BRAKE ISSUES

i'm starting to get frustrated and beginning to think i'm missing something very basic... i drained my brake system,on my '83 xj750rk seca, of all fluid, rebuilt the calipers and installed new seals and pads, flushed the hoses, cleaned the reservoir and master cyl, then, reassembled everything, filled the reservoir and tried all the normal tricks i know, finger on m/c outlet til pressure builds, keeping reservoir filled after each purge of air, bought mityvac tool to assist in purging out air... still don't have any resistance on lever... i've pumped 24oz. of fluid thru the lines and there's still air in it (anyone need some slightly used DOT3 brake fluid? :lol: )... what am i missing, any tricks from you more experienced guys??? this bike still has the anti-dive set-up on it, i'd like to keep it as stock as possible.. pls help...step by step directions would be great, just bought the 32oz. bottle of fluid so i'm ready to try anything. i'm embarrassed to have to post this basic kind of stuff but know i'll get some good answers here...thnx NJrider

 

I got just the thing (I'm guessing your talking about your 1983 seca 750 w/ awful MC)....take off your fender (hopefully your headlight is off too if your still messing with the brakes). Bleed the MC steel brake line by pumping and holding the brake, unscrewing the connection until you hear air escape, then close it and release the brake handle. Keep doing that until you've got pressure at the lever. It'll get real messy, but it got the job done for me. After you do this you should probably bleed calipers and such again just to be safe.

I had this exact problem on my seca and it drove me nuts. My theory is that you can get such a large air buble up in that connection that has nowhere to go, fluid can get pulled underneath it , and I don't think the MC can draw new fluid into that space until the air is out because it's mounted vertically.

 

thanks manbot i'll give it try and keep you posted on my progress

 

Sounds to me like you are "Draining" Brake Fluid, ... Not Bleeding the Fluid.
The Bubbles stay in place within the System because the Master Cylinder Seals are not generating "Pressure" and forcing the fluid through the System.

Undo a the Brake Line coming out of the Master.
Put some Hardware in the Banjo fitting to Seal the Line.
Bolt > Washer > Square Inch of Rubber Tube > Banjo Fitting > Another Patch of Inner Tube > Washer > Nut or Wing Nut.

Tighten the Hardware to SEAL the Line.
Pump the Master Cylinder by Squeezing the Brake Lever.
Work the Lever 8 or 10 Times.
>>Hydraulic Pressure should develop <<
On the 10th Squeeze HOLD the Lever tight to the Grip.
Release Fluid from the Line by slacking the Wing Nut.
Retighten.
Pump the Master Up ... again.

If the Master Cylinder does NOT develop Hydraulic Pressure to make the Lever STOP under PRESSURE ....

Rebuild the Master Cylinder.
The Seals have failed or the Bore is scored ... or, both!

 

Oh I just caught that he "cleaned" but didn't say he rebuilt the MC with new seals or piston. I know that I completely rebuilt mine, installed the seals in the correct orientation and all, and had the same problem he's describing, but he should definitely reconsider that choice if he's overhauling the whole system.

I really think orientation of the MC and the steel brake line (there isn't a banjo fitting on the 750 Seca MC) that runs to it creates a situation where all the MC does is compress air and it can't draw more fluid in (reservoir feeds the bottom of the MC). Since that connection is the highest point in the hydraulic system (and is shaped roughly like an upside-down U), I gather that air has to be bled from it too.

 

It happens on other bikes too; air gets trapped in the banjo fittings and the fluid is flowing right past it.

You may have to bleed more junctions than just the one at the M/C.

 

Just like NJRIDER1 I bled and pumped, bled and pumped, etc, etc.
I finally noticed the pads were moving in out in out, just not touching the rotors.

Took the hoses loose at the calipers shot a little air in, poof out they came.
Hooked everything up, re-beld 1 time AND EXCELENT brakes.

Note: I was reusing the PO’s slightly worn pads, they are not OEM.
My bore’s were pitted, I honed them.

ab

 

thanks for all the input guys, as manbot said the 750 seca doesn't have a banjo ftg on the M/C only one ftg where the steel line is attached... the reservoir is mounted to the M/C...i tried something similar to what Rick suggested useing my finger to hold back the pressure on the M/C ftg, it did build pressure there, then moved down to the splitter and had pressure there too...i was using a squeeze bottle to fill the reservoir because it is in a real inconveinient location and i think the hole in the bottle was a bit too small and may have been causing the fluid to foam up... i'll try again this weekend to see if the bubbles have settled out and send an update if i can't get 'em pumping ok....thnx again, NJrider

 

Don't forget to make sure that tiny hole in the resevior isn't plugged.

 

Thnx to all who responded, i started at the M/C ftg and worked my way down to the anti-dive unit pump-bleed-pump etc... then thought (DUH!) to tighten the cable to the M/C to get full piston movement and what do ya know it was loose...started at the top again and now i have front brakes again...sometimes in my frustration i forget the really simple things.... now onto the rear brake shoes, i've never pulled a shaft drive rear wheel before, but that will be a different post if i have trouble with it after doin' some homework...thnx again for your responses NJrider

 

Be sure to re-bleed the brakes after you put a couple hundred miles on it in the spring. A few thermal cycles will cause the microbubbles trapped everywhere to gather into one bigger bubble that you can bleed out.