Binding brakes mystery

OK, here's an odd one.

This morning, at around 6 am I rode the bike to church; about ten miles.
When I stopped, the brakes felt like they were binding.
This was early enough that the weather was cool; in the mid '70's.

When I left church, I rode about 5 miles to a restaurant. By the time I arrived, the brakes were binding to the point that I was running in 1st gear and could barely keep the bike moving.
Once I stopped, the bike was immovable.

After I ate and came back to the bike, it was no longer binding.
I made every effort to avoid braking on my way back home. During the first few miles, I would let out the clutch and the bike would continue to roll without any apparent drag.

5 minutes after getting on the highway, however, I had to pull over.

Same symptoms; once stopped the bike was immovable.

The brakes were binding and both front rotor were turning blue, due to the heat.

I called a tow truck and he arrived within 30 minutes. In that time the rotors had cooled down and the bike could be rolled.

The bike is a '01 with less than 17K miles on it.
The brake fluid has been changed within the last 2 years.
The brakes are stock, with the linked system intact.

Any ideas and recommendations as to where to start troubleshooting?

This has never happened to me, and I have replaced my linked brakes with unlinked on my 99 VFR.

Having said that, it's not uncommon, and is symptom that you need to flush your brakes really thoroughly as you may have some debris that is blocking a return port on a master cylinder or delay valve. I'd be pulling the front calipers off first and checking that the sliding mounts are well greased, and if so then (after cleaning the visible piston) I'd be trying to push each piston back into the caliper to see which one is jamming. If it is any of the outer pistons the blockage is probably at the front master. If it is one of the centre pistons then the blockage is probably in the delay valve. In either case, a vacuum bleeder and lots of flushing may help to pull the debris out of the system, if not a clean and strip is in order.

I've had this kind of issue before. It was caused by the bleed return hole on the master cylinder getting blocked by debris from behind the M/C piston. You will need to strip the cap off the M/C to check this, if its the issue the M/C will need a strip & clean.

The other potential issue is BOTH from brakes are control activated on the 98/01 5th gen from the rear M/C & there are 2 control valves in the system. One under the front right of the seat, the other on the right fork leg, its a delay valve, which should not be an issue.  On the 6th gen one one front rotor is braked by the rear pedal, so if it was the cause only one rotor would get hot !

Good luck, the debris issue would explain the random nature of the problem !

Thank you both for the quick reply.

I'll try both your approaches to tracking down which section is the likely culprit, check both M/C's, the control valves and give it all a good flushing.

Well, the mystery deepens.

I spent last Friday night and Saturday disassembling and reassembling the three calipers and the PCV and bleeding the entire system.
The only components I didn't take apart were the three master cylinders and the delay valve.

I used the guides put together by HS and jay-d.

The work gave me an excuse to buy a Mityvac bleeder kit that runs off of compressed air (new toy!!).

All 9 pistons were in excellent shape and moved well. No signs of leakage or seal degradation.

Once I disassembled the PCV, its decompression piston moved freely in the bore and the rubber seals showed no signs of wear. There was no way to access the cut piston.

It was easy enough to establish that the front and rear M/C's were working fine.

When I had the left caliper disassembled, the SMC piston moved freely in its bore and I saw no signs of leakage.

I also took advantage of situation and replaced the front rotors with a set of Galfer wave rotors I'd bought some time back.
All three sets of bake pads were pretty thin, so they also got replaced with the Galfer pads purchased with the rotors.
I don't have a 42mm socket yet, so the rear rotor will have to wait.

Maybe I was doing it wrong, but the vacuum bleeder did nothing for me when trying to bleed the linked portion of the system (RMC to right center/RMC to left center/RMC to SMC/SMC to PCV/PCV to rear center).
Without someone to pump the rear lever, there was no flow.

My house-mate helped me on Sunday by pumping the rear brake lever while I bled the various ports tied to the linked portion of the system.

The one part I struggled with is bleeding the secondary master cylinder on the left caliper assembly.
Although it moved freely when I had the caliper disassembled, I never got the impression that the piston moved at all when I would open the bleeder and push on the piston bracket.

Low speed test rides around the neighborhood  on Saturday indicated that the front and rear braking worked overall.
No binding occurred, even when I would draw down hard on both the front brake lever and the the rear pedal.

A 25 mile ride on Sunday, prior to bleeding the system with my house-mate's help, was also without issue.
I made a conscious effort to avoid using the rear pedal and didn't encounter any situation that required abrupt braking.

Riding to and from work today, however, was a different story.
I again made a conscious effort to avoid the use of the brake pedal.

Frequent braking at highway speeds, even though it was not particularly abrupt, was sufficient to trigger the problem.

I had to stop once on the way to work and twice on the way home to open up the center bleeders on the front calipers and release the pressure.

That was sufficient to free up the wheels.

I wasn't in a position to determine whether or not both wheels were bound, but I suspect they were.

The manual's technical features section on the LBS states that the front center pistons are actuated by the rear pedal; first the left front and then, if pedal pressure increases, the right caliper.

The rear center piston is actuated if sufficient rotational torque is present at the front wheel to cause the SMC to apply pressure via the PCV.

So while the mechanism to actuate the center pistons differs from front to back, the same hydraulic system services all three pistons.

