General rear brake question.

[dmoon64]

The sales comment was tongue in cheek.

 

I really appreciate your help with this. I'm pretty confident I have cleaned away the problem. If not I'll just keep working on it until I have.

 

Thanks again,

 

Darryl

[Guest ratchethack]

I'm pretty confident I have cleaned away the problem. If not I'll just keep working on it until I have.

Now THAT'S the Guzzi spirit, Darryl!

 

The fly-by-night, wishy-washy, fickle, grass-is-always-greener crowd is always coming and going, chasing the "bigger is better" juggernaut, leaving nothing behind but an unending trail of disappointment and ceaseless craving for the imaginary magic carpet ride. . . By my estimate, something close to half of newby Guzzi owners (as seems to be the case with any other marque, BTW) are so easily distracted, confused and discouraged that they don't own them long enough to get 'em though break-in. . .

 

Wattayagonna do? The woods 'r full of 'em. . .

 

And o' course, it's only after a Guzzi is fully broken in, that she really begins to show wot she's made of. . .

 

And so it goes. . .

[BrianG]

Now THAT'S the Guzzi spirit, Darryl!

 

The fly-by-night, wishy-washy, fickle, grass-is-always-greener crowd is always coming and going, chasing the "bigger is better" juggernaut, leaving nothing behind but an unending trail of disappointment and ceaseless craving for the imaginary magic carpet ride. . . By my estimate, something close to half of newby Guzzi owners (as seems to be the case with any other marque, BTW) are so easily distracted, confused and discouraged that they don't own them long enough to get 'em though break-in. . . <_>

 

Wattayagonna do? The woods 'r full of 'em. . .

 

And o' course, it's only after a Guzzi is fully broken in, that she really begins to show wot she's made of. . .

 

And so it goes. . .

The good news is that this juggernaut provides a rich source of material for the true aficionado!

[dmoon64]

I took the caliper off the bike. Got the pistons out cleaned them up, put them back and bled the brake line. Took a 5 mile ride and the damn things are still heating up and grabbing the brake disc. Bike was difficul to push once I got home. Only thing left is to replace the caliper. Brake pistons had some small scratches on them, but nothing that seemed like a big deal.

 

Thanks for your help.

 

Darryl

[mike wilson]

I took the caliper off the bike. Got the pistons out cleaned them up, put them back and bled the brake line. Took a 5 mile ride and the damn things are still heating up and grabbing the brake disc. Bike was difficul to push once I got home. Only thing left is to replace the caliper. Brake pistons had some small scratches on them, but nothing that seemed like a big deal.

 

Thanks for your help.

 

Darryl

 

You do have some air space in the master cylinder? Hot liquid expands but it cannot be compressed.......

[Guest ratchethack]

I took the caliper off the bike. Got the pistons out cleaned them up, put them back and bled the brake line. Took a 5 mile ride and the damn things are still heating up and grabbing the brake disc. Bike was difficul to push once I got home. Only thing left is to replace the caliper. Brake pistons had some small scratches on them, but nothing that seemed like a big deal.

 

Thanks for your help.

 

Darryl

Darryl, I again commend your effort. This is a bit of a puzzler. But as pointed out previously, these things aren't all that complicated. There has to be something going on here that doesn't meet the eye in your last post, but there just aren't that many possibilities.

 

I'm sure you've got all these covered, but this'd be my checklist:

 

1. Seal(s) are heat-damaged to the point where they will not retract.

 

2. Free play is improperly adjusted so that the relief port remains closed.

 

3. Improper bleeding, with excessive air and/or water remaining in the line, and/or less than fresh brake fluid.

 

4. A physical obstruction between the piston(s) and caliper remains, despite the refurb work.

 

5. You're resting your foot on the brake pedal.

 

Sorry I don't have anything more for you, my friend. I reckon that's about all there is??

