Mismatched front calipers on 911 SC suspension swap – help identifying? Options

[Nana's_914]

My 914 has front suspension swapped over from a donor '78 911 SC. The left front caliper recently started dragging hard, and when I pulled things apart I noticed the two front calipers don't match.

They share the same bolt pattern, pad size, and hose connections, but the castings are numbered differently. On closer inspection the center spacing (the gap between the halves) is also different, and the right caliper seems too wide for its rotor.

Right side: ATE, halves stamped 25G and 26G, center spacer about 11 mm
Left side (the one dragging): one half stamped ATE 281, the other half unmarked, with squared-off edges instead of the smoother blended shape of the other castings, center spacer about 7 mm

Both rotors measure about 20 mm thick.

Can anyone help me identify what I have, and which one (if either) is correct for this setup? Photos attached.

[bdstone914]

Oops

[bdstone914]

You have one early A caliper and one later A style calpier. The caliper with the 11mm spacer is meant to be used with a 24mm rotor.
It works but rhe pistons start by sticking out 2mm more.
To change it to match you would need a pair of spacers and shorter bolts.

[Nana's_914]

You have one early A caliper and one later A style caliper. The caliper with the 11mm spacer is meant to be used with a 24mm rotor.
It works but the pistons start by sticking out 2mm more.
To change it to match you would need a pair of spacers and shorter bolts.

Thanks! Sounds pretty straight forward.

[Nana's_914]

Follow-up question: since I've already got one wide Carrera caliper, I'm thinking about going the other direction and converting the left side to match, then running 24 mm Carrera rotors on both sides.

Are the 24 mm Carrera rotors a straight bolt-on for my SC hubs, or do I need Carrera hubs?

[Luke M]

Follow-up question: since I've already got one wide Carrera caliper, I'm thinking about going the other direction and converting the left side to match, then running 24 mm Carrera rotors on both sides.

Are the 24 mm Carrera rotors a straight bolt-on for my SC hubs, or do I need Carrera hubs?

The 74 to 89 911 hubs are the same. Swap out the rotors and caliper with the Carrera stuff and your good to go.

[Superhawk996]

Follow-up question: since I've already got one wide Carrera caliper, I'm thinking about going the other direction and converting the left side to match, then running 24 mm Carrera rotors on both sides.

Food for thought:

Ask yourself why you want to add more:
weight to the car as a whole
Weight to unsprung mass - degrading ride and handling
Weight to rotational mass - slowing acceleration.

Knowing that 24mm rotors won’t decrease your stopping distance.

Unless you’re having issues with brake fade at track days, 24mm rotor effects are mostly negative.

[bdstone914]

Follow-up question: since I've already got one wide Carrera caliper, I'm thinking about going the other direction and converting the left side to match, then running 24 mm Carrera rotors on both sides.

Food for thought:

Ask yourself why you want to add more:
weight to the car as a whole
Weight to unsprung mass - degrading ride and handling
Weight to rotational mass - slowing acceleration.

Knowing that 24mm rotors won’t decrease your stopping distance.

Unless you’re having issues with brake fade at track days, 24mm rotor effects are mostly negative.

(IMG:style_emoticons/default/agree.gif)
No advantage to add more rotating unsprung rate.
Your would need to change the narrow spacer caliper to accept the 24mm rotor.

[Nana's_914]

Follow-up question: since I've already got one wide Carrera caliper, I'm thinking about going the other direction and converting the left side to match, then running 24 mm Carrera rotors on both sides.

Food for thought:

Ask yourself why you want to add more:
weight to the car as a whole
Weight to unsprung mass - degrading ride and handling
Weight to rotational mass - slowing acceleration.

Knowing that 24mm rotors won’t decrease your stopping distance.

Unless you’re having issues with brake fade at track days, 24mm rotor effects are mostly negative.

(IMG:style_emoticons/default/agree.gif)
No advantage to add more rotating unsprung rate.
Your would need to change the narrow spacer caliper to accept the 24mm rotor.

Good points. It looks like the 24 mm rotors are about 1.5–2 lbs heavier each, and there isn't much to gain in actual braking performance.

[Nana's_914]

While reviewing the rest of my brake system, I found the master cylinder leaking at the rear hardline connection, and the rear pressure regulator has been deleted.

The master cylinder is a 19 mm ATE, and it seems worth rebuilding while everything is apart. It has a bit of rust on the outside, but under the boot it looks pretty clean. I'm also thinking about replacing soft and hard lines while I'm in there.

Should I add the rear pressure regulator back in, leave it deleted or is there a better option.

[Superhawk996]

Should I add the rear pressure regulator back in, leave it deleted . . .

You’re asking good questions

More food for thought:
How comfortable are you with the possibility of swapping ends on a mid engine car (ie spins quickly) if you have the rear brakes lock up?

Do you know and understand all the various conditions that make this more likely to happen?

How judgement proof are you should the worst occur on-road and you are found at fault for a potential fatality or serious life altering injury?

Do you know what this chart that is showing how the rear regulator works is telling you?



