Maybe you guys can help me out here. I am doing the standard factory front disk brake swap, onto my '76 Dart. All parts were pulled from a '76 Dart as well, a couple years back. The piston bore in my calipers got some surface rust from sitting, and I wasn't thrilled with how well they (didn't) clean up. Since I like to do things right, I decided to order a new set from NAPA. However, every caliper they had access to, had Phenolic pistons... A friend suggested getting them anyway, and just swapping my steel pistons into the new housings. Perfect, or so I thought.

My original MoPar calipers have a 2 9/16" steel piston, the NAPA calipers have a 2 3/4" Phenolic piston. So the piston swap appears to be a no-go. I feel like I'm at an impasse, and could use some advice or ideas on how to proceed. Below are a couple pictures of a piston bore.

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'76 A-body calipers were upsized to 2.75" bore; '73-'75 are 2.6". Why hating on phenolic pistons? I'd rather have them than steel, but the four rebuilt calipers I picked up last week have steel ones. I'd put the phenolic pistons back in the calipers and run 'em. If you gotta-just-gotta have steel pistons, Dorman First Stop P7504S or NAPA UP85003S.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Simply because between Tom Condran's book and reading on here, the general consensus seems to be avoid them, period. That's all... It'll be another day before I have the suspension back together to receive calipers. We'll see what gets said here between now and then, but I may just take your advice!

Thanks for the excellent info on the bore sizes, I'll have to make note of that in my book. Part #s are always good to have as well.

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Tom Condran's storybook is full of made-up nonsense.
Says who/where? They do a better job of isolating the brake fluid from the brake pads' heat. They don't rust. They're more dimensionally stable across a wider temperature range. They're lighter. What's not to like?

(Added NAPA part number for the steel piston)

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Phenolic pistons always seemed like a good idea to me but I've never performed any serious testing on them. The mfgs don't seem to use them anymore but I don't know why. It would be an interesting question to ask an engineer from Brembo or a place like that. Maybe there is some issue with those pistons that I'm not aware of. Of course, it could also be as easy as mfg cost or something like that.

I think the phenolic pistons have a bad rep for warping and sticking in their bores. Carter Thermoquads have a similar reputation but I think it has more to do with the guys who have been working on them screwing them up. I'm pretty sure Ford has been using phenolic caliper pistons on a lot of their cars up until recently. I'd just bolt them on and go, I mean STOP!

-James

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Not long after I bought my new '73 D100, I had some brake drag problems. The dealer blamed it on phenolic pistons and said it was a common warranty problem. That's the only experience I've had.

Phenolic pistons need a little more care so they do not get gouged when they are installed. I suspect some problems might be from assembly damage and the chips getting lodged in the bore.

Really, they work fine.

If you want to get rid of the rust, try soaking the calipers in white vinegar for a few days - to a week. It will clean it all up. Then just follow up with a brass brush and maybe some scotchbrite and a good rinse with alcohol.

I have a set of preloaded calipers with phenolics in them and I haven't had a problem with them leaking or any fade in stopping suddenly. They
are only a few years old and only have a few drag races and emergency stops on them.

-D.Idiot

It looks like the score is a lot vs. none, so I'll run 'em the way they came. Thanks for the input, guys!

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