Ah, I feel like a cat chasing his tail now!thesameguy wrote:That Centric part number is a plastic piston. It is what I pictured above, specifically.DPDISXR4Ti wrote:Well, that broadens the scope of the search, but since I see the Mustang is included, I wonder if some (all?) of these also have plastic pistons?
Replacement for PBR phenolic pistons
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Re: PBR phenolic pistons
Brad
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Re: PBR phenolic pistons
Doing a little more digging while watching the game and I think I have better info now which corrects some of the above... The single piston caliper uses a 60mm piston. The "Girling 60" dual-piston caliper has the staggered 40 & 45mm pistons. We'd want just the 45mm piston as a possible replacement in the PBR. (i.e. if you were going to actually use junkyard donors, you'd need 4 donor calipers) Here's a pic of what they look like...DPDISXR4Ti wrote: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.
BTW, junkyard sourcing of the CENTRIC 14645002 pistons may be more of a requirement than we'd like, if this post still holds true...
03-19-2014 05:12 PM #5
RockAuto doesn't have them in stock. There are several websites who, like RockAuto, show them as being in stock on the website, but when you go to order them, you inevitably get a phone call about how they're not in stock.
Brad
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Re: PBR phenolic pistons
Just in from a junkyard visit. Came across a '97 Audi Cabriolet which indeed had the Girling 60 dual piston calipers. Got to work on pushing out the 45mm pistons and have one in front of me right now. Diameter is 44.997mm, same as the Pathfinder piston. I wonder if they're supposed to be .003 less than the bore?Dangie wrote: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.
As long as I've got everything in front of me, overall height is 53mm. Height to the bottom of the seal groove is 45mm.
For anyone else who wants to extract these in the junkyard, 13mm socket is needed for the bolt in the pins, and I think a 17mm open-end wrench for the pins. An adjustable of some sort worked for me.
Brad
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Re: Replacement for PBR phenolic pistons
Here's a pic of the 45mm pistons extracted from the Girling 60 Calipers. Just thinking out loud, I wonder if the phenolic pistons are machined .003 bigger than the steel ones since they don't expand with heat? Or perhaps like the steel pistons in the G60 calipers, they should have been machined to 44.997 and that's why they're prone to seizure in the PBR's?
In short, I wonder if these are totally fine to use as replacements in the PBR?
In short, I wonder if these are totally fine to use as replacements in the PBR?
Brad
Re: Replacement for PBR phenolic pistons
.003 mm is 1/10 of a thousands of an inch. What are you measuring them with? You could breath on the calipers and it would make your reading change that much. What exactly did the PBR pistions mic out to?
Dangie, is the .003 smaller figure you're talking about in inches?
Dangie, is the .003 smaller figure you're talking about in inches?
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Re: Replacement for PBR phenolic pistons
I used a Starrett metric caliper, so the measured value I provided should be accurate. Maybe I should stick the G60 pistons on top of my wood stove for awhile and get them up to the "required" 45mm.jmanbball wrote:.003 mm is 1/10 of a thousands of an inch. What are you measuring them with? You could breath on the calipers and it would make your reading change that much. What exactly did the PBR pistions mic out to?
I haven't yet disassembled the pair of PBR's I have out in the garage to see what the phenolic pistons might actually measure. Regardless, I'm inclined to tear down a PBR caliper and see how the steel pistons fit.
Brad
Re: Replacement for PBR phenolic pistons
The .003 was measured in inches.jmanbball wrote:.003 mm is 1/10 of a thousands of an inch. What are you measuring them with? You could breath on the calipers and it would make your reading change that much. What exactly did the PBR pistions mic out to?
Dangie, is the .003 smaller figure you're talking about in inches?
This is the PDF I found that lists the specs for various caliper pistons- http://www.frenkit.es/docs/caliper.pdf
Thanks to Brad for continuing the hunt for some suitable replacements. I've been bogged down with other car projects and haven't had a chance to dive back into the PBR issue.
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Re: Replacement for PBR phenolic pistons
Just a little update... It would appear that the '99 - '04 Land Rover Discovery uses the same brake caliper, so the indication that it's only the 2004 that has the piston we need is incorrect. Furthermore, it would seem that unlike the G60 caliper used on the Audi, the Land Rover caliper does NOT use staggered piston sizes; they are both 45mm. Thus, one vehicle could provide a full set of four pistons.
Brad
Re: Replacement for PBR phenolic pistons
So Rock Auto shows they have these in stock "99 - '04 Land Rover Discovery" for ~$10 each. Do you have any on order yet?
Last spring one of my PBR's locked up I removed the pistons and measured them. They were larger on the front side where they would be external or right near the bore. These were on the car for ~2 years. The end that would be in contact with the fluid seemed proper. At that time i also got a rebuilt pbr and found the pistons were almost locked in the bore as well right from the parts store. The parts store caliper had a bore that was tapered and the piston locked as it was fully compressed so you could get the pads in. You could see the scrape marks on the piston where it was binding.
After a bit of frustration i returned that caliper and rebuilt mine. I cleaned up the bores and the pistons so they had full range without binding and reassembled. Personally I think the clearances are too tight. But i would definitely be interested in a metal alternative piston.
Last spring one of my PBR's locked up I removed the pistons and measured them. They were larger on the front side where they would be external or right near the bore. These were on the car for ~2 years. The end that would be in contact with the fluid seemed proper. At that time i also got a rebuilt pbr and found the pistons were almost locked in the bore as well right from the parts store. The parts store caliper had a bore that was tapered and the piston locked as it was fully compressed so you could get the pads in. You could see the scrape marks on the piston where it was binding.
