Topic: issue with phenolic brake piston

[Loki]

ok so i just bought two phenolic brake pistons off a member here, and they are incredibly lighter!! a bunch of guys at the shop couldn't believe the weight difference!!

i went and installed them today, and well when i put it all back together with my brand new pads, it seems that the pad comes out a bit more with them and now the pads are snug on the rotor.the only thing i can think of fixing this is sanding the pad down a few mm to get the clearance. is that a good idea or is there a better way of getting around this?

[754]

You can shim the caliper, then remove shim later.. just pull 2 bolts..

 Are you sure the lower part of the calper bore is clean, ie piston not sticking at the bottom..

[Loki]

ya i have cleaned the #$%* out of the calipers, made sure nothing was intruding any parts. so you think maybe a washer between the caliper and the holder would be ok?

[754]

I was thinking more like an alloy shim shaped like the raised part of your caliper mount, ie supports the whole caliper and cant flex..

[BobbyR]

I was thinking more like an alloy shim shaped like the raised part of your caliper mount, ie supports the whole caliper and cant flex..

I made a shim out of a aluminum flashing and with a pair of snips and a file it was almost invisible. When the pads wore down, I just unbolted caliper and pulled it out.

[Kevin400F]

Loki, you bought the piston from me....I'm surprised you didn't come back to me directly as opposed to posting to the forum, but I'm glad I noticed your post.

DO NOT SHIM THE CALIPER UNTIL WE DETERMINE WHAT THE ISSUE IS.

First, did you follow the enclosed instrutions and discard the OEM plastic washer that was between the pad and OEM steel piston?  

Second, did you check to make sure the "raised dome" on the back side of the pad fit without interference inside the chamfer of the new phenolic piston (per the instruction sheet)?   The chamfer is sized with proper dimensions for an OEM-spec pad, but if you have a mis-sized aftermarket pad there could be an issue.    

My home number is 713.340.2329 and my mobile number is 713.502.8984.  Please give me a call at your convenience and we'll solve the issue. Yours is the first report of this type of problem in almost 300 pistons sold.
 

[Kevin400F]

Loki, another potentially more obvious explanation just occurred to me.  You mentioned that you installed new pads.  After installing new pads, did you loosed the "travel limit bolt" on the caliper mount arm AND confirm the arm swings freely?  Occasionally, the mounting arms will sieze in place, which causes a bind when the new pads are installed.

Assuming the mount arm moves freely, if the travel limit bolt had been adjusted to limit the travel of the moun arm with a worn "inactive side" pad in place, installation of a new, thicker inactive pad will cause a bind when the caliper is bolted up.   Hope this helps.

[BobbyR]

Loki, you bought the piston from me....I'm surprised you didn't come back to me directly as opposed to posting to the forum, but I'm glad I noticed your post.

DO NOT SHIM THE CALIPER UNTIL WE DETERMINE WHAT THE ISSUE IS.

First, did you follow the enclosed instrutions and discard the OEM plastic washer that was between the pad and OEM steel piston?  

Second, did you check to make sure the "raised dome" on the back side of the pad fit without interference inside the chamfer of the new phenolic piston (per the instruction sheet)?   The chamfer is sized with proper dimensions for an OEM-spec pad, but if you have a mis-sized aftermarket pad there could be an issue.    

My home number is 713.340.2329 and my mobile number is 713.502.8984.  Please give me a call at your convenience and we'll solve the issue. Yours is the first report of this type of problem in almost 300 pistons sold.
 

Question, I am buying a used caliper. With the phenolic piston is there a reduction in brake squeel? 

[Simpson]

Just what to give Kevin400 kudos for customer service. My intuition tells me the issue is assembly but here's a seller who tracks down his customers, puts his all his phone numbers on the internet and writes up some help instructions. All in the name of customer satisfaction! Makes me wish I needed a new piston, I'd buy it right now. 

[Loki]

wow kevin your the best,and im sorry it didnt just come straight to you! i did do all of the instructions but i didint check to see if the raised dome fits in properly, im going to take it all apart tomorrow, and see what i might have done wrong......i just cant imagine what it would be? but ill get back asap.

[Jerry Rxman Griffin aka MuthaF'er]

PLEASE don't discard the plastic washer! Just don't use it. Some of these parts are impossible to find and you could help a brother that's in need.

[Loki]

actually its one of those items i have up for sale right now

[Kevin400F]

Sounds good, we'll figure it out and fix it.  If it turns out that the new pads are the issue (thicker than OEM or with a non-standard dome on the back side), I'll exchange the standard size pistons with a second set as needed to work with your setup.

[KeithB]

Loki, if you end up wanting to shim, I have one and I live in Toronto.
Let me know.

[Fabricator]

Blatant Hijack 

  What does the plastic washer between the piston and the domed piece do?  Mine is missing, and I was going to machine one from Delrin, or HDPE, but my brakes are working great. 

Fabricator

[bistromath]

Blatant Hijack 

  What does the plastic washer between the piston and the domed piece do?  Mine is missing, and I was going to machine one from Delrin, or HDPE, but my brakes are working great. 

Fabricator

Two things. Keeps the squealing down by insulating vibrations, and keeps heat transfer out of your brake fluid by insulating heat from the pad from the thermally conductive piston. If you're using a plastic piston, it will serve the same purposes without the spacer.

[BobbyR]

Blatant Hijack 

  What does the plastic washer between the piston and the domed piece do?  Mine is missing, and I was going to machine one from Delrin, or HDPE, but my brakes are working great. 

Fabricator

Two things. Keeps the squealing down by insulating vibrations, and keeps heat transfer out of your brake fluid by insulating heat from the pad from the thermally conductive piston. If you're using a plastic piston, it will serve the same purposes without the spacer.

SO if I replce the steel piston with Phenolic the sqeel is likely to diminish?

[Kevin400F]

If a given set of pads squeal with a steel piston and plastic isolation washer, they'll probably also squeal with a phenolic piston.  Its often a result of the pad vibrating within the caliper body.  Chamfering the edge of the pad sometimes helps.

[Fabricator]

Kevin,

 Thanks!  I will turn one down from high temp nylon!

Fabricator

[BobbyR]

I have to buy one of those rings somewhere. If I get this caliper I was bidding on, I will probably go phenolic, makes sense.   

[Fabricator]

Bobby,

  PM me if you need a ring.  I will make a few when I do mine. I assume that a nylon compound that can handle 600F intermittently will be adequate...

Fabricator

[Loki]

ok so here is the update, i measured both pistons and the steel one is actually less then half a mm larger.doesnt make sense because i had it all together and it was just fine, so what i decided to do is remove the plastic washer from behind the other brake pad to try to gain a lil bit of space, then i also grinded the phenolic piston on the inside hole to allow for the main pad to sit completely flush with it. not there isnt any problem,there is just enough to allow flowing movement, its still a tad on the rotor but ill take it for a ride when i get it running and have that away asap. kevin you have been nothing but amazing, and very honest, i have already recommended you to all my friends and coworkers. thanks so much ill get back to you on how much im going to love the pistons.

cheers