Blu-dot break caliper question

[Condor]

I put a set of R1 blue dots on the front of my '83 because it really needed help. Left the back one OEM and didn't rebuild a thing. And yes I did swap out the front forks and rotors for a set from an '86 MKII with progressives. Everything worked great, and one of the best handling scoots I'd ever ridden....

[7 lakes]

Fluid expands when hot and I thought we had a venture rider solved his dragging brakes with a spurt out the bleeder. And I can't see the sightglass in reservoir. And certainly the return hole will keep them dragging. But neither will make it harder to stop. I'll work on a caliper.

 

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Dealing with heat is one of things brake fluid is designed to do and one of the reasons it's expensive. If the system were hot enough to expand your fluid enough for you to even notice, you wouldn't be able to touch the brake lever without burning yourself. If the fluid expands at all at less than very extreme temps then there is water and/or air in the system and they are the source of the expansion. And yes, if the system is dirty enough inside to clog the master cylinder compensation port, or to prevent proper fluid flow in any small passage, that could hold pressure in the system but the fix is the same, servicing the internals. Also, if an issue with the brakes is solved by opening a bleeder, that is your system screaming at you not to drive the vehicle until the hydraulic internals are serviced.

 

Not trying to be argumentative, I did this professionally and am just trying to help. Brake systems really aren't complicated or difficult. Just like carbs, it's just pieces of metal with holes drilled in them and some springs and rubber parts. No mystery, no magic, no hidden high tech or engineering. Holes and rubber. If the holes are clean and the rubber is good then its gonna work. If it doesn't work right, either the holes aren't clean or the rubber isn't good. So the fix is clean all the holes, replace all the rubber and the system is functionally new again. Trust me, that really is all there is to it.

 

If you get new rubber for your master and calipers, make sure the inside of the system is really clean and free of corrosion, (don't hone anything, not a good idea) and fill it with new fluid, you can forget about your brakes for years. Otherwise they're going to be on your mind for a while.

[Condor]

Dealing with heat is one of things brake fluid is designed to do and one of the reasons it's expensive. If the system were hot enough to expand your fluid enough for you to even notice, you wouldn't be able to touch the brake lever without burning yourself. If the fluid expands at all at less than very extreme temps then there is water and/or air in the system and they are the source of the expansion. And yes, if the system is dirty enough inside to clog the master cylinder compensation port, or to prevent proper fluid flow in any small passage, that could hold pressure in the system but the fix is the same, servicing the internals. Also, if an issue with the brakes is solved by opening a bleeder, that is your system screaming at you not to drive the vehicle until the hydraulic internals are serviced.

 

Not trying to be argumentative, I did this professionally and am just trying to help. Brake systems really aren't complicated or difficult. Just like carbs, it's just pieces of metal with holes drilled in them and some springs and rubber parts. No mystery, no magic, no hidden high tech or engineering. Holes and rubber. If the holes are clean and the rubber is good then its gonna work. If it doesn't work right, either the holes aren't clean or the rubber isn't good. So the fix is clean all the holes, replace all the rubber and the system is functionally new again. Trust me, that really is all there is to it.

 

If you get new rubber for your master and calipers, make sure the inside of the system is really clean and free of corrosion, (don't hone anything, not a good idea) and fill it with new fluid, you can forget about your brakes for years. Otherwise they're going to be on your mind for a while.

 

In motorcycle braking heat is generated by pad friction, and by the slave mounted on the block of the motor with a clutch. DOT will expand enough in the caliper or slave area to lock up the brakes, and extreme heat won't even be felt at the brake lever. The service manual suggests that the DOT be replaced every two years for very good reason....

[7 lakes]

In motorcycle braking heat is generated by pad friction, and by the slave mounted on the block of the motor with a clutch. DOT will expand enough in the caliper or slave area to lock up the brakes, and extreme heat won't even be felt at the brake lever. The service manual suggests that the DOT be replaced every two years for very good reason....

