How bad is wheel bearing grease on rubber?

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Feb 24, 2021
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Without thinking I used some wheel bearing grease on some old plungers that go into the wheel cylinder seals. I then later thought about the fact that wheel bearing grease contains petroleum distillates. Should I be worried? Also, if wheel bearing grease is bad on rubber then why do they advise people to use it on the inner rubber seal used on wheel seals? Also, doesn't chassis grease contain petroleum, it's certainly in contact with rubber.

I'll try to not worry too much about this and I wouldn't do it again in the future, but I would like to make sense of it.
 
Also, if wheel bearing grease is bad on rubber then why do they advise people to use it on the inner rubber seal used on wheel seals? Also, doesn't chassis grease contain petroleum, it's certainly in contact with rubber.
Because the rubber in wheel bearing seals are made of different compounds than that in wheel cylinder parts. Kind of why one wheel bearing seal might cost $10 while a whole 4 piece wheel cylinder kit might be $5. Brake fluid doesn't attack rubber like petroleum grease. Expect yours to start swelling and eventually seeing sticking brakes.
 
That makes sense. Thanks for the info. I'm going to get two more wheel cylinders and clean up the plungers or just get new ones.
 
Ok, so I pulled the boots and they did seem kind of tight on the cylinder link. But then again that's it's job I guess, and or it was slightly swollen?. Very little grease was on it. I used some qtips and cleaned it all off. I'm going to spray the end links with some brake cleaner and call it a day.

If I notice any trouble or anything I will post to help the next guy. But I've kind of gone down a rabbit hole here and I've found people going back and forth about even using Naptha to clean rubber. So I guess with the grease only containing a diluted amount and then removed it shouldn't be a big deal. . . I'm kind of OCD in regards to this kind of stuff, so it looks like I've joined the right forum.

Thanks everyone!
 
There are many chassis components that use rubber seals and contact grease as you described.
The axle seal is rubber and that's keeping the gear oil in. The axle vent lines are also rubber, etc......

It's not 1929 rubber. The boots are EPDM. Your wheel cylinders will be fine. Wipe the excess and motor on.
 
There are many chassis components that use rubber seals and contact grease as you described.
The axle seal is rubber and that's keeping the gear oil in. The axle vent lines are also rubber, etc......

It's not 1929 rubber. The boots are EPDM. Your wheel cylinders will be fine. Wipe the excess and motor on.

EPDM is used for brake system applications because it's resistant to glycol based brake fluids, it is NOT resistant to petroleum products and will swell when exposed to them causing sticking and potentially seizing.

Chassis seals are generally nitrile or urethane based as those materials are compatible with petroleum based oils and greases.
 
My understanding at this moment is that damage doesn't occur upon acute exposure with some people arguing even that they use straight naptha to clean natural rubber with no damage. I think whatever damage that was going to happen has already happened. It was such a limited exposure to a diluted amount that was quickly removed.

I just moved the car today and all was well. I'm not going to lube any more cylinder stems with bearing grease and I'm glad I removed the grease from this one. There are people still using wheel bearing grease on backing plates. So who knows how bad it really is. But I will be using proper brake lube in the future and no lube at all on the stems.
 
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EPDM is used for brake system applications because it's resistant to glycol based brake fluids, it is NOT resistant to petroleum products and will swell when exposed to them causing sticking and potentially seizing.

Chassis seals are generally nitrile or urethane based as those materials are compatible with petroleum based oils and greases.

This. "Rubber" isn't all the same. You can search up chemical resistance tables for EPDM. It is not good for greases and petroleum oils so technically the official answer would be that you've ruined the seals and they should be changed out.

In principle, if the contact time was minimal you could wash off the seals with some brake fluid, reinstall, and it *should* be okay. But with this being a brake system and caliper seals off a rebuild kit being so cheap, if you're going to take it apart again anyways might as well redo the seals. As a bit of anecdotal commentary, I did once accidentally put DOT3 fluid in a mountain bike brake system (Shimano) designed for mineral oil. Flushed it out a few days after and have never had problems with it.
 
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