The concept of frictional force being independent of area is one of the hardest concepts for engineering students to accept as it seems illogical. But it’s true within the defined environment as explained below.
This excerpt from the referenced article does a fair job of explaining that the friction laws are for the interaction of two dry surfaces.
Traction and friction are two (slightly) different concepts. Not only that but using car tires in a physics book is stupid (and something I've never actually seen before) simply because their coefficient can exceed 1, which changes everything. On top of that the standard equation does not account for deformation of the tire (which can be accounted ... Read More for through rolling resistance). Further more, even though the contact patch is the same regardless of tire size (generally) AT REST, the shape that it takes under dynamic load is better distributed by a slightly wider tire giving better traction. While a wider tire does gain some heat benefit from a greater surface area it's only a small part of it.
Wiki has a pretty good article, also at: http://en.wikipedia.org/wiki/Brake_lining
Rubber tires on any dry road surface actually are adhering to the road surface somewhat as the rubber deforms and displaces onto and around the rough road surface. Otherwise, the maximum acceleration force would be limited to one “G”. The record top fuel dragster generated an average of 4.4 G’s over ¼ mile. Rubber compounding is critical to maintain desired traction/friction/adhesion of tires and the road surface. Big old drag slicks don’t do well on wet or icy surfaces. Narrow, hard rubber tires don’t do well on drag strips or on slick road surfaces. Snow tires and all-weather tires have those lugs and grooves to improve the frictional/adhesive force on hard wet surfaces by squeegeeing them dry or actually creating some shear force in the mud or snow.
While the interaction of a brake lining and the inside of a brake drum or outside of a brake disc may not represent pure Coulomb friction, it is much closer than a rubber tire on a road. Remember, the whole idea of brakes is to convert the kinetic energy of the entire vehicle to heating of the brake drum (or disc), all the nearby hardware and surrounding airflow. That heat must then be rejected to the surrounding air. Buick’s big finned brake drums worked well. The wider rear drums essentially create a heavier drum to absorb more heat and offer more external surface for rejecting that heat. To the extent that the relatively soft brake linings actually deform into the inner surface of the rotating drum, some additional frictional force might be generated. Brakes “fade” when the iron drum or disc and lining get so hot that the coefficient of friction between lining and drum drops precipitously. Followed by heavier pedal pressure, slower deceleration, rising panic, acceleration downhill instead of deceleration, lots of screaming and possibly loud noises. In the nearby Sierras, there are deep gravel beds on upslopes for runaway trucks to drive onto. That stops them quickly as the kinetic energy is absorbed by the action of the tires plowing and displacing the gravel.
Take out paper and pencil and number 1-10—we’re going to have a quiz.
Rich Barber
Brentwood, CA
From: LabLoverDC@xxxxxxx [mailto:LabLoverDC@xxxxxxx]
Sent: Monday, January 13, 2014 12:47 PM
To: kboonstra@xxxxxxxxxxxx; c300@xxxxxxx
Cc: TorqueChap@xxxxxxxxx; News4ge@xxxxxxx; d.verity@xxxxxxx; Chrysler300@xxxxxxxxxxxxxxx
Subject: Re: [Chrysler300] Whoa, Nelly
As far as the physics of tire performance goes, I found an interesting discussion here if anyone cares to read it.
And despite Mr. DeKlein's apparent disregard for drag racers' intelligence, they may not fully understand the physics involved, but I think in general they've figured out how to make their cars get down the quarter mile pretty darn fast, and it usually involves wide tires.
Shannon
In a message dated 1/13/2014 2:46:35 P.M. Eastern Standard Time, kboonstra@xxxxxxxxxxxx writes:
So the argument is posited that frictional force is independent of surface area? I'm neither a physicist nor an engineer, but I find find the discussion interesting. Brake shoes and smoking tires are related and I'd like to hear how this works.
