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Hi Chris,

Yeah, there are a lot of uninformed people making statements of fact on forums... Most people seeing statements in writing believe them to be true so it doesn't take long for a factoid to become gospel truth. I've been dealing with Wilwood and their 'no boot calipers' for 22 years and here's my opinion based on my experience:

Road grime, dirt and especially moisture can corrode production type caliper pistons leading to premature failure of the piston seals rendering the caliper inoperable.

Vehicle manufacturers typically design their products around a minimum criteria list which almost never includes special materials for components such as caliper pistons. Many production style caliper pistons are therefore aluminum or other easily corrodible metal for obvious reasons, not least of which is cost. It is less expensive by far to make aluminum pistons and rubber boots than to make stainless steel pistons for example. A huge percentage of production car calipers HAVE to have dust boots or they may not last to the end of the warranty.

Aside from some of the obvious weight and capacity drawbacks of production calipers, dust boots can be a hazard to high performance drivers. Brake components are designed to convert all that motion to heat energy and then dissipate that heat. The heating and cooling cycle occurs with higher frequency under spirited, or race driving conditions where it is not unusual to develop enough heat to make rotors glow red hot. Radiant and conducted heat developed under hard driving conditions can easily heat the calipers to the point where the brake fluid boils and the boots burn. Dust boots are not installed on true racing calipers.

The best solution for safe and reliable high performance calipers is to eliminate the rubber boots, build pistons from good quality, non-corroding stainless steel and make sure the caliper bores are anodized. We have been supplying such calipers for high performance street and race use for over 20 years without complaint. Our experience has been that companies who do build aftermarket calipers with dust boots make an issue of this fact to justify the exorbitant cost of their products.

If we examine the dynamics of caliper function we see that the pistons actually, stay pretty well where they are and the brake dust coats that part which protrudes from the caliper body. A typical brake application cycle sees about 0.20 mm (1/5 mm) of travel per piston. There is about 3 or 4mm of piston bore outboard of the hydraulic "O" ring before the piston sees the outside atmosphere. In that area the clearance between the piston and bore is around 0.075mm. It takes a pretty small dust particle to travel all the way to the hydraulic O-ring and when it gets there it's typically too small to create any real havoc. So, you get dirt building up on the exposed part of the pistons and that's about it.

Problems develop when it's time to change pads and your production oriented brake technician simply presses the pistons back in with a clamp and shoves all that dirt into the cylinder past the seal. The "trick" is to scrub the piston protrusion with a stiff tooth brush and soapy solution, then blow dry BEFORE you shove them back into the caliper...
The down side is that it takes and extra 30 minutes (on a bad day) to change pads which you may have to do every 50,000 km or so on a street driven vehicle. Amortized over a year or two that's not a big chunk of your life or your paycheck.

The upside is that a regular guy can afford to purchase a serious brake upgrade that works every bit as well as that $3500 Alcon or AP system he's been looking at. And if he really decides to drive all that horsepower he ‘shoehorned’ into the engine bay he won't be retiring early (as the competition may) because his dust boots are on fire....

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Originally posted by clairetoo
Sounds plausible to me .............. but how come M16 calliper's start seizing as soon as the dust seals deteriorate ?

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