Bleeding front brakes on Midnight Special

[Garry W.]

I have a 1981 Midnight Special. I'm in the process of replacing all the brakes. Took the main master cylinder out cleaned out all the crude . The Midnight special has a proportioning valve that operate the left front disk brake and the rear brake simultaneously. My dilema is that the rear brake bleed up with no problem, but I can't get fluid to move through the proportioning valve to the front disk. Anybody out there know how to fix my dilema ???? Garry W.

[stevec5000]

I would think that sucking on the front with a Mighty Vac would get it going unless there's also crud clogging up the proportioning valve.

[stpbuzz]

dont know why, but i had to take off the brake lines on the front disks, to get them to start flowing, but once it started flowing i retightened the brake lines, and it would pump out the bleeder valve thingie, as it should have in the first place.
i pumped all the old fluid out, then had to reloosen the brake lines to get the new fluid to start pumping, then retighten the brake lines, and continue pumping, adding fluid to the boul as i pumped, pumped till fluid came out the right bleeder valve, tightened the valve, pumped till the left bleeder valve was squirting, and tightened bleeder valve.
done.
dont know if this was right, but it worked.

[Snow]

Ye Old priming problem. Mity-Vac is the best solution, but is expensive. The quick and dirty solution is like what is said by stpbuzz above, about detaching the lines until they flow - the problem is keeping the fluid off painted surfaces. Make sure to have soap and water handy.

I got speed bleeders and they *seem* to help the priming problem, just sit there and pump the brake lever for a *while* instead of having to need an assistant or to loosen and tighten the bleeder by yourself.

Side note: make SURE to NOT pull the lever too far

[Red Tarrents]

Bleeding front brakes on Midnight Special

Hello Garry,
You wrote: "My dilema is that the rear brake bleed up with no problem, but I can't get fluid to move through the proportioning valve to the front disk."
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Did you disassemble the valve, and clean it too?
Did you lose pressure suddenly at one caliper or another?

If that should happen, the unequal hydraulic pressure from one port on the valve's SPOOL will close off the open port just as it should.

Odds are, that you can observe that the valve spool is off-centered, by blowing compressed air thru the fluid ports. If one port, front or rear, is partially, or completely blocked you will know which it is.........

It is possible you might be able to recenter the spool inside proportioning valve's body to the neutral or centered position......

You may be able to recenter the spool by air pressure, or temporarily reverse the hydraulic line from the the m/c to the closed port in the valve, and use hydraulic pressure to recenter it.

Foregoing the above, the valve body should have a bolt or threaded plug on one end, or the other to access the valves internal parts.

When the plug is removed from the valve body, you should be able to recenter the spool by manually pressing on the end of it, pushing it back to its centered position from the blocked port.

Normally, it should recenter when you bleed the brake system, but it may be "gunked-up", and stuck

The only reason I am aware of this is from having to reset the proportioning valve for a Ford van I used to own....... Even though the application may be different, the theory should be the same.....

Hope this helps......

PS.....Check out the comment at http://www.rctvonline.net/xs11/ :
Off-Site Tech Tips:
Ken Talbot's XS11 Page:
http://www.rctvonline.net/xs11 :
Michael Tops' Braking System Modification :

Conclusion: The linked brakes go through a portioning valve. More front (pressure) than rear. Almost no rear (pressure) applied. Unnoticable when both connected.......snip. The brackets are mine for clarity.....

I hope I didn't confuse ya more.....!

[Garry W.]

Hey, Guys! Thanks a lot. I got the problem licked !!! You won't believe what I found. I'm the new owner of this fixer upper, and when I decided to fix all the brakes the left front caliper was seized. So, I repaired it, cleaned the master cylinder and all the lines except the line from the master cylinder to the left front caliper, thinking I would just pump clean fluid through that line before hooking it to the rebuilt caliper. Well as you know, fluid wouln't move through that line. Hence, my call for help. Well, on futher investigation I found that the previous owner had inserted a small "nail" in one of the line connections to prevent the fluid from entering that caliper. I guess this was his answer to fixing the caliper from seizing onto the disk. Go figure!
Thanks for all your response and encouragement. The old special is ready to roll we just need the weather.

Garry W.

[xssiveone]

Gary, I would go over this from front to back with a fine tooth comb before I rode it too far, if at all. If the PO was "brilliant" enough to come up with this solution to avoid repairing what is one of the most, if not THE MOST important thing on the bike, who knows what other surprises lay in store for you.

Congrats on finding this problem... it certainly was hidden in a place one would never think to look.

[Garry W.]

Thanks Brian. I've spent the winter going over this old bike the brakes were the last and most important thing to overhaul. I fired her up today and took a spin around the block even though it was minus 20 degrees. The brakes check out 100%. That old 4 cylinder has an awsome growl, gotta like it !!!!!