print tells you, the front outlet (small chamber) goes to rear. The Aft (large) chamber goes to front. 2 reasons. The larger chamber for the disc because more volume of fluid needed as piston pushes out. Second, the first piston to move and be directly connected to pedal is the primary piston, for the primary front brakes.

Then all the plumbing is correct.

I'm wondering if the prop valve is stuck. It is brand new, but that doesn't always mean it's good.

 

[Dragon Slayer]

You have 2 prop valves in series with this set up. Didn't you state you also have a stand alone prop valve? If the proportioning valve fails to limit pressure that could contribute to over heating, but you still should have good front brakes. I am more concerned you don't get a front brake application until end of petal. That implies under volume master cylinder or some leak in MC.

 

[Daytrepper]

You have 2 prop valves in series with this set up. Didn't you state you also have a stand alone prop valve? If the proportioning valve fails to limit pressure that could contribute to over heating, but you still should have good front brakes. I am more concerned you don't get a front brake application until end of petal. That implies under volume master cylinder or some leak in MC.

Just the single prop valve. 72 and up style.

Yes bottom three inches of pedal the front applies. New factory disc brake MC used 66-72. It was difficult to bleed them when everything was assembled. Could be a MC issue. I bench bled the MC and vacuum bled the system as well as manual. Pedal felt good and solid and car stopped fine...except the rears doing all the work and overheating.

I hate to start throwing parts at it but I'm not sure what to look at...has to be prop valve or MC. Can't be much else.

 

[64fury74charger]

Maybe you can temporarily plumb around the proportioning valve and put a pressure gauge on all 4 corners and see what the master cylinder is doing straight up. If pressure is good then you found the potential problem.. If it’s not right then look at the master cylinder.

 

[davek]

you could bleed the front discs and see if that changes things. I just went down this rabbit hole with my Bee,fronts were dragging. Changed hoses ,calipers and in the end it was MC

 

[TrackPack]

Then all the plumbing is correct.

I'm wondering if the prop valve is stuck. It is brand new, but that doesn't always mean it's good.

Seem to remember that there have been some problems with the reproduction distribution blocks.

Question: did you convert the power brake pedal linkage with the booster install?

 

[Daytrepper]

Seem to remember that there have been some problems with the reproduction distribution blocks.

Question: did you convert the power brake pedal linkage with the booster install?

Yes, did the complete conversion with pedal linkage. OE style.

 

[R/T Boy 67]

With the rear brakes slacked all the way off, what you are describing with the pedal is normal. All the slack will be taken up in the rear brakes before there will be much pressure in the front calipers. All that slack takes up a lot of pedal travel. If you drive somewhere without using your brakes, like a back road without much traffic, do they still get hot?

 

[MoparLeo]

We haven't seen anything but a picture of a M/C.
You say you used a 90's style disc brake setup. What does that mean ?
You can't just mix and match brake parts.
And the rear brake adjustment is how you adjust the height of the brake pedal. Loosen the rear brakes and the pedal will go to the floor.
You will see lots of postings on brake conversion problems and most don't give all the details and want a guess.
Remember that it would be different if we were there and could touch and feel, but we only know what you tell/show us.

 

[Daytrepper]

With the rear brakes slacked all the way off, what you are describing with the pedal is normal. All the slack will be taken up in the rear brakes before there will be much pressure in the front calipers. All that slack takes up a lot of pedal travel. If you drive somewhere without using your brakes, like a back road without much traffic, do they still get hot?

Rears get hot no matter where it's driven, unless I very sparingly use the brakes.

 

[Daytrepper]

We haven't seen anything but a picture of a M/C.
You say you used a 90's style disc brake setup. What does that mean ?
You can't just mix and match brake parts.
And the rear brake adjustment is how you adjust the height of the brake pedal. Loosen the rear brakes and the pedal will go to the floor.
You will see lots of postings on brake conversion problems and most don't give all the details and want a guess.
Remember that it would be different if we were there and could touch and feel, but we only know what you tell/show us.

