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Rear Brake Pedal Suddenly Stiff and No Braking Power

12K views 45 replies 17 participants last post by  shadango 
#1 ·
OK, just took a trip to CO after having recently replaced seals in the rear caliper and bleeding the system. Also replaced rear rotor and one of the front ones, as well as pads all around. Cleaned and lubed caliper parts as well.

So everything seemed pretty good with my braking system throughout most of the trip, but then on maybe the last day the brake pedal started feeling weird. Like I'd push it and very little braking power would result. If I jam it really hard the bike dives forward as if I'm squeezing the front brake (probably because the front piston is activating and working well).

So I thought maybe there was some gunk in the system, blocking brake fluid from getting to the rear caliper pistons? Today I jacked the bike up, spun the rear wheel, and pushed the pedal. It did stop the wheel from spinning -- so at least something is happening with that caliper. Then I figured I would bleed the rear caliper some more, and then see if that helped. Did that and went for a test ride, and the problem is still there.

Any ideas about what might be causing this? All this brake stuff has been a learning experience along the way, but man, this is just one thing after another.
 
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#15 ·
I that case are the brakes still linked?
I have never been fond of linked brake systems. I prefer to have total control of my front and rear brakes, particularly in slippery situations, such as snow, mud, and non paved roads with steep down hill sections.
 
#11 ·
Rear rotor is not discolored at all. Rear wheel spins nicely, and does stop when I press the pedal.

Regarding the front rotors, one of them was warped and that is why I replaced it. The other front one was just fine so I kept it.

The brakes worked perfectly for several days of my 3,500 mile trip... It was only the last couple of days where the rear was (and still is) acting up.

When I got home I bled the rear caliper some more (pedal method only), and no air came out. Do you guys think I just need to go back to the vacuum bleed method and do both front and rear calipers for the rear brakes? Is it common that the brakes would work perfectly for a few days of riding but then have some air decide to affect things afterward?
 
#13 ·
OK, I'll try that again, thanks. Is it common that I would bleed properly the first time, the brakes would be working fine, but then after riding some air still trapped in the system would decide to mess up my braking performance? I would think that if air was in the system since the beginning the brakes would not have worked normally for those first several days (but I am not an expert -- just trying to understand)?
 
#17 ·
It doesn't sound much like air in the system. If it were air I'd think that you'd have a soft pedal, not a hard pedal.

It sounds more like blockage in the line more so than air. You may have to pull the brake cylinder and check it.

I'd start by checking all the moving parts for binding and then go from there.
 
#18 ·
OP didn't say the brake pedal was soft or hard, just weird. If there is air in it, it would be soft, as you said. If that valve does almost nothing, no matter where the air is in the system, pedal would be soft, and brake power woud be equally weak on both rear and front.
 
#19 ·
Pedal is definitely not soft and has not been from the start. At first the pedal just seemed "stiff" because I would press it and nothing or little would happen... But after paying closer attention, it presses in like always but just lacks any significant bite. If I press the pedal really hard the front end of the bike dives down, so I feel like most of the braking power from the pedal is coming from the 2 pistons activating in the front calipers and almost nothing from the rear pistons.

I re-bled the brakes (right front, left front, then rear) last night using the pedal-pressing method and there is no difference. This is the same method I used initially, when I had good braking for several days after. I bought a MightyVac, so now I will give that a try to see what happens, but I'm getting the feeling that all the bleeding in the world is not going to help.

My non-expert sense is that there is some kind of blockage somewhere. I will do the pressure bleed first, and if no luck my next thought is that I will need to somehow blow out the entire system. That seems like it will be very frustrating and tedious, mostly to control the mess of corrosive brake fluid from getting on anything.
 
#20 ·
Just a quick thought about possible blockage... If I am able to bleed the calipers with fluid coming out readily, shouldn't that mean there can't be any blockage in the lines or in the PCV? This tells me that it can suck fluid from the master cylinder all the way to the bleeder valve on the caliper, but it doesn't necessarily tell me that nothing is obstructing fluid at the (rear) piston level. Does that seem correct?

If my assumptions (above) are correct, and I want to rule out blockage (after one last effort using a pressure bleeder this time), I should really only need to focus my efforts on the rear caliper itself (which was pulled off the bike, cleaned, and got new seals before the CO trip)? What would be the best way to make sure there are no blockages, just pop out the pistons and visually inspect everything, then connect a compressor to the hole for the banjo bolt and blast away?
 
