Do I have two different front brakes?

[drcoastline]

I have a 1974 911S Targa. While addressing some minor rust issues I decided to remove the front suspension to clean, paint and freshen up the components.

Today I removed the brake calipers in order to clean and make a list to replace worn components. I blew air into each caliper to release the pistons. One piston from each caliper came out. The other remained. At the moment I have them soaking in PB Blaster. I will try again tomorrow to blow out the other pistons. I noticed that the piston that came free from each caliper was opposite the brake line. When the pistons came out I also noticed that they are different. The cylinder inside the caliper also appears to be different. The cylinder from the driver side has a stud where the passengers side caliper does not. Also, both pistons measure 48mm.

The caliper on the left in the photos is the passenger side.





Thank you in advance for your help and thoughts.

Don

[Flieger]

The one on the left appears to have been rebuilt at some time using the more modern, cup/inverted style piston which reduces the brake fluid's exposure to the extreme heat of the pad/rotor interface. The one on the right has the original anti-knockback mechanism that keeps the pad close to the rotor for quicker brake response.

It is fine to mix styles.

[drcoastline]

Thanks Flieger,

That makes me feel better. Do I need to split the calipers to get the anti-knock back mechanism out?

[Flieger]

If you had special tools probably not, but I would ask the expert on early calipers, Eric Shea at PMB Performance. On Pelican he is "Eric_Shea".
PMB Performance: We Don't Rebuild Your Brakes... We Restore Them

[drcoastline]

Thanks again. I will co9ntact Eric.

[Eric_Shea]

Hey Don,

Max is correct, one of your M-Calipers has been replaced at one time. Probably by the dealer as they simply used a superseded part.

You sent an email about piston positions; did you get the other two out? If not, you need to cap or plug the bore that the pistons came out of and then go again with the air. If air doesn't do it then you will need to use fluid. McMaster-Carr has some rubber plugs that can fit in those bores. You'll need to fab a scab plate to hold the plug in place while you extract the other two pistons. You may have to drill a hole 1/2 way through the plug to accommodate the knockback pin in the original caliper.

Positioning them is rather simple: Draw an imaginary line up the center of the pad cavity. Place your lower notch on this meridian with the cutout facing the bleeder at the top. If your lower notch is on this line your pistons will fall naturally to the 20degree angle. I'm on my iPad but I'll try to find a link or a picture of what I'm talking about.

[Eric_Shea]

I can't upload the images with my iPad but here's an article for you that I drafted on 914world.

914World.com - A Porsche 914 Community / Forum / Club

[djdsc]

[drcoastline]

Eric tahnks for replying to my email. djdsc thanks for the diagram.

At this point I am still trying to determine if my calipers are rebuildable. I think the passenger side is but the driver side I am not so sure. There appears to be a bit of rust on the cylinder. At this point I am trying to determine if this is something I want to tackle or just send them to you Eric. Also I checked out your website and i see the SC calipers are the same price. Is there any benefit of me changing to those? Is this a straight bolt on application or do I need to change other components. This car is a weekend driver with the occasional DE event.

Thanks again for your input.

[Eric_Shea]

You would need SC cores for that price and, you would need 3.5" struts. "And" I'm not a fan of SC calipers (A-Calipers) but don't let that sway you...

Those are the heaviest calipers Porsche ever put on a 911. They are a garden variety sedan caliper used on BMWs, Alfas and Mercedes, they were also on the Ferrari 308s. At 9lbs. 6oz they're 4lbs. heavier than an S-Caliper.

That said, those are a fine caliper for most applications and I'm probably picking nits about the weight. It would just be a lot of work (new struts) and money (new struts) that probably isn't needed.

I wouldn't worry about the rust issues. Tear them down and take them to a local zinc plater. Once you separate them you will see the original yellow zinc plating on the mating surfaces. ATE calipers were zinc not cad. They should come back rust free.

[drcoastline]

Thanks again Eric,

I'll keep working on my Calipers. I appreciate all your help.

[83_Silberpfeil]

Originally Posted by Eric_Shea

I wouldn't worry about the rust issues. Tear them down and take them to a local zinc plater. Once you separate them you will see the original yellow zinc plating on the mating surfaces. ATE calipers were zinc not cad. They should come back rust free.

Eric ---

For replating with zinc, I saw on your website's video, that you don't mask/block-off the caliper bores. You just plate the whole unit. Would there be any reason or advantages/disadvantages to mask/block-off the bores?

Thanks!
Jonathan

[Eric_Shea]

You want the bores plated. Otherwise you'd have fresh steel on steel. I don't believe in brake hones for that reason as well. If you feel you must hone, hone before you plate.

[83_Silberpfeil]

Originally Posted by Eric_Shea

You want the bores plated. Otherwise you'd have fresh steel on steel. I don't believe in brake hones for that reason as well. If you feel you must hone, hone before you plate.

Thanks for the advice Eric.

I've started splitting my calipers. On 1 front SC "A" caliper, I used a grease gun and removed 1 piston easily (the side/half that has the brake line). The other piston moved about 1/2 way out.

I proceeded and split the calipers halves. What now? What's the best way to remove the 2nd piston?

Also, now that I have all that grease in the bores and inside cavity (where brake fluid flows), what's the best way to clean all that grease out?

BTW --- here's my first post (of on-going series) on my rebuild...

83 SC - Caliper full tear down and rebuild


Thanks!
JC

[Eric_Shea]

What now? Put them back together until you get the other piston all of the way out.

It has more than likely cocked in the bore. You will need to look down and asses the angle and use a large screwdriver to realign the piston.

For the fluid journals, they are straight bores. Blow them out with compressed air or, use a coat hanger or other suitable straight object to get the mass quantities out then follow up with brake cleaner.

[cdrik915]

Strangely , i have had the same problem on my 2.4 E /1972 , that comes from usa.

Rear right & left calipers came from two differents cars.

Exactly the same differences than shown on the pics.

One came from a 69' model , the other was original one.

[Eric_Shea]

It's a very common issue guys.

Imagine you purchased a 72E back in 1972. Four years later you went to the dealer complaining the car pulled to the right under braking. They didn't restore calipers back then, they simply went to the shelf and bolted on the latest model.

In or about 1975, ATE switched from the "Knockback Pin" method to the "Cup Style" pistons. All later M-Calipers, Rear M-Calipers, A-Calipers etc. had these newer cup style pistons. They're easier to install. No complicated pin mechanism and more surface area for better fluid cooling.

So... there's probably hundreds of cars driving around out there with this situation.