Yes, the teflon seal is the only fluid seal. Omitting the dustboot sounds ridiculous, given that.

Cheers

Greg Locock

Alrighty :) thanks.

I used to work for an OEM brake supplier. All of our caliper piston seals were square cut EPDM rubber.In addition to sealing, the seal resilency also causes piston retraction when the brake pedal is released. I've never seen a teflon seal.

Any drawings?

As with Swall, I have seen many piston seals cut in a square profile, but also seen some that are more trapezoid in shape, and must be installed in a particular orientation.  The theory is that the profile helps retract the pistons from the rotors, reducing drag.  The downside is that it requires more piston travel (more pedal travel).  US GM vehicles, trucks in particular, had this problem.  Many were retrofitted with standard square cut seals to eliminate the excessive pedal travel issue.
I have not seen teflon piston seals, or any caliper without any dustboot for that matter.  There may be some limited application very high performance calipers without dustboots, but that seem counter productive to me.  Its amazing how little disk pad dust it takes to foul a caliper piston.
Franz

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Thanks for the info, keep it coming ... maybe because of the super high heat, some discs go quite high.

If you look at the wilwood range, you see quite a few of them not having dust boots.

ZoRG,

You may be interested in searching through the United States Patent and Trademark Office database. Patents typically have interesting drawings, cutaways, etc. One patent that may be of particular interest is this one:

5,181,588 Open framework disc brake caliper having an elastomeric cylinder liner

Enjoy!

Best regards,

Matthew Ian Loew
"I don't grow up. In me is the small child of my early days" -- M.C. Escher

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

Thanks

I used to in past use the patent office alot to do research, but found so many bogus inventions :)

Will look into it.

The biggest heat problems we saw were with medium truck hydraulic disc brakes.The silicone rubber boots would deteriorate, the phenolic pistons would deteriorate on the ends but the EPDM piston seals would hold up just fine.

I don't know if this is relevant, but many years ago (1970 something) I had a link pin front end VW beetle. A motorcycle company called Maiko (Maico?) made an aftermarket disk brake conversion for link pin VW and B series Porsche.

Being low volume, they used existing parts for seals etc, and being for a car with very light front axle loads they had very small calliper pistons, so other calliper parts were to small. They were a very high quality part with the disk being steel, the hub being magnesium and the calliper and piston being mainly magnesium and stainless steel.

To cut to the chase, they sealed the calliper piston with a Reo truck master cylinder rubber cup type seal and used what looked like a cylinder ring with a coil spring behind it in the land to retract the piston. The ring and spring package was set up maybe 0.020" from coil bind.

The stainless steel piston ran in a stainless steel sleeve, so corrosion was not a problem. The bulk of the dust was kept out by an "O" ring seal close to the outside edge of the calliper bore. There was no further dust seal.

As pads were not available, I had my original aluminium backing plates relined with DS11 material.

These were a very unusual design with 5 spokes from the hub bending in just inside the tyre change well of the rim and the disk mounting to the spokes, with the friction area on the stub axle side of the mounting bolts, and the calliper straddling the disk from the stub axle side.

This gave about a 12" disk on a very light car with a rear weight bias, so I guess the brakes never got real hot despite my efforts to the contrary.

I used to reduce dust contamination by coating the area where a dust seal would be with lithium based grease. In over 100,000 miles, I never had a problem with the callipers binding.

This is all from memory from the 1970's so there might be some inaccuracies, but the concepts and most details are correct.

Regards
pat   pprimmer@acay.com.au
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Another thought.

Dust seals are essential on daily use cars as they must continue to operate in dust, mud and dirt for sometimes years, without maintenance.

A race car would receive maintenance after every outing.

As race components are not nearly so cost sensitive, the use of expensive materials like magnesium, titanium and stainless steel can help overcome problems with choices not available to a production car, but also, the cost of amortising moulds for very small volume can be prohibitive, even when the extra budget per item for race cars is considered.

Regards
pat   pprimmer@acay.com.au
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As noted earlier,  the seal cross-section is usually square, rectangular, trapezoidal - something that will twist under small amounts of piston travel but slide with large displacements,  thus compensating for pad wear.

The twist in the seal produces the "rollback" necessary to prevent excessive brake drag;  this parameter is carefully tuned to prevent excessive rollback, with the resulting excessive piston travel and therefore excessive pedal travel.

Still,  if you want the very minimum in brake drag,  you'd need the old standby, drum brakes,  which can be adjusted for zero brake drag and because of their relatively small wheel cylinders still not have excessive pedal travel.

On the wilwood catalog is says dustboots are required on the calipers with aluminium pistons, the ones with stainless pistons all have a dustbootless design, they are all high performance models I suppose with high maintenance in mind.

My Wilwood 6-piston brakes have no dust seals.  There really is no room for them.  Not ideal for street use.  I guess wilwood is saying the stainless can withstand the abrasiveness of fine brake dust better than soft aluminum.  Aluminum pistons are a terrible idea anyhow.  They conduct heat to the fluid.  I guess if the fluid is continuous flow through the calipers and has a fluid cooler inline somewhere, this is a good thing, but 99% of cars don't use that feature.

As stated above, I have never seen a road car caliper without dust boots to keep dust and gritty water away from the piston.

Real racing calipers rarely have these dust boots fitted. The pistons retract flush with the inside face of the caliper allowing more room for a thicker pad.

What I have sometimes seen on racing calipers, is a thermal insulator placed between the pad backing plate and the piston.

I'd like to know more

IMO Wilwood used no dustboot on the infamous DynaLite caliper I think it's called.  SS pistons, no dust boot - made for smaller sprint cars that get rebuilt often they are inexpensive.  Some designs also use a seal at the edge of the bore - but this does not protect the piston when it is more fully protracted (pads near wear limit)

The boots melt pretty readily under racing conditions hence no boots on many racing only calipers.

I like the mentioned idea of putting some silicone grease, or whatever goop will stay there at those temps and not interfere with piston movement.  One problem with grease is as well as it may block dust from entering, it keeps much more dust there to begin with.