11 replies to this topic

[edi57]

I need to refurb a set of calipers in the next few weeks. I was going to just place an order with Minispares as you do for these Stainless Pistons.

However, a browse of ebay led me to these Aluminum Pistons.

I've never heard of aluminium brake pistons before and just wondered if anyone had any thoughts on them.

Ed

[sixwheeler]

I need to refurb a set of calipers in the next few weeks. I was going to just place an order with Minispares as you do for these Stainless Pistons.

However, a browse of ebay led me to these Aluminum Pistons.

I've never heard of aluminium brake pistons before and just wondered if anyone had any thoughts on them.

Ed

Not suitable for passenger vehicles really. Corrosion, scoring, boiling brake fluid and leakage....

[edi57]

Ok sounds rubbish. I'll stick with Stainless.

[robson]

Not to mention how weak aluminium is compared to ss. SS will have a much more reasonable lifetime too

[lorry]

Also aluminium has a lower melting point than stainless steel and it will become a lot weaker when at the temperature of brakes.

[Strontium Dog]

Do any of you actually have any evidence to back these statements up?

Firstly, anodised aluminium has a megga hard surface which is ideal to resist wear and/or corrosion. anodised aluminium is oxidised alloy with the pits formed filled with a dye. Aluminium oxide is used as an abrasive on stainless steel!

Secondly, the heat generated by braking is going to be the same regardless of the piston material.

Thirdly the aluminium pistons should be lighter thus reducing unsprung weight!

That's my twopennith anyway although I have not looked at the Jonspeed pistons myself so can't comment on them specifically!

Oh yes, and as to the aluminium not being up to the job because of working temps. then why do people use alloy one piece callipers for racing?

Cheers. Si.

Edited by Stronteum Dog, 09 October 2008 - 09:22 AM.

[Ethel]

I'm not sure I'd trust technical information off someone who doesn't spell braking correctly! Even so, I don't see why they wouldn't work. But, even though your brake fluid would have boiled away long before the aluminium melted, aluminium would expand more giving the seals a harder time. More critically being a better conductor just means more heat would be transmitted from the back of the pads into the brake fluid.

I don't think hardness is much of an issue, I'm sure they will be harder than the rubber seals they run on. It's the friction and abrasive effects on the rubber we ought to be considering.

[Strontium Dog]

I'm not sure I'd trust technical information off someone who doesn't spell braking correctly! Even so, I don't see why they wouldn't work. But, even though your brake fluid would have boiled away long before the aluminium melted, aluminium would expand more giving the seals a harder time. More critically being a better conductor just means more heat would be transmitted from the back of the pads into the brake fluid.

They may well as you say transmit heat better than stainless but as I am sure you know, it is very hard to get two components to do so without the use of heat sink paste etc. Two non rigid coupled parts (especially with a squeal shim between them) will not conduct very well at all! Alloy pistons are used in race applications so I don't see a problem using them on the road. You could/should use dot5 fluid for severe use anyway which will reduce any tendencies to boil!

I don't know how much more abrasive to the seals though but if they are well made I doubt there would be a significant problem.

Edited by Stronteum Dog, 09 October 2008 - 09:34 AM.

[Ethel]

The heat that makes my calipers too hot to touch must come from somewhere and the anti squeal mastic gunk on the back of the pads on my van has a piston shaped hole melted in it. For the conduction issue - if the caliper can dump the heat faster than the piston picks it up you're on to a winner, quite possible on a race car with alloy calipers and ducting. I'm not so sure about a road car where a spot of heavy braking could be followed by a minute or two of standing in traffic.

I agree that they can't be too bad or the compo claims for bent cars would have seen them withdrawn from sale.

[stardude]

bear in mind that these are 'hard anodized'

its like super anodizing. hard anodized aluminium is highly resistant to corrosion and wear, and had good thermal insulation

if BMW use it to line the cylinders of their modern V8 engines, its obviously more than capable of taking the heat from the brakes, and there are no problems with it scratching or wearing

[Strontium Dog]

The heat that makes my calipers too hot to touch must come from somewhere and the anti squeal mastic gunk on the back of the pads on my van has a piston shaped hole melted in it. For the conduction issue - if the caliper can dump the heat faster than the piston picks it up you're on to a winner, quite possible on a race car with alloy calipers and ducting. I'm not so sure about a road car where a spot of heavy braking could be followed by a minute or two of standing in traffic.

I agree that they can't be too bad or the compo claims for bent cars would have seen them withdrawn from sale.

The heat transmitted to your calliper is not only via the pistons. In fact I'd suggest that they only play a small part in the total heat transfer. They are only firmly in contact with the pad under braking and will not be making a very positive contact when not. Where the pad sits on the calliper is likely to transfer more heat for more of the time.

As too heavy braking and then having to sit in traffic then I would wonder where you are driving. I think I would get told off if I mentioned doing that! If you are getting your pads hot enough to boil your fluid then you have probably glazed your road pads anyway and if you run fast road/track pads then you'll find it hard to keep them warm enough to work properly on the road most of the time these days anyway!

[robson]

hard anodized or not, think of it like this:

if you had a sheet of both, a nail and a hammer, using the hammer with equal force on both, the dent to the al will be much greater than ss. It is only a coating, not a material hardening process. I can cut through a hard anodized tube with a hacksaw in seconds, id like to see you try the same with a ss tube!

(slightly stray from intended usage) Id still go with SS, weight saving of 20g isnt worth it!