Members with 4 wheel disc systems: Can you lock your wheels?

-
72Duster440 said:
So I have done this on mine. I run SSBC 4 piston calipers up front and the same Dr Diff 10.7" kit out back. I also cannot lock up my brakes. I tested pressures at each caliper, the fronts were ~1600psi and the rears were ~1250psi during what I'd consider panic stopping pedal effort.

Could it be that the pads you (and I) are running aren't the best, and can't overcome the traction of soft sticky tires to get them to skid?
Click to expand...

What master cyl? That's some gnarly pressure.
 
I got 1250 psi at the right rear. I'm using a 15/16" MC.
 
plumkrazee70 said:
Yep. Mine has that exact block. Truly a distribution block. I'm going to gut mine as I don't really care for the warning light anyway. Should be able to just remove the "plug" from the bottom and.the guts will come out, right?
Click to expand...
That defeats the safety system. A leak anywhere, is or can be, catastrophic. I urge you not to do that; there is no benefit
 
My friend Brian put this manual master cylinder on his '72 Duster, he is very happy with the way it stops now.

20230209_053919.jpg


I would call Cass at Dr. Diff.

These look like the factory masters that the Chrysler Mini Vans Use.

2003 Grand Caravan has the Disc/Disc system on it.

Believe the 2002 Grand Caravan had the Disc/Drum system.

Better talk to Cass for the correct Disc/Disc master for your system.

Also has the "new junction blocks" too. As I believe your used Drum/Drum junction block is suspect to your brake problem.

Screenshot_20230209-053836_Firefox.jpg


___________

On a side note, swapped out this 15/16" master onto the '69 Satellite drum/drum system over the stock master.

Stopped great with reduced foot pressure. Very happy with that simple improvement on a completely stock system.

Screenshot_20230209-054210_Gallery.jpg
 
Your used drum/drum junction block looks to be a different configuration than the one Dr. Diff sells to go with his master cylinders.

Screenshot_20230209-061012_Firefox.jpg


Screenshot_20230209-060743_Firefox.jpg

Dr. Diff junction block ^^^.
 
The picture you posted from Dr Diff is his proportioning valve for a disc/drum setup. It says in the description for front disc brakes. The one the OP posted a pic of matches the distribution block that Dr Diff sells to be used with drum/drum or disc/disc.
 
If you have a Valve like the first one shown in post 57, or a Combination valve like the Second one, that has been gutted
And
The switch is grounded to the brass case, (which would turn the dashlight on), then one side of the system is not working. If it is the front system that has been shut off, then yur gonna have OP's condition. If the rear brakes have been shut off; then, depending on their efficiency, you might never realize it.
The way to center the valve and fix this, is to press on the brake pedal, and; open one side, or the other, one side atta time, until the light goes out.
If the dashlite is not on, go check the switch for continuity from pin to case-ground, which would be a bad thing. Afterwords fix the switch circuit. That shuttle-valve has to be centered, in order for both front and rear brakes to function properly and independently.
 
Last edited:
72Duster440 said:
So I have done this on mine. I run SSBC 4 piston calipers up front and the same Dr Diff 10.7" kit out back. I also cannot lock up my brakes. I tested pressures at each caliper, the fronts were ~1600psi and the rears were ~1250psi during what I'd consider panic stopping pedal effort.

Could it be that the pads you (and I) are running aren't the best, and can't overcome the traction of soft sticky tires to get them to skid?
Click to expand...
If you gut that valve and blow a line in the front or rear will it cause you to loose all braking power?
 
92b said:
If you gut that valve and blow a line in the front or rear will it cause you to loose all braking power?
Click to expand...

I think you quoted the wrong person. I'm not sure, I don't run that valve. My front and rear are separate, I don't use a factory block, I use an adjustable one from Wilwood.

260-11179-lg.jpg
 
92b said:
If you gut that valve and blow a line in the front or rear will it cause you to loose all braking power?
Click to expand...
It appears that way. Because of that, I'm leaning toward SKIPPING the idea.
The alternative is running the lines without any block, just from the MC to the brakes directly.
 
Kern Dog said:
It appears that way. Because of that, I'm leaning toward SKIPPING the idea.
The alternative is running the lines without any block, just from the MC to the brakes directly.
Click to expand...
Seems like that would serve the same purpose and provide an extra layer of safety. Thanks for providing the pictures of what's inside. Hope you get your problem solved.
 