It reminds me of a statement I recall being made over a half century ago by my high school physics teacher that has stuck with me all these years. I so clearly remember Mr. DeKlein stating that the width of a tire used for drag racing makes absolutely no difference inasmuch as the tire's grab on the pavement is dependent solely upon the coefficient and the force (and John Force). Drag racers just weren't smart enough to realize it.
Why are my radials harder to break loose than the bias tires were? And why does the big fat drag tire grab more and defy poor old Mr. Deklein's physics?
Keith Boonstra
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On Mon, Jan 13, 2014 at 1:58 PM, Rich Barber <c300@xxxxxxx> wrote:
Not to continue beating on old Nelly, but…
Several sources indicate the “HD” brakes are standard on ram cars and available as part of an “HD” suspension option for all other 300’s. The supplemental 300K manual and the 1963 service manual show the linings on the F&R primary shoes are only 9 ¼” long as compared to 11.97” (AMA specs) or 12 1/8” (Chrysler specs) for all other F&R linings. Differences in color coding indicate different composition and/or frictional effects. The 1965 Service Manual shows 3” wide rear drums on all Chryslers except Newports and the 9 ¼” long linings on “Police Special” only.
As engineers, we are taught that frictional force is only a function of coefficient of friction and FPST (Force pressing surfaces together), and is independent of area. So, the length of the shoes should not affect stopping force. However, the longer linings produce more brake area and this affects heat transfer between the linings and the brake drum. Shorter linings on the primary shoes might let the drums and the brake and brake hardware run a little cooler or go to fade slower. It might also shift a little of the heat transfer duty to the secondary shoes and even out wear.
I spent way too much time last night in the 1963, 1964 and 1965 parts, service and supplemental manuals and with the 1964 AMA specs. With the result being that I could not rationally interpret or consistently correlate which of the ’63-’65 Chrysler line of vehicles had or could be ordered with “HD” brakes. As David noted, the main difference is in the 3” wide rear drums and shoes. The manuals also indicate the different length and material of the lining on the primary shoes. Whatever options owners might have had in the ‘60’s are probably long gone. My ram K conv came to me with 2 ½” shoes inside of 3” wide rear drums. It was a little challenging to find the proper 3” wide rear shoes, but I did find them. I think they were listed as for a New Yorker wagon which appears to have come equipped with “HD” brakes as standard.
The variance of material and length in the HD brakes for the ’63-’65 years indicates some work and experimentation had been done to make braking better for the cars with HD brakes—whatever cars they were on. Perhaps this work was driven by problems with the HD brakes with standard linings. At this point, the original molded asbestos lining options are not available, even if we knew what they were. It seems that we are stuck with 12” +/- long linings on all 3” or 2 ½” wide shoes. Any better information on original shoe and lining configuration on ram-engined J’s & K’s and/or current best sources of brake shoes and linings that work best in these cars would be gratefully appreciated by those of us driving and stopping these Beautiful Brutes.
C300K’ly,
Rich Barber
Brentwood, CA
From: David [mailto:TorqueChap@xxxxxxxxx]
Sent: Monday, January 13, 2014 5:15 AM
To: News4ge@xxxxxxx
Cc: c300@xxxxxxx; d.verity@xxxxxxx; Chrysler300@xxxxxxxxxxxxxxx
Subject: Re: [Chrysler300] J / ram K
Hi George,
The Ram K has 3x11 brakes (vs 2.5x11 for non ram cars of the same year).
David Morrison
New Jersey
On Jan 12, 2014, at 11:47 PM, News4ge@xxxxxxx wrote:
Rich Barber and J/ramK owners,
Thanks Rich, for the information. I noticed that in the 64 supplement you sent the link for, the ramK and non-ramK have different brake shoes. The ram cars actually have smaller front primary shoes. Does anybody know why this would be? Also, the shoes that are available now (at least at Rock Auto) don't distinguish between ram and non-ram cars (or even between 300 and 300K). Has anybody had problems getting the right shoes for a ram K? Would either or both size shoes fit?