The calipers are pictured below. Used on many 80s 90s Dodge vehicles. MC and booster are 67-72 Bendix style for cars equipped with disc/drum brakes.

This setup was put together with the help of Dr Diff. The master is a 1.125 bore. Plenty.

As far as the rear brake adjustment, I understand that controls pedal height, but it is basically that they are doing all the braking. Fronts are hardly applying except at the very bottom of the pedal. Brakes have been power bled and manually bled.

 

[Dragon Slayer]

Need to put a pressure gauge on the front and rear, to figure it out, or try swapping the MC. If Prop valve is bad and letting full pressure go to the rear, that should not prevent the front getting full pressure too. I think the rear piston on MC is leaking by causing low pressure to front disc.

 

[Daytrepper]

Need to put a pressure gauge on the front and rear, to figure it out, or try swapping the MC. If Prop valve is bad and letting full pressure go to the rear, that should not prevent the front getting full pressure too. I think the rear piston on MC is leaking by causing low pressure to front disc.

I just ordered a pressure gauge. It should be here tomorrow. I'll follow up.

 

[icetech]

Any chance you have the part # (or year/car if i missed it in the thread) for the MC and valve.. those are the 2 pieces i'm missing for my 62 still and just wanna get the right one from rock.

 

[Daytrepper]

Thanks for all your inputs guys.

Cass over at Dr. Diff saved the day. Big shout out to him.

It was the booster push rod; not adjusted correctly. Cass told me to adjust the rod on the booster so that the piston on the MC was flush with the mounting pad and not sticking out of the MC when mounted.

I pulled the MC off, sure enough, piston was sticking out about 1/8". I bought the $10 adjuster tool off of Amazon and it worked like a charm.

Made the adjustment, 10 mile test drive, rears and front temperatures were almost equal, around 160*, instead of 100* front, 275* rear.

Insane braking difference when I drove the car. Pedal is solid, much higher than it was before. Stops on a dime.

 

[Daytrepper]

Any chance you have the part # (or year/car if i missed it in the thread) for the MC and valve.. those are the 2 pieces i'm missing for my 62 still and just wanna get the right one from rock.

This is the MC/booster kit I used. It is what would have been on 66-72 front disc/rear drum with BB.

66-69 Mopar B Body 8 Inch Dual Bendix Brake Booster Kit

 

[Dragon Slayer]

Interesting and thanks for the feedback. So that implies that as you pressed petal no pressure was built up in either front or rear brakes until the pistons covered the compensating ports. You had enough petal to get the rear pressure up, but the front brake piston was insufficient to generate the necessary pressure to apply them. When you remove the MC of that variety the piston does stick out. But when push rod adjusted correctly it will push the pistons in so that the compensating ports are uncovered just .010" or so. At first application those ports get closed off by the lead seal and you start building pressure in both chambers. Makes sense with you not getting any front brakes until the end of the pedal travel.

 

[Daytrepper]

Interesting and thanks for the feedback. So that implies that as you pressed petal no pressure was built up in either front or rear brakes until the pistons covered the compensating ports. You had enough petal to get the rear pressure up, but the front brake piston was insufficient to generate the necessary pressure to apply them. When you remove the MC of that variety the piston does stick out. But when push rod adjusted correctly it will push the pistons in so that the compensating ports are uncovered just .010" or so. At first application those ports get closed off by the lead seal and you start building pressure in both chambers. Makes sense with you not getting any front brakes until the end of the pedal travel.

Lengthening the pushrod at first didn't sound right; as it would maybe make things worse -- but truth was it was not the proper length to start with to setup the MC to apply the brakes correctly.

I've seen alot of threads on here questioning the booster pushrod length, and it may be different depending on MC. I'd have never thought to lengthen it to change the resting place of the piston.

At the end of the day I'm glad it was this simple and hope it'll help anyone else having brake issues -- get the tool on Amazon, find the correct booster rod length for your MC!