oldmanbob
New Member
Thank you, I will check Rock Auto out. What a great solution if it works out! Appreciate it.
Wrong brake booster? Holes dont line up
- Thread starter oldmanbob
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oldmanbob
New Member
I took the old one out of the car and gave it to an auto parts store for their inclusion in the weekly pickup of all the cores collected during the week for rebuilding. I had bought my wrong one online and the cost of shipping it to the seller was way more than the core charge. I couldn't see just dumping it in a landfill. In the intervening years the supply of remanufactured boosters has apparently largely dried up. Lesson learned, check your new parts for fit and completeness, etc., when they arrive, not five years later when you actually get around to installing them. I tend to learn things the hard way.
oldmanbob
New Member
Thank you!
oldmanbob
New Member
Do you know if the plunger thing connecting to the brake pedal on your New Yorker connects straight to the pedal, or is there a linkage thing? What a great car to have.
oldmanbob
New Member
I pulled the trigger and ordered it. When it gets here we'll see if the mounting holes line up, if the plunger thing's loop on the end is the right diameter for the brake pedal mounting bolt, and whether the brake pedal ends up in the right position. If these stars align, woo hoo! Thanks for noticing that that one was available. I can't believe this vintage of the c bodies is entering the land of "ancients", where you can't readily get run of the mill stuff like brake boosters. It's a '69 Plymouth, not a '43 Talbot Lago Emperor or something, jeez!
oldmanbob
New Member
Hey Big Mopar - I just want to say thank you for your suggestion. I did find the booster you referred to at Rock Auto, and it arrived today. The mounting holes line up on my 69 Fury, and the brake plunger/actuator thing has the right sized hole to bolt up with the brake pedal. So thank you very much. Your suspicion that this booster would work was right on. Take care, Bob
Sixpactogo
Well-Known Member
I would not use a single diaphragm booster with front discs. Disc's require about twice as much PSI as drums do. That is why Mopar upgraded to the dual diaphragm. You could get by with the single but you won't be able to lock the front brakes. There are tons of threads out there dealing with this. Read up on it. Brakes are one of the worst things you should be miss-matching parts on.
bigmoparjeff
Senior Member
1971 and newer cars came equipped with a large diameter, single diaphragm booster with disc brakes, which can be used on earlier cars. The dual diaphragm booster is needed on slab cars to clear the shift linkage on the column.
The booster in question is the '71 and up disc booster. Since his car is a 1969 fusey, there's no clearance issues. You can safely swap this booster for the dual diaphragm Bendix.
Jeff
Sixpactogo
Well-Known Member
I agree that if you have the room, a single 9" booster could give you 572psi of force. That plus a master cylinder with a 1" bore adds another 400 psi.
Considering disc brakes need at least 900psi, you should be good.
A single 8" booster gives you about 400 psi. That plus the 400 psi from the master only gives you around 800 psi. Plenty for drums but not quite enough for discs on a 4000+ lb car.
Considering disc brakes need at least 900psi, you should be good.
A single 8" booster gives you about 400 psi. That plus the 400 psi from the master only gives you around 800 psi. Plenty for drums but not quite enough for discs on a 4000+ lb car.
fury fan
Senior Member
Can you share how you arrived at those calculations?
You're the first person I've seen to ever put numbers to the 2 boosters.
You're the first person I've seen to ever put numbers to the 2 boosters.
Sixpactogo
Well-Known Member
T
Here is a site that may interest you and help explain how to use the formula for other applications.
https://www.brakeandfrontend.com/brake-math-calculating-the-force-needed-to-stop-a-car/
They are not my calculations. I am not a design engineer by any means. I got some info off of the internet a few years ago while trying to figure out why my 68 Charger single 8" diaphragm booster worked fine with drum brakes but not after I upgraded to front discs. . I posed a question on how much pressure is required for disc brakes and found a formula that the designers use. The formula used my single 8" booster for reference. The math for my 8'' booster worked like this: 4 X 4 X 3.14=50.24 sq. in. X 8 =401.9 pounds of force. I learned that drum brakes require about 400 psi and disc brakes require about 900 psi. That is why they designed the dual diaphragm booster because it doubles the force to 803.8 pounds of force. There is more to it than that because the size of the master cylinder bore add to the pressure as well.
Here is a site that may interest you and help explain how to use the formula for other applications.
https://www.brakeandfrontend.com/brake-math-calculating-the-force-needed-to-stop-a-car/
fury fan
Senior Member
Thanks!
As I was reading your previous post, I was wondering how the boost could be calculated without knowing hte vacuum input and the brake pedal force input.
Looking at the page you linked, I see they used some 'average values' to get there. (which is fine)
A person could push 1 foot on a bathroom scale and see what they can generate to get more accurate results.
I'd be interested in knowing whether boosters amplify solely based on vacuum input, or if there are any upper or lower thresholds. We all know that low-vacuum engines don't work PB as well, but does that mean a high-vacuum engine has better braking than an 'average' engine? Or could you put a 30 psi vacuum pump on it to get phenomenal brakes?
As I was reading your previous post, I was wondering how the boost could be calculated without knowing hte vacuum input and the brake pedal force input.
Looking at the page you linked, I see they used some 'average values' to get there. (which is fine)
A person could push 1 foot on a bathroom scale and see what they can generate to get more accurate results.
I'd be interested in knowing whether boosters amplify solely based on vacuum input, or if there are any upper or lower thresholds. We all know that low-vacuum engines don't work PB as well, but does that mean a high-vacuum engine has better braking than an 'average' engine? Or could you put a 30 psi vacuum pump on it to get phenomenal brakes?
Sixpactogo
Well-Known Member
I know the vacuum has an affect on how much pressure a booster can muster. Luckily I found out enough to decide on what I needed for components for my needs. I find it alarming how much mis-matching parts can effect the final outcome. It is no wonder why there are so many threads on brake problems after people alter their brake systems hoping for an improvement but ending up worse off than when they started. I know we piss n moan about how things were designed but I guess maybe those guys are not as dumb as we think. They fixed a lot of problems before we even knew they were problems.
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