 

A properly operating modern brake system, with good fluid, in the service that it was designed for, is never going to generate enough heat to seize a caliper. It just isn't going to happen unless there is already a real problem with the system. Can a caliper seize from boiling fluid? Sure, if there is a significant problem that caused that heat, but again the problem is that the system needs service, not that somehow the fluid just boiled out of nowhere on its own. Could you make it happen by riding the brake down a mountain pass? Yes, but most likely you'd notice pad fade, or other drivers waving and pointing to the smoke rolling off your rear end, and pull over first. And yes, of course it would be possible for the caliper to be hotter than the lever, I should have given a more precise example and you're correct for calling me on that.

 

I'm sure you didn't really mean to say that braking heat was also generated by the clutch slave cylinder, but I'm confused about your reference to it. I don't how a clutch slave could get hot enough to seize unless the fluid was really, really bad.

 

It is possible for heat below the boiling point (we're talking good fluid here) to constrict caliper movement, but it's the result of reduced clearance from "crud" (actually corrosion and powdered rubber) which doesn't allow for normal heat expansion of the caliper body and the piston. I've worked on systems that came into the shop with a complaint of dragging brakes and wheels very hot to the touch that were suffering from this. The problem was always a lack of hydraulics service, except for a couple of times I saw calipers frozen to their mount from the car being used on salted roads and then being parked for months, all the clearances had been taken up by corrosion of the mount and caliper and when things got hot the assembly couldn't compensate, it was just too tight.

 

And you're correct about changing the fluid every 2 years, the reason for that recommendation is that it is impossible to prevent brake fluid, which is hydroscopic at a molecular level, from absorbing moisture from the air and the more moisture, the lower the boiling point. Brake fluid will absorb moisture through the pores of rubber brake lines and the seams in the system, its that hydroscopic. I know that sounds crazy but its true. It wants moisture, it needs moisture, it will get moisture. This is the reason for the 2 year change recommendation, that's how long it's estimated to take for a sealed system that hasn't been opened to absorb enough moisture from the atmosphere to compromise the fluid. Leave the system open for 15 minutes so you can pour in fluid while bleeding the system and you've taken 25% off the life of your fluid. 30 minutes, 50%. Less of course if you're in a high humidity area. Take the top off your master and leave it overnight, you've just ruined your fluid. Really. It will still work the brakes, but its corrosion preventative abilities and thus its heat resistance are gone. Here's a chart I stole from someone on the net, notice that the title is "The Impact of Water Content ..." -

 

 

I was trying to make the point that everyone seems to want to imagine some exotic reason for brake issues, when it really does just come down to clean holes and rubber. (Same deal with carbs) Most of the brake discussions I see in bike forums are like someone asking why they're having trouble pounding nails with a hammer whose handle is coated with axle grease, and they'll get all kinds of advice on the best kind of grease to use on your hammer, how to duct tape the hammer to your hand, the right gloves to use with a greased hammer, or which new bigger hammer should be purchased, and for sure there'll be a guy or two who suggests that the old hammer just be cleaned really well, but that advice will be discounted because that's just too easy. Why doesn't anyone want to service their brakes?

 

Really, 99% of brake issues are just the internals needing service. It's all about clean holes, good rubber and smooth surfaces. It really is just that simple, and without those, there really isn't any point in doing anything else.

Edited July 1, 2018 by 7 lakes

[camos]

I would like to point out that if the rear MC is overfilled just normal braking can warm up the fluid enough to cause the pads to drag which will make the fluid heat up faster leading to a seizure of the rear brake. I had that situation happen to me once although it was not from overfilling the fluid but improperly adjusting the pedal clearance.

[videoarizona]

I would like to point out that if the rear MC is overfilled just normal braking can warm up the fluid enough to cause the pads to drag which will make the fluid heat up faster leading to a seizure of the rear brake. I had that situation happen to me once although it was not from overfilling the fluid but improperly adjusting the pedal clearance.

