Prius XW20 aluminum front caliper upgrade for ZZW30

[Hammond]

yes.

It´s a straight swap. No other mods needed.

Have you fitted these all four corners then?

[jvanzyl]

Have you fitted these all four corners then?

It's only for the front.

[atlex]

For additional info on these they are actually handed, they have L & R on each caliper but you fit them with the letter facing up, this should orientate the bleed nipple at the top. Also from Autodoc they come with the OE Phenolic (plastic) pistons. These will be absolutely fine for road, but for track I changed them out for steel pistons as I dont want to take a risk of them melting.

What's the part code for the steel pistons ? I'm tracking my car too and don't want a melty.

[atlex]

I've ordered some steel pistons code 47731-47010.

The phenolic/bakelite pistons that came out were 54mm od and 46mm tall.

I did some testing with the phenolic - it's an interesting material.

TL/DR: @JB21 is spot on we shouldn't run these with phenolic pistons on track.

Longform:

It's an amazingly strong material and exceptionally heat resistant for a plastic - and an excellent stock piston / for a non-sporty use brake system. It's almost closer to a ceramic, to me.

I baked the phenolic at around 220c to heatsoak it. It didn't smell too bad. Didn't melt, either. A regular commute driven prius will probably never reach these temps either. Hence.. it's a good solution for this.

But under a heatgun it got to 300c and it was literally starts making a crackling sound [bacon frying] - remember your pads will get very hot on track and as the heatsoak in the caliper builds up you will get well over 200c. 10 laps maybe ok, but 30 could get it to this point.

Interestingly under the heatgun I could smell laphroig - the phenols of a nice peated whisky XD

See https://www.sumibe.co.jp/english/product/hpp/molding-compound/phenolic/index.html

"This makes it look like it loses at least 10% of its strength by 200C"

Remember that on track you will trying to get heat into the brakes to get the friction material up to temp. If you look at a track pad friction graph you will see they only get better as the temp gets over 200c.

The longer you stay out doing laps and harder you drive, the more likely these phenolics are to fail on you. We typically see the pads fade or the fluid boil first as a factor there. Caliper piston melting or cracking isn't really a normal thing.

As a final move I took the blowtorch and set it on fire - surface cracks appeared on the outside of the piston within seconds. Also the smell went from whisky to burning pvc. I could you could call this simulating putting the pads on fire. I've got (poorly edited) video of this if you want to see.

Tests suggested by @moca2cv aka John

[Petrus]

Thanks for sharing that factual test!

I baked the phenolic at around 220c to heatsoak it. It didn't smell too bad. Didn't melt, either. A regular commute driven prius will probably never reach these temps either. Hence.. it's a good solution for this.

Ergo even better for a 300 kg lighter ZZW30 also when spiritedly driven on the public road.
Ergo² for my 150 kg lighter still itsiebitsie. Barrelling down a smoldering southern slope in summer might look iffy at first idea, but the speeds are very low so the energy dissipated relatively moderate.

The lower unsprung weight of Enkeis & Prius calipers does make a notable difference in better road holding i.e. shorter stopping. Imo way more important on the public road than on track. The traffic density where and when I drive eliminates (knocking wood) the risk of being clobbered from behind by a less short stopping modern übersized car.

[MrChris]

An excellent and informative post by @atlex about changing out the pistons for steel ones that I was keen to find out the answer to.

@atlex what an excellent and informative post, I was keen to find out the answer to your original question and you went ahead and did a science experiment!

[atlex]

Also wanted to add that the phenolic pistons were amazingly heavy - I guess all that density goes towards maintaining strength under potential mild heatsoak - they were around 170 Grams each - I doubt the steel pistons will be much heavier.

Also consider what a track pad gets peak friction at - it's more like 500c on a trackday pad and it will be higher on a race/competition pad.

[Ardent]

Having given up with ebay I might as well just pull the autodoc trigger

[Joesson]

Having given up with ebay I might as well just pull the autodoc trigger

When I used Autodoc I was somewhat uncertain about what I wanted/ what was offered  and so took up their "return" deal. Did not seem overly costly. I did send some parts back , rubber front suspension bushes that I decided against and returned to Autodoc , without much trouble, and got SuperPro from TCB.
It was not an overnight service from Autodoc but within their stated time frame.
Would I use them again, yes.

[Ardent]

@Joesson thanks for that. I have been very reluctant to buy from them. But the time has come to grasp the nettle.
I always have this image of a good price then being spanked by HRMC for import or whatever duties. But I am not hearing that from those that have gone before. (or they have chosen not share that bit)

[inigopete]

Great work @atlex! I'll be interested to know the weight of the steel pistons; if it's within a few grams of the phenolics, seems like the upgrade is a no-brainer?

