Replacement for PBR phenolic pistons

[DPDISXR4Ti]

apparently the Audi 90, Audi 100, Land Rover, and a few others use this exact size piston.

Audi 90/100's are found often enough in junkyards that I might have to blow a couple pistons out one day and do a test fitment into a PBR.

[thesameguy]

As most know my XR sat all of '13 and most of '14, and when I went to put it back on the road this year I found the pistons in the FR caliper were seized in their bore. One pedal application pushed them out to stop the car, but they never retracted. I replaced the caliper, flushed the whole system, called it a day.

I've been driving the car at least a couple times a week for three months. Last drive was last Tuesday, today I went to drive it to work. Over the past six days, I'm pretty sure the other caliper has won seized pistons. Light brake application starts a fun and controllable drift to the right. Hard brake application starts a scary dart to the right. Pretty sure the FR caliper is working, the FL caliper is doing nothing.

Interestingly, there is a thread about seized phenolic pistons on Fords on a motorhome BB I frequent.

[Dangie]

Here's the list I mentioned in my earlier post- http://www.frenkit.es/docs/caliper.pdf

Since I ruined a phenolic piston trying to remove them from the caliper I figured I'd at least investigate other options since I had the time. I went to my local u pick it yard and got a piston out of a Pathfinder and it looked nearly perfect. Nearly. Let's just say that 45mm is a general term because the Pathfinder piston was .003 smaller than the Mustang piston and a little sloppy in the bore. The hunt continues and while I will likely use the phenolic and some high grade brake fluid to start, it would be nice to have a Plan B if they ever became an issue.

Has anyone ever machined their own caliper pistons with either 6061 aluminum or stainless?

[thesameguy]

Did you happen to look at C5/C6 pistons? The PBR calipers between the Mustang and the Corvette are quite similar. It would be interesting to find they share some moving parts too.

[DPDISXR4Ti]

I wonder if they're all 45mm slugs which are then machined to something just less than that? And as such, each manufacturer machines to a different final diameter. Just a thought. I guess we'll have to look for Audi pistons next. What's the actual diameter on the PBR Phenolic piston?

[thesameguy]

Centric says 45mm, pn145.45006

The C5/C6 piston is apparently only 40.5mm. Mustang > Corvette?

Interestingly the Cobra caliper also uses a 40.5mm piston.

Various hi-po RWD GM cars used 146.45009, which is a 45mm (45.3mm?) metal piston.

[Dangie]

The C5 rear caliper uses a 45mm piston and Rock Auto shows that this piston is also a direct replacement for the '98-'02 Camaro/Firebird.

[thesameguy]

Yes, because like I said various hi-po RWD GM cars used 146.45009, which is a 45mm (45.3mm?) metal piston. Like the Corvette and the Firebird and the GTO and the XLR and the Camaro.

[jkxr4ti]

OK that GM piston could be a good option. What about just swapping the corvette front caliper out for the Mustang PBR they do look awful similar. That would get a little less piston area as well and could better match the XR master.

[thesameguy]

I can probably take a closer look this weekend. I have C6 calipers on my Fiero and a spare Mustang PBR on a shelf.

The reason to use the Mustang calipers is probably because they are cheaper, by a lot. $25 vs. $150 for a reman.

It is weird that the Mustang Cobra caliper shares the smaller piston area with the Corvette caliper, though.

[Dangie]

Yes, because like I said various hi-po RWD GM cars used 146.45009, which is a 45mm (45.3mm?) metal piston. Like the Corvette and the Firebird and the GTO and the XLR and the Camaro.

I was just trying to be more specific on the year because while there are no C5s at pick n pull, there are plenty of Camaros and Firebirds.

Thanks for checking the fit of the parts you have on hand.

[thesameguy]

Good God man, why would you crawl around a junkyard dismantling calipers and sorting through all the rusty & pitted ones instead of just giving rockauto $10?

[Dangie]

Good God man, why would you crawl around a junkyard dismantling calipers and sorting through all the rusty & pitted ones instead of just giving rockauto $10?

As I found out when I pulled the Pathfinder piston, it wasn't exactly the same size as the PBR phenolic despite them both being listed as 45mm. There were other 45mm options out there so I figured I'd continue searching until I found a near perfect replacement and then order new from Rock Auto.

[thesameguy]

Ah, got it.

[DPDISXR4Ti]

apparently the Audi 90, Audi 100, Land Rover, and a few others use this exact size piston.

Audi 90/100's are found often enough in junkyards that I might have to blow a couple pistons out one day and do a test fitment into a PBR.

Might go junkyarding on New Year's Eve (doesn't everyone do that?), and so will try to go hunting for 45mm pistons to test fit. I think this is the application range I'm looking for...

AUDI 200 (1989 - 1991)
AUDI 5000 (1986 - 1988)
AUDI 90 (1990 - 1995)
AUDI CABRIOLET (1994 - 1998)
AUDI COUPE (1990 - 1991)
AUDI S4 (1992 - 1994)
AUDI S6 (1995 - 1997)
AUDI V8 (1990 - 1994)
LAND ROVER DISCOVERY 2004 (only 2004???)

But doing a little digging, it appears that Audi used both a 2-piston and a single piston caliper on the above listed cars of this era. Despite the fact that we want to use it on a dual-piston caliper (the PBR), it's the single piston caliper that has the 45mm piston. Part# 146.45002 or sometimes just listed as 14645002

Don't take the above as fact just yet. Doing some reading just now on Audi calipers, there's all sorts of stuff used including something call "UFO brakes". I also read something that indicates the 2-piston caliper uses staggered pistons of 40 and 45mm.

Let's try to update this thread with data as it's discovered.