V. hot brake caliper

[belfastguzzi]

It turned out that I needn't have bothered doing a temporary repair to the broken-off rear brake lever on the Highland Fling trip. When I applied the brake, I could hear a bit of 'unpleasantness' – my rear brake pads had worn out.

 

The metal must have been dragging on the disk during the long run home, because when I went to change them later, the black plastic cover was gone – all that remained were lumps of melted plastic. Must have been hot!

Has anyone else seen this happen?

 

[Guest ratchethack]

Great Gertie's galloping garterstraps, BFG!

 

Looks much like the symptoms I've observed on the road on 2 other V11's -- certainly not me own! Heaven forfend!

 

I posted about rear brake groan and the underlying causes years back, and can't recall the 3 main causes I'd identified (OK, well sure I can: water in fluid, air in fluid, and caked-on brake dust & dirt in the calipers. If you're interested, I think you'll find a fairly comprehensive analysis if you do a search on hygroscopic ). But neglect of proper brake maintenance, including brushing out with solvent between pistons and calipers, combined with the usual neglect of proper bleeding had at one point conspired to make one set of dragging pads I looked at overheat and discolor the disk rather spectacularly, as well as to generate enough water vapor from boiling water in the fluid to cause the brake to first fail, and then lock up, causing the brake lever to drop straight down without resistance, despite an acceptable level in the reservoir.

 

The good news is that it appears that a thorough cleaning, along with new pads and proper bleeding with fresh BF would more'n likely have you back on the road PDQ.

 

Just my opinion, of course. Hope this helps.

 

Who wants to look up any o' my old blather? Well, I did. Here's the short version:

 

For those not prepared for my overly-verbose coverage (no offense taken ), I'd summarized things in two points, which I copy below:

 

1. The V11 rear brake requires special attention exceeding that required by most other motorcycle rear brakes. This is due both to it's high susceptability to accumulation of brake dust and crud, and the fact that it can't be bled properly using bleeding procedures that work just fine with most other motorcycles. The caliper bleed nipple is NOT at the top of the caliper. This means that it's IMPOSSIBLE to get all the air out of this caliper without taking it off the bike. Someone posted a bleeding procedure that calls for leaving the caliper on the bike and pressing the pistons all the way back in their bores to get "virtually" all the air and water out. Now this may just be me, but I'm not happy with "virtually" safe brakes! I find that taking the caliper off isn't much of a chore, (you've got to get it off to get the crud out anyway!), and I'm far more confident knowing with certainty that it's been bled with the bleeder nipple pointing UP, and at least ALL the air is OUT.

 

2. I maintain that because the V11 rear brake is sensitive to conspiratorial attack by "THE BIG THREE" (air and water in the fluid, and accumulated crud between pistons and caliper), it's at the very least UNWISE to rely solely on adding free play at the lever as a "solution". I consider this false insurance. I've demonstrated, at least to my own satisfaction, that no amount of added free play at the lever is atonement enough for neglect of a proper defense against the root causes. Proper bleeding and cleaning knocks THE BIG THREE out of consideration. Since I began doing this with every other rear tire change, I've been confident with next to ZERO free play at the lever - and no symptoms whatsoever -- not one hint of a problem of any kind.

 

There now. Have I finally made a coherent point without stepping on my own foot (- err...brake)?!

[dlaing]

 

The good news is that it appears that a thorough cleaning, along with new pads and proper bleeding with fresh BF would more'n likely have you back on the road PDQ.

 

I disagree

I suspect BFG cooked his seals.

Since apparently nobody can verify that one can buy the seals, I nominate BFG to buy the ones of a similar model and risk his life and try them out, or play it safe and buy new calipers.

So, does BFG now stand for Brake Fried Goose?

[belfastguzzi]

Colonel Belfast's Scottish Fried Goose indeed.

 

I don't believe that it was dirt, as I do keep it clean.

Seals? The thing must have been right hot, so if the seals weren't fried before, they might be now. Hope not.

The fluid was fairly fresh. I have been meaning to bleed the caliper properly, with it dis-mounted. I can't honestly remember whether I ever did do this.

 

The rate that these pads wear at and the well-known the brake moan, plus this extreme manifestation of friction, could indicate that there is always a degree-too-much of drag in the rear brake. Just an unfortunate and difficult to remedy combination of poor caliper location, air/moisture...?

[stogieBill]

I had a similar occurrence on my Daytona. Had been on the freeway for about 6 miles (not riding the brakes), got off the freeway and slowed for a roundabout and 1/4 mile further on while making a turn felt the bike being dragged down. Completed the turn (barely) to find the rear brakes had locked up. Melted the little dust cover too. Parked the bike and following about an hour appointment, checked the brakes to find that they were fine I guess the fluid had expanded and caused the rear brake to engage.