After a bit of frustration i returned that caliper and rebuilt mine. I cleaned up the bores and the pistons so they had full range without binding and reassembled. Personally I think the clearances are too tight. But i would definitely be interested in a metal alternative piston.
Jeremy Kemp
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RIP: the Mutt….1988 XR4Ti Chestnut Brown/Spice Leather
MC2 Coilovers and Bushings, Contour Rims and Rotors, Ported Motorsport Head, Cosworth 4x4 Intercooler, Holset HY35 Turbo, 80LB Injectors, Megasquirt2 EFI
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Re: Replacement for PBR phenolic pistons
Sorry Jeremy, no. I think I'd want to verify the sizing with some junkyard donors first. Mostly just because I like to come up with semi-legitimate reasons to go the junkyard. Ironically, I also have another reason to find Land Rover Discovery II's at the junkyard. I want to fit a set of headlights from one into my '91 F150.jkxr4ti wrote:So Rock Auto shows they have these in stock "99 - '04 Land Rover Discovery" for ~$10 each. Do you have any on order yet?
Regarding the binding issues with the phenolic pistons, I wonder if they swell at all? Or perhaps as you suggest, they're just sized too tight, and a little more room might be welcome.
Brad
Re: Replacement for PBR phenolic pistons
Not sure if this was posted here before but i read this a few years back.
http://www-odi.nhtsa.dot.gov/acms/cs/ja ... -35282.pdf
I hate to say our cars have something in common with RV's but....
"The RVs are typically assumed to be parked for six
months then driven for two weeks. The brakes are not regularly exposed to heat to drive the
moisture out of the phenolic, like the other medium-duty vehicles using the same brake caliper."
http://www-odi.nhtsa.dot.gov/acms/cs/ja ... -35282.pdf
I hate to say our cars have something in common with RV's but....
"The RVs are typically assumed to be parked for six
months then driven for two weeks. The brakes are not regularly exposed to heat to drive the
moisture out of the phenolic, like the other medium-duty vehicles using the same brake caliper."
Jeremy Kemp
RIP: the Mutt….1988 XR4Ti Chestnut Brown/Spice Leather
MC2 Coilovers and Bushings, Contour Rims and Rotors, Ported Motorsport Head, Cosworth 4x4 Intercooler, Holset HY35 Turbo, 80LB Injectors, Megasquirt2 EFI
RIP: the Mutt….1988 XR4Ti Chestnut Brown/Spice Leather
MC2 Coilovers and Bushings, Contour Rims and Rotors, Ported Motorsport Head, Cosworth 4x4 Intercooler, Holset HY35 Turbo, 80LB Injectors, Megasquirt2 EFI
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Re: Replacement for PBR phenolic pistons
I don't ever recall seeing this - thanks for posting Jeremy. It just confirms my suspicion that cars which are driven on an irregular basis should not have calipers with phenolic pistons.jkxr4ti wrote:Not sure if this was posted here before but i read this a few years back.
http://www-odi.nhtsa.dot.gov/acms/cs/ja ... -35282.pdf
I hate to say our cars have something in common with RV's but....
"The RVs are typically assumed to be parked for six
months then driven for two weeks. The brakes are not regularly exposed to heat to drive the
moisture out of the phenolic, like the other medium-duty vehicles using the same brake caliper."
Brad
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Re: Replacement for PBR phenolic pistons
I'm wondering now if the info on the LR Discovery having 45mm pistons is wholly incorrect. I say this having blown a piston out of a 2001 Discovery front caliper at the junkyard and the piston measures 48mm. Indeed they're dual piston calipers, but both measure 48mm. Perhaps if I ever come across a 2004 Discovery I'll check that one, for now, I'd suggest sticking to Audi 90's with G60 calipers as your piston donors.DPDISXR4Ti wrote:Just a little update... It would appear that the '99 - '04 Land Rover Discovery uses the same brake caliper, so the indication that it's only the 2004 that has the piston we need is incorrect. Furthermore, it would seem that unlike the G60 caliper used on the Audi, the Land Rover caliper does NOT use staggered piston sizes; they are both 45mm. Thus, one vehicle could provide a full set of four pistons.
Hopefully I'll get a chance to try rebuilding some PBR's with the G60-donated pistons soon.
Brad
Re: Replacement for PBR phenolic pistons
I have registered on this forum for the sole purpose of reviving this thread. I am interested because I am swapping SN95 spindles onto a fox body T-bird and was planning to use the PBR calipers. So, anybody come up with anything since this was last discussed on here?
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Re: Replacement for PBR phenolic pistons
I think it comes down to the use case. If it's for your daily driver and you keep up with maintenance, you won't have any issues. If your car tends to sit a lot, or you're the type to never change your brake fluid as you should, you may have issues.
I have had PBRs on my car for over a decade. I had zero issues for the first six years. Then it sat for two years, and when I revived it both calipers were seized (although one took two days to seize...). I rebuilt the calipers and it's been fine for another four of semi-daily use. My car goes on average 200-250 miles per month across four or eight days. Sometimes I drive it four days per week, sometimes it sits for a week or two. But, 250 miles per month reliably. And as long as it's in use, I change the brake fluid every 2-3 years.
I have had PBRs on my car for over a decade. I had zero issues for the first six years. Then it sat for two years, and when I revived it both calipers were seized (although one took two days to seize...). I rebuilt the calipers and it's been fine for another four of semi-daily use. My car goes on average 200-250 miles per month across four or eight days. Sometimes I drive it four days per week, sometimes it sits for a week or two. But, 250 miles per month reliably. And as long as it's in use, I change the brake fluid every 2-3 years.