Pads Now Retracting

[Beemeridian]

22

[MIXR]

Read this thread on my brake problem.
http://r1150r.org/board/viewtopic.php?f=2&t=20175

You didn't say if you loosened the front wheel. If the forks slightly twisted during the fall, you will end up with binding brakes just like I had. Loosen the two pinch bolts, then the main axle nut, and do the settling bounce on the front suspension. Helps if the caliper bolts are also loose.

The test will be the un-doing of the axle bolt. If the nut is very tight, then something has moved. It should be fairly loose.

Then torque it up in the following sequence, spinning the front wheel at each step.
1. Axle bolt
2. Pinch bolts
3. One caliper
4. Other caliper

If that doesn't fix it, or you have already done that, then I can't help.

[CycleRob]

Beemeridian,

This is a common problem with all fixed caliper, floating rotor front brakes, which is every opposed piston caliper system. That is pistons pushing a brakepad from the left and right sides of the rotor. That is unlike most rear brakes that have a single sided piston in a floating caliper with a fixed rotor.

The same thing happened to my OilHead when I disassembled everything for a thorough cleaning. See for yourself in Pic 1 and Pic 2. The first time you put on the brakes, no matter how clean and friction free the caliper pistons are, the rotor gets pushed away from dead-center-middle of it's free movement range. The rotor sways left/right real easy and opposing pistons never seem to move equally under identical brake hydraulic pressure. That causes a two rotor brakepad drag that stops the front wheel from a vigorous spin in 1 turn or less. As you found out, repeated attempts at removing the calipers and pushing back the pistons does not solve the problem. Most just ride the bike only to find out some days later the problem has lessened or gone away completely. There is an easy way to fix it quickly -IF- you are sure there are NO binding gummy pistons, age-hardened rubber piston seals or a clogged bleedback hole in the master cylinder -AND- the wheel/axle/calipers/pinchbolts were correctly assembled. Ride the bike and when traffic conditions permit it STUFF THE FRONT BRAKE HARD ENOUGH TO SKID THE FRONT WHEEL. Speed up and do it again. Next, find a parking spot to place your bike on it's centerstand, then elevate and spin the front wheel. It spins easily over 3 turns, doesn't it?


.

[riceburner]

Beemeridian,

This is a common problem with all fixed caliper, floating rotor front brakes, which is every opposed piston caliper system. That is pistons pushing a brakepad from the left and right sides of the rotor. That is unlike most rear brakes that have a single sided piston in a floating caliper with a fixed rotor.

The same thing happened to my OilHead when I disassembled everything for a thorough cleaning. See for yourself in Pic 1 and Pic 2. The first time you put on the brakes, no matter how clean and friction free the caliper pistons are, the rotor gets pushed away from dead-center-middle of it's free movement range. The rotor sways left/right real easy and opposing pistons never seem to move equally under identical brake hydraulic pressure. That causes a two rotor brakepad drag that stops the front wheel from a vigorous spin in 1 turn or less. As you found out, repeated attempts at removing the calipers and pushing back the pistons does not solve the problem. Most just ride the bike only to find out some days later the problem has lessened or gone away completely. There is an easy way to fix it quickly -IF- you are sure there are NO binding gummy pistons, age-hardened rubber piston seals or a clogged bleedback hole in the master cylinder -AND- the wheel/axle/calipers/pinchbolts were correctly assembled. Ride the bike and when traffic conditions permit it STUFF THE FRONT BRAKE HARD ENOUGH TO SKID THE FRONT WHEEL. Speed up and do it again. Next, find a parking spot to place your bike on it's centerstand, then elevate and spin the front wheel. It spins easily over 3 turns, doesn't it?


.

Interesting.


Mind you don't come off when the bike lifts the rear off the ground either.

[MIXR]

And one more to add. Some of the brake pads (such as the newly tried Goodridge I fitted and dislike) have a very rough finish on the pad carrier. The carrier is the metal bit the pad material is bonded to. On the Goodridge pads, there is a very rough stamping edge (from manufacture) all the way around the edge of the metal carrier plate. No big deal, but it makes a rough edge that won't 'slide' as readily as it should on the caliper body where it touches. Check your new pads and smooth any 'knife-edges' off the pad carrier where it has to slide (move/jiggle) in the caliper. Look at the old ones to see where they touch - It should be shiny and smooth in those places. Not talking a coarse grinding wheel here. Just a fine hand file. You are only removing rough 'catch-points', not trimming the pads!

