brake caliper seals - o-rings now? 2

[Tmoose]

some Corvette specialists are supplying 0-rings seal as the primary pressure seal for disc brake calipers. Unfortunately they are referring to the OEM seal as a "lip" seal. I would describe it as a square or rectangular section O-ring, but not a lip seal. Anyhow, I believe all the calipers I've worked on (Volvo, yamaha motorcycle, various Ford, Mopar and GM of the 70s and 80s) have used square section rings.

Are o-rings really used in brake calipers (since 1982)?

http://www.cssbinc.com/images/ads/howto/frontbrakecaliperrebuildinstructions.pdf

thanks

Dan T

 

[MikeHalloran]

The barriers to entry for "xxxx Specialists" are rather low.

O-rings can't be relied on to pull the piston (and pad) back from contact with the disc, so they're a completely inappropriate choice. I'm sure they're much cheaper than the real OEM square seal rings.

On second thought, they might work, after they've allowed the pads to rub on the rotor enough to warp it, so the resulting wows in the rotor will knock the pads back a bit. Fine, I guess, if you don't mind the pulsating pedal and short pad life.



Mike Halloran
Pembroke Pines, FL, USA

 

[patprimmer]

I have only sen square section rings in all but one caliper. The odd man out was an aftermarket disk brake conversion for early Beetles. It used a truck master cylinder, lip or cup seal and the spring back was via a metal coil spring arrangement that gripped the piston and allowed it to apply and pulled it back just like the square section rubber ring seals do.

An O ring will eliminate the pull back effect that a square section ring gives.

Regards
Pat
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[MikeHalloran]

The average customer for a "Specialist" will never know.
He'll blame the pads for their short life and everything else.



Mike Halloran
Pembroke Pines, FL, USA

 

[swall]

Then he'll try cryo treatment.

 

[MacGyverS2000]

Mike / Pat,

I'm curious... how does a square cross-section allow for pullback that a round cross-section doesn't? My guess would be a standard o-ring would not completely fill the square channel in the piston and therefore would shift itself (rather than the piston) during pullback. If so, could that not be solved by using a semi-circular cross-section channel... although that would likely create other issues by allowing the o-ring to slip right out of the channel, taking us back to where we started.

Dan - Owner

http://www.Hi-TecDesigns.com

 

[MikeHalloran]

I don't think the channel is quite square; more trapezoidal, so the seal can distort axially as pressure is applied while still gripping both piston and caliper surfaces. Then as pressure is released, the seal tries to return to square-ish cross section, pulling the piston back. As the pad wears, the piston slips slightly within the seal, sort of resetting the trap.

Disc brakes of the 50s had complex and unreliable mechanical pullback mechanisms. All of this stuff with square seals was worked out as disc brakes entered serious mass production and encountered serious price pressure and serious performance, life, and warranty cost pressure. The current OEM seals (and gland shapes and micro-finishes of every mating part) comprise a highly evolved and highly interdependent system. Substituting generic seals of other shapes is the height of arrogance.

Maybe 'arrogance' is too strong a word; I'm sure no malice is intended; 'ignorance' might be a better choice.


Mike Halloran
Pembroke Pines, FL, USA

 

[swall]

Mike's got it right.

 

[evelrod]

Never too old to learn something new. I'm not much into Vettes these days, my old Vette had drums...I have, however, rebuilt more than my share of calipers for race cars, none of which use common 'O' rings. I think I'll stick to what has worked and leave the round O rings to others to play with.

The question of "pull back" better referred to as 'knock back' is something I prevent by keeping my rotor run out to between 0.002" and 0.005". If it gets more than this, approaching a hard brake corner will require a double pump. I do the double as a matter of habit, but some racers find it disconcerting.

Rod

 

[Tmoose]

I think "pull back" is what the rubber seal does to the piston when the hydraulic pressure is released. I think "knock back" is what the rotor does to the piston as a result of runout, loose wheel bearings, etc.

 

[dgallup]

"Reverse Air Oscillation" ???????????

"suck air into the caliper fluid area causing a loss of brake pedal" ????????????

I call BS.


In volume, there really is no cost difference between square or rectangular cross section seals and o-rings. Quad rings & other special shapes get a bit more expensive just because the tooling is a bit more difficult.

 

[littlekix]

Just to toss some more fuel on to the fire ... (This is on the second page I believe of TMoose Link)

"Furthermore, when lip seals are used on
a Corvette with warped or out of spec rotors and or
spindles, loose bearings or a Corvette that is driven
hard; they can actually suck air into the caliper fluid
area causing a loss of brake pedal"

Also why did GM move away from square seals to O-Rings in 82? That in itself I think is an rather interesting question....

From a vette forum
MrVette

"....
what happens is any runout that is there, the pistons follow the rotor back and forth really quickly, so that makes them suck air.....sure if you follow the old aircraft specs from the '50s when these thing were designed/adapted aircraft probably use springs....but this is a car, and not turned around and petted over every 2 minits of use....

..."

 

[patprimmer]

Mike definitely has it right.

Tmoose also has the terminology as I have always understood it. Pull back id designed in as desirable to avoid drag, knock back is an undesirable consequence of flex in the system and results in low pedal.

Pumping the brake brings back the pedal until the next hard corner, but bleeding the brakes makes no difference whatsoever even after extended cycles of knock back, pump up, so no air is entrapped.

The angles of the sides of the grove, the hardness of the rubber, the clearance between piston and caliper, the finish of the piston skirt and the friction between the piston skirt and the rubber ring all impact on pedal feel, self adjustment and drag and therefore brake pad life, fuel economy and brake performance as they build heat without deliberate application.

If some repairer put O rings in my calipers, I would be furious. Come to think of it, similar workmanship issues from dealers is why I do my own work on cars.

