Here is the link to the article as well: http://www.fastcorvette.com/CaliperSchool.htm


I get emails almost every day on the subject of ‘new’ O-ring calipers. The fact is they are not new at all. Only the marketing is new.

There is no requirement in the patent office that an idea has to have merit, only that the application be unique. In my opinion, for C-2 and C-3 Corvettes that are driven on the street, O-ring pistons are an idea without merit.

I have condensed the following from a 20-page engineering paper written by Zora Arkus-Duntov and copyrighted by the Society of Automotive Engineers in 1982. Direct quotes are indicated:

There are three disc brake design types, each with their own unique advantages and disadvantages. The C2-C3 caliper is a floating piston design. The other two types are floating caliper and floating disc. (The C4 caliper is a floating caliper design, and has O-ring seals.) As you can see, the common factor is that something has to float in all three disc brake types.

Floating piston-type brakes (like the C2-C3 brake system) must address piston knock-back resulting from deflections generated primarily from cornering forces.

The C2-C3 brake system was designed with a feature known as a ‘constant contact shoe’. The brake pad floats on the surface of the rotor (at a friction loss of approximately .8 HP at 100 MPH) in order to reduce response time and increase pedal pressure reserve. This float is a delicate balance between the lip seal and the spring behind the piston.

“...it has been found to be necessary that the piston be free to follow the disc. This is accomplished with the spring urging the piston toward the disc. This spring force must be light enough to avoid a dragging situation. In turn, the seal friction must be less than the spring force. A lip style seal satisfies this requirement and provides complete freedom from the piston knock-back problem.”

The reduced piston to wall clearance inherent with the O-ring design (when installed in a floating piston caliper), eliminates what Duntov said was necessary. Obviously, the O-ring piston is not free to follow the disc (rotor). The designed-in balance between the lip seal and the piston spring is completely ignored with the aftermarket O-ring pistons. When cornering forces cause spindle deflection, the brake system is put in a bind. As Duntov said, lip seal pistons have the clearances necessary to eliminate this bind and piston knock-back. O-ring sealed pistons do not, and are subject to sticking in the bores unless the caliper in which they are installed is a floating caliper design.

Here is a graphic from the SAE report:



The floating shoe feature is a safety, as well as performance advantage. Only 5 thousandths of an inch retraction (of the pad from the surface of the disk) equals an inch of pedal travel and 410 PSI of pedal pressure reserve. The C2-C3 brake system was designed to rely on that 410 PSI pedal reserve, which is not available unless the pad is floating on the surface of the disk.

Bottom Line: If your Corvette is a static display show car, O-ring calipers are a good option. If you drive your Corvette, stick with Duntov’s design. If you drive your car only once a month, just depress the brake pedal every couple of weeks, and your lip seals should be leak free for at least a decade.

--------------------------------------------------------------------------------
Copyright 2005, Duntov Motor Company


What's everyones opinion on this subject?

 

First, I must say that I found the article and your post very interesting. I'm not sure that I agree with your conclusions though. I've never tested to see if the friction is different between an o-ring or lip seal piston but I would expect them to be similar. if anything, I would expect the o-ring to cause less friction. if this is correct, the spring would be able to keep the pad slightly tighter to the rotor and reduce the amount of pedal travel. I would think the difference is very small, but i don't think the o-ring would be a disadvantage.

 

I think what Dontouv was identifying as a disadvantage in his article doesn't deal with pad to rotor clearance/friction so much but more of a bind when hitting road imperfections causing caring of the rotor b/w the pads. The floating design allows the piston to move with these bumps and return to its position holding the floating pad close to the rotor. With the O-ring's the piston is "sandwiched" so if the rotor was to knock it away the piston would have a tendency to stay put and not return to its position holding the floating pad close to the rotor.
If you were to drive on a bowlinglane alley I'm sure both setups would work very similar but when your wheels/rotors are bouncin around, the o-rings may cause some binding to the caliper piston.
This is what I got from the article, I have no personal basis for comparison. I was actually considering the VBP O-ring conversion up until this article & seeing the price.
But I'll stay tunned to see what comes of this discussion.
Good article!

 

As long as those springs are still behind the pistons, I really don't think there is going to be much of an issue.

 

I saw no information in that article that gave empirical evidence that an O-ring increases the resistance of the piston travel in comparison to a lip seal. I do see a statement of opinion.

