As a general proposition I agree with what John is saying. Especially for cars that are not used as daily drivers. My 300K as of today has a completely rebuilt drum system. I have my own brake shoe arc machine
and know how to use it. The car is stopping well for a car of this vintage.
That said, yesterday on the highway in traffic with a lot of stopping distance we almost, three car lengths, hit someone. A long line of cars hit the brakes hard and in the .5 seconds it took me to react,
another car jumped into my lane and hit their anti-lock brakes as well. I had to lock the drums up and then back off to get stopped. Directional control was ok, but it did want to pull left a bit.
I am working on a 15-wheel front disc conversion. Mainly for brake fade in the mountains. This is going to be a daily driver for us both until we are dead. If something happens to me, where is my wife going
to find someone to do a proper drum brake job? They are all retired or dead. NONE of the shops in California will arc a shoe. In fact one shop I know sent a kid to find me with his cut drums and new shoes!
As to pressure. Yes, one needs to understand fluid pressure as well as fluid volume and displacement. It can be done correctly but one must do the math!
The very short pedal ratio on the power brake cars makes this even more important. Getting everything to work in harmony takes a lot more work that advertised.
In my case I have done several custom disc brake conversions, so I know what I am getting into. On the 300k, non-ram, I will use one of the larger diameter Master Cylinders that Chrysler used around 1970 to
deal with the displacement issue. Now that will affect line pressure. This is a delicate dance to get the volume-pressure correct.
I have the Midland-Ross pressure curves for the remote power brake boosters. The graphs give me an idea of what pressures they were looking for when it was all drums. I can get a sense of the curve (slope)
of the lines and use that to assist me on M/C bore sizes.
If need be, One can use a larger bore M/C to deal with the disc fluid displacement and not having the pedal go down as far and then see if Booster Exchange can change the booster reaction plates to increase
the output pressure for 100 pound leg push.
Nothing simple about a conversion.
James
From: chrysler-300-club-international@xxxxxxxxxxxxxxxx <chrysler-300-club-international@xxxxxxxxxxxxxxxx>
On Behalf Of John Grady
Sent: Friday, May 31, 2024 6:05 AM
To: RICK AND DEBBIE CLAPHAM <rixpac@xxxxxxx>
Cc: MILTON SIMON <msimon317@xxxxxxx>; chrysler-300-club-international@xxxxxxxxxxxxxxxx
Subject: Re: {Chrysler 300} 1960 Cross Ram power brake booster
hi — your problem is magnified is if you fitted a larger bore disc master ( that what you meant?) you have thus reduced line pressure ; this is a hard trade , if you use original bore size you will get the lower pedal force / correct
pressure in lines as designed , on foot pedal— but then it will travel maybe 20 % more to get the added cc disc brakes need over drums . Long pedal travel makes driver uncomfortable . “ almost hits floor” That is because of the large piston in a disc vs
drum needs more fluid . I assume you have 10 psi residual pressure valves on discs to keep them “ out” and balance valve on rears if drums ?
.This has been discussed quite a bit on here , — the “ problems” with the stock drum are almost all due to “experts “ who have no idea how to do it right ; Done right they will stop just as fast as any disc , they will lock wheels .
The superiority of discs comes into play in the mountains , ( multiple hard stops down hill ) or more than two stops in a row from 100mph or so . Or racing . Drums cannot store as much heat as large discs ,cool faster — although the necessarily small discs
to fit inside 14” wheels are like what is on a dodge dart , weighs thousands less than 300 — Right? may even be weaker storage than drums . Weigh rotor weigh drum .
I am not being a wise guy , i could not get the drums to work right either , when I started on 300 ‘s in 1970 or so , 3 attempts on same car ( G) all new stuff, all poor results . frustrated me and local brake guys too( who were not very
good). so so they said “ those brakes are a poor design” etc etc . And I bought that . Lived with it . Slowly got better .
But then I found a young guy at a specialty brake place in Cambridge ma, ( Cambridge Brake) all they did was brakes.
He says leave it , I did , next day , Perfect . At first he would not tell me , later became a great friend . Precision fit of shoes to drum is key . Brand new parts do not meet the fit requirement , do not touch fully , often for thousands
of miles if fitted wrong .
I knew brakes were terrific new from mopar as my dad had new a 60 dodge no booster , same design , brakes were fantastic . Best modulation or feel in industry and did fine in nascar right? arguments on this in 60’s with friends with GM
power brakes confirmed this . A B comparisons. GM had “ all on , all off , feel”
So knowing that I next built a 300 with no booster , like the dodge ( you have to change pedal ratio , relocate master on firewall , lot of work ) AND front discs , . This was also no good , pedal way too hard and long travel . Discs
take more PSI . And more volume.
Then same , front disc with a booster = ok , travel a bit long , but for sure not better than drums done right .But seemed not to have the “ whoa” power of stock drums if you really stepped on it . ? Disc too small?
Despite everyone saying it’s better —( they just did it— has to be better! laugh ) it’s not better than drums working right . Which is frankly rare . And drum disc matchup has a history of problems of its own that balancing valves do
not fix . They do not “ track” each other .
Just sharing 50 years of this , =keep it stock
READ EVERY WORD in chrysler service publication on these brakes ( circa 59 or 60) especially the part about matching shoe diameter to drum to the tolerance which is tight . But today no shoe grinding machines around , fear of asbestos
dust etc . . Or if you have used ones with 1/2 the lining left don’t grind drums or put in new linings . You will start the dance . You are not going 100k more miles , old ones are nicely matched .
4 wheel big discs maybe , but that is 16” wheels , wrong wheel covers non stock large or remote booster etc etc
Just where I am after all this time , admittedly opinion , but no rose colored glasses either about “ improvements “ . Been there.
I noticed Big Red at Philly meet , the race 62 ram that set a lot of records was exactly like that 60 dodge — no booster , single master , pedal ratio / pedal from a dodge or plymouth six , drums . 5 years in —— on exact same brakes —-
the race pros came to same place as I did . No dependence on vacuum either .
On May 30, 2024, at 8:22 PM, RICK AND DEBBIE CLAPHAM <rixpac@xxxxxxx> wrote:
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