RPO 684/687 finned drums..1957 to 1962

[Joseph T.]

When did the drums change from having the fins on the vertical surface wrapping over the horizontal edge...to only having the fins on the vertical side of the drum.

Were the original finned 1956/57drums with the fins that wrapped around and over the top of the drum..only used with 15 x 5 1/2 inch wheels...in order to clear the fins on the face of the drum?

Many early drums surface with the top fins milled off to clear the wheel...later drums were made without these top fins.

I suspect this happened in 1958 or 1959 production...however..I have pictures of the March 1957 Sebring factory racecars that already had the later or milled drums!

Thanks for any insight on this running change.

Joe Trybulec
trybulec@aol.com

[Justin B.]

Re: RPO 684/687 finned drums..1957 to 1962

Joe,
My early production 1958 #1327 RPO 684 (Final assembly date Nov. 27, 1957) did not have the wide wheels. Its wheels which I believe to be original were dated (3) Nov. 57' and (1) Oct.57' plus they all still had their original Inca Silver paint. The fins were completely wrapped around the face unlike the later RPO 687 style. After 96k miles with standard wheels I think its safe to say that there weren't any interference problems with this wheel/drum set-up. Maybe the fins interferred with either the wide wheels or Hildabran (spelling wrong) wheels. I also read in Noland Adams book on pg.264 that the wide wheels (although available on 1957 models) weren't re-introduced as an option for the 1958 madels until 11-18-57. Maybe this is why my car didn't have them as they wouldn't have been available until after it had already been ordered. What are your thoughts?? I think that most people with or without big brake cars think that all big brake cars HAD to have these wheels. What is your opinion on this also?

[Joseph T.]

Re: RPO 684/687 finned drums..1957 to 1962

Justin

I don't have any hard evidence..but I don't think the 15 x 5 1/2 inch wheels were required for all heavy duty brake cars. What I see written is that the addition of the 15 x 5 1/2 inch wheels allowed for bigger tires to be used...and was offered as an RPO option but not tied to the RPO 684/687 big brake option.

What I am trying to find out is at what time in production did the change occur from your early style wrap around finned drums to the revised non wrap around style. Was it sometime in 1958..or the start of 1959?

I would also like to document at what point in time..the front finned drums were no longer riveted to the hub assembly. Maybe this all occurred at the beginning of the 1959 production.

Regards,

Joe

[Mike M.]

Re: RPO 684/687 finned drums..1957 to 1962

big brake wheel option didn't include 15 x 5 1/2" wheels in 61 for sure. ya had to pay extra for the wide wheels.mike

[Dennis C.]

Wide Wheels were...

...a NO cost option and were totally independent of the big brake option.

[Loren L.]

Re: RPO 684/687 finned drums..1957 to 1962

The creases in the old memory gap seem to indicate that the wraparound fin ceased at the start of the '59 model year. I'll try to through some of the product books, etc., and see if I can find something to back that up.

[Joseph T.]

Re: Wide Wheels were...

Dennis..I seem to remember seeing an invoice posted concerning a car from the famous L.A Corvette dealer showing a price of about $15 each for the 15 x 5 1/2 wide wheels..either ordered on a car or they could have been an added expense from the dealer.

Maybe this was the over the counter price.

Can't remember the exact details.

Joe

[Justin B.]

Re: RPO 684/687 finned drums..1957 to 1962

Joe,
I did have a mid-production UNRESTORED 1959 basket case big brake car which was used for racing and then retired after it was wrecked many years ago and it did have its original, unrestored rear 5 leaf springs, rear shocks, rear brake cylinders, all four drums and backing plates. I know for sure that it was in the 4300-5500 serial number range. All of the parts I just listed were RPO 684 parts...fine screens, wrap around fins on drums. However, the frontside of the fins had been milled down by someone other than GM to where only about 1/16" of the fins where still there and visible. They had to of been milled for some special wheels?

[Dave S.]

Re: RPO 684/687 finned drums..1957 to 1962

Joe et al,
I did some research and this is what has been written about the brake drum change.
1. Gerald Wagner's RPO article says "The later ones(meaning second style finned brake drums) began appearing in 1959. He also says "The fins (wraparound style) interfere with base 5" wheels where the flat attaching pads of the wheel center spider are welded to the rim."
2. Restorer article from Volume 19 #4 by Masciarella and Bartush says "Sometime during 1959, the drums and backing plates may have changed to RPO-687 style." He also says "The fins on the initial drums (meaning first design) may have interfered with various wheel applications."
The two Mike Ernst articles make no mention of the early drums as he wrote about 1960-1962 cars in one article and 61-62 cars in another article. Both are excellent sources of information.

[Joseph T.]

Re: RPO 684/687 finned drums..1957 to 1962

Justin..I would think that 59 big brake cars would have course screen vented backing plates...since the fine screens were identified as a problem..clogging up. However there is always the chance of existing inventory being used...if engineering did not delete their use.

You bring up a good point that some owners may have milled their wraparound drums when changing wheels and having a clearance problem.

The question remains..when did production drums appear without the wrap around fins?

Is there anything in the 57/58/59 judging manual?

Interesting.

Joe