Front caliper problem

[jjander]

I have a '80 XS650 Special. I have completely rebuilt my front brakes. New master cylinder, new caliper, new pads. I am having a problem with pressure building and not allowing the caliper to retract, gradually locking up the front brake. If I open the bleed valve, it releases the pressure and then it is OK for a while. I'm pretty sure that the vent hole in the master cylinder is open since it's brand new and all of the fluid is fresh since the rebuild. The only thing left that I can think of are the hoses. I've had a bad hose lock up a caliper on a car so I am inclined to go ahead and replace them. Before I replace them, does anyone have a suggestion of other things to check?

[grizld1]

I think you have the bases covered--lines or MC. Every Japanese factory manual I've ever seen, old or new, specifies service life for rubber brake lines as 4 years, so those old lines need to go anyway. But don't assume that the MC doesn't have issues because it's new; where was it bought, and who was the vendor?

[jjander]

Thanks,
Bought it on MikesXS, I don't know who the manufacturer was. I think it's time to replace the lines.

[grizld1]

I thought that might be the case. Check that MC carefully; the Brand X stuff from Mike's XS often presents problems. "Chinese quality control" is my favorite oxymoron.

[jjander]

Thanks,
I will check out the MC while I have everything apart to replace the lines. In looking at the lines, it looks like it would make sense to replace the two lines and the connector under the headlight with a single stainless steel line. Is there any reason not to do that? Do you know the correct length and do you know a good source?

[grizld1]

A one-piece stainless line is the way to go. I drop mine through a standoff on a lower fork clamp bolt and another standoff on the fender. 5twins uses a longer line and runs it through the OE routing, securing it to the center of the lower fork clamp where the junction block for the old lines used to live. I use a Russell universal line. To measure, jack up the front end so that the wheel hangs free and run a piece of plastic tubing through the path you want to use. Allow a little slack to be sure you don't stress a line if the forks top out.

[jjander]

Thanks again, I ordered a universal line and new banjos and washers. I'll work out the routing and clamping on the fly.

[jetmechmarty]

You probably know this, but who knows who it may help. That tiny hole has to be open.

[motormike]

..... the caliper bolts to the bottom of the bracket.... there's a slide inside the rubber boot..sometimes it sticks.. which will cause a drag'n caliper. I always press the side out..even on new units... a heavy thumb does the deed if it's not frozen... then I lube the inside with brake grease.. Brake.. not standard bearing grease... the small ends of the rubber cover for the slide I also fill with brake grease.. this help the caliper slide and also helps keep condensation from form'n and it's related rust issues...
this may not be your problem but is worth the time. I have seen hoses go bad..one Xs and a few cars. Usually someone clamps the hose too tight to service the caliper.... prevent fluid drain... and it forms a internal flap.. a one way valve much like the four in yer heart... brake fluid can't flow back after the lever has been released,

[5twins]

As mentioned, I use a small homemade strap bracket attached to the lower triple tree for a brake hose guide. A short length of fuel line split down one side and slipped on the brake line pads it through the guide. The holes in the lower triple tree are already there for you, drilled and tapped .....