Nothing posted in the "excerpt' from Zora speaks to the o-ring issue.

It is an interesting bit of tech though I do agree...if someone can produce real evidence that the O-ring exhibits increased drag over the lip seal then you may have a point.

 

I bought the "O"rings in the early 90's from the guy that developed them. Aviation engineer, I believe.(Zero Tolerence Inc).


In the past 12-15 years I have had no issues with braking. Still the same ones. Prior to installing the Orings I couldn't go for much of a ride before the pedal went to the floor.(The old air pumping thing)


BTW, He told me not to put the springs back, and SS-inserts were only needed in extreme situations.


I found the best article on the O ring /air pump problem, was in a 1980 "Vett Magazine" article. I still have the mag somewhere.

 

I read up on this before I made my caliper decision a couple years ago. I still purchased the new Delco o'ring calipers because I feel it is a better design as I don't race this car. I wasn't able to find enough technical information aside from Fast Corvette about piston knock back and spring pressures at the time, but I am going under the assumption that since these are licensed by GM they had to pass engineering testing and approval past the legal department to avoid future warranty issues and lawsuits if problems develop. I believe GM has their ducks in a row for that much. After about 3k miles I am happy with the performance of the brakes and don't notice any difference in driveability. Time will tell.

 

I just know that I had calipers leaking on my vette with the lip seals. We rebuilt them several times and after a while they would start leaking again. The car was driven about once every 1-2 weeks, which might have caused the problem. We replace the caliper pistons with ones with the lip seals about 10yrs ago, and have not had a problem since.(The car still gets driven once every 1-2 weeks).

 

ditto Dennis
I had a very frustrating time a decade ago with air pumping in my SS sleeved calipers. Even with rotor runout within tolerance, I could not drive more than 30 miles without brake lines full of air.
I installed the Zero Tolerance billet pistons with O rings and haven't have any pumping problems since.
While I certainly cannot argue with Zora on the subleties of brake pad pushback and the time and hydraulic pressure necessary to overcome several hair's width of separation between pad and rotor, I can state that I'd much rather have brakes that work reliably with no air in the lines a few milliseconds slower than unreliable brakes with so much air in the lines that I get almost no pad contact and pedal to the floor.

 

While I am not a brake engineer I would like to point out that Zora was not working with rotors that did not run true.

O-rings on a C-3 are a band-aid. Legitimate fix when used to solve a problem but not an upgrade IMHO.

=Mark.

 

stingr69,
Right you are. Zora had unlimited access to excellent machinists and was dealing with all new parts. My somewhat more limited resources and 35 year old Vette need band aids.....

I realize that o rings are not for everyone but they sure have worked for me.

 

I believe lip seals work fine if the brake system is not overhauled by Bubba or his relatives. Too many people treat the vette brakes as a floating caliper. When the C2-C3 was new the brakes worked great. Keep the rotor runout in spec and you will have great brakes. I have great brakes, hard pedal compared to some newer cars but they are firm and will lock up if pressed too hard. They start to grab firmly after about an inch of pedal travel. Those who have problems with the brakes should probably look for a mechanic who knows how the system operates.

 

I still have the original calipers and rotors and with good soles and heals on my boots the car stops. I just have to change boots ofter

 

I have VBP O ring callipers up front & stock lipped seal type on the back. I feel very confident with the front ones, but the back have given a few hiccups after the car has stood over the winter (pulling to one side).
Following on from the article, my bike has AP Lockheed brakes fitted as std. These are floating piston design, with 2 opposed pistons. There are no springs behind the pistons & I think there's a lipped seal in there (cast iron callipers without stainless sleeves, have never needed rebuilding in the 25 years they've been on there). I'd expect the deflection is going to be far more significant than on a Vette as the rotors have more runout & there's more flex in the system (I can heave on the edge of the tire & actually see the calliper deflect. Can't do that with the Vette). In addition, the rear wheel is very unlikely to be running perfectly true (not with me adjusting it!), so there's also massive rotor runout induced due to this. With no springs behind the pistons, plus the pistons being knocked back into the calliper by runout, plus the layer of air following the rotor pushing them back, I could read the above article expecting them to be terrible in operation. But they're not. If I do long distances at highway speeds then, when I first use the brakes, there is more lever travel before they work, but it's not much & the brakes still work extremely well (wish I could say the same about them in wet weather). Maybe just the weight of the fluid "above" the pistons help to keep them fairly close to the rotor??? There's no stops in the bores & the pistons can be pushed right back into them under finger pressure.

