Machining Calipers for 1965 Corvette

[Don52]

Thirty years ago, my friend Mark rebuilt the calipers on this 1965 Corvette by adding stainless steel sleeves to prevent corrosion of the bore of the cylinders. At the time they used the original piston. They replaced the seals with lip seals that were the original seal design that had a very high failure rate. The original pistons guided on a small bore at the bottom of the cylinder. In the following picture you can see the small bore at the bottom cylinder.

1. Full boss in place


Here you can see the post on the bottom of the old piston that used to guide in the small bore on the bottom of the cylinder.

2. Old piston with post


Because of the short life you can no longer purchase the old pistons. The newly designed cylinders eliminated the bore in the bottom of the cylinders.

3. New cylinder


The new pistons, which are available, eliminated the post on the bottom and added a raised ring on the bottom as shown below. They also replaced the lip seal with O-rings.
Unfortunately, the raised ring on the bottom of the new piston interferes with the split boss on the bottom of the old cylinders. As a result of the interference, you can’t retract the pistons enough to install the new brake pads.

4. New Piston without boss


The solution is to remove the boss around the bore, at the bottom of the old cylinder to eliminate the interference. In the process of machining for the stainless-steel, the machining vender also machined the side of the caliper. I took advantage of this new flat surface that was parallel to the center line of the cylinders, to clamp in my vise on the Bridgeport.

5. Setup for machining

[Don52]

My first attempt to face the boss was to use a 1” endmill and use the quill to plunge the cutter into the boss. Due to the interrupted cut the finish was badly chattered. For my next attempt I locked the quill in the fully retracted position and used the knee of the Bridgeport to control the feed for cutting. This worked fine but took forever to crank the knee down to clear chips and to verify the depth of cut. For my last attempt, I used the quill to approach the face to be machined and then used the knee of the mill to do the actual machining. This saved a lot of cranking, which in turn saved a lot of time. I was machining with the quill extended from the head about three inches, which is a no-no. I felt that I could get away with this because there was very little side loading in the mill because of the fact that the plunge cut only used the end of the end mill, not the side.

6. Bore machined


7. Two bores machined


I find that while machining and welding, I always learn something, even on the seemingly simplest of jobs.

-Don

[ryanjones2150]

You need a boring bar that can face, Don.

[Don52]

You need a boring bar that can face, Don.

I do have a nice Innerstate boring and facing head, that looks like this.
The facing head would have certainly worked. I felt that feeding in with a 1” diameter cutter would be quicker. Once I figured out how to eliminate the chatter, I believe that it was quicker.

-Don

[ryanjones2150]

Oh man, those ain’t cheap.