Sticky brake piston

[Srodden]

so I rebuilt this master cylinder and still have s sticky brake. The piston slowly comes back up into position. I was told by Derek (Bigdogpartsking) it’s the fault of the chromers and to hone it out. Well that’s what I’m doing. I’m just waiting for hone tool to arrive Monday. Anyone else have this issue ?

 

[SimpleMan_Omen]

While you had it apart did you test your fitment on all the pieces? That's what I do when I take anything apart and it will generally tell you what is causing the binding. Chroming does add thickness so that could be it. Especially if this thickness is too uneven. It is never perfectly even (that's why chrome lined barrels, rule of thumb, are less accurate than non).

 

[Srodden]

While you had it apart did you test your fitment on all the pieces? That's what I do when I take anything apart and it will generally tell you what is causing the binding. Chroming does add thickness so that could be it. Especially if this thickness is too uneven. It is never perfectly even (that's why chrome lined barrels, rule of thumb, are less accurate than non).

It’s still apart till Monday. I rebuilt it once and it worked good for about half of the season then back to sticking. Derek is trying to save me 400 for a new chrome master.

 

[Srodden]

Shouldn't be chromed inside the cylinder itself I'd think if it was the problem it woulda done that originally, honing it tho should help.

No I don’t see any chrome in there. I wonder if there’s something to the chroming process that Derek’s talking about. I ordered a very small hone should be here Monday. Was curious who else had this issue ?

 

[SimpleMan_Omen]

It’s still apart till Monday. I rebuilt it once and it worked good for about half of the season then back to sticking. Derek is trying to save me 400 for a new chrome master.

If it worked fine for half of the season then I wouldn't think that it had anything to do with your tolerances and if that is the case then a honing wouldn't help and may do harm.

It's not like the tolerances between your components is fluctuating. Can you think of any other variable that would have come into play about the time it started acting up?

I'm transitioning my system from DOT5 to DOT4 right now; you didn't accidentally mix anything did you? Contaminate in the lines that could cause an obstruction? I'd blow the lines out with compressed air just in case.

 

[Srodden]

If it worked fine for half of the season then I wouldn't think that it had anything to do with your tolerances and if that is the case then a honing wouldn't help and may do harm.

It's not like the tolerances between your components is fluctuating. Can you think of any other variable that would have come into play about the time it started acting up?

I'm transitioning my system from DOT5 to DOT4 right now; you didn't accidentally mix anything did you? Contaminate in the lines that could cause an obstruction? I'd blow the lines out with compressed air just in case.

No I don’t think I’ve mixed anything. Pretty sure it’s all been dot 5. The piston from the very first rebuild was side loading. I know because it wore off center so I thought it was a bad piston.

 

[SimpleMan_Omen]

Depending on the acceptable tolerances then it sounds like honing could fix it. If it hasn't been worn too far out of spec. But I've never taken that part of the brake system apart and my two cents aren't valid currency anywhere.

 

[Srodden]

I found the pic of the piston but photobucket gave it to us up the rear

 

[Srodden]

Dumb question but did ya lubricate the new parts before installing

On the first rebuild ? Probably not.

 

[Srodden]

No this time? Who get parts from? The front and rear are different I know cuz I did my pitbull rear master

This time I’m re installing the piston etc. everything looks good so .....

 

[Srodden]

I got the rebuild kit from Curtis wildsteedworx.com

 

[Srodden]

Hmmm well double check you have the correct parts I got the front one from him When I ordered the rear,,,, so I called Donna and Derek and they sent me the correct one for the rear it's definetly a good chance you may not have the right parts

Wow ok I will ! Usually Curtis is on top of things

 

[Srodden]

I’ll just order a new rebuild kit

 

[SimpleMan_Omen]

Why would you transition from dot5 -4 ? Dot 5 is the best to use and WiLL NOT damage paint/powder coat if you get a leak or accident spill it, I'd stick with Dot5 its in there for a reason all manufactures or most are using it.

