I posted this in the paddock, but didnt get much traffic over there.
I have three calipers ready to put back together on my bench and I am waiting to make the decision based on this question below.

Anyone here ever modified their calipers by breaking out the knock back pins?
As usual Eric's site has the most information regarding these pins, but he doesnt go into detail about the possible benefits of doing so.
I was hoping to hear from at least one other racer that has done this, why, and what were the results?
And.... just to confirm: it is the late front calipers that fit the rears , correct?
(I have measured, but not test fit them yet)


Based on some advice from other racers, I am installing some front calipers on the rear of the race car.

Currently I have stock front calipers, stock rears, and a 19mm MC, and still have the stock rear prop valve.

I have a few sets of late front calipers that I disassembled to rebuild for this change.
One of the calipers had the pins for the knock back mechanism broken out by some previous owner.

I understand that the newer A-calipers do not have this mechanism from the factory.

How many others here have done the front caliper installation on the rear?
Did you keep the rear prop valve, or go for an aftermarket like the tiltons?
Has anyone heard of breaking out the knock back pin?
If so, what advantage is this supposed to provide?

Should I use calipers with the knock back system intact, or should I break the pins out of another caliper so I have a matched set?

I plan on running KFP Gold pads on the front and Porterfield AP31T R4-S pads on the rear for some front bias.

Any more tips or tricks ?

Not Porsche, but Datsun (NOT NISSAN). The front calipers had knock back pins. On the race cars, we broke the pins out to make sure the pads "retracted" away from the rotors due to the intense heat generated in SCCA racing. Can't say that it was an approved method, but several Regional and a few National Championships said we didn't do anything wrong.

We started pulling the pins after a race at Firebird in Arizona. When the front brakes caught on fire due to fluid boil and distended piston seals we figured we had to do something. Yes, we had brake cooling ducts to the front calipers/rotors.

Ever tried to find caliper seals on a Sunday? Ran the race with rear brakes only as I had plugged off the front calipers.

G Production - 2 car team

SLITS - thanks for the input.
I guess I will remove the pins on the second caliper and run without the knockback pins.

Anyone else have any experience with theses pins and racing applications?

Forgive me for not understanding... do you mean knockback "clips"? That's what I'm thinking in my head at least. The term pins has me confused. Interested in what you're talking about though Stu.

Heres the difference:
the caliper on the left came with both pins missing cleanly.
I figured it must have been intentional so I looked into it.
Some apparently DO remove these pins.
So since I cant replace pins, but I can remove them, I think I going with the 'remove them' crowd.

You need to use the early offset calipers. There is a difference Btwn early/late.

I can't fully remember but perhaps a spacer on the mounting points can allow the lares to work.

AH, that makes more sense. I traded out the front calipers early on when I got my car, so I never got to see the pistons out. The BMW calipers I have now didn't have those pins. We tracked it for 10 hours with no problems. I got myself in the habit of doing a left foot tap of the brakes on a long straightaway for pedal feel a long time ago, but it never really was necessary with my setup. The brakes (Porterfield R4-1 pads) were right there every time.

Brant thanks! Your comment made me check again.
I had selected the calipers with the correct offset from my pile.
I just had not labeled them correctly as late vs early.

So Early front calipers fit on the rear.


Time to order a few more rebuild kits from Eric

Of course Murphy's law - when I rebuilt a pair to put on the front, I chose late calipers at random (and then got the correct rotors to match).
If I had picked Early, then now I would have the same type all the way around.
Now I'll keep two spares, one early & one late.
At least I have one of each with dual bleeders so theyll fit on either side.