Brake pistons - Do you red rubber - Brake fluid or cyclinder paste to lube?

[jedibiker]

Ive always used a little red rubber grease on pistons to help keep it moving smooth,. but yes needs cleaning a lot.

Ive heard mixed ideas, so what do you long time bikers do?

cheers

[husoi]

Dry with a smear of brake fluid on the seals to get them in place.

Any grease just accumulates the brake dust turning it into a nasty paste.

[RideWithStyles]

Agree with husoi.

If your really good to the bike and regularly clean, strip a caliper down to remove its pistons then clean the inside, replace seals say every year or two max you could go with the lightest of smearing of grease behind it because youll be cleaning it out before any problems.

as the grease especially if you use too much wil break down like marmalade and hide in the cavities of the inside caliper mixing it with brake fluid, not good. As below.

 

But if youre not gonna do that id just id just stick with a light coat of brake fluid on the outside piston and seals to make slipping them in easier. 

Edited September 8, 2023 by RideWithStyles

[megaross]

Whatever the manufacturer says in their book, which is invariably brake fluid.

[jedibiker]

I do clean them regular was just curious on general practice.

seems its not a topic many think about haha

[Stu]

Always and only brake fluid  

[Fozzie]

I've just seen this, so apologies for it being a late reply. 

 

Book says brake fluid is all you need. But I use red rubber grease on them, as my old metal working lessons always taught me to. Only a very light smear to "shine" up the seal and the piston, and only on the working surfaces, the dust seal needs only a very light smear on its inner diameter, otherwise it gets road debris all over it and you end up having to jet it off with brake cleaner.

 

I see people lather it on all the time, and usually it all comes off when they then push the piston in and the seal scrapes most of it off and they have to wipe most of it off. Which admittedly is a good way of catching/removing any dust in the bores, but you really only need a light smear to do the same. But there's some who literally line the inside of the bore and the entire piston with the stuff, and that's just wrong. I've never seen any residue inside on follow up rebuilds, always clean. 

 

But I would still say just do what the book says. I've been involved with one too many bikes where someone misinterpreted advice they were given. Worst being a 125 with a toast engine as they'd put the wrong oil in. The oil they'd been told to use would have been fine, but they went with a slightly different one they thought was the same as: "the container was red like the other one". So I just say, do what the book says, and if you're not confident with what you have, get someone technical to check that it matches what the book says

[megaross]

Think about how the seals work.

 

Your inner seal is in contact with the dot4, it'll get it's feeding to keep supple and nice. It's job is primarily to stop fluid exiting.

 

Your outer seal has the opposite job - stop shit getting in to eat the inner seal. On the working area it's pretty good at keeping it clean til the next bit goes out as the pad wears.

 

The thing that F**ks calipers is salt/ shit getting in behind the dust seal so it can't do it's job any more, red rubber grease on piston outers will just cause more shit to stick. Your pistons should be mostly dry once they're out in the open.

 

When you're assembling you hoof on a bit of fluid just to allow the piston to slip and give it something on the arse end to cushion against when it hits home. Once it's in, wipe off excess and install pads as usual

[Fozzie]

On 19/09/2023 at 08:28, megaross said:

Think about how the seals work.

 

Your inner seal is in contact with the dot4, it'll get it's feeding to keep supple and nice. It's job is primarily to stop fluid exiting.

 

Your outer seal has the opposite job - stop shit getting in to eat the inner seal. On the working area it's pretty good at keeping it clean til the next bit goes out as the pad wears.

 

The thing that F**ks calipers is salt/ shit getting in behind the dust seal so it can't do it's job any more, red rubber grease on piston outers will just cause more shit to stick. Your pistons should be mostly dry once they're out in the open.

 

When you're assembling you hoof on a bit of fluid just to allow the piston to slip and give it something on the arse end to cushion against when it hits home. Once it's in, wipe off excess and install pads as usual

 

Worth noting, the red rubber grease is more for the assembly process, than ongoing lubrication which the DOT4 provides to the main seal (and why it's a good alternative). The advantage of the grease is that it offers ongoing corrosion protection to the areas DOT4 doesn't reach, and pistons being reused can often have defects that grease is better at protecting the seal from during assembly, especially as the forces applied to the piston are often not perfectly square. 

 

If the seal is healthy and goes in cleanly, any dust sticking to the grease after this will be caught on the outer side of the seal, preventing direct contact, and can be easily cleaned off. Once debris can breach the seals, it's very quickly game over with or without grease. Although grease is very good at catching debris, and preventing deeper penetration when outer seals fail. 

 

The problem with using it is it invites problems when you use too much. And that's why DOT4 is the suggested, as it's hard to get it wrong. So while I would likely suggest DOT4, the red grease is not without its advantages. It's used all the time in industrial settings for large hydraulic brake builds/rebuilds. 

[Fozzie]

Just to add to it: https://www.frentech-uk.co.uk/useful-information/

 

They do a handy demonstration of what happens when you use the wrong grease. Another reason it's likely not in Haynes manuals, some people tend to think any grease will do. 

[megaross]

I must admit this us the first time I realised I've 6 types of grease in the shed.

 

Red rubber, silicone, copper, general spray grease, extreme performance and lithium. I'm a one man lube emporium 

[Fiddlesticks]

3 minutes ago, megaross said:

I must admit this us the first time I realised I've 6 types of grease in the shed.

 

Red rubber, silicone, copper, general spray grease, extreme performance and lithium. I'm a one man lube emporium 

Same

[Fozzie]

14 hours ago, megaross said:

I must admit this us the first time I realised I've 6 types of grease in the shed.

 

Red rubber, silicone, copper, general spray grease, extreme performance and lithium. I'm a one man lube emporium 

Grease can cause some fights on other groups. Copper is corrosive to aluminium so using copper slip can cause “debate” among some people.

 

I’ve built up supplies over the years. But I mostly use a marine anti-seize I pinched from an old garage. Suitable for ally into steel and the other way round which does me nicely! 

[Bianco2564]

Just replaced the caliper seals on the Kawasaki, instructions say you can use brake fluid or rubber grease, they do supply a small sachet of grease aswell.

Maybe the consensus in manuals is its safer to say use brake fluid as you can't really get it wrong if you put too much on the seals.