mechron

guys, i think john neas meant .050 instead of .500, no biggie, just a typo. running thin drums (or rotors) is just a BAD idea. a little off topic but not really--there is a max. dia. drums can be turned (or a min. thickness for rotors) before they are junk. my 64 has the origonal drums cast in "max. dia. .120" some drums are .060. thin drums (and rotors) have a tendency to to overheat, warp and/or crack very easily. rotors have the min. thickness cast into the outside edge. we turned tons of drums and rotors on a delux AAMCO brake lathe in the old days (can't remember the model number, it had the brake shoe arcer on it. inspecters came in in the 70s and told us to lose the shoe arcer-it was now illegal due to asbestos dust coming off the shoes during arcing the shoes. we said OK, we'll take it off and put it in the back room. they said "NO, if any later cal-osha inspecter comes in and see that thing anywhere you will be fined".

drums were easy to turn and mike. as for ventelated rotors the brake pads never wore evenly, one side of the pads would always go to metal long before the other, so even though the rotor would be within min. specs, one side would be MUCH thinner than the other and the rotor was junk.

i also learned from taking automotive engineering in college-never use the parking brake on drum brake cars unless you have to, the drums are hot and by pressing the shoes against them they will cool down and become egg shaped. i found this to be entirely true by turning rear brake drums on the AAMCO. i could tell when somebody used the parking brake all the time by just turning the rear brake drums

YesA59

I count 44 fins on my circa 1961 finned drum. All of the finned drums were 11 inch. Fronts were about 3 inches deep, rears about 2.5 inches deep. Give or take.

For the best article on the net about the rpo 684 option:
RPO 684 Article

Russ

YesA59

I'm guessin' that John really meant .500

Russ

JohnZ

Here's an original front drum from a '58 "big-brake" car:

gord holden

that is a newer drum 59-62 as the 57-58 finns rolled right over the top of the drum.

gord holden

Re turning drums,turning drums from a new casting is a art.as when in a chuck they will sing ,wobble. to properly turn you need 4 adjustable turn buckles spaced evenly on the outside of drum to take the whipping motion out or they will turn off centre,after each cut they are tightened.picture of uncut drum with 1 inch of meat available.as i don"t know how to post to forum.

YesA59

Here is Gord's pic:

cameo

cameo

cameo

QIK59

I read years ago in an NCRS article that the backing plates came from a GM sister division ( real mysterious - NCRS !).
I deduced from the recommendation to use Olds shoes (for street driving) that the backing plates must have been Oldsmobile derived.

I was able to get blue prints from GM many years ago for the backing plates but was not able not reverse engineer back to the basic original backing plate application..

Checking the drum sizes of all other GM divisions during the same time frame (early to mid 50's) Pontiac, Oldsmobile, Cadillac & Chev trucks used 11" brakes.

A number of years ago, armed with that "information", I spent 1/2 a day in a southern boneyard checking backing plates.

I did not find a single backing plate that matched the early Chev / Corvette center hole size and mounting bolt pattern.

Vehicles checked :
Pontiac - '50 , '51 , '53 ('54 on were 12")
Oldsmobile - '49 , '50 , '54 , '56 ('57 on used ball joints (different spindles)
Cadillac - '49 & '51 , ('54 on were 12" ?)
Buick - '55 , ('57 were 12")
Chev truck - '53

So what was the original application of the RPO backing plates (prior to RPO modification) ??


Did I screw up assuming that stock Corvette backing plates are the same as '51 & '53 Chev which I was comparing dimensions with ?

Jerry

Plasticman

It's unlocked.

Plasticman

SLO69

I was wondering Tom, when I emailed you about getting called a spammer and getting thrown off the forum, why "the lack of support".
I'm starting to understand about freedom now LOL !

Maybe a SLO69 will be better than a QIK59 !

Thank you Plastic Man !

Jerry

pullin-gs

Question:
What is the difference between front and rear RPO687 drums?

DZAUTO

Front drums are wider. The fronts have to be wider for the 2 1/2in shoes. The rears use 2in shoes up through 59, then went back to 1 3/4in for 60-62.

Tom Parsons

mashinter

Front:



Rear:



Different machining and mounting plate:

Both drums are cast 3745534, but notice that the front (left) drum sits off the table and the rear sits flat on the table. The ridge that fits into the backing plate groove is machined differently. Also, the level is flat on the front drum mounting face. Notice the gap to the rear drum mounting face. The front mounting plate sits "higher" than the drum edge. The rear sits "lower".

Del Toro

Is there anybody out there offering a big brake kit for C1, front and back in a repop?

jim lockwood

Not that I'm aware of. It's strictly a "roll your own" proposition. There have been repop drums made but metalurgy is unknown and I wouldn't consider them for anything but a trailer queen.

Tom Parsons (DZAUTO) has come up with a novel way to achieve big brakes with 2-1/2" front shoes and finned drums all the way around. Some precision modifications to the front drums he uses are required.

I've developed what I call Big(ger) Brakes for my C1 (sorry Tom). My system uses 2-1/4" front shoes and finned drums all the way around. To implement my system, a set of 2-1/2" shoes are modified in a creative way, but the drums are a bolt on.

The drums I use weigh more than original RPO drums and, therefore, have improved heat management capability. If shoes from, say, Porterfield or Carbotech were used, my system would probably be usable in a vintage racer.

Front drums:




Wide front shoes:






Special hardware:




Large bore wheel cylinders (1-3/16")




Rear drums:



Jim

DZAUTO

For those who have not seen mine, or, as a refresher for those who are aware of my brakes, here are a few pictures-------------------Front and rear.
The drums start out as what is used on mid-70s GM A-body wagons, such as 76 Cutlass (and probably other cars as well).

I have a brake lathe, so I can turn drums to meet my own specs. I also have a cheapo 20ton press that came from one of the discount tool sources, and it works fine for home use.

Here is a raw drum on a 76 Cutlass wagon axle housing. Notice the 1/4in wide flange that connect all the fins. I cut off this flange, simply to show the fins better when installed on the car (takes forever to cut off that flange!!!).


The center is raised, so I push it down in the press.
Before, after pressing, and a comparrison.






Once the modifications are done, I true up the drum on the lathe.


I use 2 1/2in shoes for the FRONT of late 50s/early 60s Oldsmobile. Here is a comparrison of the 2 1/2in Olds and stock 2in shoes.


Front and rear drums installed with "elephant" ears on the front.




For vented backing plates (which are 100% identical to 51-54 Chevy pass car front backing plates), instead of cutting out the big holes in the backing plates, I use a real HD brake backing plate to outline the vent opening locations on stock backing plates. Then I lay out a grid, and using a drill press, I drill about 300 holes/backing plate with a 3/32 drill bit (any size hole will work, I went through several drill bits).






Because of the wider front shoes, the front wheel cylinders needed to be spaced outboard, so I fabricated spacers starting with big, thick washers. On my 56, this setup works just fine with ZERO issues.




The arrow points to the installed spacer.


The HD brakes on my 56 is a pure home made setup. NONE of the parts are available from any source. Fortunately, I have the equipment and ingenuity to fabricate everything as well as plenty of time. So I could fit, machine, fit, machine, fit, machine as needed as well as learn and correct my own mistakes.
After I ran these brakes for a few years, I then added self adjusting kits from my local O'Reillys.


Tom Parsons

jerry gollnick

Tom, i going through old posts and I see you pressed the center down on some drums. i purchased the same drums and I'd like to press them down also. Do you have to heat the drums or anything or just put them in press and push until at desired height? Jerry