Front brake pressure disappears

[64Y80]

If it's your left side rotor, isn't this the one linked with the rear brakes? Do you see the same tendencies with the rear brake pedal?

Never mind my bad. Right side is the linked side.

 

[RaYzerman19]

My recommendation before you go all expensive by replacing rotors, is to do a proper bleed with the lever and not the vacuum thing. Also keep in mind the rotors are 'floating', and might have crud build-up at the rivets. Don't know if that could translate into lateral runout (shouldn't), but you should be able to rotate the rotor back and forth on the carrier a teeny bit (just enough so they click). If not, wash/blow out any build-up of brake dust, etc., recheck your runout with a proper dial indicator. And .2 mm is miniscule (.0078 inches), and I question whether that is really causing your issue.

 

[Mihalis fjr]

2 mm I don't think that can cause all this trouble in your brakes!Mine has about 2 mm side to side movement in the left rotor and the only issue is a light pulse in the lever.

 

[Fred W]

I would approximate the side-to-side movement of the left rotor to be approximately .2mm. I do not feel pulsing in the brake.
I change my tires with a Cycle Hill changer and MoJo lever. Yesterday, I was having a lot of trouble balancing the front tire and put it back on the Cycle Hill several times in order to turn the tire on the wheel. I don't remember hitting the rotor against anything but the left side rotor does have some visual side-to-side movement while the right side rotor does not.

I'm just going to replace the rotor and I'm going to open the brake reservoir, tie the lever to the grip and see if an air bubble will come out of the lines because I know that the bike will not build pressure with air in the lines but I also know that if there was air in the lines, the lever will be soft whether I'm moving or not.

I don't think that you would even be able to see 0.2mm of runout. It must be significantly more than that.

I also have a Cycle Hill Changer and I can definitely see how the mojo lever could contact the brake rotor (during de-mounting of a tire) and put enough pressure on it to bend the rotor carrier.

Replacing the rotor is a PITA job (due to the high strength loctite on the rotor bolts) and not an inexpensive one. Try to get a better measurement on exactly how much runout is present.

Low tech method in case you can't get a dial indicator: You can hold your straight edge relatively firmly on the fork leg and rotate the wheel to push it out to the high spot. Then hold it from moving, rotate to the low spot and use feeler gauges (stacked up if necessary) to measure the gap.

 

[Bill]

I can't get to this again for a few days but the brake fluid is fairly new and I use Speedbleeders. I'll open the reservoir cap and tie the lever to the grip over night. If there's an air bubble in there, that should get rid of it.

I still believe that an air bubble problem would exist if I was moving or sitting still and this problem only happens when the bike moves. That movement can be as little as backing out of a parking space so it has to be one of the rotors bumping the pads far enough out to require a couple of squeezes on the lever to pump it up.

If I set the lever out a few clicks on the Pazzo, the brake will fully engage before the lever contacts the grip. If it's set at 2, or 1 the lever will bottom against the grip before fully engaging the brake pads.

I had to have bent the carrier when I was dismounting or mounting the tire.

I should have the answer by Saturday.

 

[infrared]

I can't get to this again for a few days but the brake fluid is fairly new and I use Speedbleeders. I'll open the reservoir cap and tie the lever to the grip over night. If there's an air bubble in there, that should get rid of it.

Bill,

Not meaning to complicate matters there, but brake fluid will absorb water from the atmosphere. If you leave brake fluid in an open container, it gets waterlogged and that means dangerous. Hot brakes can boil the water out, and this steam pressure will lock the brakes from any speed. Brake bleeding should be a complete replacement of the old brake fluid with new, to remove any water from the system. I can't help with the original problem, but I don't want you to have two problems, there.

 

[RadioHowie]

This is like a mystery movie! What dunnit?

Easy! It was Mr. Bill, in the Garage, with a tire iron!

Thnx, Fred....homemade "Sloppy Joe" all over my monitor now. 'sokay, though...the cat will clean it up!

 

[Bill]

The problem was completely fixed by replacing the left brake rotor. As little as it may have been bent, the rotor carrier caused the problem and it has now been fixed.

Thank you to everyone for your thoughts and suggestions.