Vintage 911S Caliper Restoration Thread

[Neunelfer]

Hi Gang,

Andy Seward (Nordschleife here) sent us his vintage 911S calipers for restoration. I thought the process might be of interest to those here.

These are fairly rare calipers as they represent the first time ATE used the spacers on these calipers for vented rotors on a road going Porsche. The fronts are your basic 911 M-Caliper but there are some different indentations in these early castings that make them noticeable and unique. These calipers used 8M fasteners with R8 Ribe heads. To allow vented rotors these M-Calipers received 7mm spacers. The piston is the standard 48mm steel variety that we saw on all 911 front calipers through the Carrera caliper (A-Caliper with larger 17mm spacers).

The rears are a new version of the first L-Caliper called the Wide L-Caliper. These are differentiated by 7mm hardware (vs. 6 on the first series) with R6 Ribe heads and, 10mm spacers to allow for the vented rotors. Each 1/2 of an L-Caliper is a closed circuit similar to our beloved S-Caliper hence there are crossover lines feeding the other 1/2 of the caliper. There are no seals in the caliper 1/2's or the spacers. These first 911 rear calipers used a 35mm piston. When the rear M-Caliper debuted on the scene the 911 saw the 38mm rear piston that would stay through 1983. We recently finished a set of L-Calipers for Jamie Torres but neglected to get photos. They had the 6M hardware and no spacers.

A lot of these early steel calipers are locked up solid. After sitting for years in a field, junkyard, barn or garage they are all but immovable. The old "blow some air in them to pop the pistons out" method can be tossed out the window but, if you're like me, you don't necessarily want to toss vintage 911S calipers out the window. 99.9% of these calipers can be restored. I mention restored because I cringe every time I see some of these cool calipers being rebuilt and the owner sprays some zinc. plating "look-alike" paint on them and then proceeds to bolt them on his or hers $30,000 car...

The idea here is to show the process of properly restoring these calipers to like or better than new condition so you can emulate it yourself and do the job right. On with the show:

Here are some pictures of the tear down of these calipers. First the M-Calipers:


...and the Wide L-Calipers with the 10mm spacers and crossover lines:


Here's the interesting part, these SWB cars had 2.25" spacing out back:


Here's a close up of the Ribe R6 head on the L-Caliper. A Ribe bit set is required if you are going to tear down virtually "any" Porsche ATE caliper. Torx are "similar" but, the demands of some of these rusty fasteners will quickly demonstrate the differences and you will have a worthless priceless 7mm fastener (every try to source any 7mm hardware letalone Ribe?)


A look at the underside of the rare Wide L-Caliper. The inside piston has been stuck for a while:


Let's get dirty. We first start by taking off the crossover lines. Be "extremely" careful with these. We use the proper 11mm line wrench and go slowly. If you feel or see any twisting of the line STOP. Use PB Blaster and a torch to get it into the joint and start over. If you've torched it, wait for it to cool or you'll simply twist the lines.


After the lines are off we plug the inner 1/2 hole with a plug and get ready to literally pump the piston out:

[Neunelfer]

In preperation for the pistons removal you'll need to remove the old dust cover and clips. A set of dental picks is priceless here:


Classic example of a damaged dust cover that will let moisture in and rust your piston:


Yes, new kits are available for these older calipers:


With that out of the way the caliper is prepped for piston removal. Your first method would be air. If your calipers are on the car and working fairly well with decent fluid, you might have a shot at air working. Pad the opposite piston face with a complete piece of paper towel folded in 1/8's:


In our case, air will not work. One of the most accessible solutions for the home mechanic is an air powered grease gun. Fluids, like grease, will not compress. They will simply force the pistons out. You'll have a blast cleaning up afterward but, you've just saved a set of priceless calipers. Get the El Cheapo Harbor freight gun and unscrew the tip... the threads are an EXACT match for the fluid inlet on all ATE calipers:


Miracles do happen. What seemed impossible slowly starts pushing out:


With the pistons out, the caliper can be disassembled. A look at the inside, which has been hiding for 40 years, shows the original yellow zinc coating. Everyone thinks that calipers are Cad because Porsche used Cad on most of the yellow fasteners and latches. Well, Porsche didn't make these calipers, ATE did and ATE uses Zinc. Zinc has a superior corrosion resistance over Cad. Here's the unique 10mm spacers:


The fasteners will be sent out to receive the proper black coating as well. Again, 7mm Ribe hardware is NLA so this stuff has to be handled with care:


Here's a shot of the bore which is suprisingly clean:


And finally, the pistons. These are actually in excellent shape. What many mistake as rust is actually coked on brake fluid. A simple polishing wheel will remove all of this and give these pistons a nice mirror finish. The tops will then be prepped and painted with a grey heat paint to emulate the factory finish:


Next we'll dig into the M-Calipers.

