Master Cylinder Question

[Daytrepper]

Silly question.....

I'm chasing a rear brake overheating issue on my car.

Question is, which ports on this master go to the front, and which go to the rear?

Car was converted recently to Bendix style master and power booster. Left outlets.

I want to make sure this is right before I go down another rabbit hole.

Currently front port is connected to rear brakes (and under small side of reservoir) and rear port to front brakes (under large reservoir), which is how the lines in the conversion kit fit.

 

[davek]

Yes that is correct ,small back larger front.

 

[RJRENTON]

Silly question.....

I'm chasing a rear brake overheating issue on my car.

Question is, which ports on this master go to the front, and which go to the rear?

Car was converted recently to Bendix style master and power booster. Left outlets.

I want to make sure this is right before I go down another rabbit hole.

Currently front port is connected to rear brakes (and under small side of reservoir) and rear port to front brakes (under large reservoir), which is how the lines in the conversion kit fit.

View attachment 1483077

IMO.....CORRECT.....Front connection small reservoir to REAR wheel cylinders; large reservoir rear connection to distribution/proportioning valve to front calipers. CONSIDER using DOT 5 SILICON FLUID TO ELIMINATE CORROSION....pros and cons.....i've used DOT 5 FLUID FOR 20 YEARS in my RS23V0A ****** GTX without any problems......you choose......
BOB RENTON

 

[davek]

drums all corners? discs upfront more info please. What was the setup originally?

 

[Daytrepper]

Yes that is correct ,small back larger front.

Want to make sure it's not reversed on this master.

I've seen some where front port under small reservoir goes to front brakes, rear goes to rear.....

The way the pedal feels; rear brakes are doing all the work....

 

[Daytrepper]

drums all corners? discs upfront more info please. What was the setup originally?

Front disc rear drum.

Originally manual 4 wheel drum.

Upgraded fronts to disc -- 90's style single piston calipers -- and kept rear drum brakes.

Added Bendix style power brake booster and master along with it;

Added 72 and newer style 1 piece prop valve; with brake line kit from Dr Diff.

Stopped GREAT after that. Solid pedal.

But rear brakes overheat to 350-400* in 10 miles of driving. Drove 80 miles to a car show last weekend got brake burning smell from the rear. Have already verified they are not dragging due to adjustment or parking brake issue. Fronts are normal temps.

Also ran it up in the air no load, hit brakes, went thru gears etc, nothing got hot.

Tonight while doing some tests I backed rears all the way off, backed parking brake all the way off. Then drove 8 miles. Pedal sucked. Had to pump pedal to get good stop.

The fronts were applying at the very bottom of the pedal. Rears applying first -- which I thought was always the case.

Seems like rears are getting all the action from the master and fronts are getting the least. In other words, doing all the work, causing the overheating.

Since this was a custom setup I am questioning if the master is hooked up properly.

 

[WileERobby]

Overheating... during stops ? or generally overheating ? are the shoes adjusted correctly ?

 

[Daytrepper]

Overheating... during stops ? or generally overheating ? are the shoes adjusted correctly ?

Generally, seems like they are doing all the work.

 

[PurpleBeeper]

That master cylinder looks similar to my 70 front disk/rear drum factory setup. Front/small goes to the drums. Rear/big goes to the rotors up front. If your rear brakes are overheating, that makes me suspect one/both of them are sticking on. If it's both sides, I would be looking at the proportioning valve or I guess more correctly, the "hold off valve" (name?) Maybe it's stuck? You might also take a look (or just replace) the flexible rear brake hose. I think if those get soft, they can suck in when you let your foot off the brake and keep the rear brakes engaged. Somebody correct me if I'm wrong please

I guess you might want to make sure the front brakes are actually engaging too. Maybe pull a front wheel and have a buddy push the brake pedal and look to see if the calipers are moving.

 

[WileERobby]

so, you got pressure on the shoes without applying the brakes ?

 

[33 IMP]

Rear brakes are dragging. Either the adjustment is wrong, or the emergency cables are wrong/adjusted wrong.
OR: you have a residual pressure valve in the port to the rear brakes that you shouldn't have. (I have had that problem on a four wheel disc car. In gear at idle, it doesn't creep. Apply the brakes, release, car cannot be pushed by three people).

 

[Daytrepper]

so, you got pressure on the shoes without applying the brakes ?

No; there is no dragging that I can see.

Backed them all the way off today; ran it up in the air; brakes applied, released no problem.

Ran cooler backed all the way off but still too hot for an 8 mile drive.

 

[WileERobby]

My opinion is, when you do a conversion, you replace all the soft brake hoses.

 

[RemCharger]

When they're dragging and hot, try pulling over and cracking a rear bleed screw. That will tell you if something further up is holding the pressure

 

[Daytrepper]

My opinion is, when you do a conversion, you replace all the soft brake hoses.

Everything is new. All hoses and lines.

 

[Daytrepper]

Front brakes apply at the bottom of the pedal with the rears backed off. Seems the rears are being applied 3/4 of the pedal travel.

Shouldnt it be opposite?

The lines were custom made so I'm trying to make sure I've got the correct ports hooked up on the master.

 

[64fury74charger]

Just a suggestion, verify that the connections to the proportioning valve are not reversed. The problems you’re describing sound like the valve is holding off the front brakes and applying the rear brakes.

 

[Dragon Slayer]

What does your distribution block look like? Starting in 70 with the single caliper disc, you had a metering (hold off) for the front disc. Rear did have proportioner like 67 yo 69 models. If proportioner setting is not right, maybe rear appling with too much pressure (front piston of MC) limiting how much fluid goes front disc.

Residual valve should be in the front port for drums. True that in later models Mopar changed seal on the rear drum cylinder so it wasn't required, but if your rear are not hanging up, this is not the problem.

Now if the back set up is correct, the meter valve could be limiting pressure to front, or the MC rear piston has leakby limiting pressure to front.

You really need to put a gauge on the rears and see pressure, followed by a fronts. You could have an imbalance of pressure that is making rear do all the work.

 

[Daytrepper]

What does your distribution block look like? Starting in 70 with the single caliper disc, you had a metering (hold off) for the front disc. Rear did have proportioner like 67 yo 69 models. If proportioner setting is not right, maybe rear appling with too much pressure (front piston of MC) limiting how much fluid goes front disc.

Residual valve should be in the front port for drums. True that in later models Mopar changed seal on the rear drum cylinder so it wasn't required, but if your rear are not hanging up, this is not the problem.

Now if the back set up is correct, the meter valve could be limiting pressure to front, or the MC rear piston has leakby limiting pressure to front.

You really need to put a gauge on the rears and see pressure, followed by a fronts. You could have an imbalance of pressure that is making rear do all the work.

This is the prop valve I have. This replaced the old distribution block for the drum brakes. This was part of the disc conversion. From the diagram I have it is plumbed correctly.

I am suspicious that the MC may be plumbed backwards the way things are working.

 

[Dragon Slayer]

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?