Seventy911 Posted Saturday at 00:26 Report Share Posted Saturday at 00:26 Morning everyone! As these things do, I started replacing a leaking fuel pump and have refurbished the front end!!! I found some corrosion on my M caliper pistons and decided to replace them all with stainless from PP. As I believe is the case for most early pistons the Knock Back Mechanism (KBM) is peened in place unlike very early versions retained by a clip. The new pistons are recessed for a clip. What's the best method to remove the KBM from my old pistons? Obviously this is a destructive process and one where I want to not damage the KBM so I won't be cutting the piston in half with a grinder 😂 Many thanks!! Quote Link to comment Share on other sites More sharing options...
Peter M Posted Saturday at 22:45 Report Share Posted Saturday at 22:45 I would think the easiest way would be to mount the old pistons in a lathe and carefully machine off the peening from the outer radius in. Do you actually have to reuse them? No caliper has used them for nearly 50 years. I'm sure there are lots of posts on say the Early 911 Register on this topic. Good to see someone get their hands dirty! Quote Link to comment Share on other sites More sharing options...
Seventy911 Posted Saturday at 23:06 Author Report Share Posted Saturday at 23:06 Thanks Peter, I don't have a lathe so I think next best thing will be drilling out the peening. There appears to be washer under the peening that isn't needed with the SS pistons so no harm destroying that.... anyone with a different opinion is welcome to comment. Yes, no fear in dirty hands on this car. Such impressive engineering from the analogue age. It is a testament to the skills of designers and engineers who developed all the technical drawings for production by hand on long boards! Quote Link to comment Share on other sites More sharing options...
Seventy911 Posted Sunday at 02:01 Author Report Share Posted Sunday at 02:01 So I got it out without damaging it.... different story when the drill broke and skewered a finger on my left hand 😂... talk about getting my hands dirty!! anyway.... This was my process: 1. Center punch each of the peened fingers. 2. 3.0 mm pilot drill. 3. 5.0 mm drill - when the chips get bigger you are cutting the washer retained by the peening. 4. I used a small flat screwdriver (shaft through handle) and hammered into the non-peened interface between the washer and the piston. 5. Inverted and hammered from the brake pad side in an anvil to break the washer free ... out it all came. 6. The new pistons did not include circlips so I'll need to see what's available. tk111 and Peter M 2 Quote Link to comment Share on other sites More sharing options...
Peter M Posted Sunday at 10:02 Report Share Posted Sunday at 10:02 Good work! Having a sacrificial washer to protect the unit made it much less fraught! Quote Link to comment Share on other sites More sharing options...
sus911 Posted Monday at 21:14 Report Share Posted Monday at 21:14 I would have re-used those pistons....😉 Peter M 1 Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.