K75S brake issues

[szabgab]

Did you watch the video?  I had a pile of those mouse turds come out of the brake lines on a '91 K100RS.  They plugged up the banjo fittings and made the brakes drag.  It's a good reason to change to new stainless lines.

The good news is that it appears that the crap doesn't get past the banjo fittings, so there shouldn't be a need to disassemble the calipers or the master cylinder.

I will try this at the rear, fortunately the front seems to be fixed for now...

[szabgab]

It sounds really silly, but I had a similar front squeal problem with a bike back in the day. After loosening up the triple clamps and realigning the forks, it mysteriously was exorcised and never returned. It wasn't a terrible noise, just really irritating. Good luck.

It does not sound silly. I had once used the wrong sequence to button up the front axle and even that resulted in misaligned brakes...

[szabgab]

Oh one more thing.. Worn disc + pads could lead to drag? I think, I might be on the last legs of the rear rotor - pads combo, pads measure 3.88mm (that is still well inside the usable range) disc I don't know, because my digital measures the edge, that is obviously factory standard still :) (I could have used some shims of a known thickness to bridge the shoulder, but I got lazy :) )

[szabgab]

OK, so I have gone back and has taken the rear brake to the tiniest bits, I could. Drained all the fluid, cleaned the reservoir, mc, piston, there are no banjo bolts on the tubes, but I have taken the connections apart and stared through the lines, cleaned, if necessary. Popped the caliper pistons with a bike pump and cleaned them again all around, bottom side and all. Also checked the bores, they are fine, but I have cleaned them as much as I could. Put everything back, bled the brakes and it is still dragging slightly. The rear rotor gets hot to the touch ridden the bike, warmer than the fronts. Fuel light came on today at 230 kilometers and I know from experience, tomorrow it will swallow around 16 litres of petrol, so fuel consumption is ultra-shite. I have never checked rotor temperatures before this issue, so I do not have a benchmark and I use my rear brakes quite a lot through city traffic, so that might be normal, who knows? Is there anything else I could try? I also measured the pads and rotor, pads are 3.88mm, rotor is at 4.2, so the PO was actually completely wrong about the rear worn beyond limit, actually it is all very good for now.... And yes, I have torqued everything down properly this time :D

Thanks!

[Laitch]

The rear rotor gets hot to the touch ridden the bike, warmer than the fronts. Fuel light came on today at 230 kilometers and I know from experience, tomorrow it will swallow around 16 litres of petrol, so fuel consumption is ultra-shite. I have never checked rotor temperatures before this issue, so I do not have a benchmark and I use my rear brakes quite a lot through city traffic, so that might be normal, who knows? Is there anything else I could try?

Try not touching the rear rotor.

If the rear master cylinder piston is operating smoothly, then there's not much left to check except rotor runout to determine if the rotor is warped, or cleaning the rotor's surfaces with an abrasive pad to eliminate embedded dirt. If the wheel can be spun to rotate a couple of times when the moto is on the center stand and in neutral, if it were my moto I'd move on instead of obsessing about the temperature of the rotor. I'd be using the front brakes more, too.

If you haven't checked the spark plug gaps, checked the condition of the air filter, checked the throttle body rubbers and crankcase vent for leaks, checked and adjusted the valve clearances, then followed with a throttle body balance and throttle position sensor adjustment, your complaining about mileage is premature. If you've done all that then do leak-down and compression tests. They're fun. :giggles

[szabgab]

If you haven't checked the spark plug gaps, checked the condition of the air filter, checked the throttle body rubbers and crankcase vent for leaks, checked and adjusted the valve clearances, then followed with a throttle body balance and throttle position sensor adjustment, your complaining about mileage is premature. If you've done all that then do leak-down and compression tests. They're fun. :giggles

From the list I have done nearly everything already, but obviously there is some much else to do (like the compression and leakdown tests). The mileage dropped suddenly, after I have taken the FD off and started to have rear brake issues, hence I think, they are somewhat related. But again, it could be anything, as I was doing other stuff at the same time, bike could be running too rich, now that I don't have air leaks (the bike smells like unburnt gasoline and if I press the starter button on a warmed up bike the revs do nothing, or drop slightly)... Obsessing about pitty little things is unfortunately my forte, I might have a slight OCD not diagnosed as of yet :))

[rbm]

So, have you confirmed that there is no drag due to the rear calliper.  Try following Laitch's suggested test - spin the rear wheel manually while the bike is on the centre stand and the transmission in neutral, with the calliper attached to the bike.  Observe the behaviour of the wheel, making sure that it spins somewhat freely.  Obviously the transmission and driveline will offer some drag and prevent the rear wheel from making multiple revolutions.  But the behaviour should suggest that nothing is hindering the rotation of the wheel.  Then try the same test but with the calliper removed.  See if there is a marked difference.  It will point to either a problem with the brake calliper - rotor, or it might start to point to issues with the FD or driveline.

