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
Like J if you have rams
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 .
Hope this helps you ,
John
Sent from my iPhone
On May 30, 2024, at 8:22 PM, RICK AND DEBBIE CLAPHAM <rixpac@xxxxxxx> wrote:
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