 

The bike has not repeated this episode in over 3 months. I have since properly flushed and cleaned the caliper assembly, but now I don't trust it and only use it sparingly (the rear brake).

[pasotibbs]

I had a similar occurrence on my Daytona. Had been on the freeway for about 6 miles (not riding the brakes), got off the freeway and slowed for a roundabout and 1/4 mile further on while making a turn felt the bike being dragged down. Completed the turn (barely) to find the rear brakes had locked up. Melted the little dust cover too. Parked the bike and following about an hour appointment, checked the brakes to find that they were fine I guess the fluid had expanded and caused the rear brake to engage.

 

The bike has not repeated this episode in over 3 months. I have since properly flushed and cleaned the caliper assembly, but now I don't trust it and only use it sparingly (the rear brake).

 

I'd check the master cylinder and pushrod adjustment, if the piston can't fully return to the "off" position it is possible that the hole to the fluid reservoir is not uncovered stopping expanding fluid from escaping.

I've had this on my Ducati (chasing a 748 down an Alp on the way to WDW 2004)and the Guzzi, with both it was caused by me adjusting the rod to give just the right amount of freeplay on the master cylinder,which would have been fine if the master cylinder piston had actually been fully returned ! (cleaning rust,dirt from inside the Cylinder and repairing the scratched nylon bush on the piston cured this).

If I'd not adjusted the freeplay the pressure would have pushed the piston to its true "off" position and the pressure would have been released but with nowhere to go other than the caliper pistons you just get heat causing pressure causing more heat and so on...

 

As a rough guide if you can bleed the system ok then the master cylinder piston must be fully returned otherwise the fluid level wouldn't go down.

[txrider]

I agree those caliper piston seals need to be looked at for heat damage. By design/application they're selected to handle high heat but those pictures show an extreme heat situation.

 

There are lots of bikes that have rear calipers mounted under the axle like the Lemans does and yet have little problem. I guess the inverted bleed nipple could be contributing to the problem but could be the caliper isn't well suited to the application.

 

In any case I want to pass along an experience on brake bleeding we had recently in hopes that it might confirm something already mentioned. Last Friday a buddy and I could not get a firm front brake lever on his K12RS. I figured all the ABS plumbing was partly to blame and had finally brought the Vacula vacuum system out for an ultimate attack on the problem. After a run with that we had improvement but still a spongy lever. Then we dismounted one caliper, removed the pads and pushed in each of the 4 pistons. Big result with air bubbles and fluid rushing up into the master cylinder. After repeating that process a couple of times on both front calipers we had the best brake lever he'd ever experienced on that K12.

 

So, I suggest the ultimate bleed is to dismount the rear caliper, clean it up ( pistons extended to get out all the crud) then press the pistons in to displace any air/fluid mix that might be in there. Cautionary note- Use a paper towel to cover the open mastercylinder top as fluid can shoot up and out when this is done.

 

Another idea I want to try is to use a dry film lube like Dupont's Teflon/Krytox General Purpose lube on the caliper pistons. This might contribute to keeping those pistons free moving through all the crud/brake dust buildup. Dunno but I'm going to give it a try and will post any results.

[Guest ratchethack]

There are lots of bikes that have rear calipers mounted under the axle like the Lemans does and yet have little problem.

Since so many riders neglect brake cleaning and bleeding altogether, let alone doing it properly with caliper dismounted, having the caliper facing up, as in the "frontbottom" config., where gravity tends to capture brake dust and road grit rather than dropping it out, and then ALSO having the bleed nipple on the bottom, where it can't possibly release air when it's bled without dismounting, would seem to be two additional contributors to the aforementioned Big 3 that aren't as much of a problem with other rear brake configurations. Might be "little problem" indeed for years, maybe for the typical entire ownership period of the bike -- all the way up to the point where the brakes start the inevitable heat/drag cycle, which rapidly escalates into the BIG SURPRISE! that so many have posted about so many times and for so long here (and elsewhere, BTW). . .

 

. . .Then we dismounted one caliper, removed the pads and pushed in each of the 4 pistons. Big result with air bubbles and fluid rushing up into the master cylinder. After repeating that process a couple of times on both front calipers we had the best brake lever he'd ever experienced on that K12.

Congrat's, Txrider. I've had much the same experience with the V11 P32B rear caliper on the Guzzi. Simply getting the bleed nipple pointing UP is usually all it takes, but I've also found that rapping on the dismounted caliper with a block of wood or plastic-faced hammer while held in this position releases many stubborn pockets of air from out of internal nooks & crannies.

[Guzzirider]

I just remembered this thread.

 

May be worth considering simply buying a new one at less than £50 if the old ones trashed.