[Alex Knight]

Having given up with ebay I might as well just pull the autodoc trigger

What's wrong with an actual motor factor?

[Petrus]

Great work @atlex! I'll be interested to know the weight of the steel pistons; if it's within a few grams of the phenolics, seems like the upgrade is a no-brainer?

In the first thread on this (search Prius calipers is easy enough),  JB weighed the steel pistons to make the caliper 200 grams heavier.

For road it makes no sense whatsoever, for (serious) track use it is a must.

A3VT!

[Joesson]

@Joesson thanks for that. I have been very reluctant to buy from them. But the time has come to grasp the nettle.
I always have this image of a good price then being spanked by HRMC for import or whatever duties. But I am not hearing that from those that have gone before. (or they have chosen not share that bit)

No other bits to share J and sufficient time has passed that I can be very reasonably confident that I won't be having a knock on the door!
I also returned items and that was relatively painless, only having to print out a label and take the parcel to the Post Office.

[atlex]

I weight the phenolic vs steel and the steel I got are 466g, the phenolic 165g, call it 300g more?

the Prius calipers with the steel pistons are 1560g

I've yet to weight the stock calipers but others report those are 2500g, if that's true, this is still very much worth it.

[Petrus]

I've yet to weight the stock calipers but others report those are 2500g, if that's true, this is still very much worth it.

Go figure with the phenolics for the road. I réaly enjoy them.

Being aluminium the calipers dissipate more heat there too   It´s all win.  And that for a cheap straight swap!

[Joesson]

Go figure with the phenolics for the road. I réaly enjoy them.

Being aluminium the calipers dissipate more heat there too   It´s all win.  And that for a cheap straight swap!

All well and good but this "find" came after my brake overhaul when I replaced the rear calipers and renovated the fronts.
I did repaint the fronts with aluminium paint though, so maybe that will help!

[Petrus]

All well and good but this "find" came after my brake overhaul when I replaced the rear calipers and renovated the fronts.
I did repaint the fronts with aluminium paint though, so maybe that will help!

As with all things shared by anyone, it is take it or leave it @Joesson.
As with all things shared, it may very well be of hardly any or even no use to many others.

In general progressing insight is often a pita.

In the case of these calipers they probably came too late for the ZZW30 production too.
Does not change the factual benefits over the OEM ones

[atlex]

Now the question is.. what can be done for the rear ? XD

Is there some aygo or camry rear caliper drops a few grams ?

[ucb]

Now the question is.. what can be done for the rear ? XD

Is there some aygo or camry rear caliper drops a few grams ?

Good question, but there aren't any other mid engined Toyotas to choose from I suspect.
To my unenlightened mind the issue is the handbrake not the hydraulic foot brakes

[moca2cv]

I've ordered some steel pistons code 47731-47010.

The phenolic/bakelite pistons that came out were 54mm od and 46mm tall.

I did some testing with the phenolic - it's an interesting material.

TL/DR: @JB21 is spot on we shouldn't run these with phenolic pistons on track.

Longform:

It's an amazingly strong material and exceptionally heat resistant for a plastic - and an excellent stock piston / for a non-sporty use brake system. It's almost closer to a ceramic, to me.

I baked the phenolic at around 220c to heatsoak it. It didn't smell too bad. Didn't melt, either. A regular commute driven prius will probably never reach these temps either. Hence.. it's a good solution for this.

But under a heatgun it got to 300c and it was literally starts making a crackling sound [bacon frying] - remember your pads will get very hot on track and as the heatsoak in the caliper builds up you will get well over 200c. 10 laps maybe ok, but 30 could get it to this point.

Interestingly under the heatgun I could smell laphroig - the phenols of a nice peated whisky XD

See https://www.sumibe.co.jp/english/product/hpp/molding-compound/phenolic/index.html

"This makes it look like it loses at least 10% of its strength by 200C"

Remember that on track you will trying to get heat into the brakes to get the friction material up to temp. If you look at a track pad friction graph you will see they only get better as the temp gets over 200c.

The longer you stay out doing laps and harder you drive, the more likely these phenolics are to fail on you. We typically see the pads fade or the fluid boil first as a factor there. Caliper piston melting or cracking isn't really a normal thing.

As a final move I took the blowtorch and set it on fire - surface cracks appeared on the outside of the piston within seconds. Also the smell went from whisky to burning pvc. I could you could call this simulating putting the pads on fire. I've got (poorly edited) video of this if you want to see.

Tests suggested by @moca2cv aka John

God's work, Alex, thank you for doing this! Job for when it's time to replace the brake fluid next.