Ate brake caliper rebuild question

D@vid · D@vid's Garage

Hi guys,
I'm rebuilding my ate brake calipers ('73 911T) front and back and seem to have some trouble sliding the "guides" (inside the piston) over the pin inside the caliper.
It will only slide over the pin with some force. Is this normal or should it slide down more easily?
I've removed the plating from the pin.

I greatly appreciate your help

With kind regards,
David

D@vid · D@vid's Garage

bump

mo-mon · mo-mon's Garage

Can't help you David but maybe these youtube videos can:
https://www.youtube.com/watch?v=dleSq_iViKk
https://www.youtube.com/watch?v=Wt3huX8llsE
https://www.youtube.com/watch?v=cvl5N2MLevg

D@vid · D@vid's Garage

Thanks,

Kav actually uses different calipers.
Mike has the same calipers as I do but there's no information in his video regarding the force needed slide the actual "guides" down the pin.
But he does go into installing the rubber seal and piston.

fizeus · fizeus's Garage

put the pin inside the piston, replace the collar gasket in the calipers and use brake fluid to lubricate all components.... then gently press the piston inside the caliper.

some resistence is normal

jtsilverfox · jtsilverfox's Garage

Hi David
I've had the same issue & question about the 'guide' and 'pin' inside of my ATE Caliper Pistons on my '69 911E, which I'm trying to rebuild.
I found the pistons on my front Calipers are very difficult to get back in. So I took them apart, removed the 'guide' (snap ring holds it in), and found that the lower sleeve slides on & off the pin just fine, but that there's a smaller diameter section at the top of the guide that the pin doesn't fit through. The lower sleeve and pin measures 5mm, whereas the upper part of the guide is only about 4.8mm (as best I can measure it).
I've been searching for info on this for many hours, and I can't believe that no one else has discussed this!!! (until I finally came across your 2'21 post & pictures).
I saw some comments that ATE may have did away with the guide & pin it subsequent years.
Have you found any more info on this? Is it supposed to be that tight of a fit? I'm tempted to just leave them out...
thanks, cheers, jt

djpateman · 06-25-2021, 09:18 AM

The bell shaped part is supposed to grip the pin. The purpose of the device is to allow the piston to move slightly along the pin out of the bore when hydraulic pressure is applied to the caliper. When the pressure is released, the spring inside pulls the piston back into the bore. The objective is to allow the hydraulic pressure to force the piston against the pads and the pads against the brake rotor to provide braking action. When the pressure is released, the piston is retracted by the device and the rubber piston sealing rings. This allows the venting clearance to be re-established so that the pads do not drag on the rotors when the braking action is not desired. As the pad wears, the device will creep along the pin, continually adjusting itself. I cannot really help guide you on the force required to force the piston into the bore, but it is significant. Just be sure to use the alignment tool to get the correct angle required on the front pistons as it is difficult to rotate the pistons after insertion.

jtsilverfox · jtsilverfox's Garage

DJ..., Thanks for the info! I didn't realize that there was a spring inside the 'guide', gripping the pin to help retract the piston. That explains some of the other comments I've seen in a couple other threads. If I didn't rcv any responses, I was going to reassemble the caliper & piston without the guide - since I see that newer pistons don't seem to have that mechanism in them.
Also, there's been a number of folks who've claimed they could press the piston back in by hand. Maybe they're using the newer pistons w/o the guides. The ATE factory video shows them pressing the piston back in with a press.
When I try to slip the guide over the pin (guide out of the piston as in the above photos by Dave), there's a definite 'clink' when the pin hits that top section inside the guide, and it won't go any further by hand. Guess I'll just have to try my bigger 6" (vs 3") C-clamp.
Thanks a lot, Cheers, jt

djpateman · 06-25-2021, 10:25 AM

The newer calipers have inside-out pistons. This reduces the required fluid volume. It does affect the ability of the piston to retract, but I guess the engineers accepted the consequences; or maybe the bean-counters overrode the engineers, again.
I use specialized tools when working on my rebuilds, also special brake cylinder lubricant to wet the seals.