[Beemeridian]

21

[chibbert]

Ride the bike and when traffic conditions permit it STUFF THE FRONT BRAKE HARD ENOUGH TO SKID THE FRONT WHEEL. Speed up and do it again.

Ahhhhh Stoppies on a german boxer twin - aint it grand?!

[MIXR]

Might be a terminology thing.

The pinch bolts are the lower fork leg allen bolts that clamp the axle in place once the axle bolt is tightened. I'm talking about the bits that hold the front wheel on, so way down at the bottom of the legs. The main axle bolt, and the two screws that clamp (pinch) the axle to stop it from moving. Simple bits, but oh so important as I found out.

All new pads will have a degree of 'tightness' before they settle in. I've now done over 1,500 kms since I did everything correctly on the front end. I will not get three rotations from a wheel spin. If I spin it hard enough, I'll just get two. That's a lot better than the one rotation I started with! They are getting looser, but very slowly. That's not unusual. You may still hear the pads lightly rubbing the disks for many thosands of kilometres. So long as you know the brakes are not grabbing, or shuddering, or pulling badly to one side, then all should be ok.

You have been checking the right things, but go back and do them again. Undo the axle clamps (pinch bolts), loosen the axle, and loosen the caliper bolts. Do the bounce to settle everything. Does the wheel spin freely? Do up the axle. Check spin again. Do up the pinch bolts. Check spin again. Do up the calipers, one at a time. Check spin at each one. It should all get a little bit tighter at each step. USE A TORQUE WRENCH. Then go riding.

[riceburner]

Ride the bike and when traffic conditions permit it STUFF THE FRONT BRAKE HARD ENOUGH TO SKID THE FRONT WHEEL. Speed up and do it again.

Ahhhhh Stoppies on a german boxer twin - aint it grand?!

was doing them yesterday evening trying to get a new set of pads worn in. ;D (the crash when the rear lands isn't pleasant though!)

[riceburner]

Might be a terminology thing.

The pinch bolts are the lower fork leg allen bolts that clamp the axle in place once the axle bolt is tightened. I'm talking about the bits that hold the front wheel on, so way down at the bottom of the legs. The main axle bolt, and the two screws that clamp (pinch) the axle to stop it from moving. Simple bits, but oh so important as I found out.

All new pads will have a degree of 'tightness' before they settle in. I've now done over 1,500 kms since I did everything correctly on the front end. I will not get three rotations from a wheel spin. If I spin it hard enough, I'll just get two. That's a lot better than the one rotation I started with! They are getting looser, but very slowly. That's not unusual. You may still hear the pads lightly rubbing the disks for many thosands of kilometres. So long as you know the brakes are not grabbing, or shuddering, or pulling badly to one side, then all should be ok.

You have been checking the right things, but go back and do them again. Undo the axle clamps (pinch bolts), loosen the axle, and loosen the caliper bolts. Do the bounce to settle everything. Does the wheel spin freely? Do up the axle. Check spin again. Do up the pinch bolts. Check spin again. Do up the calipers, one at a time. Check spin at each one. It should all get a little bit tighter at each step. USE A TORQUE WRENCH. Then go riding.

what he said - I went through this last night (after doing up the front spindle so tight I snapped the screwdriver I was using as a brace in the spindle - DOH! ) and it made a big difference.

(Note to self - if you break a tool, you're doing it wrong!)

30 Nm on the spindle
22 Nm on the pinch bolts.

[Beemeridian]

22

[Boxer]

Wear a seatbelt when doing the "stuffing" thing.

[MIXR]

The problem with this sort of thing (as I found from my own experiences) is that if you tighten the calipers first, you may have already 'loaded' the pads against the rotors, which in turn loads the forks to one side or the other. Then your tightening of the axle simply locks things in a mis-aligned position. With old pads, it's not critical. With new pads, the amount of free-play is seriously reduced. It matters.

