Our C2 & C3 calipers use an iron housing, with aluminum pistons, and the small lip seals fit onto the aluminum pistons, and rub against the iron bore.
The aftermarket stainless sleeved calipers retains the aluminum piston and lip seal, but the seal now rides against a smooth stainless surface.
Yet the leaking problems persist:

These are all SS sleeved.

All sleeved, all leaking


Modern brake systems use different metalurgy, as do the Wilwood DB-8 calipers.
The Wilwoods are aluminum caliper, with stainless steel pistons, with a square cut o-ring on the stainless piston, rubbing on the aluminum caliper bore.
Some of the factory systems are similar, but at least some of them also use iron calipers.

All of these more modern designs seem to be more leak free than our original design. So what is going on here?

I propose they are several root causes and multiple issues going on, all at once.

• The aftermarket has inserted stainless steel sleeves into our iron calipers for many years. Supposedly to address corrosion. The lip seal would slide against a smooth non-pitting surface. This is an improvement. But it has not stopped the corrosion or leaking problems completely. In the photo above all of those calipers were SS sleeved.
• Lip seals are not used anymore. They are presumed to relax with non-use, as in long term multi-month storage, and then leak. Regular exercise, like monthly, seems to prevent most of this. They are relatively thin, and they protrude outward like a lever, and only the thin edge seals. The thin sealing edge could also get cut and damaged buy corrosion easily. I propose it is the lever effect that is at fault here. These seal by rubber tension only.
• Modern design almost exclusively use square cut seals that seal by compression. There is no way they could relax. They also are thicker than the above, hence stronger. They are noticeably tighter than the lip seals, and have more sliding friction. Try and handle them and you will notice how much more difficult they are to move with your fingertips. They flex laterally slightly in use, and slightly retract when pressure is released, allowing the pads to retract a few thousandths. This lessens brake drag and improves pad life and gas mileage.
• The aftermarket has come up with o-ring seals to combat this problem. They function much like a square cut seal, and seal by compression. They may or may not retract slightly after braking, unknown, but does seem likely. Apparently the round o-ring compresses enough to seal well, even tho it's surface is not flat.
• There is a galvanic corrosion component going on here. Aluminum, iron and stainless steel are all dissimilar metals, and a battery or ev voltage potential will be created when water is present.
  
• Our al/iron calipers develop a 0.3 ev potential, with the aluminum acting as the anode, meaning the piston corrodes, And deposition occurs on the iron.
• The stainless sleeved C3 calipers and aluminum pistons, develop an even higher 0.5 ev potential, with the aluminum pistons still corroding. This should result in a perfectly smooth seal surface at all times. But as witnessed in the picture above, this metalurgy change has still not stopped the corrosion.
• Modern cars, or the Wilwoods, reverse the metalurgy, with the aluminum caliper sacrificing themselves and deposits forming on the stainless pistons. This should mean the metal sealing surface slowly gets removed, like an anode. But apparently not enough pitting occurs to affect the square seal.
• My modern car has stainless pistons with iron calipers, and the seal surface should corrode, but they seem basically leak free.
• So what is going on here? I propose that generalized galvanic corrosion via dissimilar metals is not a serious problem in these cars.

• The replacement of the aluminum pistons with stainless means much less thermal conductivity, and less boiling of the brake fluid in racing. But this has little to do with corrosion. Some of the vintage C3 racers even tool up titanium pistons for even less thermal conductivity, to help with brake fluid boiling. Titanium pad backing plates are used for the same reason. The SS pistons may transmit up to 68 times less heat to the brake fluid than the Al pistons, 387 Watts, vs 26,000 W.

• I propose the major leaking problem is the corrosion and pitting of the iron. When iron is exposed to both water and oxygen, and given a little activation energy, it oxidizes, forming F2O3 or FeO. AKA the way your chromed steel bike parts rust not in the dry, or even during the rain, but right after the rain while it dries out. Iron creates a tiny galvanic corrosion cell in the presence of both oxygen and water. It does not care if aluminum or other dissimilar metal is present. This is the type of corrosion cell that makes those deep iron corrosion pits, that will eat holes in a car fender. The pits, once formed, turns into an anode, and will continue to get deeper and deeper. It also reacts with the water, and makes Fe(OH)2. In our calipers it creates a heavily pitted surface, that will not seal well. And leaks brake fluid. And with lots of "rust" particles floating around. This creates the pitting in the iron, which is what we see in practice. And even in SS sleeved calipers, the rust particles cut the seals and make them leak, We do not typically observe aluminum pitting, or corrosion depositing on the iron, which is what the galvanic corrosion of dissimilar metals of al & fe proposes.

