Weird experience with old separating brake grease

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On the RX-8's front brakes, one of the slider pins for each caliper has a rubber sleeve on it: (Photo credit: Atkins Rotary) Until recently, I had been using an old tub of CRC Synthetic Brake and Caliper Grease for all my brake jobs. The stuff was around 10 years old -- maybe more. It had been visibly separating for a couple of years, but I kept using it anyway. No excuses; I was just lazy and never had a problem with it. Then, when I went to replace my rotors a few months back, those rubber-sleeved pins were stuck. It took real effort to pull them out. I cleaned and re-greased them, but they still took way too much effort to push back into the holes. After that brake job, I started to get a click/knock sound from the front brakes whenever I applied them. It got louder and more frequent over time. Eventually I took everything apart again, cleaned it thoroughly, and re-greased with Sil Glyde. The front brakes have been quiet as a church mouse since then. Is it possible that whatever separated out of the old grease tended to shrink elastomers, and whatever was left tended to swell elastomers, causing the rubber seals to swell? That's the only hypothesis I could come up with, but I basically don't know jack about grease. If that's likely what happened, how did it get better? Could the Sil Glyde have reduced the swelling a bit? Or maybe the small amount of brake cleaner I used directly on the rubber sleeves when cleaning them?
 

Kestas

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I don't think the grease separation threw anything off balance. It just makes the grease a tiny bit thicker with a bit less oil in the thickener. I think the CNC paste is petroleum based and I believe the slider pin seal may have reacted adversely with the grease. I use silicone grease for these applications. Silicone is virtually inert, waterproof, and will not harm elastomer, with maybe the exception of silicone elastomers.
 
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This is a common issue for CRC brake and caliper grease. For some unknown reason, the rubber slide pin bushings tend to swell. Your solution is to either cut the bushing very slightly (at the end), or replace the bushing. Unfortunately, many OE's do not sell the bushing separately unless you purchase the caliper rebuild kit. Fitment of the aftermarket bushings is a hit/miss.
 

Tomioka

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Non-silicone petroleum based brake grease (black, green, purple) does not play well with caliper pin rubber bushings. Those get sil-glyde or silaramic instead.
 

d00df00d

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Interesting. Thanks, folks. Those sleeves might have had that grease on them for something like 50k miles. Should I replace them if I'm not having obvious problems?
 
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Interesting about CRC brake grease. I used that 3 years ago when I replaced rotors and ceramic pads. I used O'Reilly Brake Best parts and CRC synthetic grease. The brakes began pulsating since it got hot so I decided to replace rotors and go with semi metalic pads this time. The CRC grease on the slide pins seemed odd. I wiped it off and used NAPA sil glyde this time. I don't know what was wrong with the old grease it just didn't seem right, just black and gunked up, looked liked it wanted to harden but it wasn't. The rubber was fine. It concerned me because it had only been 3 years. Since I was in the middle of a brake job I just wiped up the pins and moved on. I had already bought the NAPA grease when I picked up the new parts. maybe it didn't like the heat.
 
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Originally Posted By: spasm3
After trying different things for years, i only use sil- glide.
I am so glad, I am a member of BITOG. Happy that I am in the same camp too and so far, nothing to complain thumbsup Just curious, do you guys lube slider pins every brake job or occasionally other times too?
 
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