I’m working on the front S calipers on the GT build and hit a snag.
The pads do not seem to be for this application. Wondering if different pads are warranted. I know these Porterfields have more meat on them. That could be the reason.
The pistons are seated all the way in. (Fresh rebuild). I even tried moving them with a wooden dowel. They budge just enough to collapse seal slightly but when relaxed sit as they are. Am I doing it wrong? Help appreciated!! Note: no fluid in system yet.
Any brake pad recommendations?

Pics

Remove the backer plate ?

I seem to recall that is what I did with S brakes and Porterfield pads. But I am not certain.

I’m not against that if It won’t disintegrate as I destroy it:-)? I know it handles brake forces. It would prolly yield breathing space. But....

I be worried they would squeal like a mofo if you pulled the plate. No?

Let's turn on the Bat Signal and see what the super hero says: @Eric_Shea

Sand the pads a bit?

Take off the backer plate & run them...after a bit of wear you can fit the plate back in if they're squealing....
Also it's the seals that are pushing the pistons a bit proud of being fully seated....so you could try slipping in the backer plate first then wedging the pad in--might work...

Are you sure you have the right rotor paired with those calipers? Looks too wide.

Not much space between the rotor and the caliper housing to account for lateral hub deflection. A bit hard to tell what the gap is between the rotor and the caliper housing from the photo's but looks tight.

A rotor that is a couple millimeters too wide would explain why the pads don't fit and would need pad compound taken off to fit.

If rotor is correct, I'd machine off pad material before I took off the backing plate noise isolator.

Regardless . . . go with whatever Eric chimes in with.

Phil the rotor is one that was recommended for this set-up. I’d have to find the box for specs. Thanks. Hopefully Eric may chime in. Thanks Brent for alerting him :-)

Thanks John. This is an option. Thanks guys.
I was also checking the 911S registry. Seems like Textar was well received brake pad.
Wonder if the dimensions would be different.
The porterfields have a nice rep for performance/track combo. I’m not sure I’ll be doing
“Track” events but mostly street/autocross. Maybe the Porters are just too large.
Maybe just order the textar and see. Thinking out loud ....
Appreciate the input as always. Keep the info coming.

I'm not an expert on S brakes but I was under impression that the early S rotor was 20mm thick for front and rear.

Quick check with calipers, micrometer or even a tape measure would be quick rationality check.

The smart move would be to phone PMB.

Looks to me that the rotors are too thick. Here's a pic of a new Sebro rotor from Pellican. I'm redoing the system on my 74 but essentially back to stock. Click to view attachment

S was running vented rotor...

Measured the vented rotors. They are 20.3mm thick.
I’ll massage these pads. I will probably order different pads. I’ll call Eric on Monday. Thanks fellas.

Sounds like the right size rotor. Carrera rotors are 24mm.

Yup - you're good on rotors.

It's likely the noise isolator adding thinckness. Back in 70's - pads didn't usually have noise isolators. Just the bare backing plate. Noise fix was often "brake grease". Even if there was a isolator, they were often clip on affairs with limited effectiveness.

Modern bonded constrained layer noise isolators are more way more effective than brake grease and clip on isolators of old.

You would think Porterfield would have removed enough pad compound to offset the added thickness of the isolator.

We used to machine pad compound all the time to insert thermocouples and/or for custom rotor setups. Easy to keep it all square with a mill.

Can be also done sucessfully with careful measurement, marking / guide tape, and use of belt sander to keep the pads square and level. Use shop vac to suck up all the dust as you "sand" the pads.

Thanks Phil.

Looks like a 24mm Carrera rotor. S-calipers take 20mm. Hard to tell from pictures but that rotor groove appears VERY tight.

@Eric_Shea Thanks for checking in. Haven’t had a chance to ring ya.
Here’s a pic of caliper measurements. 20.3mm Sebro. I ordered some “ate” pads from your store just to see any pad thickness variation. Thanks mate.

From Porterfield's information:

Porterfield 45T pad is 0.75" thick
Porterfield 45 pad is 0.59" thick

The thicker pads can be milled or sanded thinner.

@Driver174 thanks so much for that info! appreciate that.

I recommend pulling the backing plate off the 45T's. That's standard procedure here.

Also, on new pads, new rotors and S-Calipers, it is not unusual to have some rubbing until the pads have been bedded properly. The "knockback" mechanism in the pistons is designed to push the pistons out a bit keeping them right on the pad and facilitating a higher pedal in the cockpit.

Finally, crack a bleeder when installing brand new pads on brand new calipers and brand new rotors. New seals in the caliper can contribute to pistons being pushed out excessively. New pads with (again) the backing plates that they began installing over the last two or three years (still don't like them) can be a few .000's thick. Cracking a bleeder allows each piston to relax to their base position allowing you to insert the pads. Don't be alarmed if there's rubbing however, the wheel should turn by hand. A bedding session will have you in perfect form.

Hope that helps.

P.S. I don't recommend milling pads. The material is extremely abrasive. To do it properly will take some specialized carbide bits and a good mill.

Perfect info Eric, thank you very much. Will heed the advice. Always learning.
This is very helpful.

So the “Ate” pads came in. They fit perfectly. Did a measurement. To compare with @Driver174 findings. 0.71” was the measure. Rotor turns freely. No binding.
Fellas.

Gotta' be nice to have that figured out!