Regards
Pat
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[RossABQ]

Can anyone confirm that GM really went to O-rings?

My understanding from disc brake conversions popular on old Ford trucks is that GM master cylinders come with 2 psi residual pressure valves on the disc circuits. Wouldn't that negate the pullback effect anyway?

 

[LionelHutz]

Wow, it seems no-one understands these calipers.

These Corvette calipers used a lip seal, it would look something like this;

/----\

The seals in a master cylinder or a drum brake cylinder look similar.

This seal is attached to the piston. There is a spring behind the piston pushing it out. If the piston is pulled out the seal will easily collapse and let air into the fluid since that type of seal will only seal in one direction. These calipers are fixed mounted, meaning that with run-out the pistons will be moving in and out as the rotor turns. So, as the rotor turns and the piston is pushed out, air can get into the brake system.

Besides this possible air pumping issue, these calipers are also just very prone to leaking. The lip seal moves out into the "dry" side of the piston bore and any crap that manages to get into the piston bore can damage the seal. Also, the dry side of the cast iron calipers tended to rust and the rust would cause leaks as the seal moved into it. This is the reason why these calipers are always SS sleeved.

So, enter the o-ring seal. These new o-ring caliper kits are supposed to help stop the leaking and the introduction of air. I suppose the idea is that the o-ring is more robust compared to the lip seal. There was no piston pull-back in the original design so it's not expected in this o-ring modification. There is still a spring pushing the piston out. There are now many Corvette owners who have been running the o-ring design for years without issue and many of these converts had issues with the lip sealed calipers leaking that the o-ring design has helped eliminate.

FYI, that same caliper was put on model year 67 Chevy full-size cars (and intermediates too I think). The floating single piston caliper design was then released in 68. I suspect the 4-piston calipers on these heavily used and higher production volume vehicles produced so much warranty work and customer complaints that GM had to get them changed. Either that or GM just stuck the calipers on the 67 models to say they had disk brakes when they knew the better/simpler design was coming. GM used the same floating caliper design released in 68 up into the 90's and beyond. You can bolt a 68 caliper onto a spindle from a 96 GM full-size rear wheel drive car.

 

[patprimmer]

Lionel

Well we don't see many American made cars here. The market is dominated with mostly Japanese and locally made Japanese and American brands and a few European and other Asian imports.

I certainly have overhauled many Ford, VW, GM, Nissan and Honda calipers. Not one of the OEM calipers had lip or O rings. They all had square section rings exactly as Mike described and all functioned well without the problems you mentioned.

I really wonder why GM would not use a tried and true and simple method to fix a problem when it occurred.

If they are that bad at specifying brakes for a prestigious sports model like the Corvette, I can see why their products are generally not considered suitable for our market.

Certainly every caliper I have seen made by Girlock in Aus, Asin in Japan, ATE in Germany and I think Bendix in Aus and the UK. Whatever was used on early Jaguar and Mini Cooper.

The only caliper I ever saw anything like you describe was made in Austri (not Australia) by Makio for conversions for link pin front end Beetles and B series Porsches. They had an inner seal that was a Reo truck master cylinder seal, an outer dust seal, a silver coated SS piston and a SS sleeved aluminium caliper that floated by sliping in a rubber bush in a swiveling action rather than sliding. They had a short travel spring that compressed entil coil bind as the brakes applied, then on coil bind the piston slipped through the pin. On release, the spring retracted the piston until the spring was restrained by a seat or travel limiter. I nguess the spring had 0.010" travel maybe. It was like 1070 that I played with it. They had a second seal to keep air out and had an outer dust cover that lso sealed pretty well. They worked fine due to the build quality and a few little maintenance tricks I used to improve the dust cover seal.

I'm not saying that certain model Corvette brakes are not as you say, however I am saying that is an unusual system in our market which has models represented here from diverse sources world wide.

IIRC which is not a guarantee after 20 to 30 years, starting around approximately the late 70s or early 80s through to about 1990, Corvette brakes where supplied by Girlock from Australia. Patrick Sawyer was the Chief Engineer on the job. While I never paid particular attention to the seals as I was discussing originally brake booster body and controller valve parts with him, and later asbestos substitutes for pads, I am sure I would have noticed something as unusual as an O ring seal on the cutaway sample in their foyer and at times on his desk.

Regards
Pat
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[evelrod]

I don't like being confused, not that I have much to say about it. So...I went to the Chebby house and played dumb with the parts guy. Amazing how helpful these young fellers are to a dumb old guy...

Both repair kits are available. The std. and the updated "O" ring rebuild kits from several automotive parts stores. The parts guy seemed fairly knowledgeable and pretty much said the same thing that Lionel posted.

There is so much that I do not know about most of the modern era cars that I am embarrassed, being the local car guru and all. Seems the kids all know this stuff. Man...Sometimes it sure sucks to get old...

Rod

 

[MikeHalloran]

Thank you, Lionel, for depleting a tiny part of my vast store of ignorance.



Mike Halloran
Pembroke Pines, FL, USA

 

[LionelHutz]

Pat - This Corvette caliper is 1965 technology and was likely GM's first production disk brake caliper, and was also one of the first production calipers from a US manufacturer. I'm not sure what tried and true technology you believe they were supposed to be using back in those days.

Girlock likely supplied brakes for the 4th gen Vette which ran from 84 till 96.

The o-ring kit is not supplied by GM. GM has not used that caliper for almost 30 years now and would have no reason to re-design an obsoleted caliper to use an o-ring.

 

[LionelHutz]

Rod - You've got one valuable bit of knowledge. You know where to find a parts house with knowledgable staff If I hadn't been spending time working one a 78 (dad's car) then I wouldn't know much about the brakes either. I had a caliper apart last year and I spent some time reading the pro's and con's of the o-ring retrofit.