Only brake options that I can see on Gen2 Camaro were J50 (power brakes) and J52 (front discs). Over the 12 year life span both gradually became standard on Camaro. It doesn’t appear that rear discs even became available until 1982. Except for a special JL8 4 wheel disc setup for dealer fitment in 1968 or assembly line fitment in 1969. J56 was heavy duty brakes for 1967-9, got you better front brakes and I think improved rear linings. The JL8 package got you the J56 front brakes plus a whole different rear axle assembly to suit the rear discs (just like a HZ or WB). JL8 was recognised for Transam racing which was under FIA Group2 which aligns with what you found, so probably just carried through into Gen2 Camaro homologation for 1970-1972 even though you could not option a road going Gen2 with it. Which ultimately means KB was not recalling the facts right when he made the statement that rear discs were optional and accepted under FIA Group1. They were fitted to later 70’s Pontiac Transams (like Trigger from Smokey and the Bandit) though. Maybe KB should have run a Transam with a 400 or 455 Pontiac engine or the 1977 403ci Olds engine!

Looks like in Corvette J56 got you 4 wheel disc brakes.

Upon the Camaro recognition documents FIA #5310 (Group 2 only) the J56 Heavy Duty Disc Brakes Option is listed as:
Part number 3957992 - Front Hub & disc W/Caliper LH
Part number 3957993 - Front Hub & disc W/Caliper RH
Part number 3965733 - Rear axle W/Disc brakes.

What is interesting is all specifications and pictures of the J56 package have had the rear brakes information crossed out which would indicate the rear discs were never factory fitted to at least the 1000 cars required for Group 2 homologation.

If we then look at the FIA rules for Group 2 we find that specific options were allowed in Group 2 without reference to minimum build numbers - Brakes, Brake Calipers and brake cooling equipment was one of those options. As long as any person, without prejudice, could walk into their dealer and purchase such optional equipment.

I think this sentence by the author holds the answer.
Quote "The inclusion in the 1968 documentation apparently was either in preparation for a proposed option release that never occurred, or as part of a subterfuge for convincing racing authorities that the 4WD brakes were a factory option and thus qualified for Trans Am racing use. "

Would appear that the American Trans Am Series was initially contested by cars that were recognised as FIA Group 2 but changed in '73 to more of a GT category, then in '76 reverted back to it's roots in Improved Production.

Quote from Wikipedia: In 1976, the Trans-Am Series returned to the two category (class) format, classifying FIA (Fédération Internationale de l'Automobile) Group 4 and 5 cars as "Category 2".

Edited by user Saturday, 9 January 2021 10:54:32 AM(UTC)  | Reason: Not specified

A9X was a standard vehicle though with pollution engine. I get CAMS making them go back to a standard vehicle which A9X was. It was an evolution of type of a standard SLR or SS. So A9X then should have been able to race as it had in 1979 but with the XT4 heads and intake. In 1980 it looks like they still got to keep wheel flares, Salisbury, T10 and A9X front suspension. But lost the boot spoiler, bonnet scoop, rear discs and the L34 engine. If they had switched to sedans in theory they should have been able to keep the boot spoiler?

Actually, in theory, rather than try racing a hobbled hatchback in 1980 Allan Grice could have either got hold of an old race L34 or an A9X race sedan (surely there would have been a glut of either of these around) and raced as an L34. It wouldn’t have been hard to convert a 1977-79 GroupC sedan back to L34, would just need a HZ 6cyl passenger banjo housing and shorten it to suit L34 axles (avoids modifying the floor again as a HZ banjo uses the same UCA mounts as the A9X Salisbury). Remove the bonnet scoop and possibly change the front crossmember back to L34. Plus put an Aussie 4spd back in. It’d get to keep its performance but get the fragility of the driveline back.

Edited by user Saturday, 9 January 2021 7:32:30 PM(UTC)  | Reason: Not specified

I know that, but they weren’t. The argument that they were made to run an LX SS hence the removal of the L34 heads, rear spoiler, hood scoop and rear discs doesn’t wash as the car still has other A9X bits.

It is seeming more and more like the CAMS did in fact bar the A9X from competing in 1980.
Under the revised 1980 Group C rules there were more freedoms than there were in 1979.

The STD SS 5000 L31 engine could be built up to as good as or better than L34 spec with the exception of the std L31 valves and inlet manifold.
Engines could now have dry sump oiling systems too.

The rules state 'it is permitted to fit mudguard flares as described in the relevant recognition documents as issued by CAMS'.

'Gearbox and final drive ratios must be as nominated on the recognition documents'.

The above rules should account for how a garden variety SS 5000 could compete with A9X flares, T10 and Salisbury drum brake rear axle assy.

And for the 1st time the rear axle assy could be modified to be fully floating.

Edited by user Sunday, 10 January 2021 9:19:00 AM(UTC)  | Reason: Not specified

If that was the case they’d have stopped Torana being competitive after 1977 or at least the start of 1978 as Commodore went on sale in 1978.

Question. VH Commodore SS (not HDT) gone on sale since March 1982 (1982 MY) or September (1983 MY)? Groups 1,2,3 since Summer 1982, so I'm sure since March, but some sources write that September.

Thanks.

Both. VB had TH400 and changed to TH350 mid 1979 when HZ did. TH350 was replaced by Trimatic late in 1981 during WB and VH.