Caliper O-Ring Conversion

[Joe L.]

Re: Caliper O-Ring Conversion

Joe,
I went back some of the "similar threads" listed below and saw one of yours which said something to this effect:" I (Joe) was skeptical of o ring system originally, but now think they're OK." You haven't changed your mind again on this, have you?

William------

Yes, perhaps a little bit. Since then, I've heard of folks that have had problems with the o-ring conversions. Second, that business about GM never using this design still gnaws at me. As I've mentioned, the technology was well-known at the time and there was no reason GM could not have used it. t.

One other thing that's always bothered me: I don't understand how the o-ring design can hold the hydraulic pressure that the lip seals can.

In any event, I think the o-ring conversion is probably OK. Would I ever use it? Probably not.

[Gary B.]

Re: Caliper O-Ring Conversion

If more of us were at least occasionally willing to reconsider statements, actions, or positions, the world would be a better place.

Gary

[Domenic T.]

Re: Caliper O-Ring Conversion

William------

Yes, perhaps a little bit. Since then, I've heard of folks that have had problems with the o-ring conversions. Second, that business about GM never using this design still gnaws at me. As I've mentioned, the technology was well-known at the time and there was no reason GM could not have used it. t.

One other thing that's always bothered me: I don't understand how the o-ring design can hold the hydraulic pressure that the lip seals can.

In any event, I think the o-ring conversion is probably OK. Would I ever use it? Probably not.

Joe,
I can't see the O-ring holding pressure better than the O-ring either, but it does work. The lip seal gets tighter with pressure, but we shove over 2,000 PSI on the O-rings and they hold??

Dom

[Dennis D.]

Re: Caliper O-Ring Conversion

I may be missing something here, but the failure with the lip seal isn't that it doesn't hold pressure. The problem is when the wobble from rotor run-out allows the lip seal to collapse letting air in, then trapping the air in, becoming a very efficient air pump. The o-ring doesn't collapse.

[Joe L.]

Re: Caliper O-Ring Conversion

I may be missing something here, but the failure with the lip seal isn't that it doesn't hold pressure. The problem is when the wobble from rotor run-out allows the lip seal to collapse letting air in, then trapping the air in, becoming a very efficient air pump. The o-ring doesn't collapse.

Dennis------

No, I'm not saying that the lip seal doesn't hold pressure; I'm saying the opposite. It would seem to me that the lip seal would hold pressure better than the o-ring. As pressure is applied, the design of the seal causes it to increase its ability to hold pressure. With an o-ring, no increase in pressure-holding capacity can occur.

[Dennis D.]

Re: Caliper O-Ring Conversion

We may be saying the same thing. The running-out of the rotor when the brake isn't applied causes the lip seal to allow air to pass by. When the brake is applied the lip seal does such a good job of sealing, the air gets trapped, causing petal loss. The oring doesnt do that.

[Joe L.]

Re: Caliper O-Ring Conversion

We may be saying the same thing. The running-out of the rotor when the brake isn't applied causes the lip seal to allow air to pass by. When the brake is applied the lip seal does such a good job of sealing, the air gets trapped, causing petal loss. The oring doesnt do that.

Dennis-------


In that case, the solution to the problem is to get the rotor runout to specifications. The design specs are quite rigid. I'm sure that was a problem for GM, too. They had to hold these specs in production. In about 1974, they changed the rear wheel bearing SERVICE procedures to specify the rotor and spindle be removed as a unit and not separated as the earlier procedure had instructed. A new special tool was developed to allow the new procedure. They never did publish a specific procedure to deal with the runout issue if either the rotor or spindle had to be replaced. However, for all practical purposes, the runout specs never changed.

Installing the o-ring calipers to "get around" out-of-spec runout on the discs really amounts to a "band-aid" solution. Of course, there might be other benefits (and possibly detriments) to the o-ring installation.

One thing I want to stress again here and make abundantly clear: o-ring caliper piston technology was known and used at the time the Corvette disc brake system was designed. For one thing, it was used for Bendix 4 piston fixed calipers which I believe were used on some Chrysler and Ford cars of the 60's period. For some reason(s) unknown to us, GM chose not to use that design for Corvette. If o-ring technology had not been known at the time but came along much later, then I could conclude that it would now represent a functional upgrade and I'd be very interested in it. I'm all for functional upgrades, especially if they can be done in an "unobtrusive" manner. An example would be thread locking. In the old days, thread locking compounds had not been developed. Lock washers, as ineffective as they might be, were used to help retain fasteners from loosening. Much later, thread locking compounds became available and these began to be used in PRODUCTION and specified in SERVICE. While I still install the lockwashers, I use thread locking compound, especially on critical fasteners. It's a functional upgrade and I love it. I figure that GM would have originally used it on the cars if it had been invented then.