[pasotibbs]

I took the caliper off the bike. Got the pistons out cleaned them up, put them back and bled the brake line. Took a 5 mile ride and the damn things are still heating up and grabbing the brake disc. Bike was difficul to push once I got home. Only thing left is to replace the caliper. Brake pistons had some small scratches on them, but nothing that seemed like a big deal.

 

Thanks for your help.

 

Darryl

I think the problem lies in the Master cylinder, but the weird thing is that you where able to bleed the system ok Did you adjust the freeplay in the linkage afterwards? If you did back off the adjustment to give say 5mm or so clearance and road test it. The brake applying itself when it gets hot to the point where you can hardly push it seems to imply that the fluid is expanding and being unable to get through the master cylinder drilling is pushing the caliper pistons out, creating more heat so more pressure and so on....

 

As the pads are so small I can't see the pads not retracting fully due to a caliper fault is causing this alone, it may start the problem by generating more heat than normal but replacing it may not be a complete cure.

 

Even resting your foot on the pedal shouldn't cause this fault, you will go through pads/disks (and petrol )at an exteme rate but no mater how hot the brake gets it should still be possible to roll the bike when you take your foot off the pedal and let the pressure escape through the master cylinder

 

good luck

 

Dave

[Tom M]

I took the caliper off the bike. Got the pistons out cleaned them up, put them back and bled the brake line. Took a 5 mile ride and the damn things are still heating up and grabbing the brake disc. Bike was difficul to push once I got home. Only thing left is to replace the caliper. Brake pistons had some small scratches on them, but nothing that seemed like a big deal.

 

Thanks for your help.

 

Darryl

 

I had a similar problem with the front brakes on an old Honda. The problem was not in the caliper, it was in the master cylinder. The fluid return circuit was clogged so pressure remained in the lines after applying the brakes so the brakes dragged. You could check for this on your rear brake by pumping the brake pedal hard a few times then crack the bleeder screw. If the fluid shoots out under pressure I'd say the MC is the problem.

[dmoon64]

I'll look at the freeplay thingy first. That seems simple enough. Just loosen the bolt and turn the threaded rod. Am I looking for 5mm of play at the toe end of the brake lever?

[Guest ratchethack]

I'll look at the freeplay thingy first. That seems simple enough. Just loosen the bolt and turn the threaded rod. Am I looking for 5mm of play at the toe end of the brake lever?

Darryl, a few mm of play at the end of the lever is usually considered sufficient. Any free play at all, assuming that the master cylinder return spring is capable of properly returning the MC piston fully, ensures that the relief port is fully open when there's no pressure on the brake lever. Per previous posts on this, I've seen guys put an INCH and more play in their brake levers in wot I consider to be a futile and sloppy attempt to side-step the usual root causes and resulting symptoms of brake neglect. Because I stay on top of my brakes and prefer the feel and control of tight brake linkage, I prefer little to no free play at all, but to repeat from a previous thread, I DO NOT, CANNOT, and never have recommended this for anyone else. . .

 

Again -- if you have SOME play in it, the relief port will be fully open, allowing any built-up pressure from the caliper and line to escape into the reservoir every time the lever returns to its resting position.

[Dan M]

I took the caliper off the bike. Got the pistons out cleaned them up, put them back and bled the brake line. Took a 5 mile ride and the damn things are still heating up and grabbing the brake disc. Bike was difficul to push once I got home. Only thing left is to replace the caliper. Brake pistons had some small scratches on them, but nothing that seemed like a big deal.

 

Thanks for your help.

 

Darryl

 

 

Darryl,

 

It's easy to isolate the trouble. Ride the bike and get the symptom to show it's face. When the brake is hot and dragging, open the bleeder. If the brake releases, the trouble is not the caliper, but something else blocking the fluid from return to the reservoir. Now, sometimes brake hoses collapse internally and keep fluid from returning to the master. Get it to happen again and open the line at the master cylinder end. Again, if the brake releases, the trouble is further up stream, (master or lack of free-play as has been suggested). If it does not, you need a hose.