V. hot brake caliper

[belfastguzzi]

Here is BFG's brake lever

Hey, is that a satellite shot? Are you in the CIA?

 

How could the force of hitting a bum hold the relief port closed?

Medical opinions are beyond the expertise of this Forum

 

I doubt that his girder is that massive

You're confusing me with Mike Wilson

[belfastguzzi]

Not likely thers's enough weight in that lever to apply the brake. The internal spring in the master has considerable force. It may be that the lever return stop or linkage is out of adjustment and there is no free-play. This coupled with heat expansion can cause dragging.

Ok chaps.

I suppose that I should point out the one pertinent defect in these speculations.

 

– Er, ahem, etc... the melt-down occurred on the run home from Scotland – when half the lever broke off and before the massive appendage was constructed and applied.

 

Since the repair (or bodge, if you will) and fitting of new brake pads, careful adjustment of freeplay etc, etc, the rear brake (with lever as pictured) operation has been as spiffing as ever it was. However I will check it at some point, particularly the condition of the seals – and to see if it may be dragging / not fully releasing. And as a new rear caliper seems to be relatively inexpensive (compared to the price of the blessed brake levers), I'll try to get around to ordering one to be on the safely precautionary side.

 

PS

I'm quite keen to post some more pictures of the glued-up timing chest saga. I'll endeavour to do so before the summer is out.

[jrt]

PS

I'm quite keen to post some more pictures of the glued-up timing chest saga. I'll endeavour to do so before the summer is out.

 

I suggest you use the appropriate thread.

[leafman60]

Not too long ago, my riding friend had a similar meltdown with the rear caliper on his 04 Rossa Corsa. I was following behind him and noticed his trail of white smoke from burning brake fluid. The caliper got so hot it melted the pistons and even melted the plastic seal on the wheel bearing. We have mulled this over many times and concluded that, because of the position of the brake pedal, his foot was riding on the pedal and causing the caliper to drag. Verifying this was that I noticed his brake light burning before I could stop him. I also have a V11 but Im accustomed to riding with my right foot splayed away fromt he pedal.

[dlaing]

A)Hey, is that a satellite shot? Are you in the CIA?

B)Medical opinions are beyond the expertise of this Forum

C)You're confusing me with Mike Wilson

A)shhhhhhh (Culinary Institute of America...)

B)But I play a doctor on TV (sorry I meant bump, not bum)

C)I thought you were Valerie Plame's husband Joe (Depleted Uranium Girder) Wilson. Sorry about the mistaken identity. (I feel almost as stupid as a Scooter)

What time is it?

Time to get your posts in the right chronological order!!!! so I don't make an arse of meself

[dlaing]

– Er, ahem, etc... the melt-down occurred on the run home from Scotland – when half the lever broke off and before the massive appendage was constructed and applied.

Wait a minute!

Did the melt down occur before or after the fracture of the lever?

If after, it certainly could have been the result of a bent master cylinder rod or the massive appendage

Good Heavens! Did you adjust the freeplay after all the duct tape and zip ties!??!

[pasotibbs]

Not too long ago, my riding friend had a similar meltdown with the rear caliper on his 04 Rossa Corsa. I was following behind him and noticed his trail of white smoke from burning brake fluid. The caliper got so hot it melted the pistons and even melted the plastic seal on the wheel bearing. We have mulled this over many times and concluded that, because of the position of the brake pedal, his foot was riding on the pedal and causing the caliper to drag. Verifying this was that I noticed his brake light burning before I could stop him. I also have a V11 but Im accustomed to riding with my right foot splayed away fromt he pedal.

I think I'm right in saying that the brake light sensor is a pressure switch,if so an increase in fluid pressure due to heat would possibly apply the brake light as well as the brake ?

You may be right about the cause in this case but it could also be another visible sign of impending doom

[guzzijack]

I don't see any mention made of a modification I've done to the brake linkage on my V10 after my own caliper jam.

 

To ensure that the lever returns positively I have placed a small spring working in extension over the actuating rod 'twixt brake lever and master cylinder. It bears on a small 6mm washer at the lever end and a larger outside diameter washer (8mm) which is located and retained under the rubber boot on the m/c.

 

GJ

[Guest ratchethack]

Clever, Jack. But I'm curious, having done a few modifications to my linkage myself, but not this one. Why not just let the existing return spring do wot it was designed to do? It's perfectly capable under normal circumstances. If it doesn't return the lever in a positive manner, the lever might benefit from lubing the pivot shaft.

[Dan M]

Er, is there a dust boot on the caliper? I thought there were twin seals on the piston but no dust boot. And BTW if the teflon type coating on the piston has lifted slightly due to heat or one of the seals hardened for the same reason, it is possible for the brake to drag enough to overheat and not be noticeable - or is my Centauro so much more powerful than a V11S that it overcame it

(flak jacket on )

 

GJ

 

 

On any caliper there is an inside, square-cut seal that is the hydraulic seal and an outside seal, either boot type or lip who's function is to keep dirt (dust) off of the inner seal & piston. Sorry if I'm using automotive terms (dust boot) but that is what I've called the outer seal, regardless of type for 30 years. Usually on larger calipers it is a boot but as you stated Jack, on the little Brembo it is a seal.

 

As for a piston's coating, be it chrome plating or anything else, just how hot does the piston need to get to lift the coating? Glowing red? How do the seals cope with these temps without complete failure? I've never seen a caliper piston's surface damaged by anything other than rust. If it lifted could it have been faulty to begin with?

 

The ability to notice a dragging brake certainly depends on what kind of riding you are doing at the time. During a long stretch on the highway, it may feel like no more than a headwind robbing you of power and go unnoticed. In slower or stop & go riding, indicators like noises, odor, and strange handling would have to be ignored for awhile.

