Topic: Making My Own Phenolic Brake Pistons?

[DaveBarbier]

I'm slowly doing an R6 fork swap on my 550. I got the calipers used and they're in fine shape, but 3 of the 8 brake pistons have heavy pitting, the others have very light pitting. Only one is in perfect shape. New steel pistons go for like $50 each, that's crazy. What is the likely hood that I can machine my own pistons out of a phenolic material? Is that more of a job for a very experienced machinist? I see it as just making a cylinder to a specific size. Doesn't seem that hard but because this is the brake system I wanted to ask. Anyone here machine phenolic material?

I don't know if there are different kinds of the phenolic material, but on eBay I can get 1.5"x20" round bar for $40.

[eigenvector]

I think regardless of what you use you'll need to machine the piston to very tight tolerances.

I would only trust this to a machinist - in which case go with steel.

Did I read that right - 8 pistons?  Is that 4 in front (dual caliper) and 4 in back (dual caliper)?

[DaveBarbier]

It's dual disc so two calipers and each caliper has 4 pistons. Yeah, that's a lot, haha.

Yeah, I see that it has to be very precise, but if I were going to do steel it would have to be stainless just to prevent corrosion. OEM ones are chromed.

And I'd only use them if they mic up exact after machining.


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[DaveBarbier]

Hmm, not so sure how easy this is to machine. On some machining forums it seems like a pain in the a$$. Dust everywhere and it tends to leave fuzzy finish apparently. Might be getting dissuaded.


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[BobbyR]

I believe that some cars use the same size phenolic piston. There was a thread on that somewhere in here.

[RAFster122s]

I think it is a Lincoln LS or Jag model that was shared that sourced the Phenolic pistons that Godffery sells now as the original guy quite handling them  they were cut down to fit the stock single piston caliper used on many cbs and other bikes.

There are some versions of the Ford Crown Vic which used phenolic caliper pistons but I do not know the size of those.If you could talk to a brake remanufacturer/rebuilder here in US they might know the sizes.  Getting to speak with an engineer that was friendly and would take the time to help might be another challenge.  Short of that, if you had a friendly manager or employee at the local NAPA they might be willing to let you mic out some of their replacement pistons.  It could be like trying to find a needle in a haystack...

The phenolic pistons have a very very smooth finish that carries a glossy sheen, any machining of the surface will not have this ultra smooth finish.  Any texture to the part will cause drag...
So, the ideal method is to find one of proper diameter and trim the open end of piston to length required.

Many high performance brake systems will use phenolic pistons, but the industry still uses mostly chromed steel pistons.

What diameter pistons do your R6 calipers have?

David

[DaveBarbier]

Hmm, yeah maybe that is an option. These are small pistons though. I don't see a car having pistons this size. Also, and this makes it double hard, each caliper has 4 pistons, but two are smaller than the other. Each caliper has two different diameter pistons.

Sizes:
Big one = 30.17mm (1.1875") x 21.62mm (.85")

Small one = 26.98mm (1.062") x same length obviously


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[DaveBarbier]

I just noticed that even on a metric bike those are imperial sizes. 1-3/16" and 1-1/16". Interesting.


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[RAFster122s]

The ones for SOHC4 that available are nominally 38mm.  I had asked the original guy who had found these if he could get 43mm pistons for another Honda bike I had...no source.  Not sure how he found them...

I did a search for Phenolic caliper piston and there is a Chrysler piston that is 30.xx mmin diameter.

The Ford F250 uses a 60mm phenolic piston.

The rear caliper on the Ford Crown Vic could be either a steel or phenolic piston until 2003.  After that point they went to a metal pistons exclusively.  Many applications will use the phenolic for heavy duty or high performance...this is especially true on motorcycles where the light weight and heat insulating properties are great for not transferring the heat to the fluid.  Far less or eliminating brake fade caused by the hot fluid.
But, you probably know these benefits and reasons.

The Chrysler piston is metal capped for some reason.  It also appears to be quite tall.

David

[RAFster122s]

Audi Q7 phenolic piston is 32 x 28 mm
apparently they used a 30, 34, and 38mm piston

Some Ford F250s used 56mm pistons, also phenolic...

[DaveBarbier]

In posting a thread over at an R6 forum it kind of appears that people rarely disassemble calipers and replace pistons. I've read multiple threads and watched videos of them saying to pump out the pistons a bit when off the rotors and use a tooth brush with brake fluid to clean off the exposed dirty piston, then you're done. One guy who's replying said he's never seen these pistons pit before, he's alluding to me buying another used set and seeing if the pistons are better.

Where are you finding the piston sizes? I've been looking but no place I find lists the actual dimensions.


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[RAFster122s]

Ebay searches, digging through threads.  Centric makes a boatload of replacement pistons but you will not find them listing the size.  I am pretty good at digging up some details, having been a technical writer for a decade did not hurt those abilities when sources (SMEs) couldn't be bothered to give you a lot of info.
Communication was our business, not our policy was the joke amongst some of us while working at AT&T, long ago...

I need a set of 30mm for a twin pot Honda caliper, well not really sice I already bought a pair of K&L pistons, but it might improve brake performance when pushing the bike through the twisty mountain roads when riding for fun...

The twin pot common Honda caliper used in 80 s and beyond was either a 30mm or 32mm. FYI

Imagine they opt for the replacement route more often and their focus is on other aspects of the bikes rather than we typical Honda guys who focus on details more...they focus on perf and improving riding and since they need not worry about brakes and improving them then it is not a focus point for them...

[simon#42]

i make mine out of alloy then get them anodised , they work fine and have yet to wear one out

[DaveBarbier]

i make mine out of alloy then get them anodised , they work fine and have yet to wear one out

Alloy mean what? Steel? Or an aluminum alloy?

[simon#42]

aluminium , its easier to get a good finish and its light . brembo and nissin use them in their better ranges of calipers .

[RAFster122s]

Hard anodized or regular anodizing?

[DaveBarbier]

aluminium , its easier to get a good finish and its light . brembo and nissin use them in their better ranges of calipers .

Experience any brake fade from boiling liquid? Normally the aluminum pistons have an insulator between the pad and piston. I believe some Corvettes have an option for aluminum brake pistons too.

[simon#42]

i get them hard anodised but normal would be fine
have experienced no difference in brake fade compared to steel pistons even after six laps of the isle of man .

[DaveBarbier]

Thanks Simon, I'll keep this in mind.


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