I clearly remember reading several articles on brakes in the late '70's. At the time all the Japs were throwing bikes at us with floating callipers, saying that the design (& theory) was far superior to that of floating pistons. Many deaths & injuries later (the pins they floated on regularly corroded up enough to seize solid), I read a snippet saying that floating callipers were used due to AP having a patent on their design & the Japs didn't want to pay to use it (don't know if it's true, but it'd be interesting to see if all those people were killed/maimed in the interests of maximising profits). There were arguements flying around left, right & centre, engineers claiming one design was better than the other, etc, etc. The proof was in the eating. In '79 a leading magazine did a test on various 750's, including mine (starting off with the normal "Old technology, the brakes are the same as in '73, blah, blah, prejudiced crap, blah"). They were shocked. The bike had the best brakes of any 750 on the market at the time, with stopping distances sometimes greatly exceeding the competition (these were on new bikes, before corrosion got to the floating calliper designs). Not bad for primitive cast iron brakes very similar in design to the Vette's brakes, but without the return spring behind the piston (which some people remove from their Vettes) & with vastly greater runout (probably measured in tenths instead of thou!!!).
The bottom line is do O ring callipers work? Last summer I had a heart in the mouth/nearly poop myself moment. On a dual carraigeway late at night I was cruising in the "overtaking lane" (we can't overtake on the inside) at about 80mph. A modern car (Audi?) was behind me at a safe distance & I was about to pass a very slow moving car (& then pull over to let the Audi(?) past). Just as I was (rapidly) coming up to pass the slow car, the dumb b***h driving it just pulled into my lane, directly in front of me. There was nothing else on the road in front of her, no reason for her to change lanes. She was doing 30mph, I was doing 80mph. I slammed on the brakes & was rapidly debating whether to swerve past her on the inside, but would she also change lanes again (meaning that I'd been overtaking her on the inside at the time of collision, making the accident my fault)? The decision was made for me by the Audi(?) behind swerving into the inside lane to avoid going into the rear of me. Crash barrier to the right, Audi(?) to the left & some dangerous idiot rapidly approaching in front of me. All I could do was grip the wheel & stand on the brakes. The front dived down, both of us were thrown forwards by the heavy braking & I watched in despair as my freshly painted & restored front end headed into the back of the econobox she was driving. We must have been fractions of an inch from hitting it before a gap started opening up & about 5 gallons of adrenaline started coursing through me. She sat in the outside lane for another 2 or 3 miles, at 30mph in a 70mph limit, completely oblivious to what she'd done (during which time a huge tailback built up behind) & then pulled into the inside lane. Some people shouldn't be on the roads (if I'd collided with her it would have been another "accident caused by excessive speed" according to the safety brigade). The point of all this? While I was waiting for a collision & the possible death/maiming of my wife & the certain destruction of my pride & joy, I was aware of the Audi(?) next to me. He was obviously also expecting psychobitch to realise her mistake & swap lanes again, so was under full braking. I could see the nose of his car trying to kiss the ground as it came alongside & I could also see the ABS system in operation (by the way it was rapidly juddering as the system was preventing the wheels from locking up). By the time I'd slowed down enough to avoid a collision, the Audi(?!) was level alongside me. My mix of O ring & lipped seal stock design brakes were, before my very eyes, outperforming a modern ABS system fitted to a high spec modern car. I'm impressed by them, whatever the theory says about them.

In previous forum threads in the past many people said that they'd left out the springs behind the pistons (in an attempt to prevent pumping & sucking air in). It'd be interesting if some of them reply with their findings.

 

 

like I said. No springs, (as per the ZTI), and no problems over 10 years now.

I could dig up the 1980 Vette Mag article on the runout/ air pumping and post if anyone is interested

 

Yup, I am

 

Please post. Thanks!

 

Uk Paul, wow nice read!

My only point is that most modern floating piston calipers use a square o-ring and even less piston to bore clearance than the Vette O-Ring calipers.

And they work VERY well under extremely harsh condtions like high speed autocross with big sticky tires. No binding at all.

 

No problem Does it show that I'm having a boring day at work? :lol

While people are (obviously) not willing to argue with Zora on this, I'm wondering if Zora himself would argue against it in the light of modern technology, metallurgy, DoT specs, machining accuracy, etc???