It isn't used by most manufacturers. Even Harley moved away from it when they started using ABS and their brakes were never very good. DOT5 was designed for the military who had vehicles sitting for extended periods of time because it is silicone based and repels water. It's compressability and viscosity make it an inferior brake fluid as far as effectiveness compared to the glycol based fluids of DOT4, DOT5.1 and even the obsolete DOT3. So the reason that I am switching to DOT4 is because 1)that is what my other bikes use 2)it provides a better bite on the brakes.

 

[SimpleMan_Omen]

Hmm I use Harley dot 5 I like it because it won't damage surfaces

That is everyone's favorite aspect of the DOT5. And with such pretty surfaces on these kinds of bikes I'm sure it is the primary reason the builders use it. I'll just be sure to be careful.

 

[Sven]

This is my understanding of your generic caliper hanging up:
1. Hot oil bubbles. What is in the bubble? Air/water.
2. Water is heavier than oil so it sinks to the bottom or lowest part of the caliper, which is the groove the quad-seal sits in.
3. Quad is made of 4-sides so it sits square in the groove. However, the water now crystallizes and this raises the seal in the groove.
4. The piston is now stuck and sits there dragging on the disc. The quad has to 'return to memory;' pulls the piston away from the disc.
5. Any crystal in that groove will lock the piston so it has to be scraped out clean so the quad goes back to square.
6. With the seal removed, along with the oil off the piston, plus out of the caliper, the dry piston should freely spin by hand.
7. The only material that should touch the finish is a paper towel and vinegar to breakdown the crystals. Vinegar swells rubber!!
8. The piston should not rock in the caliper but slide out on its own no matter piston position. Any honing of the finish will expand the 'tight tolerance,' and then send [more] oil between the parts, leak out the seal, because the piston can now be cocked to one side when braking... Hello!?

 

[Srodden]

Did you get a new rebuild kit?

Not yet should be here this weekend

 

[Srodden]

This is my understanding of your generic caliper hanging up:
1. Hot oil bubbles. What is in the bubble? Air/water.
2. Water is heavier than oil so it sinks to the bottom or lowest part of the caliper, which is the groove the quad-seal sits in.
3. Quad is made of 4-sides so it sits square in the groove. However, the water now crystallizes and this raises the seal in the groove.
4. The piston is now stuck and sits there dragging on the disc. The quad has to 'return to memory;' pulls the piston away from the disc.
5. Any crystal in that groove will lock the piston so it has to be scraped out clean so the quad goes back to square.
6. With the seal removed, along with the oil off the piston, plus out of the caliper, the dry piston should freely spin by hand.
7. The only material that should touch the finish is a paper towel and vinegar to breakdown the crystals. Vinegar swells rubber!!
8. The piston should not rock in the caliper but slide out on its own no matter piston position. Any honing of the finish will expand the 'tight tolerance,' and then send [more] oil between the parts, leak out the seal, because the piston can now be cocked to one side when braking... Hello!?

That is all presuming that the cylinder is not the problem right ? This is 3rd time I’ve rebuilt this front master so I thought what have I got to lose. I honed it out gently to clean it up just waiting for new rebuild kit to arrive.

 

[Sven]

You figure the groove is the problem. Take the caliper outside and work in the sun. I use a scribe to scrape the groove; a spray of contact cleaner to wash the groove; a wait for the cleaner to evaporate; a certain pitch of the caliper so the sun can reflect the still remaining white crystals in the groove. You need to find dull gray aluminum as the reflection, not white powder. That's my experience working that powder out of the groove so it returns back to a clean square groove.
It's 3 parts to inspect:
1. Sort of saying; if the dry piston falls out of a dry caliper and shows X as the dropout, it's not a warp of the piston.
2. Equally saying; if the caliper shows no warp and the piston can be spun, that's your Y in action.
3. Then say; if all that is left is the groove and the quad ring [being new is the given], then it's a dirty groove still pushing up the quad ring.

 

[Th3InfamousI]

I think it's a caliper issue not the MC. Did you replace the pistons when you rebuilt it? They are cheap.

I always wetsand the pistons before I put them back they wear pretty easy actually.

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