67 Front Brake Caliper Rebuild.

[Thomas S.]

I had a leaking front caliper and it turned out to be one leaking piston seal. The calipers were sleeved. I've seen a lot of rebuild kits that seem to offer o-ring seals for stainless steel sleeved conversions. I also read a fairly detailed post on this site about sleeved and original versions which was helpful, but I still have some questions.

Can the standard rebuild kit with the original style seal (grooved) be used on a sleeved caliper?

Is the hardness of stainless steel the reason for using an o-ring.

The pistons do not have phenolic tops. Pros / Cons.

[Joe L.]

I had a leaking front caliper and it turned out to be one leaking piston seal. The calipers were sleeved. I've seen a lot of rebuild kits that seem to offer o-ring seals for stainless steel sleeved conversions. I also read a fairly detailed post on this site about sleeved and original versions which was helpful, but I still have some questions.

Can the standard rebuild kit with the original style seal (grooved) be used on a sleeved caliper?

Is the hardness of stainless steel the reason for using an o-ring.

The pistons do not have phenolic tops. Pros / Cons.

Thomas-----


1) Yes, the standard, lip seal type rebuild kit can be used on sleeved calipers. In fact, the majority of 65-82 Corvette calipers are rebuilt with standard lip seals;

2) The hardness of the stainless steel sleeves has nothing to do with the use of o-ring type pistons seals. The primary reason for using o-ring type piston seals is to alleviate some of the problems associated with lip seals. This includes "air pumping" and leakage over time. In order to convert to o-ring type seals both the pistons and the seals must be changed. Lip seal pistons cannot be used with o-ring seals. Keep in mind, though, that o-ring type seals for disc brake calipers was a technology known at the time that the Corvette disc brake system was designed. Other automotive manufacturers of the day did use o-ring type seals in their disc brake calipers. The Corvette engineers chose not to use them. I'm sure they had a good reason and, personally, I have chosen not to second guess them.

3) Phenolic piston insulators were used for all 1st design calipers which were used from 1965-early 1967. For 2nd design calipers used from later 1967 through 1982, only J-56 brake systems utilized phenolic insulators. However, the 1st design pistons/insulators were different than the 2nd design pistons/insulators.

[Joe L.]

By the way, I should have mentioned that most 1st design calipers have been converted by caliper rebuilders over the years to 2nd design. As such, these calipers cannot be used with 1st design pistons and insulators. Original configuration 1st design calipers can be identified by the piston guides cast into the center of the caliper bores. When converted, the piston guides are machined away and the caliper irreversibly becomes a 2nd design.

[Thomas S.]

Thanks for that explanation. My VIN ends in 6407. Mine have already been converted and have the anodized aluminum piston with lip seals. I'm inclined to stay with that setup. There's only 45,000 miles on the car and I put roughly on 1,000 miles on it since it was purchased a year ago. The pads are like new so the breaks must have been done recently. Surprised it hadn't been leaking before as the outer metal seal ring was really manhandled when it was installed.

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[Joe L.]

Thanks for that explanation. My VIN ends in 6407. Mine have already been converted and have the anodized aluminum piston with lip seals. I'm inclined to stay with that setup. There's only 45,000 miles on the car and I put roughly on 1,000 miles on it since it was purchased a year ago. The pads are like new so the breaks must have been done recently. Surprised it hadn't been leaking before as the outer metal seal ring was really manhandled when it was installed.

IMG_5481.jpg
IMG_5475.jpg

Thomas-----


These are originally 2nd design calipers. They were not converted from 1st design.

[Timothy B.]

Thomas,

If the brake caliper casting number starts with 546 it's a first design (65 66 E-67) caliper. I see the casting armasteel in the caliper, Joe can explain better than me about the castings.

[Thomas S.]

Starts with 545
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[Joe L.]

Starts with 545
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IMG_5488.pngIMG_5486.pngIMG_5487.png

Thomas-----


Yes, I noted the "545" prefix in your first photo. This is why I mentioned that your calipers were originally 2nd design and were not converted from 1st design. Your photos of the caliper bores also indicates this as, characteristic of 2nd design calipers, these calipers never had cast-in piston guides.

1st design caliper halves have "546" prefixed casting numbers and were used from 1965 through early 1967. These caliper halves were cast of nodular iron and do not have the word "Armasteel" cast on the outside front caliper halves.

2nd design caliper halves used from later 1967 through about 1973 have casting numbers prefixed "545". These caliper halves were cast of ductile iron at the old GM Danville Illinois foundry. They have the word "Armasteel" cast on the outside front caliper halves. "Armasteel" was a term for a GM-patented form of ductile/malleable iron.

2nd design caliper halves used from about 1974 through 1982 have casting numbers prefixed by "547". These caliper halves were cast of gray cast iron by a non-GM foundry.

[Thomas S.]

Thank you. Very good info to know.

[Mark F.]

...1st design caliper halves have "546" prefixed casting numbers and were used from 1965 through early 1967. These caliper halves were cast of nodular iron and do not have the word "Armasteel" cast on the outside front caliper halves.

2nd design caliper halves used from later 1967 through about 1973 have casting numbers prefixed "545". These caliper halves were cast of ductile iron at the old GM Danville Illinois foundry. They have the word "Armasteel" cast on the outside front caliper halves. "Armasteel" was a term for a GM-patented form of ductile/malleable iron.

2nd design caliper halves used from about 1974 through 1982 have casting numbers prefixed by "547". These caliper halves were cast of gray cast iron by a non-GM foundry.

Joe,

So it appears GM went from more expensive nodular/ductile iron castings to cheaper gray iron castings.

Maybe after the first two years of analyzing caliper failures based on their casting compositions, they thought why bother with the higher strength nodular/ductile earlier versions ?

Plus outsourcing was probably cheaper as well...