The brakes actually work fine and feel good. I may be reaching for an unattainable level that isn't there.
There is a vacuum pump and tank to provide vacuum. The car starts and builds vacuum, then I drive it normally. The fat cam produces insufficient vacuum, hence the need for the pump.
I found that during repeated hard stops, the brakes were using up the vacuum faster than the pump could provide it. The pedal got hard to push and the effort was high. The addition of the tank helped with that.
Over time, I made several small changes to improve matters. Some changes resulted in small improvements that when added together, have resulted in better performance than I had with the previous 11.75 Cordoba front brakes.
The idea of different "EBC" brand pads is a good one. I have tried different pads on cars and trucks that made a dramatic difference over other brands.
Dr Diff sells quality stuff but for the past couple of years, he has been impossible to speak with. Every transaction is through email. Maybe he is short staffed and is doing the best that he can. I recall years ago, I'd call and he would chat for far longer than I expected, to the point where I wondered how he could earn a living by spending so much time on the phone.

22 2 B.JPG


IMG_E1393.JPG
 
I didn't see much discussion about brake pads until the end. I've read that "racing pads" don't work well in normal driving and only "bite" when hot. No personal experience.
 
I put some PowerStop pads and rotors on my daily driver, it was a huge improvement. I'm going to look into a set for my Duster, I know they have rear pads, not sure they have a D11 equivalent front pad.

Make sure your brake fluid is good too. Rated for high enough temperature, and no moisture in it. I tested mine, that looked brand new, it had 11% moisture in it, I flushed it all out with new high temp stuff.
 
72Duster440 said:
I put some PowerStop pads and rotors on my daily driver, it was a huge improvement. I'm going to look into a set for my Duster, I know they have rear pads, not sure they have a D11 equivalent front pad.

Make sure your brake fluid is good too. Rated for high enough temperature, and no moisture in it. I tested mine, that looked brand new, it had 11% moisture in it, I flushed it all out with new high temp stuff.
Click to expand...
What did you use to test the moisture in your brake fluid?
 
72Duster440 said:
I put some PowerStop pads and rotors on my daily driver, it was a huge improvement. I'm going to look into a set for my Duster, I know they have rear pads, not sure they have a D11 equivalent front pad.

Make sure your brake fluid is good too. Rated for high enough temperature, and no moisture in it. I tested mine, that looked brand new, it had 11% moisture in it, I flushed it all out with new high temp stuff.
Click to expand...
I had the engine-trans-K member and suspension out from June until October. When I put it all back together, I switched to DOT 5.
 
Probably a stupid question, but is it even realistic to expect to be able to lock up all four tires on a car that heavy with wide modern tires on it?
 
Kern Dog said:
I can't. I rarely ever have.
Well, I have locked one or two on wet pavement and the dirt surface in front of my shop. On the road though? Only a few times

I am having a hard time making sense of my brakes. I've tried multiple combinations and no matter what I do or try, I can't get them to skid on dry pavement.
I'm not a trained mechanic but I do have years of experience with these machines. One method that I use is the process of elimination. If the system has faults and you change enough parts, eventually you will find the problem. This is not easy on the wallet but sometimes it is the only course of action you have to work with.



This car stops well but it isn't awe inspiring. I never feel like I need to lift from the brake pedal because I am about to skid or stopping faster than I want. I have good parts in the car but something just isn't right.
Originally, it was a 4 wheel 10" drum system. You all know how those perform.
My first change was an A body power booster and 11" front discs. It stopped well and never had me feeling like I was scared to drive it fast.
Later, I upsized to the Cordoba 11.75" front rotors.
In 2006 I pulled the rear drums and installed the Dr Diff 11.7" rear disc brakes. From this point forward, the car got faster but the braking stayed the same.
Last year when I had the engine out, I decided to upgrade the brakes. I installed the Dr Diff 13" front kit and went down the rabbit hole in a failed Hydroboost swap. That resulted in a complete failure either due to a faulty HB unit or my impatience in the bleeding procedure. Regardless, the HB came back out and I tried a manual 1 1/8" master cylinder. TERRIBLE. Hard pedal with horrible stopping force. I tried a 15/16" MC. Better, but still not nearly good enough to be content with it.
I put the A body booster back in along with a vacuum pump and tank and that is where I am today.
It stops good enough but I'm still wondering why it won't skid. To me, it seems like if it can't skid, then the system isn't at it's potential.
I bought a brake caliper gauge....