 

Back to the free play issue, go out to your bike and feel by hand how much downward force on the brake lever is needed to overcome the master cylinder's internal spring. I haven't measured it with a fish scale but I'd guess it is at least a pound. If there is free play in the linkage, no additional springs are needed and no bumps are going to activate that brake (unless of course your boot is resting on it)

 

I'm thinking most of these troubles are dirt & brake dust related. It doesn't take much to bind the pads. I wonder if things would stay cleaner if the little plastic cap was removed, allowing more air to circulate.

 

[Guest ratchethack]

Good stuff here, guys.

 

FWIW, one quick and easy way to get an accurate read on whether or not the rear brake drags (as has been reported so many times over the years) is to take a trip of at least 10 miles or so without using the rear brake at all. Then feel the edge of the disk. If it's warm (let alone hot!), you have a potentially serious problem just waiting to happen.

 

Just my opinion, but this means it's a good time to go chasing the Big 3, as mentioned previously.

[guzzijack]

As for a piston's coating, be it chrome plating or anything else, just how hot does the piston need to get to lift the coating? Glowing red? How do the seals cope with these temps without complete failure? I've never seen a caliper piston's surface damaged by anything other than rust. If it lifted could it have been faulty to begin with?

 

I think with my own overheating scenario it was a bit difficult to diagnose which was cause and/or effect. The bike had been sitting for a few years prior to my ownership so I gave it a full service and checked the brakes out fully. However, the rear caliper must have been dragging intermittently as it never showed itself when I examined it but I'm guessing that (maybe?) the seals had hardened to such an extent that the pistons were not retracting fully - but only intermittently and not to any noticeable extent.

 

After the grand finale of the smoking disc episode when it did stick on, I stripped the caliper and found that the seals on one side were toast and the piston had blistered the teflon coating. So okay the seals may have degraded due to to age and lack of use but the piston coating blistering? That's why I put it down to being caused by the heat.

 

GJ

[dlaing]

Good stuff here, guys.

 

FWIW, one quick and easy way to get an accurate read on whether or not the rear brake drags (as has been reported so many times over the years) is to take a trip of at least 10 miles or so without using the rear brake at all. Then feel the edge of the disk. If it's warm (let alone hot!), you have a potentially serious problem just waiting to happen.

 

Just my opinion, but this means it's a good time to go chasing the Big 3, as mentioned previously.

After the first time I bled the brakes and cleaned mine, I did that test and they were warm, about body temperature, maybe a feverish body temperature. I periodically check to make sure they don't get hot, and so far it has not gotten worse, and the brake groan never returned, so I did not worry.

I guess I need to pop the pistons all the way out so I can clean the seals.

I imagine if they don't reach body temperature the pads should go many more miles

Thanks Ratchet, I thought it was normal for the rotor to be above room temperature, but now I know a more detailed cleaning is in order, and if that does bring down the fever 20 degrees, a new caliper, possibly one with available seal and piston kits

[Guest ratchethack]

. . .

Thanks Ratchet, . . .

Por nada, mi compadre.

 

However, I reckon if you're thanking me today instead of telling me why and where I'm completely WRONG, you've clearly missed post #26 above.

I thought it was normal for the rotor to be above room temperature. . .

Well, I reckon (Part II) that "ambient" is "normal" as long as you never use the brake. Anything above ambient means the brakes have been applied to some degree -- intentionally or otherwise.

 

Not to belabor the point, but the principle behind braking is very simple:

 

Braking directly converts kinetic energy into heat.

 

No heat generated = no braking force.

 

Heat generated = braking force.

 

NOTE: There may be several heat sources at work near the rear hub OTHER than brakes, that exhibit varying abilities of that source heat to travel to different parts of the hub area: Normal friction from wheel and bevel drive bearings (small), normal friction from bevel drive gears (larger). I've run out o' examples. . .

[dlaing]

Back to the free play issue, go out to your bike and feel by hand how much downward force on the brake lever is needed to overcome the master cylinder's internal spring. I haven't measured it with a fish scale but I'd guess it is at least a pound. If there is free play in the linkage, no additional springs are needed and no bumps are going to activate that brake (unless of course your boot is resting on it)

I put a 2# weight on the lever and that closed the piston 1/10 of an inch beyond the force of the brake lever, and I could start to feel the increased force to roll the bike around. I am sure some friction was occurring before the 1/10 inch. I'd be curious how far it needs to go in before the piston is closed, my guess is starts closing at a little more than 1/14 inch and fully closed at about 1/12 inch.

I guess I am the only one that thinks that that girder could get enough rhythmic momentum on a bumpy road to close it that much.

Anyway it does not matter, as I am sure BFG replaced it.

For the rest of us, I have had some concern that the spring is not robust enough.

I don't like the fact that the weight of the lever pushes the piston towards brake failure.

But more importantly, I don't like that the spring is so light that friction at the piston or on the dust seal of that the rod goes through can over-power the force of the spring.

Personally I would double the rate of the spring if knew how.

GuzziJack's solution appears to be an excellent one

BAA

 

Por nada, mi compadre.

 

However, I reckon if you're thanking me today instead of telling me why and where I'm completely WRONG, you've clearly missed post #26 above.

 

I missed reading it....I'll get back to you...

 

Not as massive as 2 lb., but "it may well be over a kilogram"??!!

 

Um, a kilo is 2.2 lb., Dave.

 

But let's concentrate on your words above, "momentarily activated" and explore this a little, shall we?

Yes one kilo is more than 2 pounds

But the force of 2 pounds on the tip of foot lever is greater than the force of a kilogram spread out over BFG's Bodgeful Fulcrumous Girdoid.

...back to reading the rest of post 26 ....