Friday, January 22, 2016

Rear Brake Maintenance (Part 1)

In connection with my recent chain/sprocket replacement on my 2015 Kawasaki Versys 1000 LT, I also got to some past-due maintenance on my rear brake. Routine maintenance for both front and rear brakes every 3,800 miles includes inspection of fluid level, pad wear and lever/mechanical operation. Every 15,200 miles the brake fluid requires replacement.

At the 15K mile mark I was on a road trip and didn't get to the maintenance items at that interval until about 18,500. However, I got caught up with other things and didn't do the rear brake pad wear and fluid change. So I figured at 20,000 miles and nothing fun to do during a stretch of crappy weather, now would be a good time to get to it. 

So what I've documented in this post was:
  • Removed the rear brake pads an measured thickness of each.
  • Replaced the rear brake fluid.
  • Bled the rear brakes.
The first step was to remove the muffler can to get access to the rear brake caliper. The muffler cover came off with three 5mm allen bolts. Then the clamp was loosened and the retainer bolt (6mm allen) was removed. At that point the can slid out of the exhaust pipe and the brake caliper was fully exposed to be worked on.




The caliper is set up very similar to an automobile caliper where the piston/pad assembly pivots up and away from the brake rotor and caliper mount. To allow the caliper to pivot I removed the brake pad pin plug, loosened the brake pad pin and removed the pivot bolt ... in that order.


The photo below shows how the brake pads are held in the rear of the caliper of my Versys. I'll show a photo how they are held in the front of the caliper later. By removing the brake pad pin, I was able to remove the brake pads. 



Once removed, I could measure the wear and service limit on each of the brake pads.

New pads have a factory spec of 5.0 mm and a service limit of 1.0 mm; under 1.0 and they'd require replacement. However, for brakes I'd exercise an abundance of caution and replace at 1/2 of the new thickness or 2.5 mm in this instance. 

Since each pad consists of the friction material and a backing plate, I had to measure the total thickness, measure the backing plate thickness and then subtract the backing plate thickness from the total thickness. I used a digital micrometer for this procedure and I took four measurements (around each of four corners) of each pad to get a good average.


From my notes below, the left friction pad ranged from 3.38 to 3.49 mm thick. The right friction pad ranged from 3.58 to 3.95 mm thick. As previously stated, replacement would have been required at 1.0 mm and I would have replaced at 2.5 mm. The actual pad measurements all exceeded my personal replacement level and by quite a bit. I thought that was pretty good considering they've got 20,000 miles on them.


Just for the record, although I didn't need pads, new factory brake pads would have been around $65. That's a lot for rear pads. However, there are some aftermarket providers of brake pads in the $25-$40 range that I'd have gone with if I needed pads. They're well branded, as well. Names like EBC and Galfer. In fact, EBC has a kevlar pad!

Onward...

Before reassembling the caliper I carefully inspected all the parts for signs of wear or damage. I found that the brake pad pin was rusty so I cleaned it with steel wool, applied some rust treatment and grease. I always use caution applying grease or lubricants around brake parts not to let any fluids drip on the pads or rotors.


This is a view of the front of the caliper. Where the brake pad pin holds the pads to the rear, the brake pad guide and spring hold the pads in place from the top and front of the caliper. When the pads are installed I took care to make sure that the pads were properly fitted. 


Before the caliper (with the pads installed) can be lowered onto the rotor and caliper base, I had to compress the piston. The piston is better shown in the photo above. Essentially, it forces the two pads to grab and slow the spinning rotor of a moving motorcycle. Unlike where a clamp is needed on an auto caliper, I was able to compress the piston with my fingers ...


...but it's important to note that I first removed the cap from the brake fluid reservoir that is located under the seat. That's because when the piston is compressed it forces brake fluid back through the system and the only place it has to go is the reservoir. Removing the cap/diaphragm makes room in the reservoir for the backwash. Also, if the reservoir was too full it could spill out; something to be prepared for, although it didn't happen in this case.


Once the caliper is lowered onto the rotor, the reassembly is the reverse of the disassembly. 

Then the process of replacing fluid and bleeding can be accomplished. I don't use sophisticated bleed tools so it's easier for two people to change fluid and bleed brakes. My son and I had the following items to do this...
  • A fresh bottle of DOT4 brake fluid (you won't need that much, I have other bikes too)
  • A rubber drain hose
  • A "Ratio-Rite" measuring cup (or any vessel to add fluid to the reservoir)
  • A drain bucket to collect old fluid
  • A 10 mm open ended wrench

The caliper has a bleeder valve through which old fluid can be purged. When the valve is opened using a 10 mm wrench and the brake pedal is depressed, fluid will be hydraulically forced from the reservoir through the brake system and out the bleeder valve until it the valve is closed. 

DO NOT let the reservoir (two photos up) run dry because the hydraulic action of the fluid is necessary to make this process work and it's a real pain to re-prime the hydraulics. The reservoir only holds a few ounces so I kept a close eye on it and had my Ratio Rite measuring cup full of fresh fluid for when it got close.


Also important to keep in mind is that since the fluid is under pressure throughout the brake system, engaging the hydraulics will cause the brake fluid to shoot out of the bleeder valve under a great deal of force. A rubber hose and drain bucket as shown below are necessary to direct and capture the spent brake fluid and, while we were at it, both my son and I had on a pair of safety glasses because I once had a bad experience bleeding a car brakeline where the rubber hose popped off and I got brake fluid in the eyes. Learned my lesson.


Onward...

With all this set up, my son and I proceeded to purge the old fluid. He was responsible for opening and closing the bleeder valve and making sure the spent fluid hit the bucket. I was responsible for pumping the brake, which forced fluid out the bleeder valve, and keeping the brake fluid reservoir full using the measuring cup. Did I mention not to let the reservoir go dry?  Letting the system run dry is not a good idea. 

Anyway, the way it worked is we kept refilling the reservoir and pumping fluid until only clean fluid was flowing out the valve. How could we tell?

Here's a photo of clean brake fluid going into the reservoir...


Here's what came out the other end...


The good news is that this process actually effected bleeding the brakes along with the fluid replacement. If just the brakes needed bleeding, it would be the same process except that you wouldn't be replacing the fluid. Rather, the bleeder valve would be opened and fluid would be purged so long as air bubble can be seen in the fluid coming out of the bleeder valve and hose. That's what bleeding is, bleeding air from the brake lines. Same as the replacement process, when bleeding the reservoir should not be allowed to run dry.

Lastly, I took the motorcycle out for a run around the neighborhood and made sure that the brakes worked properly. All was well and I shouldn't need to do this again for another 15,000 miles, although given how dirty that fluid was I may cut it down to 10,000.


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