750seca front brakes

conflicting info on bleeding
I'm wanting to fill the lines by gravity. Which is the best position for the lever to allow brake fluid to drain
down into the two main brake lines. Some say tie the lever to the grip and some say leave it open. which
alternative provides the clearest pathway from the reservoir to the
lines ?

 

Tying the lever to the grip opens the circuit. Do that.
https://www.xjbikes.com/forums/threads/bleeding-the-xj750-seca-front-brakes.124736/

 

Thanks.

 

OK, I'm having strange results with those xj750 seca front brakes. I pumped fluid up from the bottom bleeder to the top bleeder on both calipers with a cattle syringe. Opened the bottom and top bleeders, pumped fluid, stopped when clear fluid came out of the tubes attached to the caliper bleeders and closed them off. Then I tied the lever back and let the fluid drain down through the splitter and hoses. I made sure the reservoir was topped up while the levers were pulled. Then with a H.F. vacuum bleeder I tried to bleed off air from the caliper bleeders. I kept getting foaming bubbles at
10 lbs of vacuum. Closed them both off. and tried to get pressure by pumping the lever and holding it down while loosening the bleeders. This time I got resistance . I had a couple of props under the
forks with the bike on center stand. The wheel spun free until I pulled the lever, the wheel stopped but got hard to turn after.
So, then I removed each caliper, pried the pads apart and reinstalled them, drained the reservoir, disassembled the MC and made sure the pressure relief hole was clear with a wire brush strand.
Then I reassembled everything and repeated the process of filling with fluid and bleeding. ------ this time I got resistance on the lever but the same thing happened . the brakes grabbed and the
wheel could only be spun with difficulty.
Having checked the pressure relief hole in the MC, I don't know what else could prevent the calipers from releasing. The calipers were rebuilt with new kits as were the anti dive units. New "o" rings
seals etc. Any Ideas Please

 

You’ll get bubbles when using a vacuum bleeder unless you use Teflon tape on the bleed nipples.

Were you careful to not overfill the brake reservoir? It doesn’t take much extra for there to be no room to allow the pressure to drop when releasing the brake lever.

 

So how do I get the pressure to release so I can start over ?

 

I don't know if this is the easiest way to relax the calipers' grip on the rotor, but, I pulled the calipers and pried the pads apart. then once again pumped the anti dive units full
of fluid with a syringe. now waiting for gravity to fill the splitter and hoses. Another question though, If I use a vacuum brake bleeder to suck air out, should the lever remain tied back.

 

That won't matter. Either way is fine.
Honestly, since my original writeup I've found that using a vacuum bleeder is not necessary. Vibrating the system is a more reliable method to remove all of the air bubbles. The vacuum bleeder does speed the process up a bit though.

 

I have let the fluid drain down from the reservoir while vibrating the lines with my sander from time to time. When I release the lever to bleed the brakes normally, should the cover be replaced on the reservoir ?

 

You need to keep the cover off while bleeding, because you’ll need to add fluid to the reservoir while you’re bleeding the system, otherwise you can end up sucking air right back into the system.

 

That's what I did . I finally got some good resistance in the lever after several attempts. I put a stand under the front forks to let the wheel spin free. After getting good results on the lever, there was some dragging. If I spin the wheel by hand it will go about half way around and stop. Is this ok. Will it loosen up
and wear in if I drive the bike ,or will the calipers heat up and possibly warp the rotor ?

 

The right caliper on mine will lock up intermittently. It usually is either fully locked up when I leave work or it starts clamping down within 5 miles of leaving work so I keep an 8mm box end on my key ring. I open and door the bleeder on the right caliper and I'm good to finish my ride. I thought maybe I'd overfilled the reservoir but I've opened the bleeder enough times that it should be low enough now. I've flushed the lines twice so I thought I'd gotten any little particles out of the lines. Next time it happens I'll have to see if it's just the right caliper that's locked up.

Guess I'll have to bleed again and double check the little hole in the master unless anyone has a better idea of what's going on. Could the caliper piston/bore maybe need polishing?

 

I’d be having a look at the piston for sure

 

New brake lines? They have been know to deteriorate and become close to one way valve

 

Of course, now that I've mentioned the problem, it won't come back. Maybe the fluid level is down far enough that it doesn't block the return...or...it's on to me....

 

A common cause of brakes starting to apply themselves is the small return hole in the master being blocked with crud. As brakes are used, the fluid heats up and expands, the tiny hole is for pressure relief (it gets blocked by the piston passing by it, when you apply the brakes, so its presence is only needed when the brakes are in the rest position).

 

750 seca brakes again. All cleaned out w/ SS brake lines, MC rebuilt w/chacal kit (return hole clear). Rebuilt calipers w/new pistons, seals and greased pins, new pads. Have gotten good at bleeding and
got good resitance on the lever. had blocked the wheel to test the brakes, pulled lever the brakes stopped but rubbed. I tapped on the calipers and the wheel spun free. I disassembled everything and it all
looked fine, reassembled, bled,tested again with he same results. the wheel stopped but rubbed after. OK, So if the calipers release when tapped, would pavement vibration up through the forks/calipers etc
also cause the pistons to retract ? By the way, when I replaced the cover on the res. the fluid was down 5/8-3/4" Lots of room for the cover belows

 

On another forum, it was mentioned that some brake caliper seals (K&L, I think) don't sit on the piston right, so they don't pull the piston back when the pressure is released. It's not much, just a few thou but enough to make the difference.
Only time I've had sticking calipers it was caused by the sliding pins being old and worn and sticking, so I used to carry a soft mallet and give them a whack every hundred miles or so.
It was such a relief to finally fit a rebuilt pair of calipers.

 

Found my problem, I hope. I never took apart the master cylinder. Took it out today and found it would stick sometimes when pushed in. Took it all apart and found some rust and other crap in it (see pictures). Cleaned it all up and it no longer sticks.

 

Calipers were still sticking this spring after I ride for a bit so I have to pull over to release pressure from one of the bleed screws.

I decided to polish the heck out of the guide pins and see if that helped. There were some pots and groves in the guide pins so I filled them smooth and then polished them with some little rotary tool balls similar to Scotch Brite. They come in different roughnesses and they're fairly cheap (much like the little rotary tool wire brushes I was using that would throw little steel brushes everywhere and would investigate the up in my wife's foot).

Anyway, they turned out very skinny and I applied brake lube to them before installing them. I was able to ride 15 miles to work today without once some to bleed excess pressure. Also, when I got to work and was backing out around I noticed the brakes weren't binding no matter how far I turned the bars. Maybe it is finally fixed.?