 

Guy

[dlaing]

I suspect the cause of the incident was the massive brake lever overpowering the return spring and causing either intermittent braking when you hit a bump in the road, this could have been combined with the possibility that the mass may have been pushing the master caliper piston past the point of the return valve being open causing more drag and the risk of brake lock up.

Be sure that the mass is not so massive and that there is sufficient free-play.

Ratchet likes it set to zero free-play, I prefer just a little more.

 

You may also need new rotors.

 

I suppose it is possible that the seal is fine, and who knows, baking it may be the cure to reducing brake drag. But not knowing the cause of the failure with 100% certainty, nor the health of the seal with 100% certainty, it may be a good idea to replace the caliper for good luck and a happy long life.

Wrench to live and live to wrench

[nose2wind]

Simply getting the bleed nipple pointing UP is usually all it takes, but I've also found that rapping on the dismounted caliper with a block

 

I had a similar brake drag overheating (due to mentioned push rod play). My seals were fine.

 

Also I have had major bleeding issues and found dismounting the caliper un-clipping the brake line from swing arm and passing the whole caliper with line through to the other side. Then raise caliper high as possible then bleed with tapping quick and easy.

[Guest ratchethack]

I suspect the cause of the incident was the massive brake lever overpowering the return spring and causing either intermittent braking when you hit a bump in the road, this could have been combined with the possibility that the mass may have been pushing the master caliper piston past the point of the return valve being open causing more drag and the risk of brake lock up.

Um, from repeat previous experience, I assume this is not suggested in jest.

 

It would be an OEM first for all terrestrial vehicles I know of on the planet.

 

How many G's of downforce from hitting a bump (that is, assuming Earth gravity) d'you s'pose it would take to hold the relief port in the master cylinder closed (for many minutes!), let alone get the rear brake to drag??

 

Now this is just me, but considering the Physics involved, and applying a little elementary logic and common sense, it would hardly seem likely that "hitting a bump" would:

 

1. generate anywhere near sufficient downforce on the brake lever to cause the leverage of its tiny mass (the "massive brake lever" weighs only a few ounces, and it's just several inches in length) to first overcome the master cylinder return spring, let alone apply some number of pounds of downforce long enough to cause any dragging, let alone (Part II) consistently enough to cause heating of the caliper?? Would it be enough force if the "bump" required to do all of this (wot a walloping "BUMP" it would have to be even to do it for an instant!) create a large enough impact force to bottom both front and rear suspensions hard enough to break the frame and shatter the fork stanchions. . .??

 

2. Assuming that the impact to the chassis of hitting a "bump" COULD depress the lever enough to counter the master cylinder return spring, hold the relief port closed for a period of time long enough to build more pressure from heat, AND actually get the brake to engage, how could any kind of a momentary impact -- or (considering even well beyond the earthly realm of extreme possibilities) even a series of impacts, say from bottoming-out the suspension repeatedly over mile after mile of continuous deep, suspension-bottoming whoopers -- ever result in a sustained enough depression of the lever to replicate any downforce on the brake lever even close to that generated by the shortest application of the rear brake in normal brake use -- let alone drag the pads long enough to start a heat/drag cycle??

 

To suggest the above would seem the equivalent of suggesting that hitting a bump with a car could cause the mass of the car's brake pedal by itself to apply the brakes hard enough and long enough to cause brake fade. . . Maybe the force of a free-fall drop off a couple hundred foot cliff would do this for a split second? Repeatedly dropping off multiple cliffs for several minutes, long enough to hold the brake pedal down so that the brakes overheat??

 

Where's Wiley E. Coyote and the Roadrunner?

 

Rapt once again in wonder and amazement , enquiring minds (well, you know). . .

[DeBenGuzzi]

ah screw it BFG, just throw that rear caliper out, it's just muddlin up the back end, save some weight, who uses the rear brake anyway?

 

 

 

 

 

seriouslly, I only use the back brake when I really have to stop, and there are nearly no roads around here I need that semi-useless back break. I would still like it to be there just in case tho. Worthless as it may be.

[guzzijack]

I agree those caliper piston seals need to be looked at for heat damage. By design/application they're selected to handle high heat but those pictures show an extreme heat situation.

 

I'd also have a serious squizz at the pistons as well. After my own caliper and disc 'afterburner' experience which was mentioned on This thread I found that the Teflon type coating on one piston had blistered and lifted.

 

BTW. Has anyone who maintains that Brembo do a seal kit for this caliper actually managed to get one yet? If not Ian ellison now has them in stock at near to £40 inc. pads.

 

GJ

[belfastguzzi]

Ian ellison now has them in stock at near to £40 inc. pads.

Good one, Gj and Guzzirider.

 

DL and Ratchet: LOL

 

seriouslly, I only use the back brake when I really have to stop

Seriously?

 

I think you're doing the right thing. It's pretty frustrating using it when you really want to accelerate.