Rd 350 Front brake issues after bleeding

[Overphil]

I reverse filled my front brakes, bled them and have solid brake action on the stand. As soon as I move the bike the brake will do one pull to the bars then is solid again .
I read previous posts and bled each banjo, removed the caliper and tapped everything. I also zip tied the brake overnight and still get the same results...

[kobra]

A 'double pump' at the lever means the pistons are retracting back into the calipers so the first pump puts them against the rotor and the second pump applies pressure.

You say it only happens after you move the bike? I would check the rotors for runout that could be pushing the pistons back in. It should be 5 thou or less ideally.

Another scenario if it happens even if you don't move the bike is that the piston seals are 'twisting' and so they pull the pistons back after a few minutes. Lubing them with silicone grease can help that issue slightly.

[Overphil]

Ah. That makes sense. I’ll see if I can experiment with it on the stand. I know the rotor is slightly warped but it worked fine before I changed the seals in my caliper.

Thanks!

[Overphil]

You nailed that one kobra. I spin the wheel when it’s on the stand and the warped disc pushes the left caliper in.
I guess I need a new rotor...

Thanks!!!

[kobra]

You nailed that one kobra. I spin the wheel when it’s on the stand and the warped disc pushes the left caliper in.
I guess I need a new rotor...

Thanks!!!

What kind of rotor? If it's a floating rotor it could be a stuck "bobbin" causing the warp and they can be freed up by wiggling it.

I've seen some wheels corroded badly enough that the rotor mounting surface is uneven. It could possibly be fixed by making sure it's smooth.

Other than that it would had to have been bent by something most likely.

[JonW]

Ive seen people accidentally bend brake disks when removing tyres on the machine. the bead breaker exerts a lot of pressure and if you use a car wheel machine it can easily damage a bike disk.

[Overphil]

I’m pretty sure the rotor is fixed and not floating but I’ll remove it before I order a new one and make sure I’m not missing an easy fix. Can you resurface these if they are warped? I see some resurfaced ones for sale...

[kobra]

I’m pretty sure the rotor is fixed and not floating but I’ll remove it before I order a new one and make sure I’m not missing an easy fix. Can you resurface these if they are warped? I see some resurfaced ones for sale...

I would not do that for a motorcycle rotor. They are only 5mm to start and the wear limit is 4.5 or 4.6mm. Just get new or used ones that are in good shape.

[Hooligan]

A bent rotor is BENT. Resurfacing will give it a nice new surface without touching the BENT section.

It is possible to use a large adjustable wrench to try to straighten out the rotor but that is really a bit redneck solution. I have done it on my dirt bike though.

[Bare]

Rotors Can be resurfaced. A local machine shop does it on their Flywheel Resurfacer. Warps are removed (within reason) And thickness minimums are to do with caliper piston extension limits. Not Disc or brake efficacy. Caveat emptor tho.
Also costs ~75$ per surface, making doing so Fairly uneconomic Vs buying New,