• I believe the mechanism is, the hydroscopic brake fluid absorbs humidity from the air. The weak sealing pressure of the lip seals has a hard time keeping these "gases" out. This humidity gas is absorbed by the brake fluid and becomes liquid water. The water has oxygen in it. The activation energy required for this corrosion cell to start can come from heat generated by the brakes, or even just temperature swings. Once the battery cell is started, it is self-perpetuating, eating away at the iron, even while the car is sitting still. Heat does speed this process up. It is the galvanic cell pitting of the iron that is the real problem.
• Look again at the picture above, with all the iron corrosion particles, in the SS sleeved bores.

These are the pistons from those same calipers. I still see smooth aluminum, but lots of reddish brown iron corrosion particles. Clean the crud off, and the pistons do not look bad.

Even in SS sleeved calipers, there is enough iron corrosion going on that the "rust" particles themselves cause a huge sealing problem. This occurs even if the iron and aluminum do not touch, due to the SS sleeves. The SS sleeves can not prevent this iron corrosion. The jagged rust particles tear the delicate sealing surface of the seals. Likely more of a problem on the thin lip seals than the thicker round or square o-ring seals.



Lots of reddish brown iron corrosion.

How do we slow down the problem in our OEM style calipers?

• SS sleeves - address primarily saving the smoothness of the sealing surface
• Excercising lip seal calipers monthly should primarily slow down the leaky limp seal problem inherent with lip seals
• O-ring seals should address the leaky seal issue if you store your car for long periods of time, as well as slow down water intrusion by more compression.
• Changing brake fluid annually or semi-annually is likely your most effective preventive measure. Prevent the water from getting very high in the first place.
• Testing brake fluid - There are inexpensive brake fluid moisture testers, that I would suggest. Check the brake fluid both at the master cylinder, and at a brake bleeder, after a years time, and see how long you want to let it go. 2% water seems high enough to me.
• Silicone brake fluid - does not absorb water, and solves the corrosion issue. But it does have several other things to be aware of. Read up on it first before using. Seal compatibility, temperature, expansion, pedal feel, paint damage, etc.
• IF you stay on top of the fluid change maintenance, you should be able to stay ahead of it. But with the iron calipers, you better not slip up.
  

So how do the modern systems virtually eliminate the problem?

• Primarily by eliminating the iron caliper and it's corrosion & pitting tendencies.
• But some cars with H.D. brakes still have iron calipers, so the more robust design of the square lip seal must slow moisture and oxygen intrusion.

Wilwood DB-8 calipers upgrade advantages:

• I believe the advantages of these is more in their modern leak-free solutions area than any perceived performance benefit.
• No iron in the system. Only aluminum and stainless steel. This is the big one. No iron corrosion or pitting. Aluminum and stainless do not suffer from this pitting issue.
• Square cut piston seals. This is another big one. These seal by compression and reduce humidity intrusion to the brake fluid.
• SS Pistons are the sealing surface as the square cut rings slide against them So no pitting issues there.
• Roughly 4# lighter per corner for less unspring weight. So it should ride better. Realistically it is 4# out of 150# so don't expect to notice much.
• Stainless steel pistons transmit much less thermal energy to brake fluid, so much less brake fluid boiling issues, if you track the car. Again most would not notice.
• General Galvanic corrosion of aluminum and stainless is slow enough that generalized erosion of the aluminum bore surface is smooth and does not seem to cause much issue. That occurs at the atomic level, and does not create corrosion pits. Aluminum is not subject to the same severe pitting of a localized galvanic corrosion cell that occurs with iron.
• Changing brake fluid every couple of years. I'll have to admit going 4-5+ on my daily drivers, and rarely had a problem. Most of the issues have been with the sliding pins themselves.

Wilwood DB replacement pistons and seal, the seals mount in the caliper, and slide on the SS piston, for a smooth surface.


Any other thoughts?

Yeah, I thought all of this through, before I decided on the Wilwoods.

 

I've been running DOT 5 and SS lined o-rings for years without issues. My Vette still stops better than any of my other vehicles even with manual brakes.

