No rear brakes on K75 but plenty of pad - what gives?

[90288]

My wife reports that the brakes on her K75 "went out".

She's right - mash down on the pedal and (almost) nothing happens. A check of the pads reveal there's plenty left on the shoes.

An inspection with the rear tire off reveals nothing strange - when you step on the pedal the pads move outward as if to rub against the wheel.

Any ideas as to what's going on? The real stange thing is this seems to have happened all of a sudden - like one minute they were working fine and the next they are not.

Now admittably, my wife uses the front brake almost exclusively - much like I do.

Anyone else have this happen? Any speculation??

 

[dbrick]

Sounds like the master cylinder piston seal failed. A little pressure causes the pads to move; more pressure and the seal's broken and no movement occurs.

 

[wmubrown]

Sounds like the master cylinder piston seal failed. A little pressure causes the pads to move; more pressure and the seal's broken and no movement occurs.

Agreed... they were known for corroding too... a rebuild kit is available, if the inner wall of the cylinder is corroded it will take a little work to clean it up, and you must do that or it will tear up the new seal. If corrosion is the fault, it might be easier just to replace the whole assembly.

 

[98lee]

[QUOTE=gsmetal;199586
when you step on the pedal the pads move outward as if to rub against the wheel.


It sounds like he's talking about a K75C. They had mechanical drum rear brakes. Unless it was an ABS model.

If it is indeed a C with drum rear brakes, then the only two things I can think of are a mechanical linkage problem (broken or out of adjustment) or contamination on the drum or shoes (oil or grease from the final drive).

If it is a disc rear brake, then the rear master would be the first suspect.

 

[90288]

It's a K75c

You're right....it's a K75C so there is no Master Cylinder - it's a mechanical system.

The weird thing about this is no amount of foot pressure on the pedal gets the brakes to work any better.

Let me say here that I'm no stranger to brakes. I've rebuilt more calipers than I care to remember - I generally understand what makes a braking system work. Admittably I've never done a mechanical system before but it doesn't appear complex.

I looked at the pads (shoes) and they don't appear to have any type of build up on them - I did buy new pads (at $65.00...geeze!) but haven't installed them because they don't look any different then the pads that are already on. All the springs seem to be in good working order.....everything "works" but it doesn't "stop". The bike only has 15,000 miles on it.

I'm hoping someone else had a similar experience and can advise me.

 

[MOTOR31]

Maybe they are glazed. Use a wire brush to roughen up the pads a bit, so they are not smooth to the touch ands see if that helps.

By any chance, did you wash the bike with a pressure spray wand spraying soap? You may have contaminated the pads with soap in that case.

 

[PGlaves]

The K75C drum brake has the actuating cam-shaft passing through the housing. It is possible for the tube that contains the shaft to leak which passes oil onto the brake drum and shoes. Check this first.

 

[st3ryder]

Are they adjusted? The push rod linkage has the butterfly adjuster on the threaded end, and the brakes are adjusted by spinning the wheel and turning the adjuster to the point where it stops the wheel, and then back- off 1/2 a turn. Are they fully seated? If the shoes, (not pads) were removed/replaced they may not have been fully seated against the back of the final drive and slipped and are now not making full contact with drum. They should sit straight up and down, no inward angle. Is the return spring set properly? Has the pedal's mount or height shifted/changed? Just a few thoughts.

I like my drum brake, it has excellent stopping power and feel. Good thing your sp goes easy on it because one needs to replace the whole wheel once the drum is run-out. :-(

 

[90288]

Adjusting nut

Thanks for the insight.

I did adjust the brakes using the butterfly adjusting nut....this hasn't helped.

I'm going to put the thing up on the lift Thursday and dig a little deeper but until then, if anyone has any additional thoughts, I would like to hear them.

I'm going with the glazing on the pads and roughing them up a little suggestion but like I said, if anyone else has a thought or suggestion, I would entertain them.

Thanks!

 

[PGlaves]

That mechanical system is too elegantly simple to not work. Push pedal - pull rod - pull lever - turn cam - spread shoes - stop.

The pedal should be adjusted to move about one inch, or a little less. That is achieved by turning the wingnut tighter till the shoes just drag and then backing of 2-1/2 to 3 full turns (5 or 6 half turns - it stops every half turn).

It is possible the lever has loosened and slips on the splines on the actuating shaft.

You can lightly dress the drum with some emory paper and can deglaze the shoes the same way.

Check carefully for any sign of gear lube in the brake drum and on the shoes.

That's all I can think of that is possibly wrong.

 

[TOM1911]

You might want to check the brake actuating cam for abnormal wear. It sounds like you cant cam the brake shoes out far enough.

 

[kayseventyfive]

Does the pedal feel hard?

Can you compare it to another K drum brake?

 

[st3ryder]

Soooooo, what was it?

 

[90288]

Update

Well I took the rear tire off one more time to inspect what was going on and I found a light amount of a grease / oilly type substance on the hub.

I'm wondering if I my final drive has a bit of a leak in the hub somewhere although the rest of the area seem high & dry (centrifical force at work?)

I cleaned off the hub with brake cleaner and roughed up the shoes with a wire brush and the brakes are remarkably better - but not great (I have ABS so I'm used to that)

I'm going to keep an keep an eye on it for the next few weeks and take another look then to see if anymore oilly substance appears....if it does I have bigger problems than poor braking.

Thanks for all the insight!

 

[PGlaves]

Reread post #7 in this thread.

 

[90288]

You da man!

 

[PGlaves]

No rear brake was the first symptom of my ABS brain failing. An easy way to check it out without much trouble is to simply unplug the ABS brain and then see how that rear brake is working. It'll lock up with relatively little pressure on the pedal if everything is OK mechanically & hydraulically. If plugging the brain in again results in the "no rear brake" feeling again, then it's the ABS brain that's failing.......Pray that's not the case for your bike.

Except that this is a K75C with a mechanical rear brake - no master cylinder - no hydraulic fluid - and no ABS.