67's

IF you are an NCRS member there is a pic in the current Restorer.

VetteJohn

I've been following this thread with great interest and thought I'd jump in. There seems to be some concern for the short length of the pistons used in this system. While I don't a picture of the original pistons I can tell you they are about the same as the o-ring style. The hydraulic force applied to the back of the piston forces it out towards the pads, both move out until they are stopped by the rotor. Because the force on the back of the piston is equal across the entire face of the piston face the piston should move out informally. The only things that would cause the force to be higher at the bottom verses the top is; the pads catching on the pins, the piston catching on the bore, the pads being tapered (new), the rotors being tapered (new) or some crazy run-out at the rotor/baring. If it's the pin there will be a noticeable amount of wear visible. If it is the piston/bore you should be able to see where these parts are hitting. The most likely answer is that the pads were dragging. Since the outer edge of the rotor dissipates heat better than the inner portion the heat would build up more closer to the center and cause more wear. You'd end up with tapered pads on all four wheels all from the same source. Why would the pads be dragging on all four wheels? Master cylinder/booster/pedal issues. Something is generating hydraulic forces to the calipers when the pedal is not being pushed. Figure out what's going there and you've got your problems fixed.


I know this because years ago I had a pedal rod that was misadjusted. It stayed against the booster which pushed the MC and I ended up with pads that dragged.

Hope this helps.

Sky65

Haven't been able to get back to the car this week but I did hear back from VBP. I sent them the pictures and they are confused as well. I am sending the calipers back to them to check out and see what they find. Regardless they offered to rebuild all four at no charge. Very fair and very customer oriented. I knew it was a good decision to purchase from them.

66jack

Sounds like Very Good Customer service....

Classic-Chevy-Guy

There is an article in Summer 2012 Corvette Restorer from NCRS about rebuilding brake calipers. Don't know if it is relevant to this issue, but I thought that I would mention it. The author is Ed Vignone, and he might be a resource.

Good luck.

Plasticman

Are they going to rebuild them as "O" ringed, or revert back to the original style lip seals? I would assume you could make that call.

Plasticman

w1ctc

The pads shown just don't look right. The few I have in my pile of stuff have the friction material almost to the ends of the backing. When new, there is very little space for the pad to tilt.

67's

Would be nice for them to throw in some new pads also

toddalin

Was thinking about this the other day and it occured to me that the problem is probably that the pads are not sliding along the pin like they are supposed to do.

Maybe the pin is too fat or has a "hitch" or corrosion, or maybe they should have used anti-seize and didn't, or, etc.

Or maybe Bubba just bent the top on installation and that turns a round hole into an oval relative to the plane of travel restricting its movement causing it to hang.

If you look at the top of the pad you can see how it is bent out because of/or causing the top of the pad not to slide away from the side like it is supposed to do.

Hitch

Hey now don't be using my name in vain here... lol

As for the OP problem it is very interesting for sure. If it is the bores on the calipers I would not be surprised...

David

Sky65

I have modified this post. When I read it this morning the first part sounded like a smart azz response. I didn't mean it that way so rather than take a chance it would be misinterpreted I removed it.

I am happy with the VBP offer. The pads would have been worn out anyway and they were very pleasant to deal with. In researching the stock caliper operation and construction I am considering changing to the Wilwood D8-4. Kinda expensive but not terrible with some sales going on right now. They use a square cut seal fixed in a billet aluminum caliper. The pistons are ss and are full bore diameter the entire length if that makes sense. They cannot **** in the bore and would tend to square up a pad if it was getting worn on an angle like my old pads did.

Thanks for all the suggestions and input. When VBP checks the parts out I will post their assessment.

Tom

bighouse

How does an o-ringed piston retract? It is my understanding the a square-cut lip seal is needed to retract the piston. And if the lip seal worked for so long in everything that has disc brakes, who decided that o-rings are better? Something stinks

Plasticman

A lip seal and a square cut seal are 2 different seal designs. An "O" ring seal is a 3rd design. The lip seal was the type used in the C2/C3 calipers. The Corvette brake aftermarket is offering the "O" ring seal version for those calipers (and I don't know why).

From what I understand, you are correct that a square cut seal (as used in most "modern" calipers) retracts a piston away from the rotor (by a very small amount), and does not use an internal spring. It deflects as the piston is hydraulically forced towards the rotor, and then retracts that deflection when pressure is released.

But the lip seal design predates the square cut seal design, and required a spring to keep a small pressure on the piston (always forcing it towards the rotor). I "assume" that the "O" ring design also uses that spring.

Plasticman

Bluestripe67

Tom, Just got back in town and read the thread. Do the caliper pins flop back and forth in oval holes of the pads? Dennis the

Sky65

Hey Dennis.
The pins slid right out on disassembly so I would say yes. Everything practically fell apart. No build up of any debris or anything.

KC John

I just went through a period of not being able to get rid of a very slight drag I had on my brakes. It turned out to be a bad brake booster. I don't even know if you have power brakes or not, but when the brakes got hot, the booster wouldn't return the pedal all the way back to the bump stop.

I replaced the booster and everything is back to normal. I guess if the rod between the pedal and M/C or the M/C and the booster was a bit too long, it would also create heat by keeping the pads against the rotors.

I figure it must be something like that being that all 4 sets were worn the same way. It has to be further up the system don't you think? What are the odds that all 4 calipers are defective in some way?

Bluestripe67

Tom, The pic of the pads/pins makes me think the pins are fat. If so, the pads could get caught and ware as shown. I know my pins make a klinking sound when going from forward to reverse. That tells me they have room for movement. Dennis

Sky65

O ring.

Yes the O ring style does use the spring.

What was the symptom of the "slight drag" you were chasing? Did you just notice it while turning a wheel on jack stands or did you also have irregular worn pads?

The pads, calipers and caliper pins all came together and were installed together. The pins fit in the calipers fine. They will drop right out if the caliper is tuned on it's side with the cotter pin removed.

Tom

TheSaint

Have you measured the pins?

Here is the measurement of the new pins i have for my car

Sky65

Thanks. I did not measure the pins. They fell right out of the calipers with the pads installed so it did not appear to be an interference issue. I guess I should have done some measuring before I sent them to VBP to inspect.