 

Great read thanks for posting!

I think fixed calipers and rotor run out contributes too
And sitting up as you say.

 

I'm not looking at a Wilwood caliper. Perhaps you are. In the photo above of a seal kit, I see no dust seals. Factory calipers always have dust seals to keep grit from getting into the end of the bore. I have used aftermarket calipers on Harley's many times, (for customers). And these generally do not have dust seals as well. And are NOT road legal here in Australia because of that.
I have seen first hand several times now where grit gets into the bore in the area between the square seal and the outer end of the bore causing a stuck piston.
There is a reason for dust seals on the piston bores. Do these wilwood calipers have them?

 

Bought my 1979 8 years ago with lip seals, stainless sleeves all 4 corners with Silicone brake DOT5 fluid. Brakes were poor, pulling, flushed many times. Next season noticed leakage. Rebuilt the calipers, flushed the system with Silicone fluid being careful of air bubbles and still had poor braking. Next 3 seasons replaced 1 or 2 calipers for leaking, flushed and still poor brakes and the brake light would come on occasionally. Kept being told get rid of the Silicone fluid from caliper vendors, seals no longer compatible but heard others were having good results with it Finally bit the bullet and flushed the whole system with denatured alcohol. Found the rear cross over was crudded up with rust and gunk. Rebuilt the front with ring seals, kept the rears lips since they were brand new last season and went to DOT4. I planned to rebuild the rears with ring seals if still leaking. Brakes work great and haven't leaked since. 4 years trouble free. My conclusion stay away from silicone brake fluid with the seals currently available. Have 5 pint bottles of DOT5 for pickup by the first taker.

 

I think getting away from non-stainless bores and lip seals is the thing to do. Stainless steel sleeved units that use orings on the pistons instead of lip seals is the answer

 

Leigh
You're keeping pace with tech work in retirement. Good

I will only add, for close to 50 years of vette ownership, ss lined calipers, lip seals, runout under 003", bearings dialed in for no lateral play, and bleeding the system, the brakes were fine.

Now, with that said, not driving the car as I once did, letting it sit for months, NOT changing the Brake Fluid as I know I should have, I have to do a complete brake job. Completely my own fault, I just haven't had time for my own car.

 

I was fooling around with the thought of replacement stainless pistons in our OEM units kinda still working on it 😂😂

 

Many of the replies are anecdotal and mine is no different...
My '67 has had the same SS lined calipers, lip seals, and, until last summer, the same pour of DOT 5 from the mid-'80s. This car sits in the garage probably 355 days a year and it's never had any leaks.

I don't think the lip seals rely on the thin edge; when installed, most of the seal's side wall is in contact with the bore. Piston to bore clearance (with no seal) should be 0.005" to 0.010" (1 to 2 sheets of paper). That's not much clearance for the lips to extend outward much at all.

Our brake systems exert about 600 psi with about 100 pounds of pedal pressure. There's an important design characteristic of lip-seals under fluid pressure: with the reversed "cup" design, lip seals expand against the bore and become more effective as they experience more pressure. O-rings certainly don't behave this way and while I'm unsure about square-cut rings, I'd think their sealing abilities do not increase either.

 

Anyone have direct experience with DOT 5.1 fluid ? (Not DOT 5) repeat DOT 5.1 ?
If so, your direct experience's assessment please ?

*Have no interest in comments about any fluid other than DOT 5.1 Not interested in arguing pros & cons of x, y or z either; Nor speculation.
? What is YOUR direct experience with DOT 5.1, please ?

 

None. I ran DOT 4, then skipped DOT 5.1 and went straight to BOSCH ESI6-32N. (Amazon link). Kinda spendy, but check the specs.

I've taken apart a fair few calipers. None of them have looked as bad as the images above. Perhaps I'll find something like that when I get to the calipers that have sat since 1995.

 

I did not know that the Wilwood D8-4 calipers do not have dust seals.
Someone brought that up.

Someone else pointed out that the aluminum OEM pistons have a very short piston skirt. They certainly do. This very likely leads to more piston rocking, and would cause increased seal leakage. I did see several scored bores where pistons were cocked and jammed in their bores, in the dozen or so that I dissassembled above. Several pistons had to be hammered on to knock them loose, they were jammed so badly in their bores. The pistons are necked down to accommodate the groove for the dust seals. The piston skirt is very short, and only exists around the lip or o-ring seal.


