I was replacing rotors and pads and noticed that there is a rubber boot on one caliper's piston and only the remains of one on the other piston on that caliper. The other front caliper only has the remains of the boots.

How important is this boot? I can't say I've noticed them on any other calipers I've ever messed with.

Do I need to rebuild the calipers and replace this boot?

Thanks!

Karl

 

Karl,

Those are piston dust boot seals. They are very important. As the name implies, it keeps contamination out of the very fine and precise piston bores. If something abrasive (sand) gets in there, they will score the surface and cause leaks. If dirt gets in there, the piston could get stuck and not retract causing rotor, pad and caliper damage. All hydraulic brake calipers have these rubber boots...... even the drum brakes.

You could just manually push the piston out a bit, use a brake cleaner to wash everything, then replace the dust seals. Bleed the brakes and hope. However, GM spec calls for caliper overhaul if the seal even shows deterioration, let alone a tear or not being there. You could consider this a temporary fix.

Personally, you should remove the calipers and take them apart. Clean them in brake cleaner followed by alcohol. Blow all passages with compressed air and let dry overnight. Inspect them for cracks or other damage. Put all new seals (dust and piston) and reinstall. Bleed brakes.

You do need to have your pistons and calipers fully inspected in good lighting. Also check to make sure they slide easily without any binding. Don't be surprised if you have to replace these parts. The missing dust boot can cause rapid wearing and rust to enter this area.

 

:iagree:

The boots are very important. They keep debris off the piston and out of the bore. Damaged or missing boot will allow debris to enter the bore and eventually damage the pistons/seals resulting in a brake leak/failure in that brake hydraulic circuit.

Kevin

 

Thanks for the info. I'll get on it!

 

We melt those on the road course all the time, and we really don't worry about them. The only time to pay extra attention is when you push the pistons back into the calipers - you need to clean them off before doing that if you don't have the boots. Otherwise, don't lose sleep over it. It may differ for you as here in AZ we really don't have to worry about moisture, and we bleed the brakes regularly for track anyway.

Sam

 

Sam,

That is good to know. I don't expect that water will be much of a problem. I rarely drive the car in the rain, and part of the pistons are exposed even with the boot on and they don't show any signs of rust (I guess their aluminum or stainless steel).

I was concerned about how to prevent this and don't really want to have to rebuild the caliper each and every time I do a track event.

I'll probably do what you recommend and just keep and eye on them . . .

Karl

 

Lack of dust boots is why Wilwood says their calipers are not recommended for street use, but plenty of racers leave the dust boots off. If you pay close attention to your fluid and pedal feel, and bleed as appropriate, you'll be ok.

 

You racers :rolleyes: :D

I picked a few excerpts of the internet. Seems the rubber boots aren't able to handle the heat........

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Dust boots: Rubber shields that fit over the exposed portion of the caliper pistons to prevent the ingress of dust and road crime. As no known rubber compound will withstand the temperatures generated by racing brakes, dust boots are not used in racing and should be removed before truly hard driving for extended periods.
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For longevity, every street car has dust boots that go around the caliper
pistons. These boots are there to keep moisture, dust, dirt, grease, oil,
etc out of the piston bore. If you get the contaminants in there then the
piston bore can rust, get scratched, and even damage the piston bore seal
("o-ring") and piston.

Calipers designed for racing applications are not subjected to the same
design limitations. Racers are expected to rebuild parts weekly, or at least
inspect them after every racing weekend. Therefore the designers can leave
out those parts that are not needed, or that can actually cause failures
(such as the melting of rubber parts due to high temperatures.) Plus, racers
are not concerned about brake noise, simply performance. Hell, even if the
brakes did make noise, some of the NASCAR applications that Wilwood caters
to are so noisy anyway that you wouldn't hear the brakes.

Wilwood calipers are designed solely for racing. Wilwood's engineers never
considered that Audi (and other) fanatics would take their bargain-priced
(yet high racing quality) components and use them on the street. Thus, these
calipers do not have dust boots, nor do they have the ability to use
rattle-reduction clips. They were designed to produce the maximum braking
torque at the expense of all other niceties.

If you use Wilwood calipers, you should expect to rebuild them annually at a
minimum (not expensive, just time-consuming), and expect brake squeal and
rattles. This is not "dangerous", it just requires your additional
maintenance and attention. In return you get a high quality caliper and
low-cost rebuild parts and many, many different choices of pad compounds.
However, it will not be supported by Wilwood, and they are quite adamant
that their parts are for "off-road use only."