[Closed] Lubing Pistons - Red rubber grease or Copperslip?

Brake fluid

Silicone spray, from a plumbers merchant.

Red rubber grease is the best thing IMO / IME to lube the seals on brakes that use dot fluid. I do not know how compatible it is with mineral oil seals.

the safest thing to use is the correct fluid for that brake - you know that will be compatible with the seals.

Copaslip is used sometimes for lubing the interface between the pistons and the pads. it is NOT suitable to lube the seals

Certainly never copperslip or any other petroleum based grease.

I'd stick with just brake fluid, it's all I've ever used on cars, motorbikes and push bikes as the seals dry out. The alternative would be a DOT4/5.1 compatible grease, SRAM sell one, but no doubt it re-badged from something else, but seing as a tiny pot should last a lifetime that's not relavent.

Silicone grease is best

Thanks - I wll try a little brake fluid first. Then something more sticky (like Silicon) after...

skiboy - Member

Silicone grease is best

Is it compatible with the seals on both dot and mineral oil brakes?

Is it compatible with the seals on both dot and mineral oil brakes?

I'm wondering the same, DOT5 is silicone though and works in DOT compatible systems so the seals should be OK, there is a recomendation not to combine the two though so I'd worry about the grease working its way into the system.

Castrol Red Rubber grease here.

Read about it on another forum years ago,and have used it on all my (Avids) pistons.
This has been as a bit of preventative maintenance ,as I had heard horror stories about them seizing up.
I have never had any problems with any of my sets ,and they get used in all sorts of conditions.

Avid issue here. Dot fluid gets the stuck piston moving temporarily, but it soon seizes up again. Just ordered red rubber grease after reading around on the subject.

from my experience as a professional bicycle workshop manager, and bike mechanic that has worked on 100s of disc brake including Sachs, Tektro, Hayes, Hope, Formula, Magura, Shimano and Avid:

don't use DOT fluid, its not a "lubricant"!!

it causes the piston seal to swell (this helps sealing), it will certainly help your initial "installation" as it will allow the piston to re-seat into the caliper bore, but it does not do anything useful once the brake is reassembled and will actually exaggerate the problem of 'stick pistons' or 'brake imbalance'

what you actually want is high temperature silicon grease - Avid and hope supply this in their workshop "tackle boxes" along with replacement pistons, seals, o-rings and MC diaphragms

Avid sell this under their "Pitstop" label, but its hard to find and expensive

Hope use the "Hunter" brand which is commonly available.

Automotive suppliers also sell ideal silicon grease cheaper than bike "brands" for motor vehicle disc brakes (which also use DOT 4 or 5.1 fluid), try your local motor factors for supplies

RS also sell a suitable silicon grease, which works just fine...

apply the silicon grease to the piston seals evenly coating all surfaces, and reinstall the seal to the caliper piston bore, once the piston is reseated degrease the caliper bay with Iso alcohol before rebuilding the caliper

I stripped and reassembled a hopetech lever assy , hope told me to use silicone grease , that was on the pistons in the lever so im sure it would be ok on the caliper, can't see why not,

Red grease is the right stuff - but a pain in the A to buy. CV grease (any car accessory shop) is fine.

Hunter silicon used in the bike shops l 've worked in.

I've been looking into this for the same reason and it appears red rubber grease and silicone grease are both the right stuff. I've already got some Servisol silicone grease, which operates up to 200C, so I'll be using that on the pistons and working them in and out of the bores to lube them rather than stripping the caliper.

Red rubber grease £7.84 http://www.opieoils.co.uk/p-999-fuchs-renolit-red-rubber-grease-grease-for-use-on-elastomers.aspx

Silicone grease £3.93 http://www.amazon.co.uk/Skytronic-Silicone-grease-50g/dp/B002KRHAK4/ref=sr_1_1?ie=UTF8&qid=1334177742&sr=8-1

esher shore - Member

from my experience as a professional bicycle workshop manager, and bike mechanic that has worked on 100s of disc brake including Sachs, Tektro, Hayes, Hope, Formula, Magura, Shimano and Avid:

don't use DOT fluid, its not a "lubricant"!!

it causes the piston seal to swell (this helps sealing),

Really - dot fluid causes dot seals to swell - yeah right. It is not the best lube in the world but it has lubricant properties and it does not cause seals to swell - don't be ridiculous. The seals are in contact with it all the time. If it caused the seals to swell every dot disc brake would seize on all the time.

don't use DOT fluid, its not a "lubricant"!!

it causes the piston seal to swell (this helps sealing), it will certainly help your initial "installation" as it will allow the piston to re-seat into the caliper bore, but it does not do anything useful once the brake is reassembled and will actually exaggerate the problem of 'stick pistons' or 'brake imbalance'

This can't be right surely? Technically you can't class it as a lubricant but I'm sure it doesn't cause the seals to swell!

Automotive brake fluid has many responsibilities. Corrosion protection and [b]lubrication of brake system components[/b] are only a portion of the role brake fluid must play.

Asking for a lube for your pistons shows that you don't understand how they work. The pistons don't move in and out of the seals, they are held very tightly indeed by the seals and only move with the flexibility of the rubber. As the pads wear the pistons do creep slowly through the seals but there is no back and forth movement in the way you are thinking.

The actuating piston on the other hand moves quite a lot in its cylinder, this is the principle by which hydraulic brakes work.

globalti - Member

Asking for a lube for your pistons shows that you don't understand how they work. The pistons don't move in and out of the seals, they are held very tightly indeed by the seals and only move with the flexibility of the rubber. As the pads wear the pistons do creep slowly through the seals but there is no back and forth movement in the way you are thinking.

The actuating piston on the other hand moves quite a lot in its cylinder, this is the principle by which hydraulic brakes work.

In the first post he says it is to help them self adjust better, i.e. the 'creep' you mention above, which keeps the pads centred as they wear down.