I only measured the rear and it registered 1200 psi.
I'm open to any and all suggestions except swapping drums back on the rear. There is something wrong and I am determined to figure it out.

View attachment 1716045435
Click to expand...
 
Kern Dog said:
This is an A body 4 wheel drum distribution block.

View attachment 1716046384

These have no proportioning to them. They serve as a junction block for all of the lines to attach and it includes the federally mandated warning light switch.

View attachment 1716046385

The threaded stud is for the warning light switch. It is a simple barbell shaped piece that slides up and down in a slot in the block. In theory, it is supposed to block off flow to either the front or the rear if there is a leak. I've never known them to work that way though. The advice that I've recently heard is to remove the "barbell" .....this turns the block into a true open distribution block where the system has no restrictions.

View attachment 1716046396
Click to expand...
It does not to my knowledge block off brake fluid in the event of a leak. The switch with the post is the differential ptessure switch which illuminates the brake failure light.
 
Looking at the parts that came out of the distribution block, it looks like it does have provisions to block flow to one side or the other.
As the shuttle moves to one end or the other, these things.....

22 6B2.jpg

......that have O rings, appear to seal off the passage. That brass barbell looking valve slides up and down but is limited by this:

22 6C.JPG
 
Kern Dog said:
I can't. I rarely ever have.
Well, I have locked one or two on wet pavement and the dirt surface in front of my shop. On the road though? Only a few times

I am having a hard time making sense of my brakes. I've tried multiple combinations and no matter what I do or try, I can't get them to skid on dry pavement.
I'm not a trained mechanic but I do have years of experience with these machines. One method that I use is the process of elimination. If the system has faults and you change enough parts, eventually you will find the problem. This is not easy on the wallet but sometimes it is the only course of action you have to work with.



This car stops well but it isn't awe inspiring. I never feel like I need to lift from the brake pedal because I am about to skid or stopping faster than I want. I have good parts in the car but something just isn't right.
Originally, it was a 4 wheel 10" drum system. You all know how those perform.
My first change was an A body power booster and 11" front discs. It stopped well and never had me feeling like I was scared to drive it fast.
Later, I upsized to the Cordoba 11.75" front rotors.
In 2006 I pulled the rear drums and installed the Dr Diff 11.7" rear disc brakes. From this point forward, the car got faster but the braking stayed the same.
Last year when I had the engine out, I decided to upgrade the brakes. I installed the Dr Diff 13" front kit and went down the rabbit hole in a failed Hydroboost swap. That resulted in a complete failure either due to a faulty HB unit or my impatience in the bleeding procedure. Regardless, the HB came back out and I tried a manual 1 1/8" master cylinder. TERRIBLE. Hard pedal with horrible stopping force. I tried a 15/16" MC. Better, but still not nearly good enough to be content with it.
I put the A body booster back in along with a vacuum pump and tank and that is where I am today.
It stops good enough but I'm still wondering why it won't skid. To me, it seems like if it can't skid, then the system isn't at it's potential.
I bought a brake caliper gauge....

I only measured the rear and it registered 1200 psi.
I'm open to any and all suggestions except swapping drums back on the rear. There is something wrong and I am determined to figure it out.

View attachment 1716045435
Click to expand...
Without ABS you should be able to lock all four wheels on dry pavement in a "panic" stop. It should be difficult to lock the rear brakes. You do not want the rears to lock first as the back then wants to pass the front.
Brake pressure is a finction of the pedal ratio and booster multiplication. Frequently the balance or bias valve is to reduce rear pressure preventing rear lockup. Drum diameter and widyh or rotor diameter and pad diameter work in conjunction with piston bore diameters to create brake torque or force. The master cylinder diameter converts the pedal force to line pressure. Wheel cylinder area converts the pressure to pounds force.
Standard accepted on our old cars is that under braking with weight transfer, the fronts do 70% of the breaking, on average. The front wheel drive cars shift that to 80% to 95%. Rear engine cars with more weight at the rear shift this closer to 50% to 60%.
In your case you should be able to lock the fronts but not quite the rears. Modern tires have considerably more grip than the skinny bias plys when these cars were new, which combined with wider tires creates more force on the brake surface to lock them.
You need to compare front and rear line pressures out of the differential valve and multiply by the piston area of the caliper. This will give the force applied to the drum or disc. Once. You know the line pressures I would talk to the component supplier for advice.
 
You must log in or register to reply here.
-

Back
Top