With the caliper pistons and seals, it's a whole different story. Like I say, that technology was well known in the 60's. GM chose not to use it for Corvette disc brakes. And, they never changed the seal design over the course of the 18 years this brake system was used on Corvettes and even considering the manufacturing difficulties and SERVICE problems associated with the seal design which they certainly had to be aware of.

This is what gives me pause regarding o-ring seals and pistons.

[Greg H.]

Thanks for you patience and for all of my fellow C-2-and C-3 brothers. Our brake systems require a high degree of special attention. Quick simple fixes are not part of this repair process. If you make any changes you will need to find a machine shop with the proper lath that can turn a full assembly.

This the link to the HIGH CALIPER BRAKING GM Document
https://www.gmheritagecenter.com/gm-heritage-archive/Corvette-News/1965_Corvette_News_1.html

[Joe L.]

Re: Caliper O-Ring Conversion

Hi Joe,
I now agree with your out of tolerance conclusions as the primary cause for the lip seals leaking. Over the past years I have drilled out both of my front and rear disks and replaced some hubs and half shafts and disks without checking the relationship of the assembly and that’s why my lip seals have leaked.

Also, I found the attached GM Disk Brake document that supports your conclusions. Published in early 1965, it has a wonderful explanation of the time and efforts invested by GM in the development of the disk brake components that became the standard production assemblies. I was unaware that their first caliper evaluations began back in 1937 and started the foundation for the production calipers that were standard in 1965.

Please look at section that describes the disks found on page 3, its the right hand column, and note how exact the machining tolerances must be for this system to work. The brake disks were riveted to the hubs and with bearings added and then machined as a single unit. Total control is required. Any uncontrolled modifications will change the initial assembly.

Also, your closing statement yesterday about how the lip seals work while under pressure jarred / forced me to realize that my past conclusions may be in error as well. You see I was confident that the brake fluid was leaking as the result of the car sitting – standing still for a few weeks and that lack of movement was allowing the weight of the piston to somehow over come the internal seal and allow fluid to leak out. Now, I must admit that in all cases when this happened to me, I had driven that car before it was parked and DID NOT check for fluid leaks after parking it for storage. My guess is that the seals were leaking before the parking occurred and as the car was static the fluid continued to leak so next time I went to use the car I found a soft petal.

Thanks for you patience and for all of my fellow C-2-and C-3 brothers. Our brake systems require a high degree of special attention. Quick simple fixes are not part of this repair process. If you make any changes you will need to find a machine shop with the proper lath that can turn a full assembly.

Unable to upload file - I will find the link and post it tomorrow.

Greg-------


Trying to correct rotor runout by machining the rotor and spindle/hub as an assembly can be problematic. Many of the GM-supplied spindles, including original ones installed on the car as well as SERVICE, were way out-of-spec with respect to runout. This was not a problem for GM as they riveted UNFINISHED rotors to the spindle or hub and machined the rotor as an assembly with a finished rotor thickness of 1.250". If one rivets or otherwise attaches a new rotor to an existing or new GM spindle (discontinued, by the way)or hub, it's possible that due to excessive runout on the spindle or hub, machining of the rotor to correct runout will cause the rotor to be machined below minimum allowable thickness. Even if it's not this bad, it will almost always cause the otherwise new rotor to be at something other than new thickness.

I recommend using shims to correct most of the runout. Often one can get them into spec with shims alone. If not, final machine shop work can get them to spec with minimal rotor material removal. There are also tapered shims available on the market for runout correction.

Another approach is using aftermarket spindles and rotors. Many of the aftermarket spindles will have very low runout on the rotor contact face of the spindle. Most aftermarket rotors have very low runout out-of-the-box on the spindle contact surface. So, fasten these together and one may have acceptable runout on the assembly. If not, the spindle can be rotated on the rotor to one of 5 different positions. One of those might have in-spec runout. Otherwise, very minimal shimming will get things right.

After runout is corrected, I highly recommend fastening the rotor to the spindle or hub. Riveting can be done but, for me, I use countersunk, flat headed 3/8-16 hex drive screws through the rotor rivet holes and into tapped rivet holes in the spindle or hub. Works great and nobody will ever know with the wheels on the car. In my opinion, much more practical and functional than riveting. In fact, considering the benefits of this, I don't understand why anyone has these riveted. For me, restoration is not a religion so I'd never go so far as riveting these things.

[William F.]

Re: Caliper O-Ring Conversion

Joe's right about the ideal, proper way to correct for original style caliper seals is to correct rotor runout, IF this can be done without removeing too much material from the rotor. BUT often the air pumping can be corrected in a quick and dirty way by using calipers with o ring seals.

[Dennis D.]

Re: Caliper O-Ring Conversion

Let me beat the dead horse a little more...... I haven't heard an argument that the oring will not seal as well as the lip seal. The theory was that when the rotor was un-riveted from the hub for whatever reason , run-out became an issue with air pumping of the lip seal. BTW believe the tolerance is .010. Shims were/are available as the fix I will attempt to locate the article that explained in great