[szabgab]

So, have you confirmed that there is no drag due to the rear calliper.  Try following Laitch's suggested test - spin the rear wheel manually while the bike is on the centre stand and the transmission in neutral, with the calliper attached to the bike.  Observe the behaviour of the wheel, making sure that it spins somewhat freely.  Obviously the transmission and driveline will offer some drag and prevent the rear wheel from making multiple revolutions.  But the behaviour should suggest that nothing is hindering the rotation of the wheel.  Then try the same test but with the calliper removed.  See if there is a marked difference.  It will point to either a problem with the brake calliper - rotor, or it might start to point to issues with the FD or driveline.

Yes it does spin, even if with a slight drag. This I would consider to be a job well done, if not for the piping hot rotor and bad fuel consumption. Next time I will try to ride without ANY rear brake (will be tricky, as my bike travels in the city nearly exclusively) and see if it heats up at all...

[Martin]

Most of your braking should be done with the front brake. Day to day riding I very rarely use the rear  I mainly use the rear for extra braking in emergency stops.
Regards Martin.

[Laitch]

. . .if not for the piping hot rotor and bad fuel consumption.

What temperature is piping hot? That description is useless. What has been the fuel consumption of the moto previously and exactly when did it change?

[szabgab]

Most of your braking should be done with the front brake. Day to day riding I very rarely use the rear  I mainly use the rear for extra braking in emergency stops.
Regards Martin.

I know, and that is, how I do it outside the metropolis. But at near zero speeds, when I navigate between lanes, cars, trucks, buses, the lot, the rear brake is invaluable, as it stabilises the bike together with fine clutch and throttle control to the point, I don't need to put my feet down, unless completely stationary. I went to a police driving course, that's what they do and it is a very useful technique. Obviously not, if you burn up your brakes though :)

[szabgab]

What temperature is piping hot? That description is useless. What has been the fuel consumption of the moto previously and exactly when did it change?

Oh yes, this is just not a very useful description, sorry. I mean you can not touch the rotor, as it will burn your fingers and it cracks, as it is cooling down, so it must be very hot, just like the engine (that cracks as cools in a similar fashion). I might try to sand the disc, as suggested, also it is getting a touch better now, as the wheel spins a tiny amount better in neutral, so probably the pads need to re-embed themselves, after being moved around (mind you, in the last week I have removed them probably 4 or 5 times and I'm not sure, if the sides weren't mixed up during those times)?

My consumption was around 5litres to 100km (47 US MPG), now it is more like 6.6-7 litres (33.5 US MPG) and it changed, when I have removed the FD to check the condition of my driveshaft... Obviously I do not fuel up daily, more like weekly, and during that time I sorted out my air leaks, cleaned the MAF (with MAF cleaner from a distance, not touching the sensor). This is also the time, since my bike "smells" rich, but I did not pull the plugs to see, what's what as yet. It is a distant possibility, that somebody fooled around with the air bypass as the bike was running lean due to air leaks and now it is just too rich, but I'm speculating only without seeing carbon building up anywhere...

[Laitch]

Burn your fingers isn't a better description.  Is the finger of a brick mason being used or that of a concert pianist? Fat finger or slim? How long does it take the skin to pass through the three degrees of burn severity? :giggles

If the air filter is clean, if the crankcase breather isn't leaking, if the throttle body rubber manifolds aren't leaking, if the coolant temperature sensor is reading to specification, if the electrical connector to the volume air flow sensor is clean and still tightly connected—something you should check because you had disassembled to access it, if all the air intake tubes are correctly connected, if the spark plug electrodes are in good condition and their gaps within specification, if the valve clearances are set to specification, then balance the throttle bodies and correctly set the throttle position sensor.

It needs to be done sometime and there's no time like the present.

[rbm]

Yes it does spin, even if with a slight drag. This I would consider to be a job well done, if not for the piping hot rotor and bad fuel consumption. Next time I will try to ride without ANY rear brake (will be tricky, as my bike travels in the city nearly exclusively) and see if it heats up at all...

My intention for this test was for you to perform it in the garage, while the bike is on the centrestand and at a standstill.  You've done the first part of the test which should give you a good idea of the "normal" resistance to spinning the wheel.  Take off the rear callipers and tie it to the frame.  Now the brake rotor cannot be hindered by the pads or other brake parts.  Spin the wheel again.  Was it easier this time, much easier?  Was it as hard to spin?  Were there any telltale noises from the driveline that might suggest parts interfering?  Answers to these questions will lead you to the problem.

It's not necessary to put your safety at risk to complete these basic diagnosis tests.

[Laitch]

This thread, and the attached video, inspired me to go riding today for the express purpose of palpating the rear rotor on my moto. As it turned out, I rode through a 40º rain shower to Montpelier where I was greeted at the Down Home Cafe with a hot cup of coffee and a piece of pumpkin pie with a dollop of whipped cream.

Maybe tomorrow I'll remember to touch the rear rotor.

