C2 Brake Question

[Rick A.]

Folks,

I have a question on the brake systems for the C2. I understand the Z06 brake system and the J56 system are sometimes confusing - in other words, they are sometimes mistaken one for the other. On the Z06, what is the RPO for the brakes, if any? What are the major differences between RPO J56 and whatever the RPO for the Z06 is? Thanks. Rick #38392

[Mike M.]

Re: C2 Brake Question

selecting the j-56 option when ordering your new vet in 63 got you a set of sintered metalic brake SHOES, the rest of the brake components(Drums, springs etc) were identical to all non-J56 equipped vets in 63. The Z-06 option got you sintered metalic brake shoes, more heat resistant shoe return springs, fans ,finned brake drums, vented backing plates wioth removable covers and scoops(referred to as elephant ears) to direct fresh air to the front brake assembly. It also got you power brake booster and a unique to Z-06 master cylinder. There were also heavy duty non-brake additions that came with Z-06 such as stiffer shocks,thicker front suspension. Fuel injection also was manditory with Z-06, not necessary with J-56.

[Rick A.]

Re: C2 Brake Question

Mike,

Thanks for the response. Couple of clarifications though:

So, selecting J-56: did you get cooling fans? did you get vented backing plates?
were scintered brake shoes same size as Z06 shoes? are the brake drums for the J-56 the same diameter size as the drums for Z06? think Z06 drums are around 11.2 inch diameter?

Still, was there a specific RPO associated with just the brakes in the Z06 option, or was it just reflected as part of the Z06 RPO?

[Mike M.]

Re: C2 Brake Question

j-56 just got you sintered brake shoes, not finned drums, not vented backing plates, and not the fans. just the sintered brake shoes. J-56 cost you 37.70. Z-06 option cost you l8l8.05. There was no RPO for just the finned drums, fans backing plates scoops. They could only be purchased as part of the $l800 Z-06 package. mike

[Duke W.]

Re: C2 Brake Question

RPO Z06 was a "special performance equipment package" that bundled several different system components. The first interation included HD brakes, HD suspension, 36.5 gallon fuel tank, and quick take off wheels. Of course, the wheels were never installed in production and the standard steel wheels were substituted. Also, ordering Z06 REQUIRED ordering L84, M20, and G81.

In February '63 the Z06 package was modified by deleting the big tank and KO wheels, so the second iteration of Z06 included only the HD brakes and HD suspension. The big tank became a stand alone option, RPO N03 (coupe only), and KO wheels, P48 continued to be offered as a stand alone option, but none were ever installed at the plant during the '63 model run.

Beginning in '64 Z06 was COMPLETELY unbundled by breaking the second iteration in into its component parts, J56 HD brakes and F-40 HD suspension. Even though there was no Z06 option in '64, you could build an "equivalent Z06" in '64 by ordering the unbundled equipment options that made up either the first or second Z06 option configuration. Also, as far as I know, there were no option restictions, which meant you could order a base engine car with Powerglide, and HD brakes, a rather unusual combination that I doubt was ever built.

To answer you specific question the '63 "Z06 brakes" and '64 J-56 HD brakes are IDENTICAL, however there IS evidence that the brake friction material did change during the '63 model run. The Z06/J56 brakes included the internal cooling fans and front air scoops, but these were shipped inside the car rather than being installed at the plant.

Duke

[Duke W.]

Re: C2 Brake Question

You are incorrect. The "metallic brake option" that included metallic shoes and standard drum castings (but a different part number because the friction surfaces were machined to a special 30 microinch finish), and special heat resistant springs was option code RPO J-65.

This option was available in both 63 ($37.70) and '64 for $53.80. It is not well understood because none of the special parts can be viewed without removing a wheel and drum. For this reason, J-65 is not judged by NCRS.

RPO J-56 in '64 (also part of Z06 in '63) included large fined drums, special metallic linings, vented backing plates with fans, front air scoops (not plant installed, but shipped inside the car), dual circuit master cylinder, and a vacuum booster. Essentially all of the brake hardware was unique with nothing shared with either the base brake system or J-65.