Getting the axle straight and then tight BEFORE you apply other loads is what matters. Remember, the caliper pistons are supposed to retract, but as you know, they can be very stiff to move the fluid and will apply a surprising amount of force to the rotor. Once the front end is 'locked', the tightening of the calipers will simply allow the piston pots to retract (or extend) aginst the rotor in the correct position.

Always look for the logical sequence in this sort of work. Sometimes, it just doesn't matter. Sometimes, it does.

[Beemeridian]

22

[Sunbeemer]

Could be...I read never to pull the brake lever all the way back to the grip while bleeding the front brakes since this can damage the master cylinder's piston seal by pushing it past the end of the cylinder where it can pop out. While this seems odd to me, I adhere to this advise, and suspect it may be the cause of your retraction troubles. Unfortuanately I have heard these piston seals are not available seperately and you have to buy a master cylinder kit to replace it. But, if the specifications of that seal could be determined, I'd bet it is offered by another supplier.

[MIXR]

Ok - 29 years of aviation and hydraulic systems here.

I cannot confirm if what you are seeing is 'normal' or not, as I have not opened my master cylinder up to check.

However, it only takes a very small 'hole' and a very small amount of very small piston movement to actuate a set of brakes. Pressure transfer and 'incompressible' brake fluid will allow that.

I very much doubt that you have damaged a brake master cylinder piston in a crash. More likely, you have some small amount of debris or crud buildup that has dislodged and partially blocked the return port. Can you carefully compress a pair of caliper pistons and get fluid returning? If so, there is unlikely to be a problem with the return port.

Try some fresh fluid and do another bleed. Fresh fluid will also behave like a cleanser, and may help flush any crud out. It will also allow you to prove that the master cylinder is working, or not. If not, the brakes will continue to 'jam on' (no return).

If you can, check the pads and see if they are 'loose' with the brakes in 'neutral' (no handle pull). If only one side of the brakes on both sides is sticking, then you have an alignment problem. If all 4 pads are hard, then it's a master cylinder problem (most likely rather than all 8 piston pots at the brakes).

You can also try and slip in a really old set of worn pads if you have some. Does that solve the problem? Leave the rattle plates off during this work. Won't hurt to do a ride with them off, and allows easy access to the pads and also removes one more obstacle that allows them to move away from the rotors and allow the wheel to spin.

One more thing that might be fall-related. Is the brake handle actually returning? Has it been bent and it's the handle that's binding where it mounts on the pivot? Or has the mounting point been 'burred-over' so as to prevent a full return. Or the return spring inside has collapsed? Any of that might give you some return problems as it will prevent the pads from fully 'relaxing'. Maybe it's that simple?

Other than that???????????????????????????

[Beemeridian]

22

[MIXR]

Great news. Pleased you got it sorted, but I'm still trying to figure out the relationship between what started this and how it ended. Maybe just too much pressure on the lever at some point and that created some internal piston problems. I know that forcing the master cylinder piston too far in during a bleed can sometimes result in a problem, but I've never known one to stay stuck. Maybe the piston was partially jammed and the return spring couldn't do its job? Anyway - A very interesting thread and something new for all of us to watch out for.

Now go riding!

[Sunbeemer]

Glad you got it fixed, and by such a reputable guy...you should have absolutely no worries about your brakes failing at an inopportune moment!

Good brakes....PRICELESS!

[CycleRob]

Beemeridian,
The piston viewed thru the hole is where it belongs. The hole that must be uncovered by the piston is the very tiny one, just one hole diameter to the right of your featured hole. The master cylinder internals look very clean but the lever sticking after a squeeze means the master cylinder bore had a time honored thin sludge film that the piston seal got pushed into. After that, the chances of the tiny hole getting plugged are increased dramatically. The expert/pro M/Cyl rebuild would correct any crash damage lever travel or adjustment anomaly. Adding to all that, your dedicated all weather (rain/snow) riding routine may additionally require more frequent F/R caliper piston servicing.
Click to see pics. Click big pic again to go full size.