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Author Topic: JL8 / J56 4-wheel disc racing brakes  (Read 1653 times)
Jon Mello
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« on: May 04, 2013, 05:30:19 PM »

Beginning in the 1968 racing season, the Camaro was homologated (passed the criteria for acceptance) with the SCCA to be able
to use a 4-wheel disc brake package in Trans-Am and A-Sedan events. This brake equipment was adapted primarily from already
existing Corvette brake components. The calipers were the cast iron Delco-Moraine Corvette units and these were the heavier duty
J56 pieces that had 3/4" thick heat insulators on the brake pistons and that used two cotter pins to retain the brake pads rather
than the single pin in the middle. The top of the caliper was milled down to remove the single pin boss because it interfered with
the top of the flanged brake pads and was unnecessary. The inner half of the front calipers had a single brake hose inlet boss where
Corvettes (typically) had two bosses. Here are some of the rare front calipers from Robert Lodewyk's collection.
« Last Edit: May 05, 2013, 12:25:22 AM by Jon Mello » Logged

Jon Mello
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« Reply #1 on: May 04, 2013, 05:35:08 PM »

Another photo of Robert's calipers.
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« Reply #2 on: May 04, 2013, 05:38:19 PM »

Closer view from the top.
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Jon Mello
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« Reply #3 on: May 04, 2013, 05:50:44 PM »

A look at the 3/4" thick J56 brake pistons outside the bore of the caliper. (Jon Mello Collection)
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« Reply #4 on: May 04, 2013, 05:52:24 PM »

A view of the insulator removed from the metal part of the piston. (Jon Mello Collection)
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« Reply #5 on: May 04, 2013, 05:55:30 PM »

A comparison of the '66 and early '67 Corvette J56 piston with its 3/16" insulator in comparison with the part that superceded it. (Robert Lodewyk photo)
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« Reply #6 on: May 05, 2013, 01:03:32 AM »

The piston bores in the Camaro and Corvette calipers are the same size They both use a 1-7/8" (1.875") piston.
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Jon Mello
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« Reply #7 on: September 20, 2014, 12:25:45 AM »

Here's an NOS set of Delco J56 heavy duty brake pads. The full set of four is part number 5468882, while apparently each individual
pad is labeled as part number 5468883. The set includes the four necessary cotter pins in an envelope, p/n 5474322 and an instruction
sheet indicating how to precondition them for the best braking performance. The backing plates on these pads are made with Inconel,
an expensive, high-temp alloy that was more resistant to warpage when they got hot, unlike steel.  Inconel is a non-magnetic material.
The thickness from the back of the backing plate to the front surface of an NOS brake pad is 1/2" (.500").           (Jon Mello Collection)








The cotter pins are around 4" long and are 1/8" (.0125") in diameter.








Instruction sheet p/n 5474920



Warning: Preconditioning of this material is necessary to
obtain maximum effectiveness. After relining the brakes,
drive the car for approximately 1/2 mile at 1/2 throttle
with the brakes held on enough to maintain a car speed
of 15 to 20 MPH.
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« Reply #8 on: September 22, 2014, 04:14:07 PM »

Wow, very cool!
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Jon Mello
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« Reply #9 on: September 24, 2014, 11:12:07 PM »

Attached are pictures of an NOS right front JL8 / J56 racing brake caliper with the brake pads and cotter pins installed. The Camaro-specific inner caliper half for the passenger
side is part number 5469588 and the corresponding one for the driver's side is part number 5469589. The outer caliper halves are taken from Corvette. It should be noted that
there are some collectors of these brake pieces that feel that if there is an X anywhere in the casting number, example X5469589X, then the part is not an authentic, original
JL8 / J56 component. I personally do not agree with this line of thinking but to each his own. I can tell you that if you are looking to buy these components individually, or
complete, you can expect to pay more money for those pieces that do not have an X. (Jon Mello Collection)









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Jon Mello
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« Reply #10 on: September 25, 2014, 12:16:42 AM »

Jon,

I'm not familiar with 'X' on brake calipers, but occasionally we see heads (particularly Corvette heads from the fifties/sixties), that have a big X on them; what I've heard speculated is that those are early castings....  maybe a first run to check out the molds??   I'd be interested to hear yours and JohnZ's input on that...
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« Reply #11 on: September 25, 2014, 10:51:44 PM »

I sent John an message about this so we'll see what he has to say. It's a bit funny/ironic that the 461X cylinder heads are more desirable than those without the X and the reverse is true with these caliper castings but I think the 461X heads have better ports (if I remember correctly).
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« Reply #12 on: September 26, 2014, 10:38:58 AM »

I sent John an message about this so we'll see what he has to say. It's a bit funny/ironic that the 461X cylinder heads are more desirable than those without the X and the reverse is true with these caliper castings but I think the 461X heads have better ports (if I remember correctly).

There is some evidence to suggest that an "X" added to a GM casting number indicates the first production pour with a minor pattern or process change at the foundry to let the customer (who machined the casting) know that a minor change has been incorporated in the casting, but I haven't been able to document it. Functionally, it's irrelevant and shouldn't affect the casting's price.

The 461X cylinder head is a different issue - those "X" heads had 10cc larger intake ports than the "non-X" 461's, and were prized by racers in classes where they had to run unmodified (no grinding, no porting) stock heads.
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« Reply #13 on: September 26, 2014, 07:38:49 PM »

I agree with you John. 

This is only somewhat related but...

I have single four barrel cast iron intake from a 348 W motor that was cast early in the 1958 model year (can't remember the exact date but it is fall of 1957).  It has an X on it with the casting number.  I will try to post of pic of that sometime.  I have other 348 intakes dated 1958-1960, but none of the others have the X on them.
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« Reply #14 on: September 27, 2014, 10:28:34 AM »

Thanks for your input, John. Nice insight.

Bryon, I don't think we need an 348 intake photo here but the info is interesting and relevant nonetheless. Thanks for your input as well.
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