Very short piston skirt. less than half of piston depth.


Wear mark from piston rocking..

However the Wilwood pistons, and all the modern OEM ones I have seen, have smooth sided stainless pistons with full depth piston skirts. There must be a lot less piston rock. Perhaps this another important reason why the originals absorb so much water.


Wilwood piston with full depth piston skirt, for a 1.88" D8-4 front caliper.

Someone correctly pointed out that this piston rocking could easily compromise the integrity of the bore seal. That compromised seal would contribute to the water intrusion or brake fluid leakage. The springs are there to help minimize this. Many other calipers do not require the assist of springs, with a deeper piston skirt.

All in all, this caliper is a 50 year old design.
It was one of the very first of it's kind, in a production car.
50 years of development has brought some improvements, primarily in resistance to internal corrosion.
The performance is still hard to beat, even 50 years later.
With careful replacement part selection, the original design calipers can still remain very reliable, for long periods of time.
They just require a little more regular maintenance, and care, than more modern designs, that people may be more accustomed to.

My intent here was just to clarify weak points in the design, and offer solutions, so that owners could ensure that they are addressing each of the potential corrosion weakness, and have safe reliable brakes.

If you treat / abuse these as badly as most people treat modern brake systems, they will leak on you.

 

Interesting post to get one thinking...
I'm thinking the necking down may have been to minimize braking heat transfer to the fluid rather than being done to accommodate the dust seal.

 

WTF
how one gent has so many junk calipers and pistons; is sumting wong ?
and, in the realm of brake fluid; it's hyGroscopic.

 

I help out part time at a local Corvette Service & Repair Shop, more for fun than anything.
My part time retirement job.
So I have seen more Corvettes than most.
That might be about 6 months worth of leaky calipers from there.

 

Great writeup, Leigh!

Im with Gary (GTR1999), though, as I have posted numerous times over the years (and others as well), about SS calipers, lip seals, and zero leaks!

I put on 4 SS calipers with lip seals all around in Fall 1986 from VBP. My car sits 99.99% of the time, often months at a time, with no special procedures like going out to the garage and stepping on the brake pedal weekly or monthly, just driving the car at will when warmer AND changing the brake fluid every 3-5 years, religiously..Dot 4. Dot 5.1 is a higher temperature Glycol based brake fluid, NOT silicone brake fluid like dot 5. Some brake seal vendors explicitly state that using Silicone brake fluid voids the warranty since it can and will swell the seals.

Honestly, Gary hit the nail on the head about making sure there is minimal rotor runout (causes air pumping into the caliper) and changing the brake fluid often (3- 5 years). Like Gary, I am going on 40 years with lip seals in the calipers with no leaks. Besides the O ring caliper seals also leak quite a bit, if not maintained.

As I have stated often, if the rotor runout is minimal, the brake system is properly maintained, primarily with brake fluid flushes, I would say the O ring seals are, at best, marginally better, than the lip seals, in a properly functioning C2/C3 brake system. Pretty tough to argue with a C3 brake system with SS calipers, lip seals and no leaks after 40 years! The brake leak system solution appears to lie elsewhere..IMO

 

Agreed there seem to be several "recipies" for making the OEM calipers live. But those 3 features do seem to come up the most often. (1) Rotor runout, (2) SS sleeves and (3) regular fluid changes. The introduction of air would certainly accelerate the iron corrosion, as well as bring humidity with it. And the 3-5 year cycle of religiously changing the brake seems to work well in that circumstance. I apperciate Gary's honesty by admitting he went many years without changing the fluid, and now he needs a full brake job. That fluid change just can NOT be skipped.

 

If the seals are not EPDM, then there is risk of swelling and softening. EPDM has been a standard seal material for over 65 years; it's an "old school" elastomer for brake components. It's perfectly fine with silicone fluid, as well as the other DOT fluids, and always has been. The Raybestos caliper seal kits contain EPDM seals.

 

I'll heed CSSB Inc.'s warning and continue to never use DOT 5.0 silicone fluid.

The O-rings in their high-heat kits are not EPDM, but have worked for 7 years on a DIY rebuild (starting with clean, previously rebuilt, SS-sleeved calipers).

It seems I'm overdue for a brake fluid refresh, though. Oops.

 

And I'll tell CSSB to take their junk parts and file em.
And I will run quality parts and DOT 5.