Upgrades to improve braking

-
7

73stroked duster

Well-Known Member
Joined
Sep 7, 2016
Messages
61
Reaction score
3
Location
streamwood
73 duster drum in rear disk up front manual brakes. any thoughts on common upgrades to improve braking. Car does stop ok with heavy foot pedal. Not sure how safe in a panic stop though.
 
My thoughts, add a power booster and MC, and, or upsize to the larger brakes from a 76-78 car.
 
No power booster needed, they don’t improve braking force just the pedal effort. You can accomplish the same thing by changing the size of the master cylinder bore. A 15/16” bore master will raise the line pressure, but also make the pedal a bit lighter. You do get a little more pedal travel, but it’s not excessive and it actually allows for better pedal modulation.

DoctorDiff sells a great 15/16” aluminum master and adaptor. I run them on my Duster and my Challenger.

For more braking force, if you have A body 73-75 calipers they have a 2.6” piston. The 1976 A bodies, as well as pretty much all the other body styles, used calipers with a 2.75” piston. So you can switch to later slider calipers and get a larger piston, bolts right on, more braking force.

If you run 15” wheels you can also go to the 11.75” rotors and caliper brackets, they bolt right on to the 73+ spindles and use the same calipers. Just upsizing the rotors adds another 8% of braking fires if I remember my old calculations correctly.
 
Wilwood 4 piston calipers cross drilled & slotted rotors will really improve braking.
 
No need for power brakes.

Sure it’s the right master cyl

Sure everything is in proper working order ?

I know our dart with stock 73 style disc brakes and 11” rear drums stops awesome.
 
72bluNblu said:
No power booster needed, they don’t improve braking force just the pedal effort. You can accomplish the same thing by changing the size of the master cylinder bore. A 15/16” bore master will raise the line pressure, but also make the pedal a bit lighter. You do get a little more pedal travel, but it’s not excessive and it actually allows for better pedal modulation.

DoctorDiff sells a great 15/16” aluminum master and adaptor. I run them on my Duster and my Challenger.

For more braking force, if you have A body 73-75 calipers they have a 2.6” piston. The 1976 A bodies, as well as pretty much all the other body styles, used calipers with a 2.75” piston. So you can switch to later slider calipers and get a larger piston, bolts right on, more braking force.

If you run 15” wheels you can also go to the 11.75” rotors and caliper brackets, they bolt right on to the 73+ spindles and use the same calipers. Just upsizing the rotors adds another 8% of braking fires if I remember my old calculations correctly.
Click to expand...
I think my best option is to upgrade to the 11.75 rotors and new calipers. Can you recommend a complete kit?
 
73stroked duster said:
Was just looking at their site. For 73 the kit list front mount caliper location and my car has the calipers facing rear. Does this mattter
Click to expand...

119E4891-B50F-4298-B79A-93D92EF2F64B.jpeg
 
If it’s a stock style 73 set up then the spindles can be used on either side. All that means is you can run front or rear mounted calipers. Sway bar interference is possible wit front mounted though
 
That's probably the problem right there.
I've had 1-1/32" MC with power brakes on my setup. I also have 2.75" calipers and 11.75" rotors and braking was just so-so.
After I installed a 15/16" MC braking has become much better and like it should be.
 
BigBlockMopar said:
That's probably the problem right there.
I've had 1-1/32" MC with power brakes on my setup. I also have 2.75" calipers and 11.75" rotors and braking was just so-so.
After I installed a 15/16" MC braking has become much better and like it should be.
Click to expand...
Would the 11.75 rotors and 2.75 calipers be a better fit with the 1.031
 
73stroked duster said:
73 duster drum in rear disk up front manual brakes. any thoughts on common upgrades to improve braking. Car does stop ok with heavy foot pedal. Not sure how safe in a panic stop though.
Click to expand...
73stroked duster said:
Looks like I am only pulling 12 vacuum so I think a power booster is out
Click to expand...
Ok so the only time he booster does not, or may not, work 100% is when the vacuum drops below it's minimum threshold required vacuum to achieve maximum assist. So when does this occur during braking? It doesn't,unless you have a monster cam and a loose convertor.
The faster you drive, the higher the rpm, and up to a point the higher the vacuum. The point is,if the car is moving, it is almost always higher than the minimum required.

