While not at all personally very knowledgeable about 55-56 cars, I believe the brakes are similar to 57-62. Following is from 55 years of this on 1960 300’s, with dual leading shoe fronts. .
I also wanted to add that the You Tube film clip of a 300B actively (and successfully) racing jags, Porsches and Ferraris which was linked to this site about a year or so ago showed all stock brakes doing a fantastic job, but with Buick finned front aluminum drums mounted to front Chrysler shoes, spindles etc. . The finned drums only add long term cooling, not really a big issue unless mountains , or racing. That said, those Buick drams were #1 through the 60’s , 12x3”, a work of art. Seeing this reinvigorated my own feelings that these Chrysler brakes are far better than ok,---as does the fact that they DID win all those races in 55-56 with those brakes. Maybe one of us contacts that guy racing the B in the clip ..he seems to have the problem aced.
My own experience has been the same, over and over--- grossly incompetent work on the brakes, mostly by opinionated “brake shops” who never saw drum brakes before you showed up. Let alone rather sophisticated s design of drum brakes. Bumbling , accompanied by a lot of mouth time has often ruined them. Leading to final pronouncement., “you need discs” Carl K did not have discs. This is especially true of “turning the drums “ and then putting new shoes on which do not touch the drums except in a small spot.(!!!!) IMHO leave the drums alone! Keep the old shoes if at all reasonable , mark with which drums (only recently started doing this) , and actual ID of your drums NOW. Turning was a way to make money ,and ok , first time-- if you DO have a shoe arc grinder . Even if scratched, today, leave drum alone . The scratch will bed in. The first day you drive it all beautiful shiny and smooth (and not stopping you well), a single pebble can bounce in and score the drums, So what? Look at modern discs after 20 k miles…looks like a 78 record. so what? Unless you have a way to arc grind the shoes (no one does anymore) you just make the whole thing a LOT worse, as most drums have been turned before you ever saw them. . And drum is then thinner, leading to new kinds of grief. (vibration, out of round, warping) Brake shoes that do not touch the drum 360 can never , ever work on the self energizing scheme . I think it takes at least 5000 miles to wear in new normal size shoes into an oversize drum. ---- during which time you experience locking, poor braking, rapidly falling pedal, constant adjusting etc etc Further they are dual self energizing in front..a wonderful Chrysler engineering idea. Twice as much stop as say GM with one leading shoe. A very sound idea. I had, --- brand new--- a 60 dodge Pioneer V8 with manual brakes , I loved the brakes, I abused that car beyond belief. ; I used to beat on my GM friend how uncontrollable his 57 Pontiac power brakes were. Liked a switch, on and off. If you stepped hard enough , and not crazy hard, despite manual brakes, you could lock the Pioneer wheels easily . Cannot use any more “stop”. Big Red (160 mph H) has manual brakes.
Another thing I have learned off this site is that in overwinter storage the drums rust and both front shoes can aggressively self energize the first time you step on them, as the rust grabs the shoe. locking the fronts. Maybe NOTHING is wrong..just use gingerly first few stops to get rid of rust coating .
I note the hot rod guys are using some kind of electric booster from current Fords, as a component in a universal electric power brake kit. I think it was CPP parts. ; sounds like an answer ; one company does sell a universal kit. Looks a little clunky though. Another is to use 67 Cuda or dart master and booster, or GM S10, both of which are small, some have two diaphragms inside. Not only readily available stuff, but takes advantage of 60 years of evolution on this stuff. If I had a J, K or C300, 330B, in 2017, I would look that way…
Related in a way, the C300 and 300B have unbelievably aggressive cams for a street car..maybe the most aggressive ever sold retail. 280 degrees! As hit on last week a Ram J is only 268, 300hP 327 chev about that too. So lack of boost can be traced to lack of vacuum to work booster . And thus very fussy booster adjustments . Today most builders of hot cars say forget power brakes over a 270 cam. Unless 900 rpm idle. That leads to weak brakes as you approach the stop sign, stalling , all that stuff. Again the hot rod guys (summit) ,have same problem, hot cam in street car, have electric vacuum pumps that keep the booster full .---another way. You can hide that , if 12v car.
