Printable Version of Topic

Posted by: vintage914racer Oct 14 2016, 04:28 PM

Without going into too much detail, the drivers rear caliper on my track car sheared a mounting hole and I need a replacement caliper. The thing is, I don't know what model the caliper originated on. I'm fairly certain they're 'A' calipers. Can any experts weigh in? I obviously need to find a replacement.

Posted by: vintage914racer Oct 14 2016, 04:29 PM

Posted by: gcrotvik Oct 14 2016, 05:04 PM

PM Eric Shea at PMB. He's Eric_Shea on this site. He will surely know.

Posted by: Dave_Darling Oct 14 2016, 05:24 PM

Does a magnet stick? Were the mounting bolt holes 3.5" on-center? Then they are likely A calipers.

--DD

Posted by: bdstone914 Oct 14 2016, 07:22 PM

it is a rear 911 based on the inlet orientation. No common 911 rear calipers were aluminum. which one depends on the thickness of the spacer between the halves. 911 SC calipers gave a 11mm spacers for use with 24mm thick rotors. I have some pairs that are cores. PM me

Posted by: Mikey914 Oct 15 2016, 11:01 AM

I know Eric has several new sets of these in aluminum with the aluminum pistons. If you want to cut weight, may be the way to go.

Posted by: Eric_Shea Oct 16 2016, 02:21 PM

That's a drivers side (left) 911 rear M-Caliper. 1969-1983

This caliper came with the new LWB cars and their new trailing arms. D31 Pad size. 38mm pistons. These had contoured flat top pistons, similar to 914 front calipers with the 20 degree angle cut in the piston top. These calipers all had knockback pins and mechanisms until 1976 when the pistons changed to a cup style (which is what this probably is based upon the casting numbers):

1969 - No spacers on standard 911's with solid rotors. 10mm spacers (not 11mm) on 911S models with 20mm (not 24mm) vented rotors.

1970 - All 911's moved to vented rotors. Spacers in these and the 69S cars were rounded and machined.

1973 - Spacers became molded, cast and then milled. They had a more precise fit (not that it matters, just more of an appearance issue).

1976 - When the cars moved to power assisted brakes, these calipers lost their knockback mechanisms and internal pins. The power circuitry kept a constant 2-3 PSI of residual pressure on the system. This is when the "cup" style pistons arrived on the scene. More surface area for cooling.

So, the same caliper lived on the rear of a 69 911T all the way through the 911RS and first 930's.

In 1984 the 911 became the 3.2 Carrera and it received a new caliper with larger 42mm pistons. This is the same time the 911 received it's first "Pressure Regulator" (not proportioning valve) like the 914 to prevent the larger rear pistons from locking up. This is when 14mm spacers were added to the rear calipers and the car received very heavy 24mm rotors.

What? TMI?

Posted by: Kansas 914 Oct 16 2016, 02:35 PM

That's what I was going to say but E beat me to it.....

Posted by: bdstone914 Oct 16 2016, 03:59 PM

I have this core caliper I can sell. Have the other one too if you want to get a pair and do a rebuild.


Attached thumbnail(s)

Posted by: vintage914racer Oct 16 2016, 04:02 PM

QUOTE(Eric_Shea @ Oct 16 2016, 12:21 PM)

That's a drivers side (left) 911 rear M-Caliper. 1969-1983

This caliper came with the new LWB cars and their new trailing arms. D31 Pad size. 38mm pistons. These had contoured flat top pistons, similar to 914 front calipers with the 20 degree angle cut in the piston top. These calipers all had knockback pins and mechanisms until 1976 when the pistons changed to a cup style (which is what this probably is based upon the casting numbers):

1969 - No spacers on standard 911's with solid rotors. 10mm spacers (not 11mm) on 911S models with 20mm (not 24mm) vented rotors.

1970 - All 911's moved to vented rotors. Spacers in these and the 69S cars were rounded and machined.

1973 - Spacers became molded, cast and then milled. They had a more precise fit (not that it matters, just more of an appearance issue).

1976 - When the cars moved to power assisted brakes, these calipers lost their knockback mechanisms and internal pins. The power circuitry kept a constant 2-3 PSI of residual pressure on the system. This is when the "cup" style pistons arrived on the scene. More surface area for cooling.

So, the same caliper lived on the rear of a 69 911T all the way through the 911RS and first 930's.

In 1984 the 911 became the 3.2 Carrera and it received a new caliper with larger 42mm pistons. This is the same time the 911 received it's first "Pressure Regulator" (not proportioning valve) like the 914 to prevent the larger rear pistons from locking up. This is when 14mm spacers were added to the rear calipers and the car received very heavy 24mm rotors.

What? TMI?

Posted by: bdstone914 Oct 16 2016, 04:30 PM

PM sent

Posted by: Eric_Shea Oct 16 2016, 05:21 PM

Bruce, let me know next time you dive the Titanic. I'd love to go along!

Suitable replacement would depend on the pistons. Are they cup style?

Posted by: vintage914racer Oct 17 2016, 08:26 PM

QUOTE(Eric_Shea @ Oct 16 2016, 03:21 PM)

Bruce, let me know next time you dive the Titanic. I'd love to go along!

Suitable replacement would depend on the pistons. Are they cup style?

Posted by: Eric_Shea Oct 18 2016, 03:48 PM

Those are cup style. They are cupped out vs. a contoured top.