[szabgab]

My intention for this test was for you to perform it in the garage, while the bike is on the centrestand and at a standstill.  You've done the first part of the test which should give you a good idea of the "normal" resistance to spinning the wheel.  Take off the rear callipers and tie it to the frame.  Now the brake rotor cannot be hindered by the pads or other brake parts.  Spin the wheel again.  Was it easier this time, much easier?  Was it as hard to spin?  Were there any telltale noises from the driveline that might suggest parts interfering?  Answers to these questions will lead you to the problem.

It's not necessary to put your safety at risk to complete these basic diagnosis tests.

Rbm, thank you for clarification. I have done that, just forgot to mention it in my comment, without the caliper the wheel spins better, not forever obviously, as the driveline is in the way. There are no undue noises whilst doing that. I have taken the bike for a ride outside town where I can safely moto around without a rear brake, and the rotor without ANY braking whatsoever got lukewarm. given, that the outside temp was in the low 20 C's, it should have been stone cold, so I still do have drag. I will wait a tad, like a tankful, if the situation is getting better and if the pads embed themselves a bit more. If not, I will take the mc apart once again to make sure, I have cleaned it as spotless, as possible...

[Laitch]

From the list I have done nearly everything already, but obviously there is some much else to do (like the compression and leakdown tests).

Meanwhile, back at the excessive fuel consumption issue—have you checked the electrical connection on the air flow sensor in the air box to be certain it is tight? Have you balanced the throttle bodies?

Is the rear drive housing uncomfortably hot after your rides?

[szabgab]

This thread, and the attached video, inspired me to go riding today for the express purpose of palpating the rear rotor on my moto. As it turned out, I rode through a 40º rain shower to Montpelier where I was greeted at the Down Home Cafe with a hot cup of coffee and a piece of pumpkin pie with a dollop of whipped cream.

Maybe tomorrow I'll remember to touch the rear rotor.

What a dedication :)  Thanks for even trying,  driving rain cools off parts anyway,  so it is better,  you spent the time warming up with a cake...

[szabgab]

Meanwhile, back at the excessive fuel consumption issue—have you checked the electrical connection on the air flow sensor in the air box to be certain it is tight? Have you balanced the throttle bodies?

Is the rear drive housing uncomfortably hot after your rides?

Good point,  I have never checked the housing itself,  will do so next time.  The electrical connection is secure,  but I will dig deep soon again,  as I have bought an un-cracked air housing elbow from Clayton,  that will go in instead of the glued one,  I have on now (it is not leaking anymore,  but it is better to get one,  that's pristine).  I would love to have the bodies balanced as that is the only thing,  I can not do myself,  as I don't have a balancer,  once I replaced the elbow,  I will take the bike in somewhere for that...

[Laitch]

I would love to have the bodies balanced as that is the only thing,  I can not do myself,  as I don't have a balancer,

Don't waste love on inanimate objects and processes. :oldguy:

You seem to be obsessive enough that you could successfully make one of the devices in this thread, then get the job done without further waffling. There are balancing instructions on this site, too.

[szabgab]

Don't waste love on inanimate objects and processes. :oldguy:

You seem to be obsessive enough that you could successfully make one of the devices in this thread, then get the job done without further waffling. There are balancing instructions on this site, too.

Wow, this is great. I have read instructions on pipe type manometers, but they were way too sensitive and it was easy to suck fluid in, the bottle version looks to be a lot more idiot friendly (e.g. made for me). I have already bought the 1/4" hose and will drink up all those fancy bottles of juice, that come in glass rather than plastic :)

Heat wise - the FD is not getting too warm, actually you can just leave your hand on the housing even after a longish ride of 20+ miles. The rear brake is dragging, but it starting to be unnoticeable, I'm barely able to hear it anymore if I spin the wheel manually and it is not hindering the rear wheel much anymore. Being anal I might revisit the MC, but I replaced to fuel pump the other day and my focus is on that too, as the new found LOUD hissing is driving me nuts :) So many things to keep me entertained with this bike.

[Laitch]

Being anal I . . .

I'm biceptual. It's cleaner. I consider it one of my strengths.

[Laitch]

Heat wise - the FD is not getting too warm, actually you can just leave your hand on the housing even after a longish ride of 20+ miles.

I recommended that check because bearing failure within the final drive can generate heat, so good luck is still in your corner.

I rode for half an hour at eighty miles an hour in 31ºF temperature to have a slice of zucchini bread at the end of the trail. When I parked, I laid my hand on the rear rotor. It wasn't quite as warm as a baby bunny. Hope that helps!

[The Mighty Gryphon]

I recommended that check because bearing failure within the final drive can generate heat, so good luck is still in your corner.

I rode for half an hour at eighty miles an hour in 31ºF temperature to have a slice of zucchini bread at the end of the trail. When I parked, I laid my hand on the rear rotor. It wasn't quite as warm as a baby bunny. Hope that helps!

I checked my final drive the other day after a quick ride to coffee with the boys.  It was about the same temperature as a bowl of chili after it's been cooling for five minutes.

[The Mighty Gryphon]

And no, Laitch, I didn't taste it to see if it was as spicy.