RE: [Chrysler300] 300J / 300K Disc Conversion - Surrender Summary
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RE: [Chrysler300] 300J / 300K Disc Conversion - Surrender Summary

Really  good, important  post, Mike ..logical and honest . I agree the remote booster is a huge PIA,. Never trusted it on my J , one reason I sold it, after a few dances with it. Car would go 140, but passenger inside highly puckered about the brakes. . Band aid approach…. although it works in millions of trucks,  ok, so I am told. Too much to go wrong there, too many single point failures. It seems attempts to get it rebuilt at that time often result in utter junk coming back. And lots of fast talk. Frustration. I remember it locking up, not good for longevity.


Did you get into changing the pedal ratio / pedal arm and height of master compared to the (fixed location) top swing pivot? ( all that changes on 60-62 at least,  to go to manual) I do not know if you know all about that. I did not, learned hard way. .I went through it on a 60 Polara (same as F) ; I also looked very carefully at Big Red 300H manual brake setup at Pa meet, as I am doing what you say did not work, 4 wheel discs on manual on an F . ..Big Red  had the stock manual setup, on a ram car ---which setup I also had brand new on a 60 dodge dart w drums , which worked perfectly—no power brakes.  . Brakes about the same,  dart or 300 except drum diameter. But using ex power parts for manual brakes seems a disaster. Big Red all drums however.


The mechanical ratio change is quite dramatic, (while from memory,  I think the factor is about 1.7 in travel ratio !!!). Bore changes are less so, but like you say, just putting a manual master on power brake linkage gave a pedal that needs superman. You cannot change the ratio  without changing the master mount height, do not even think about offset push rods.(mistake #2)   ; in theory changes on master bore do the same thing but it does not seem to  , in my experience. To go manual you need the mopar manual brake pedal arm and master location as a starting point (let’s just say they knew what they were doing to have to do; to  do that—to get right combo of pressure and travel)…so fire wall apparently built that way at start of line ..both bolt patterns are there behind that engine side metal brace plate, on 60 anyway _) . Master rod travels differently per inch of pedal on manual, and thus moves ? less  fluid , at higher pressure , means more pedal movement per cc, probably with small bore, so total to bottom the pedal is maybe a lot less cc fluid…or it may be the same, on drums, as wheel cylinders are the same in both systems .  That gets into size of and number of calipers too. In this case , more disc caliper may be much worse brake , as say two / four have to take up clearance at wheel, using up the correct (for pressure you need ) cc  . Also assume you had residual pressure valves  on discs to keep the pucks out?


On mine I also changed the “up stop” to gain more travel, rest position of pedal I think is higher on manual arm anyway, I went up some more, chasing what you describe . I think they wanted power brakes to have pedal near the floor,  seem to hardly move at all. Which equals low CC and high forces


I hear but am not sure that S10 chev booster fits in that space , possibly another way. Made for cramped engine bay. There is also the recent Ford all hydraulic booster . no vacuum. Hot rod guys love those.


Somewhat related, I have a 50 stude with 354 hemi, manual brakes , Mustang front discs and ford 8.8 rear drums. Corvette master , big bore with stock Studebaker underfloor ratio left from the old stude manual setup. That works fine. Two in line residual pressure valves. Almost raises the question , from what you say,  if manual 4 w discs can work at all. But I believe corvette has 4 wheel manual brakes at option..or did ? So “copy that” was thinking on stude--- also a stude guy, Turner Brakes sells that master kit. He may know a lot about this . Among stude guys to your point, one point of view is go all stude late,  larger OD drums( they fit, pretty good finned drums) , but Turner disc thing was fine for me, has A++ reputation there. He uses I believe corvette master. Kind of says -----Corvette master with right mechanical ratio is / has to be workable ? . On mine I am using late 60’s big bore police mopar , emulating Corvette ; bore not as large as corvette (which I think was 1.25 !) . but not done yet. (Mopar due to master bolt pattern)


I have no index of older posts , but believe we got into this pedal ratio thing in last year or so. Tony  has a lot of good brake info too.


Keep us informed..and good luck. I agree with where you were trying to go….me too.




From: Chrysler300@xxxxxxxxxxxxxxx [mailto:Chrysler300@xxxxxxxxxxxxxxx] On Behalf Of Mwl1967 mwl1967@xxxxxxx [Chrysler300]
Sent: Monday, November 07, 2016 3:24 PM
To: Chrysler300@xxxxxxxxxxxxxxx
Subject: [Chrysler300] 300J / 300K Disc Conversion - Surrender Summary


Hi Everyone,


            I thought I'd share this so that anyone out there wanting to put discs on their J/K ram car can see what I've attempted and save themselves the trouble of duplicating combinations that don't work. I've tried everything and am tired of not driving my K because the brakes suck. I've had 4 wheel discs on the car and none of the combinations of master cylinders have given pedal feel that is remotely reassuring. Of course the issue is I can't get a traditional booster on the firewall and converting to the '62 and earlier over/under style bellows setup would require major surgery on the firewall of the 63 / 64.


             I started with manual discs with a large bore master and had a high pedal that stopped the vehicle under normal driving conditions. If however I got distracted or had to otherwise stop abruptly in any panic situation I'm sure I'd flatten any Kia or Hyundai in my path while simultaneously shortening the front of my car. Pressure gauges installed at the calipers showed insufficient psi to properly activate discs. I switched to a smaller bore master cylinder and while the pressure went up, so did the required travel of the brake pedal. The end result of that was that while it was easier to apply the brakes there was not enough pedal travel, the pedal went pretty much to the floor and the car stopped no safer than the previous set up. 


            The next step was to plum the brakes through the remote slave cylinder. We did that not only running all fours through it but also just the front brakes through it; effectively having a power front / manual rear 4 wheel disc setup. Next attempt was to put the drums back on the rear under the assumption that eliminating the rear calipers would lessen the volume requirements and perhaps allow the discs still on the front to work. Nope... not happy with that either. So... all the discs are coming off and the drums going back on all four corners. Single reservoir master, through the slave cylinder, out to 4 drums. I'll just try to keep it out of snowstorms and off rain flooded roadways. 


            Needless to say the front and rear disc conversion will be listed for sale for someone who has room to put a nice powerful dual diaphragm booster where it belongs, on the firewall. 


Mike Laiserin



Posted by: "John Grady" <jkg@xxxxxxxxxxxxxxxxx>

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