Imagine this;
you are going 108mph and doing 5000rpm at WOT with 3.55s when you lift throttle and hit the brakes. If your check-valve is working right, that booster is fully evacuated and ready to provide maximum assistance.It has been since right after the car started moving. So now you are rapidly decelerating, and engine braking is keeping the vacuum up. So everything is working as it should.
So imagine you are crossing 60mph, now at 2650rpm, still hard on the brakes in third gear, and the throttle valves are closed.And engine vacuum is at or near maximum. So the assist is still 100% functional.
Now imagine crossing 40mph now at about 1760 rpm, with the throttle valves still closed. And engine braking is now fast fading, but the vacuum is still above the minimum threshold. Now we are getting to the nitty-gritty.The engine vacuum is approaching the minimum threshold, so the check-valve better be working. As long as you do not lift off the brake pedal, the vacuum chamber is more or less sealed, so braking continues as usual.
Now imagine, still hard on the brakes at 20mph, rpm now close to idle, but you haven't lifted so it's still business as usual.
Now from 20 to zero, you will be lifting off the brake pedal to prevent loc-up. So this is the critical zone. But guess what? you are reducing pedal pressure anyway. So even if the vacuum drops below the threshold, it doesn't much matter; cuz you just lift a little less.

The way I see it,for a streeter, there are just 3 times when the minimum threshold might be an issue;
1) At first start-up and backing out of the driveway,with an automatic,and with a warm engine off choke. In reverse, braking requires a bit more pedal pressure, due to the way the rear brakes work. And with an automatic two things happen; Firstly, the idle usually drops about 50 to 100 rpm when you drop it into gear, which reduces vacuum, and secondly, you don't blip the throttle before easing out the clutch. So the easy cure for this is to blip the throttle to evacuate he booster, before putting her into reverse, problem solved.
2) Multiple modulations with the trans engaged,and the throttle closed. Try to imagine the situations when this would occur. I get parallel parking, and slow traffic. Here the solution is the 15/16 M/C; I like it a lot.
3) Sitting at a stoplight, in gear,with a leaky check-valve. Simple solutions.

So my point is; yeah the fellows gave you a few good options, but if all you want is a little assist, don't think a booster can't work at low idle vacuum. I have a manual trans, and have had the 292/292/108 cam and the booster worked just fine. In fact I didn't even know it was supposed to be a problem until I came to FABO. With the current 230 cam, I never give the booster a thought, I just drive.
 
Last edited:
73stroked duster said:
73 duster drum in rear disk up front manual brakes. any thoughts on common upgrades to improve braking. Car does stop ok with heavy foot pedal. Not sure how safe in a panic stop though.
Click to expand...

If you cannot stop (lock up) an A body with front disks, there is something wrong "with what's there." Either you have the wrong size master, wrong size wheel cylinders, or the lining is badly glazed, and or the drums are not matched to the shoes. No you do not need a booster.

FIRST thing I'd do is inspect everything, front to rear. Condition of pads. If you cannot identify what/ where from they came, replace them with something of known quality. Break in the pads. Inspect the rears for adjustment and shoe fit in the drums. Read your shop manual. Determine the master bore size and make sure it is NO LARGER than factory. Smaller gives you more braking pressure

"Most likely" is glazed lining and pads and cheap lining and pads, assuming you have a nice hard pedal

My legs are not very strong, I have arthritic related problems. I cannot walk very far. I could lock mine up EASY at 35--40 and locked them up "briefly" just testing at 65. It did take some "foot pressure"
 
73stroked duster said:
Would the 11.75 rotors and 2.75 calipers be a better fit with the 1.031
Click to expand...

1-1/32" = 1.031", just what I had too.
Your braking will improve if you install a larger rotor and larger diameter brake caliper.
But if your car is now similar to my setup, it will still not be a 'perfect' match. But then again; if your car has always been a manual brake car, it will probably have a higher(better) brake pedal ratio, giving a bit more leverage to the MC, so you might be good.

But it's easier/cheaper to change a MC then it's to change rotors and calipers.
 
You must log in or register to reply here.
-

Back
Top