silicone or standard brake fluid

[mickwinf]

Just rebuilding the caliper and master cyl on Lazarus, using red rubber grease to assemble and all new parts, the question is should I use silicone fluid, is it compatable with red grease and does it cause any problems with bleeding on our old bikes? Does it have any effect on the feel?

[Johnny4428]

Hi Mick, got Dot5 silicone in 550 and 750 here without any issues. Just need to make sure the system is flushed of old fluid.

[K2-K6]

I feel that you need to get right to the outer extreme of temperature use on brake fluids to understand any significant difference in performance or feel generally. Unlikely to get even close in one of these brake system, more likely if racing.

The choices appear free to me,,without any concern really.

A point of note though, even the original Honda 750 workshop manual calls specifically for silicone grease to assemble the caliper, it's piston and seal. No alternative is given. It's the water repellent properties that give some level of protection from ingress down beside the piston area as no weather seal is in place.

Red rubber grease is vegetable oil based and doesn't, I believe,  offer the same attributes in that location. Seems more sustainable in rubber booted locations that are effectively screened from exposure directly to weather effects.

[McCabe-Thiele (Ted)]

I have silicone brake fluid in both of my bikes - aside from it not being hygroscopic it's not a paint stripper.👍👍👍

[mickwinf]

Thanks for replies, I have only done caliper up to now with a smear of red grease around the seal would it be better to replace with silicon grease?

[McCabe-Thiele (Ted)]

Thanks for replies, I have only done caliper up to now with a smear of red grease around the seal would it be better to replace with silicon grease?

For the relatively small quantity I don't see it as an issue for affecting the fluids performance. An extra brake  bleed after a few weeks might ease any concerns.

[K2-K6]

Thanks for replies, I have only done caliper up to now with a smear of red grease around the seal would it be better to replace with silicon grease?

There's not an incompatibility issue as far as I'm aware, its more the performance of silicone against water ingress is most effective in this location, next to water coming off the disc in wet weather. That's the only consideration and not a worry otherwise.

To give a more described picture of this:-  These caliper design have no cover in a secondary seal like  many road calipers have nowadays, with the silicone grease intended to mitigate this function from that aspect. The service interval would likely be arranged on that basis.
Any use in salty Road conditions is the ultimate concern as that provides an electrolyte to cause galvanic corrosion in the caliper bore to produce that familiar dry powder within the seal groove.

[Bryanj]

Never used any grease on calipers seals just brake fluid

[Trigger]

I have used OKE brake DOT 5 on all my bikes for a few years now and it is great 

[AshimotoK0]

I have used OKE brake DOT 5 on all my bikes for a few years now and it is great 

Got confused when I looked up DOT5 and some products came up with DOT5.1 ...evidently that stuff is more like DOT3 and 4 and not silicone.

[Trigger]

I have used OKE brake DOT 5 on all my bikes for a few years now and it is great 

Got confused when I looked up DOT5 and some products came up with DOT5.1 ...evidently that stuff is more like DOT3 and 4 and not silicone.

The .1 makes a big difference mate.  Oke Dot 5 is good stuff.

[McCabe-Thiele (Ted)]

I use Dot 5.1 in our cars as it's a good specification - iirc it's fully synthetic but miscible with older fluids such as 3.0 & 4.0.

[Johnny4428]

+1 for Oke dot5. 👍

[K2-K6]

Never used any grease on calipers seals just brake fluid

To me it's proven in longevity, piston retracting as designed and verified over much longer period before having to work on it again. Silicone grease takes it every time for corrosion too in my experience.  I wouldn't do any caliper without it.

[McCabe-Thiele (Ted)]

In the absence of a dust seal I do wonder how much seal lubricant of any kind will remain under the heat of braking.