Last a power brake without a booster is NOT manual brakes. The pedal ratios are all different , MC bores, MC mount height , distance below pivot, pedal arm and hole spacing. and I think even the box at top of pedal to dash board . I did not know that at first, was very disappointed in first attempts to just go manual brakes in a PB 300 car . Pedal like a rock.
I wonder if stock 300/ 300B race cars had manual brakes? Anyone know ? exact details of that setup, would really help in many ways.
The vacuum hose on a Kelsey-Hayes MC would be portrayed to the right side in a Shop Manual (e.g. page 96) whilst that would interfere with the Batwing on a C-300, 300s normally have them on the left as seen in the direction of travelling. Placing vacuum at the bottom is new to me?
Adjustment of the K-H is sort of crucial and some units never becomes right, one setup I have had did not work properly although it had been to two different rebuilders including having been adjusted to spec. The brakes would afterwards not apply enough pressure during normal operation and after some heavy stomping the rod would stick in the engaged position and only let off after myself splitting the diagram box to let in normal pressure. I now run with the original unit rebuilt and adjusted with the original MC, and the brakes are awfully non-convincing. I will still try to replace the bands with rebuilt “soft” (asbestos) linings and do an optimized adjustment before I also succumb to aftermarket disc brakes. Or maybe an Ausco Lambert setup?
But one thing I have learned is to not use DOT-5 in connection with the K-H - and that the power unit should be adjusted together with the MC for best operation.
My advice would be to replace the K-H with a 60s/70s MC when going non-original with discs anyhow.
C-300 in Norway since 85
The big rubber diaphragm inside the one-year-only Kelsey-Hayes power brake boosters on 1955 MoPars is subject to deterioration and rupture. On a good day, these boosters do not work so well. There is a reason for that 9-inch wide brake pedal. Of course, C300 boosters are significantly different from 300C boosters but are sensitive to end clearance on the rod. Clevis to firewall specification is in 1/64ths. Fluid can also accumulate in the booster unless the vacuum connection is facing downward. Disc brakes may require more fluid displacement from the MC. The ’55 MC’s worked differently with a metal piston displacing fluid from a pressurized cylinder to the system. Never caught on. See: http://www.jholst.net/55-service-manual/brakes.pdf Page 96.
I believe proportioning valves are essentially variable orifices and may not work so well if set really tight. “normal” master cylinders have a device referred to as a “check valve’ in the outlet to hold a little pressure on the brake shoes with no foot pressure on the pedal. This is to minimize moist are migrating back into the wheel cylinders. I don’t know if such a device is fitted to the K-H MC but it could be part of the problem.
Many may be interested in a successful front (?) disc brake conversion for ’55 C-300’s. Please keep us posted as to the details necessary to achieve proper operation.
I go with the problem being with booster. I imagine you pulled the booster off the firewall during the installation, as I did on my 300C. I do not think any boost is getting to your peddle. Mine acted the same way... I could go 30mph and stand on the peddle with both feet and my full 180 pounds of weight and I would coast to a stop but barely. What I discovered on my C, was as follows:
If you remove the booster, you would likely find that the little "tang" at the very end of the peddle has been bent or twisted such that it does not work against the little white button on the back of the booster, where it sets between the two blades, one on each side of the top of the pedal arm. This can happen when installing the booster blades or prongs through the firewall... it is very easy to have happen. Remove the booster and examine the upper end of the pedal arm, making certain it has a slight curve and rocks back and forth and is straight in the slot it fits into.
When you get the booster ready to mount, have a friend get below your dashboard with a flashlight and watch that those blade or prongs go on both sides of the pedal arm while you place some bolts attaching the booster to the firewall. Before you get it completely tightened up, check from under the dashboard that the tang at the upper part of the arm touches the button on the back of the boaster when you take your foot off the pedal. When it touches, it releases the vacuum. If the button isn't pushed and vacuum isn't released it can't gain access to more vacuum.
I can send some pictures later tonight showing what I am talking about. If this isn't the solution, get back to me and I have some other ideas.
George in snowy and windy Idaho!
Posted by: "John Grady" <jkg@xxxxxxxxxxxxxxxxx>
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