If you can’t answer those questions with certainty you’re better off putting the regulator back on the car.

My background: automotive engineer that has designed brake systems, tuned ABS, ESC, etc.

[Shivers]

I have heard that these cars can misbehave without it under hard braking.

@Nana's_914

[Nana's_914]

Should I add the rear pressure regulator back in, leave it deleted . . .

You’re asking good questions

More food for thought:
How comfortable are you with the possibility of swapping ends on a mid engine car (ie spins quickly) if you have the rear brakes lock up?

Do you know and understand all the various conditions that make this more likely to happen?

How judgement proof are you should the worst occur on-road and you are found at fault for a potential fatality or serious life altering injury?

Do you know what this chart that is showing how the rear regulator works is telling you?



If you can’t answer those questions with certainty you’re better off putting the regulator back on the car.

My background: automotive engineer that has designed brake systems, tuned ABS, ESC, etc.

Thanks, that's a pretty convincing argument. Not spinning and dying is high on my list of priorities.

[porschetub]

While reviewing the rest of my brake system, I found the master cylinder leaking at the rear hardline connection, and the rear pressure regulator has been deleted.

The master cylinder is a 19 mm ATE, and it seems worth rebuilding while everything is apart. It has a bit of rust on the outside, but under the boot it looks pretty clean. I'm also thinking about replacing soft and hard lines while I'm in there.

Should I add the rear pressure regulator back in, leave it deleted or is there a better option.

Any rust in the master will deem it ususeable ,you can hone the bore but generally reveals the pits in the bore ,again bin material ,not a part I would trust in this application (high risk ) area.
Yes refit the regulator ,these cars were never supplied with parts they didn't need ,certainly need to use that ,cheers .

[JamesM]

While reviewing the rest of my brake system, I found the master cylinder leaking at the rear hardline connection, and the rear pressure regulator has been deleted.

The master cylinder is a 19 mm ATE, and it seems worth rebuilding while everything is apart.

In the case of brakes, when the professionals don't rebuild something you generally shouldn't either.

Master cylinders are a replacement part.

Sort of sucks as the 19mm ATEs have become rather pricy, but its better than killing someone.

[Superhawk996]

While reviewing the rest of my brake system, I found the master cylinder leaking at the rear hardline connection, and the rear pressure regulator has been deleted.

The master cylinder is a 19 mm ATE, and it seems worth rebuilding while everything is apart.

In the case of brakes, when the professionals don't rebuild something you generally shouldn't either.

Master cylinders are a replacement part.

Sort of sucks as the 19mm ATEs have become rather pricy, but its better than killing someone.

As I read it I think he’s saying it was leaking at the outlet port probably due to a flare nut not having been tightened fully or maybe a damaged flare.

If the master isn’t leaking out the back where the pushrod actuates the M/C it should be OK and there shouldn’t be a need to rebuild a master cylinder.

[JamesM]

As I read it I think he’s saying it was leaking at the outlet port probably due to a flare nut not having been tightened fully or maybe a damaged flare.

If the master isn’t leaking out the back where the pushrod actuates the M/C it should be OK and there shouldn’t be a need to rebuild a master cylinder.

Oddly enough, every time I do complete caliper replacement on any older vehicle the master seems to die shortly after.

[Superhawk996]

Oddly enough, every time I do complete caliper replacement on any older vehicle the master seems to die shortly after.

Yeah that can happen in cast iron M/C

Under normal use m/c pistons don’t travel full stroke.

Corrosion more apt to form at untraveled end.

Then you drain fluid and have to full stroke the m/c when bleeding. Seals travel over pitting & corrosion and get torn up. Leaks then start.

It’s a good part of why the industry has migrated to aluminum master cylinders.

[Nana's_914]

As I read it I think he’s saying it was leaking at the outlet port probably due to a flare nut not having been tightened fully or maybe a damaged flare.

If the master isn’t leaking out the back where the pushrod actuates the M/C it should be OK and there shouldn’t be a need to rebuild a master cylinder.

Yes, was leaking from the rear line connection. The inside bore of both fitting ports and under the rubber boot looked pretty clean. I am hopeful that it looks OK inside. If so, I'd like to replace the old rubber seals.

I can't believe the 19mm ATE MCs are so expensive now. Is it the same as Porsche Brake Master Cylinder 911-355-012-02
Is URO not worth buying?

[porschetub]

As I read it I think he’s saying it was leaking at the outlet port probably due to a flare nut not having been tightened fully or maybe a damaged flare.

If the master isn’t leaking out the back where the pushrod actuates the M/C it should be OK and there shouldn’t be a need to rebuild a master cylinder.

Yes, was leaking from the rear line connection. The inside bore of both fitting ports and under the rubber boot looked pretty clean. I am hopeful that it looks OK inside. If so, I'd like to replace the old rubber seals.

I can't believe the 19mm ATE MCs are so expensive now. Is it the same as Porsche Brake Master Cylinder 911-355-012-02
Is URO not worth buying?

Some members on here with Uro M/Cs have had issues from what I have read ,what the issues are I don't know ....could be QC ?? ,