Duke

[Duke W.]

Re: C2 Brake Question

You are confusing J-56 with J-65.

Duke

[John C.]

Re: C2 Brake Question

The J56 drums evolved during this period, there were several iterations with the differences being very minor.

[Rick A.]

Re: Any Canadian Members on the Forum?

Duke,

thanks for the history lesson - now one final question - what is the GM Part # for these drums?

[Duke W.]

Re: Any Canadian Members on the Forum?

Drum part numbers don't mean much because more than one end item part number was made from the same casting number. For example base and J-65 drums were made from the same casting numbers, but because the J-65 drums had a finer finish on the friction surface, they carried a different part number.

Once the drum was taken out of the box and place on the car the only identifier is the casting number.

The original casting numbers on the front 2.5" drums on my J-65 SWC are 3828671. The rear 2" drums are a bit mysterious because there is one 3752623 and one 3828688. In 1968 I did have the rear shoes replaced due to a dragging parking brake, the the RO does not show that either drum was replaced. These 2" castings were also interchangeable with the 2" drums used on all four wheels of solid axle models with base and RPO 686 metallic brakes.

In the late sixties a new FMVSS required that the maximum ID of the drum be carried permanently on the drum. It's possible that some of the existing service parts were pulled and the max diameter die stamped, but eventually the molds were modified to include the max diameter of 11.090" in the casting, and the casting numbers were changed. A car that still has drums without the max diameter stamped or cast in are probably original.

Since little can be seen of the brake system in NCRS judging, there is little info on drum castings and J-65, but if anyone has any old 2" or 2.5" front drums (as used on Sting Rays) and can get the casting numbers, I'd like to know.

Duke

[Rick A.]

Re: C2 Brake Question

Duke,

so, for instance say the GM #3838125 is the part number for the J56 "finned" brake drum on a Z06, that same part # was used on 1964 and 1965 J56-equipped Corvettes? The difference is in the "casting" number used on the application?

FYI - know that other GM cars also used J56 - are these drums alos available for cross-application into Corvettes?

[Duke W.]

Re: C2 Brake Question

I don't have any part number information on J-56 brakes, so I can't tell you anything about drum casting or part numbers, but your example is backwards from what typically can occur. Using the base and J-65 drums as examples, they started out with the same casting number, but machined two different end item part numbers because the J-65s required a finer finish on the friction surface.

I don't know if there were any changes to casting or part numbers for the J-56 finned drums, but maybe a Z-06/J-56 historian can offer some comments.

Duke

[John C.]

Drum Numbers

64
LF 3828671
LR 3828688
RF 3869532
RR 3828688

[Duke W.]

Re: Drum Numbers

John - do you believe those are the original drums? Do any of them have "MAX DIA. 11.090"" stamped or debossed in the casting?

Interesting that you have two different part numbers for the front. Can you see any visual differences in the casting.

It appears that in the late OEM drum brake era the 2.5" castings progressed from 3828671 to 3869532, and the 2-inchers from 3752623 to 3828688, but I don't know what differences are in the design that would have generated new casting numbers.

Duke

[John C.]

Re: Drum Numbers

Duke, 180 from the casting number on the RF drum is "W-3", also has flat wire spring encircling it. RR drum has an "L" between the stud holes. LR drum has a "W5". LF drum has a "W-11" on it, round wire spring, stamped "R" between stud holes, and an "X" close to the "R".
Front shoes are stamped "WE-88-1" leading me to believe they are Wagner replacement shoes. Rear shoes have metallic linings with two segments on the front shoe and three on the rear.
I believe the drums to be original, unsure about the rear shoes.
That's all the notes I had taken when inspecting the brakes back in '98. I was looking for evidence of the J65 option. For reference, my '64 coupe has C60, L76, power brakes (J50 or J65, not sure which), A01, U69, T86. 6/22/64 build date.