Since I didn't use the rear pedal when riding to and from work, I don't think the delay valve is suspect.

My next step is to swap out the PCV from my other 5th gen to see if that has any effect.

I just realized, however, that I needed to open the PCV's bleeder when trying to depress the SMC piston. I was opening the left caliper's center bleeder. Doh!! :wacko:

I'll have to try again tomorrow night.

As always, any thoughts are welcome.

3 hours ago, ggathagan

The only components I didn't take apart were the three master cylinders and the delay valve.

Pull your front reservoir lid, pull out the little "protector" as the parts diagram calls it from the bottom of the fluid, and yank on the brake lever. If when you release the lever you don't get a decent little gush of fluid your return port is clogged, stab it with a needle and see if you can get it to shoot up like a fountain when you release the lever. Pull those masters apart and clean em up. The calipers are way more of a pain to pull apart and clean so if you did those, you can do these too. Only difference is you need snap ring pliers to pull them apart. 

Here is a guide i found where you can see the protector in question. Almost positive this will be your issue.

https://motofaction.org/motorcycles/honda-cx-gl/disassembling-front-master-cylinder-honda-cx650ed-part-01/

Symptoms of air in the brake hydraulic system.  When a bubble of air in the brake fluid heats up sufficiently, it expands and engages the brakes.  If I where you, bleed the system step by step as thoroughly and completely as you can. Take your time and use plenty of brake fluid to flush the air out.  Another tip is to bleed for a while, wait an hour or so, and bleed again.  During the bleed process, air bubbles can get atomized going through orifices; waiting can let the bubbles recombine and make it easier to get out.

The only thing that concerns me is that this issue developed on its own (without you breaking into the brake system).  Any signs of leaks?

Scott

Places like Advance Auto Parts & AutoZone loan out large sockets that you could use to remove the rear rotor.

lanesmatb, 7/28/2016 at 2:22 AM

Symptoms of air in the brake hydraulic system.  When a bubble of air in the brake fluid heats up sufficiently, it expands and engages the brakes.  If I where you, bleed the system step by step as thoroughly and completely as you can. Take your time and use plenty of brake fluid to flush the air out.  Another tip is to bleed for a while, wait an hour or so, and bleed again.  During the bleed process, air bubbles can get atomized going through orifices; waiting can let the bubbles recombine and make it easier to get out.

The only thing that concerns me is that this issue developed on its own (without you breaking into the brake system).  Any signs of leaks?

Scott

Aloha, all

Scott, I share your concern regarding the self-development.

Over the last several months I've had little time to work on it.

Since I can approximate when the system has warmed to the point where the expansion occurs, I ride it until it's warmed up, hop off and relieve the pressure via the center bleeder on the left caliper.
I repeat that process as needed and keep topping off the rear M/C.

I take a bus to work and back, so I generally don't ride it during the week.

Last weekend, my roommate and I  repeated the bleeding process again, going through each step carefully.

I removed the left front caliber and had it sitting horizontally on a block of wood when we bled the SMC-to-PCV portion of the system.

I used one of my old brake discs to maintain the gap in between the brake pads.

In addition, I would have my roommate pump on the rear pedal, hold it, then I would push in the SMC piston.

As I pushed on the piston, he would open and close the bleeder on the PCV valve.

Lastly, I held the rear caliper in a horizontal position when opening its center bleeder.

In all of that process, I never saw any air bubbles when bleeding fluid.

After repeating the bleeding process, the situation remains the same.

I'm at a loss as to what could be done differently to pinpoint the location of the air bubble.

Given the amount of brake fluid I've pumped through the system, I would think that any air in the PCV valve or the delay valve would have been pushed out to the calipers by now.

One of life's mysteries...

ggathagan Aloha, all
Scott, I share your concern regarding the self-development.
Over the last several months I've had little time to work on it.
 
Since I can approximate when the system has warmed to the point where the expansion occurs, I ride it until it's warmed up, hop off and relieve the pressure via the center bleeder on the left caliper.
I repeat that process as needed and keep topping off the rear M/C.
I take a bus to work and back, so I generally don't ride it during the week.
 
Last weekend, my roommate and I  repeated the bleeding process again, going through each step carefully.
I removed the left front caliber and had it sitting horizontally on a block of wood when we bled the SMC-to-PCV portion of the system.
I used one of my old brake discs to maintain the gap in between the brake pads.
 
In addition, I would have my roommate pump on the rear pedal, hold it, then I would push in the SMC piston.
As I pushed on the piston, he would open and close the bleeder on the PCV valve.
Lastly, I held the rear caliper in a horizontal position when opening its center bleeder.
 
In all of that process, I never saw any air bubbles when bleeding fluid.
After repeating the bleeding process, the situation remains the same.
 
I'm at a loss as to what could be done differently to pinpoint the location of the air bubble.
Given the amount of brake fluid I've pumped through the system, I would think that any air in the PCV valve or the delay valve would have been pushed out to the calipers by now.
 
One of life's mysteries...

Your problem sounds far worse than mine; as if you have a LOT of air in the lines or the pistons in the calipers are binding up.

In your case, does it occur only when the bike is at running temperatures or even when it's cold?