#22 ·
You have fluid flowing while bleeding, so there is no obstruction.. Usually if there is a problem with the caliper it won't release but will still apply.. Have you checked your brake pads for glazing? They may not be gripping as they should.. You can try sanding the glaze off and see if it makes any difference, but if you've had them hot it changes the hardness of the linings and the pads may need replacing.. Just some thoughts.. Good luck..
 
#23 ·
Well the problem appears to be glazed pads (and sure hope my new rotor is not shot also).

I started by bleeding the heck out of the brakes with a pressure bleeder. Took the bike for a test ride and the rear braking performance was once again unchanged (almost no stopping power). So next I pulled the rear caliper off to check the pads and this is what I found...


They are very shiny and I'd guess this means they are glazed. If I slide one against the rotor it's super smooth and seems like there is no resistance. If I slide the pads against each other, same thing... No resistance whatsoever.

So remember, I just replaced the rear rotor and pads before my trip to Colorado. At the same time I cleaned the rear caliper, replaced the seals, reassembled, then cleaned and lubed all the caliper parts per Northstar Riders video. After reassembling everything, there was only slight resistance/drag when spinning the rear wheel, similar to the front wheel if I had only one caliper mounted up front (with both front calipers mounted there was more resistance than in the rear).

This is how the rear wheel spun after completing the work and going for a quick test ride (disregard the dragging front pads -- took bike to dealer to get that corrected when I ran out of time before my trip -- whole other thread on this site)...


When I took the bike to the dealer to correct the front brake dragging I also asked them to check the rear brakes to make sure everything was OK. They said everything was OK.

So now here I am, heading to Colorado a week or so later, and after maybe 1500 miles my rear brakes are worthless. I would think that only excessive dragging would cause this, which they did not seem to be doing. This is driving me crazy -- I never had any issues when I did the brakes on my 1300 and with this 1800 I have followed all the steps but have run into one problem after another.

What might be the problem that caused this? And how do I fix it in a way that keeps it from happening again? Also, sure hope this new rotor is not toast (it looks shiny and smooth but not discolored or anything)...

UGH.
 
#25 ·
Hmm, so you think the pads are as they should be... If that is the case then it sounds like we're back to the thought that there is not enough fluid pressure getting to the pistons, and I probably need to blow/clean out the whole rear caliper?

The front pads are very rough by comparison. Are the front and rear just different compounds?

One thing I'm thinking... I also have a 1300 with 1800 braking system on it (Foots Mod). I can pull off the 1300 caliper to compare the pads to what I have on the 1800. As a last resort I would swap the pads on the bikes and see if anything changes.
 
#26 ·
Many after-market folks make brake pads for the VTX that are interchangeable, front to rear, so NO, I don't think there is a difference in compounds used for the pads themselves.


I also agree with Hans, who doubts the explanation of 'glazing'.


It would be simple and fast to swap the 1300 pads over to the 1800 and check (or maybe it's easier to put the suspect 1800 pads in the 1300 and demonstrate that they stop the other bike just fine). Whichever way you go, I believe you will learn that your rear caliper isn't clamping down with normal force for some reason.
 
#28 ·
What would make the most sense to me is that the pads are not the issue. If the pads are the issue I have no idea what I would do different to prevent this from happening again.

So I will swap the pads between the bikes (start by putting the 1300 ones onto the 1800 as suggested, but will also want to confirm the 1300 pads still don't work on my 1800 with the linked brakes) and post back my findings. I would prefer not to swap the entire caliper at this point, because that is a more involved affair and I haven't eliminated the pads as the problem yet. If I find the swapping of pads makes no difference, then it would be a good idea to try swapping out the whole caliper to see if that's where the problem lies. Thanks for that suggestion. It's great to have troubleshooting steps plotted out ahead of time!
 
#30 ·
I tried this yesterday, using an allen wrench. It was pretty easy to get out of there after. On the flip side, when I tried this on my front caliper a few weeks ago, it was much harder to get out of there... So there was definitely a difference between the front and rear.

I just put the 1300 pads onto the 1800 and they perform exactly the same, so this does not seem to be a pad issue. I only had a few minutes to mess with it on my lunch break, so this was all I was able to test.

Next thing I will test is to have someone press the brake pedal hard and I will see how hard/easy it is to spin the rear wheel. After that I'm thinking my next test is to put the caliper from the 1300 onto the 1800. One step at a time...
 
#31 ·
Quick question... What is the best way to completely clean out the caliper, once I take it off? Guessing I should pull the pistons back out and inspect, maybe blow some air thru the bleeder valve hole while I have just one of the pistons back in... Then do the other one the same way? But should I do anything else to make sure it's all nice and clean?
 
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