[Neunelfer]

Here's the M-Caliper in the vise. You can see one of the unique notches in the early castings above the last fastener by the spacer. The calipers halves here are interactive meaning fluid passes through on both sides and what affects one piston can affect the other. Because of this I like to clamp off the outer piston and force the inner piston out first. Then I take a special plate with a rubber gasket and cover the bore left by the inner piston. Once that is properly blocked off the outer piston now comes out.

Again, grease had to be used on these old calipers:


And they're out... as with the other steel pistons we saw in the L-Calipers, these are actually in excellent shape. The only problem pistons I've seen are S-Caliper pistons. 99% of all S-Calipers I restore have bad pistons. The factory plated these pistons due to issues with dissimilar metals. When these pistons sit for an extended period of time (and they do), the plating will flake and rust right where it sits against the inner seal. Here are the M-Caliper pistons:


Here's a shot of the 7mm M-Caliper spacers. You notice the indented area for the caliper 1/2 seals. New seals need to be used when putting these back together. These seals are "not" included with a caliper rebuild kit. We have them if you're doing your own project:


8M Ribe hardware ready to be recoated...


And the cores ready for the yellow zinc plating:


I'll finish up the pistons and post those while the cores and fasteners are off being plated.

[Mr9146]

GREAT THREAD!!! Eric, thanks for the in-depth descriptions and photos. Also, what's the name and contact info of your company.

[Neunelfer]

Thanks Marco!

PMB Performance
www.pmbperformance.com
855-STOP-101 (855-786-7101)

The 911 section and the caliper restoration section is under construction but... any free time I get (which isn't much) goes to adding more parts and goodies.

We currently specialize in vintage caliper restoration of:

L-Calipers
M-Calipers
Rear M-Calipers
A-Calipers
S-Calipers
914 Calipers
914 Rear Calipers
914-6 Calipers
914-6/GT Calipers (we've done a number of factory GT's and we can build GT calipers from -6 cores)
Ferarri 308 GT Calipers...

...etc.

[Bert]

Excellent thread. Thanks for sharing with this brake caliper rebuild information.

[68911+1]

=Neunelfer;

Yes, new kits are available for these older calipers:

This is such a great thread I just wanted to clarify that the above part number is for the 911 and 912 35mm rear caliper kits not the 38mm S calipers.

The '67-'68 S/L rear caliper kits are as below.

[Neunelfer]

Oooooooops. You are correct. I apologize for the error.

Here's another tip: In most cases the kit above is NLA so you can order the early 911 L kit (which has the proper dust boots) and use the later 911 rear M-Caliper kit (38mm) for your bore seals. Hope that helps somebody.

Eric

[Neunelfer]

Well, Andrew's calipers came out of plating today. We were able to get the basic assembly handled with the exception of the "bolting them together" part as we're waiting for the fasteners to come back from a separate shop.

They look a little better no?


Here's the M-Calipers:


And the L-Calipers with all their bits and pieces:


The pistons polished up nicely. We put the dust covers on at this stage of the game. They're some of the major components of a rebuild kit:


Next you install the piston seal. This is another one of the major components in a rebuild kit. You simply drop them in the groove and work them around:


Finally they fall into place:


After the seal is in we like to slather on some brake grease. Make sure you use brake grease because other greases will harm and swell the rubber seals:

[Neunelfer]

Next we align the pistons in the bores and get ready to press them in. There are notches in the piston tops that should be facing 20 degrees into the face of the oncoming rotor, meaning; they are position in the direction of the forward rotor movement. We simply use an old positioner for these. The ATE kits no longer come with the positioners but, if you get them in right the first time, they're really not needed. These pistons don't move around much. For even pad wear though, it's important to get this right.

Old positioner on the rear passengers side inner caliper 1/2:


Next you push in the piston. We use a hand press but I have a picture of how this can easily be accomplished in a standard vise:


Snap the retaining ring on the dust cover...


...and your good to go:


M-Calipers too... everything is done awaiting the fasteners: