I figured that since the rears don't lock, adding a valve to the rear line would be pointless.
Members with 4 wheel disc systems: Can you lock your wheels?
- Thread starter Kern Dog
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AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
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I concur and I gutted my valve as well; But I run big and littles. 295/50-15 on the rear and 235/60-14s on the front. She is the best-stopping car that I have ever had a ride in, except for an old Corvette back in hi-school, in the early 70s, man that BB car could decelerate!
moparlvr166
Well-Known Member
Kern Dog, which way do you prefer for power assist, H/Boost or vacuum?
Same here gutted out the valves standard kelsey hayes on the front wilwood 4 piston on the rear using Baer proporting valve using Hydroboost locks all 4 in a hard brakes situation with Michelin Super sport tyres even with the manual brakes with a Baer 1 1/8 master the car stopped pretty well.
Only problem i found with the Hydroboost they stop the car so well from high speed the standard discs can get really hot ,also buns up front pads faster than standard which is understandable.
Found after fitting discs on the rear i have much better pedal feel as the old drum pads sit further away & allow more slave cylinder piston travel that the Hybroboost doesnt seem to like also the master cylinder piston rod length is critical to good pedal feel.
Only problem i found with the Hydroboost they stop the car so well from high speed the standard discs can get really hot ,also buns up front pads faster than standard which is understandable.
Found after fitting discs on the rear i have much better pedal feel as the old drum pads sit further away & allow more slave cylinder piston travel that the Hybroboost doesnt seem to like also the master cylinder piston rod length is critical to good pedal feel.
And to answer your question......kinda....Vixen had 4 wheel drum brakes with a disc brake master cylinder and proportioning valve and she will lock them bitches down on command. Whatever that's worth. lol
I can only attest to manual and vacuum boosted brakes. I wasn't able to get the Hydroboost setup to work. The HB unit never built up pressure despite several attempts to bleed it. Either the HB was defective or I was an idiot and couldn't figure out the right way to bleed it.
I have a 15/16" manual master cylinder in this car:
12" front brakes 2.75" single piston, 10" rear drums. It has a bit of pedal travel but has great feel and it stops quite well. I've had a few non power disc-drum Darts and Dusters and have always been impressed with them.
The other car has many differences. Bigger brakes, 4 wheel disc, vacuum boosted, bigger tires, heavier car....Its as if they are barely related.
jos51700
Green Bearing thread connoisseur
Source? I want some lightweight rotors!!
Increasing the bias should help. Right now you've got more of the rears helping slow you down. Yuck.
I would think that you could dial this in and be able to stop just fine on a strictly manual system.
The Dr Diff 13" kit comes with an aluminum hub. The calipers are aluminum and the bracket to attach the calipers are steel but they are far simpler than the heavy cast iron caliper adapter. I weighed everything that I changed while I had the car apart. The Borgeson steering box saved 12, the return from Fast Ratio steering arms to stock shed 2 lbs.
Regarding the bias....
The goal was 2 to 1. Prior to the changes, I was really front heavy to the tune of around 3.3 to 1.
Driving to and from the car club meeting tonight, it performed fine. I didn't stand on the pedal but it never gave me the feeling that it was unsafe.
plumkrazee70
Well-Known Member
Since you have the tool, measure your pressure at each caliper.
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Check out this article.
Many OE 4-wheel disc setups have larger dia. discs in the rear, if the piston dia. & proportioning are correct, they work perfectly. Usually they are thinner, and many have to accommodate an internal parking brake drum setup, so the diameter is needed.
Have You done a temp check on the rotors?
Find somewhere You can do 4 panic-stops at 45mph, then run around with an IR thermometer, should be able to get the frts to 400-450° & rears to ~200° easily.
Edit; that's with them starting at normal "rolling" temp.
jos51700
Green Bearing thread connoisseur
I am wondering if we're talking about the same bias. I'm talking about braking bias, but it almost sounds like you're talking about weight bias?
The rotors on my Ram 1500 are this way....same diameter but thicker on the front with larger calipers on the front too.
There is some confusion here but I thought that I was clear. Maybe I wasn't.
The common belief I've read and heard is that the front takes on the majority of the braking and numbers between 60/40 and 70/30 have been tossed around. In between that is 66/34. Do the math.....that is a 2 to 1 ratio. The front number is double the rear.
The theory caries over to caliper sizing. The front caliper surface area is suggested to be approximately double the sizing of the rear.
With the 12" setup, the caliper surface area was 3.3 times the size of the rear.
With the 13" setup, the caliper sizing is just over 2 to 1.
plumkrazee70
Well-Known Member
Not sure that is related the "surface area" so much as it's related to caliper piston diameter front to back. With drums it's wheel cylinder size.
What I'm not understanding is how 12" has more surface are than the 13" setup.
Are the caliper pistons bigger on the 12" setup than the 13" setup?
jos51700
Green Bearing thread connoisseur
OK,
you'd said "front heavy" in another post and I just wanted to make sure we were discussing the same thing.
jos51700
Green Bearing thread connoisseur
The 12" caliper had 2.75" pistons, the 13" caliper had two pistons that were 1.58" each (which was less area than the 2.75" caliper)
plumkrazee70
Well-Known Member
Got it. Makes sense. Just wanted to be sure we we're all talking about the same thing.
@Kern Dog can you post a pic of your distribution block?
Yes....the 12" brakes were the Cordoba-Late B body unicast rotors with the iron 2.75" piston that had a surface size of 5.93"
The new 13" brakes have two pistons, each 1.58" for a combined surface area of 3.91 inches.
The rear calipers have single 1.50" pistons that have a surface area of 1.76".
3.91 divided by 1.76 is 2.2. This is really close to a 2 to 1 ratio.
The new 13" brakes have two pistons, each 1.58" for a combined surface area of 3.91 inches.
The rear calipers have single 1.50" pistons that have a surface area of 1.76".
3.91 divided by 1.76 is 2.2. This is really close to a 2 to 1 ratio.
This is an A body 4 wheel drum distribution block.
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.
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.
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.
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.
plumkrazee70
Well-Known Member
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?
I tried pulling the barbell/shuttle out of one awhile back. It was STUCK in there! It made me think that if it was that hard to get out, maybe there was a buildup of gunk on the ends. That made me wonder if gunk like that would reduce flow to the brakes.
DionR
Well-Known Member
You need to use more than the area of the pistons to determine ratios. You need to use a brake torque formula that takes into account the rotor diameter, size and how many pistons, coefficient of friction, etc.
And I know that @72bluNblu is running virtually the same front and rear brakes on his Duster/Demon and far as I know he is nothing but satisfied with the brakes. Which would suggest there is something else going on.
And I know that @72bluNblu is running virtually the same front and rear brakes on his Duster/Demon and far as I know he is nothing but satisfied with the brakes. Which would suggest there is something else going on.
Exploded view of the 1968-1976 A body 4 wheel drum distribution block:
After the springs, collars and shuttle is removed, the switch and end cap can go back in, assuming that it is all clean inside. This one isn’t. I don’t have any carburetor cleaner to soak this in so I’m trying this:
I’ve heard of people using basic household chemicals for parts cleaning.
Lime Away.
CLR.
Tilex.
In 15 minutes, the vinegar is already getting dark.
Awhile back, I considered running the brake lines without a block like this. I bought some fittings…
This for the front.
This for the rear.
This would have been a setup where the front and rear were truly separated.
After the springs, collars and shuttle is removed, the switch and end cap can go back in, assuming that it is all clean inside. This one isn’t. I don’t have any carburetor cleaner to soak this in so I’m trying this:
I’ve heard of people using basic household chemicals for parts cleaning.
Lime Away.
CLR.
Tilex.
In 15 minutes, the vinegar is already getting dark.
Awhile back, I considered running the brake lines without a block like this. I bought some fittings…
This for the front.
This for the rear.
This would have been a setup where the front and rear were truly separated.
72Duster440
Well-Known Member
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?
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