I have the 4 HD calipers SS sleeved with pads which are J56 option.I also was given 4 rotors to go with them that came off of the same car.What is the difference in the rotors from a normal brake car?Also,what else am I missing to mount these calipers to the car,certain brackets?Is the HD proportioning valve adjustable?How impossible is the valve to find?I am wondering if it is even worth the trouble or should I sell them off.Craig
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Re: J56 brakes for 69 coupe
To my knowledge, no difference in J56 rotors to stock units, even though the J56 semi-metallic linings are (slightly) larger, for more breaking area. Yes, you're missing the malleable cast iron arm (caliper mounting bracket) which is bolted between each caliper and the steering knuckle; '69 arms + differ from '66-'68. The proportioning valve is adjustable (for the rear calipers only); you see them pop up on eBay now and then; in fact there's a set of calipers, brackets and NOS P.valve there now (item 1815276535). -
Re: J56 brakes for 69 coupe
To my knowledge, no difference in J56 rotors to stock units, even though the J56 semi-metallic linings are (slightly) larger, for more breaking area. Yes, you're missing the malleable cast iron arm (caliper mounting bracket) which is bolted between each caliper and the steering knuckle; '69 arms + differ from '66-'68. The proportioning valve is adjustable (for the rear calipers only); you see them pop up on eBay now and then; in fact there's a set of calipers, brackets and NOS P.valve there now (item 1815276535).Comment
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Re: J56 brakes for 69 coupe
Craig------
The rotors for J-56 and non-J-56 are exactly the same; no special rotors were ever used in PRODUCTION or available in SERVICE for J-56 equipped Corvettes.
The caliper castings, themselves, were also exactly the same as non-J-56. However, for the front calipers the brake pad pin bosses were machined off and 1/8" holes were drilled on either end of the pad opening. Non-J-56 front calipers can be converted to J-56 configuration very easily by following these steps. However, J-56 calipers cannot be converted to standard configuration. Rear calipers used for J-56 were identical to non-J-56.
For 67-75, J-56 pistons were different than standard pistons. The J-56 pistons, front and rear, used a thick Pyroceram insulator on the front of the pistons (earlier, all 65-66 Corvettes with 1st design calipers used a similar, but thinner, insulator). Unfortunately, the 2nd design J-56 pistons are not reproduced. So, if the pistons are worn (which is EXTREMELY likely), replacement pistons cannot be obtained to use the, essentially, life-unlimited insulators on.
The proportioning valve used for J-56 brake systems was manufactured by Kelsey-Hayes. These valves are available in the used marketplace and there are even a few NOS examples around. They were used on many Mustangs as well as the few that were used in Corvette J-56 applications. However, the proportioning valve was used ONLY on 1966-68 Corvette J-56 systems; it was NOT used for 69-75 J-56 systems.
The only other parts necessary for the J-56 system are the front caliper support brackets. These are a nodular iron casting, side-specific bracket which provides additional support for the caliper to the steering knuckle (front spindle). There were 3, slightly different sets of these supports used. 66-67, 68, and 69-75. All are GM discontinued but they are (or, at least, used to be) reproduced. The reproductions are excellent and are actually manufactured of stronger material than the originals.
J-56 brakes also used different brake pads. The front pads had a curved-over top edge to add stiffness to the backing plate and that is the reason for the difference in the machining configuration of the front calipers. Long cotter pins were used on either end to retain the pads. Most (but NOT all) original pad backing plates were of Inconel material and the lining was semi-metallic. Rear pads were configured the same as non-J-56, used conventional steel backing plates, but were also of semi-metallic friction material. All J-56 pads are GM-discontinued, but functional replacement pads are available in the aftermarket.In Appreciation of John HinckleyComment
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Re: J56 brakes for 69 coupe
Craig------
The rotors for J-56 and non-J-56 are exactly the same; no special rotors were ever used in PRODUCTION or available in SERVICE for J-56 equipped Corvettes.
The caliper castings, themselves, were also exactly the same as non-J-56. However, for the front calipers the brake pad pin bosses were machined off and 1/8" holes were drilled on either end of the pad opening. Non-J-56 front calipers can be converted to J-56 configuration very easily by following these steps. However, J-56 calipers cannot be converted to standard configuration. Rear calipers used for J-56 were identical to non-J-56.
For 67-75, J-56 pistons were different than standard pistons. The J-56 pistons, front and rear, used a thick Pyroceram insulator on the front of the pistons (earlier, all 65-66 Corvettes with 1st design calipers used a similar, but thinner, insulator). Unfortunately, the 2nd design J-56 pistons are not reproduced. So, if the pistons are worn (which is EXTREMELY likely), replacement pistons cannot be obtained to use the, essentially, life-unlimited insulators on.
The proportioning valve used for J-56 brake systems was manufactured by Kelsey-Hayes. These valves are available in the used marketplace and there are even a few NOS examples around. They were used on many Mustangs as well as the few that were used in Corvette J-56 applications. However, the proportioning valve was used ONLY on 1966-68 Corvette J-56 systems; it was NOT used for 69-75 J-56 systems.
The only other parts necessary for the J-56 system are the front caliper support brackets. These are a nodular iron casting, side-specific bracket which provides additional support for the caliper to the steering knuckle (front spindle). There were 3, slightly different sets of these supports used. 66-67, 68, and 69-75. All are GM discontinued but they are (or, at least, used to be) reproduced. The reproductions are excellent and are actually manufactured of stronger material than the originals.
J-56 brakes also used different brake pads. The front pads had a curved-over top edge to add stiffness to the backing plate and that is the reason for the difference in the machining configuration of the front calipers. Long cotter pins were used on either end to retain the pads. Most (but NOT all) original pad backing plates were of Inconel material and the lining was semi-metallic. Rear pads were configured the same as non-J-56, used conventional steel backing plates, but were also of semi-metallic friction material. All J-56 pads are GM-discontinued, but functional replacement pads are available in the aftermarket.In Appreciation of John HinckleyComment
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Re: J56 brakes for 69 coupe
Thanks Joe.Who reproduces the brackets?I would like to get a set.CraigComment
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Re: J56 brakes for 69 coupe
Thanks Joe.Who reproduces the brackets?I would like to get a set.CraigComment
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