CVBowers

Just curious... getting fresh calipers and would like to keep the dust boots in a little better shape... anywhere to still get them for the OEM calipers?

Also, I'm assuming you just use them on the inner pad between the piston and the pad?

Thanks

freefall

pfyc still has them

http://www.pfyc.com/pc/GN4021/VTSUSP...t+Shields.html

davidfarmer

the stainless steel "beauty covers" that you can buy for brake pads works just as well. SS actually has very similar properties to titanium for heat insulation. Just use them on the inner pad, NOT the outter pad. I've found that using them on both retains too much heat in the pad, but you need them on the inside to protect the pistons.

I often actually drill some holes in them to let some heat through, but you want to protect the piston surface as much as possible, as I've melted several pistons out of calipers.


****actually, just looked it up. SS is quite a bit better than pure titanium, but I don't know what titanium alloys are available. SS is about 40% better than Titanum, which is about 90% better than aluminum.

On a similar note, I don't like running SS pistons in aluminum calipers, as the heat expansion rates are different. I've never had good luck with them.

Sidney004

What sort of issues have you seen with the SS pistons? Does the greater Coefficient of expansion result in a high temp seepage?

freefall

Titanium alloy (90% Ti, 6% Al, 4% V) is actually twice as good as SS, which is slightly better than pure titanium.

Conductivities:

Stainless Steel 14 - 16.3
Titanium, pure 15.6 - 21.9
Titanium Alloy 5.8

David - Does it really have time to cool down enough between braking zones (enough of a gap to not keep transferring heat to the shield)? After all, any of them will get heat soaked... I'd be really interested in seeing some measurements with the shields in there.

John Shiels

I never had a problem with SS pictons from DRM

John Shiels

I bet mica may be better.

69427

I too was trying to find insulators years ago. Reality and availabilty kept interfering with this pursuit. I had no experience with the durability of mica type products under the vibration and high localized compressive pressures seen at the caliper piston area, so I looked at metal based insulating material. Titanium looked nice, but I couldn't find a source for sheets of it. (I prefer not to pay the outrageous prices some guys are asking for custom cut shim insulators.) The thermal inpedance of SS looked good enough to significantly slow the heat transfer, while still being thin enough to fit when using new pads. I got a set laser cut out of a sheet of SS, and have been using them for years. I'm willing to move up to titanium in the future (assuming I can find sheets of it at a reasonable price), but I'm having good luck at the present time with the stainless insulators.

Bill Dearborn

John where did you get those spacers/insulators?
Bill

John Shiels

mica has been in my car for 1500-2000 track miles or more with just a slight imprint where the pistons contact them. PM sent.

If you look where the bridge bolt goes I had to file them which was a 15 second job. Material is easy to shape,

danswofford

Who sells SS shims?

Miaugi

I have a used set if you're interested?

gkmccready

How much pad thickness do you sacrifice to have those?

Solofast

Thermal conductivity changes with temperature, so when you are comparing materials you need to compare apples and apples… I doubt that there is a big swing between pure Ti and an alloy, like 6-4, simply because 6-4 is about 90% Ti anyway. What you are likely seeing is comparisons at different temps. Here is the data for a few materials from Mil handbook 5 (see note below)…

Titanium 6-4
Room temp 4.2
600F 6.1
1200F 9.5

Stainless Steels (301 in this case, but they are all pretty much the same)
Room Temp 10.5
600 F 13
1200 F 14.2

Nickel alloys (like IN-625 or Hastalloy X)
Room temp 6.0
600F 8.5
1200F 12.5

All of these things have a lot lower conductivity that alloy steel (which has a conductivity of around 30) so anything that you put in there will help. Just remember, that if what you put in there is thin, it doesn’t do all that much good. Also just having a joint in the conduction path is goodness too.

You can get Hast x or stainless sheet from McMaster-Carr, it is pretty reasonable, (not cheap, nothing about aerospace materials is cheap) but at least they will sell you a foot square and you can get it in a couple of days. A one foot square of .025 thick Hast X will set you back about $60.00. Stainless is relatively cheap, a 6” x 25” piece of .025 stainless is about $13.00. I would be using something like 302 since it is good to high temp and is cheap.

Note too, that you are looking at the conductivity issue here and less contact area will conduct less heat into the pistons. If you are putting something in there, you should really think about local drilling or cutting away material that is in contact with the piston, to reduce the surface area directly touching the piston. You have to transfer the force, but you can do that with a lot less surface area than a typical piston. If you cut away half the material, you will cut the conduction by half, which is a lot more than you will get from a thin piece of material alone between the pistion and the pad.

The best source for on-line material properties is Mil handbook 5. This has all you want to know about common aerospace materials, (hit Mil-HDBK-5), or try this link…

http://www.grantadesign.com/MILpdfs/MIL5-H/

John Shiels

I never measured them I usually do a day and then drop them in the calipers.

larryfs

I disagree with the entire theory.
adding shims would trap the heat in the pad and rotor.
I would rather dissipate the heat into the pistons, caliper, and surrounding area.

With fresh fluid, there is no concern of boiling fluild. But trapping the heat in the pads and rotor will cause fade.

davidfarmer

larryfs, I totally agree in theory. HOWEVER, I have physically melted the aluminum pistons out of the OEM calipers. They mushroom at the piston-to-pad contact point.

As I said, I attempt to drill the shims so that I leave gaps for heat to escape, just not directly into the aluminum pistons.

If you are all running full 4" brake ducts and spindle ducts, then you shouldn't be overheating anything. HOWEVER, in my real world experience, the shims help the hardware last longer.

John Shiels

you can still vaporize fluid if it gets hot enough no? Pads made to operate at racing temps should be ok with high temps. So I think it is better to isolate them.

larryfs

I run the SS pistons, maybe they are more durable with a higher melting point, but metalugy is not my thing. my setup has been very reliable with out shims, and only 3" ducts.

John Shiels

good info here Larry which your post made me search.

http://www.muggyweld.com/melting.html

1218 aluminum vs. 2550 stainless steel. Cast iron 2300 which surprises me thought it would be higher than SS