Thanks,
George Clineman
-----Original Message-----
From: Rich Barber <c300@xxxxxxx>
To: 'Don Verity' <d.verity@xxxxxxx>; Chrysler300 <Chrysler300@xxxxxxxxxxxxxxx>; News4ge <News4ge@xxxxxxx>
Sent: Sat, Jan 11, 2014 7:57 pm
Subject: RE: [Chrysler300] J / ram K master cylinders
George:
That’s what we did for our ’64 ram K. However, previously, someone had replaced the ram engine with a non-ram 383, disconnected the remote booster and installed a standard power brake booster and MC on the firewall. The standard booster has a different reinforcing/mounting plate on the firewall than does the non-boosted MC and I had to obtain the correct plate in order to install the non-boosted MC.
Removal of the residual pressure “check valve” from the firewall MC is critical in order that the actuating pressure be bled off the remote boosted cylinder. Otherwise, the brakes will drag and overheat. It was news to me that this little check valve even existed. It is commonly used on brake systems to keep a very light residual positive pressure on the brake system to reduce its tendency to inhale atmospheric air and moisture.
Another ramK owner was trying to modify his brakes to use a dual outlet MC, but we saw no way to integrate a dual outlet MC into the remote-boosted system. So great care should be taken to assure all hoses, tubing and connections are strong, non-corroded and tight as a broken line or hose will leave you with NO SERVICE BRAKES. I did run into a bad batch of wheel cylinders and the little MC which seeped from the get-go. Seemed almost like sabotage by our Asian manufacturers. I suspect poor synthetic material in the cups and improper finish in the bores, but can prove nothing.
The master cylinder body and guts for a ’63-’64 ram car is actually a common item and may be purchased new or rebuilt for a 1964 Plymouth, Dodge or Chrysler without power brakes—then the check valve must be removed from the outlet. I recall the guts had to be removed in order to poke out the little check valve wafer. The non-presence of the check valve makes the MC a technically different item but the body, guts and mounting system are the same.
There is a specific bleeding schedule that must be used to eliminate air from throughout the brake system. The process is defined in the 1964 300K Supplemental Service manual which can be viewed at:
http://www.jholst.net/64-supplement/brakes.pdf (Page 2). All readers are encouraged to visit member John Holst’ most excellent website and click on “Chrysler 300 Resources” to view a wide array of service and parts manuals and other information for all years of letter cars. John still drives the 300K originally purchased by his father.
C300K’ly,
Rich Barber
Brentwood, CA
From: Chrysler300@xxxxxxxxxxxxxxx [mailto:Chrysler300@xxxxxxxxxxxxxxx <mailto:Chrysler300@xxxxxxxxxxxxxxx?> ] On Behalf Of Don Verity
Sent: Friday, January 10, 2014 4:26 PM
To: Chrysler300@xxxxxxxxxxxxxxx; News4ge@xxxxxxx
Subject: Re: [Chrysler300] J / ram K master cylinders
From what I have learned from the guru of K’s Don Cole, just get a master for a manual brake car and take out the residual valve (the remote booster has one). I got one for my J, but have yet to install it. Looks good though and has the studs through the firewall. I got it from Rock Auto.
Don
From: News4ge@xxxxxxx
Sent: Friday, January 10, 2014 5:37 PM
To: Chrysler300@xxxxxxxxxxxxxxx
Subject: [Chrysler300] J / ram K master cylinders
Hi,
I have a ram K that has a slight leak in the master cylinder and a leaking wheel cylinder, so I'm doing a complete brake job.
I have 3 questions:
1. Are the brake systems on J and ram K identical in every way? I ask because I may find parts for a J and not for a ram K. Also, there's less confusion if I ask for something for a J because the K has both ram and non ram parts.
2. Does anyone know of a good source for a rebuilt master cylinder? All of the parts houses I've checked either don't go back that far or they have master cylinders for all Chryslers but J or K. I know there's Kanter, but their price is high.
3. Anything else I should know, like helpful hints on doing the work, procuring parts, what mfrs. to use or avoid, etc.?
Thanks in advance,
George Clineman
[Non-text portions of this message have been removed]
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