 

Me too. Just a tad too much fluid in the rear reservoir for me caused a brake drag then lock up. I know many of us have had the dreaded rear brake lock up from the teeny relief hole in the rear master getting clogged. Doesn't take much the hole is so small. in my case here it was after I thought I had cleaned the system well. Guess not.

 

But yep...a clean brake system will be trouble free for years if maintained.

[Condor]

I would like to point out that if the rear MC is overfilled just normal braking can warm up the fluid enough to cause the pads to drag which will make the fluid heat up faster leading to a seizure of the rear brake. I had that situation happen to me once although it was not from overfilling the fluid but improperly adjusting the pedal clearance.

 

Me too. Just a tad too much fluid in the rear reservoir for me caused a brake drag then lock up. I know many of us have had the dreaded rear brake lock up from the teeny relief hole in the rear master getting clogged. Doesn't take much the hole is so small. in my case here it was after I thought I had cleaned the system well. Guess not.

 

But yep...a clean brake system will be trouble free for years if maintained.

 

Yep. Have to agree with 7 tho-... In the world of a properly maintained braking system, it will be trouble free...sorta.. But that's the optimum, and in real life it ain't necessarily so... In real life the DOT will start to absorb moisture from the get-go, and the more moisture the quicker and greater it will expand over time under heat producing scenarios. Long down hills, hi-speed braking, etc. Unless there is enough room for the fluid to expand into the reserve, the front or back brakes will lock up. Once a pad starts dragging it's pretty much down hill to a lock up. So the ticket here is to bleed the brake system every couple of years. And in regards to 7 not getting the correlation between the clutch and the brake fluid expanding... they both take the same DOT fluid and operate in heat producing environments.... He'll understand once his clutch starts to slip.... :-)

[7 lakes]

You guys are right, those things definitely can happen, allow me to revise my previous statement -

 

"A properly operating modern hydraulic system, with good fluid, in the service that it was designed for, with the pedal freeplay adjusted properly, without old fluid exposed to excessive heat, without dragging the brake on a mountain pass, and without overfilling the master cylinder reservoir which overcomes the passive master cylinder compensation circuit, is never going to generate enough heat to seize a caliper. Did I miss anything?

 

The point I was trying to make is that you rarely have to worry about all this crap if the inside of the system is properly maintained, not that it can't ever happen. And yeah, I get that clutch fluid can overheat too. The way that sentence was worded kinda threw me but re-reading it I see what you meant and you're right of course.

[Condor]

You guys are right, those things definitely can happen, allow me to revise my previous statement -

 

"A properly operating modern hydraulic system, with good fluid, in the service that it was designed for, with the pedal freeplay adjusted properly, without old fluid exposed to excessive heat, without dragging the brake on a mountain pass, and without overfilling the master cylinder reservoir which overcomes the passive master cylinder compensation circuit, is never going to generate enough heat to seize a caliper. Did I miss anything?

 

The point I was trying to make is that you rarely have to worry about all this crap if the inside of the system is properly maintained, not that it can't ever happen. And yeah, I get that clutch fluid can overheat too. The way that sentence was worded kinda threw me but re-reading it I see what you meant and you're right of course.

 

Yeah, I re-read it again, and even I got confused... :-) Sorry 'bout that...

[7 lakes]

Yeah, I re-read it again, and even I got confused... :-) Sorry 'bout that...

 

[garyS-NJ]

I would like to point out that if the rear MC is overfilled just normal braking can warm up the fluid enough to cause the pads to drag which will make the fluid heat up faster leading to a seizure of the rear brake. I had that situation happen to me once although it was not from overfilling the fluid but improperly adjusting the pedal clearance.

I didn't think I made that up about our ventures. If its raining good and hard tomorrow, ill try to isolate caliper or line for the hard braking and overkill or return or caliper or line for the dragging.

 

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