XK120 brake bleeding torture

What year XK120? I’m trying to determine if it has the early single or later tandem MC.

Does it look like this?

Pat is saying adjust the items 7, 35 & 36 so there is a little bit of movement of the 1 pedal before the item 30 starts to do something, i.e. hit the item 17 disc.

Those tilt valves item 28 have given people trouble if not operating correctly.
Item 13 & 14 in backwards?

Later tandem. I just loosened the 2 fittings on the right front wheel and there is no fluid coming out.

Then something is assembled wrong in the master cylinder.

Loosen one or both of the high pressure fittings at the master and see if anything squirts out. Try not to get it on the paint, or wipe it off quick.

There’s at least half and inch movement before the plunger (35) hits #13. And 13 and 14 are in correctly. I took a lot of pictures. Why is no fluid coming out with the bleeders out?

Which ones are the high pressure fittings you mention?

when a tried and true procedure does not work…then there is something wrong…in your case it seems it is the mastercylinder. It is a do over with the mc. The rest of the system does not have the capability of the issues you describe. I do like the method of an assistant to open, then close the bleeder, the bleed hose in a full jar of brake fluid, as you do the bleed…`since you have done brake bleeds…it just has to be the m/c…you will have a flat spot on the top of your head (your head…not the cyl head) from hanging on it upside down…Nick

When dis-assembling the MC, did you follow the instructions printed in bold on page L.44 of the Service Manual before removing the tilting valves? If you didn’t, then unfortunately, the tilting valves will likely need to be replaced.

Yes, I did follow the instructions very carefully because of how hard it was to take that M/C out and didn’t want to do it again. Unfortunately it looks like I have take it out again. Obviously something is seriously wrong because no fluid comes out of the bleeders. I’ll take it out and let you know. Thanks for the help.

You’re not kidding! Taking the M/C out isn’t too bad but man, putting it back in is insane! Well, I certainly missed something so here we go again. I’ll let you all know what I find. Since it is the original M/C I may just order a new one.

Having experienced the full range of brake-bleeding frustrations, during 66 years of 120 ownership and maintenance, I have developed my own theory of both the primary cause and one, most repeatedly successful, solution.

One cause (with overhauled systems) is that air gets trapped, in the several high-points of the brake lines, above the level of the master cylinder. The low fluid flow-rates, generated by the “brake-pedal-bleeding operation” or gravity alone, are often not high enough to carry the trapped air past those high-points.

Increasing the brake fluid flow-rate has been one answer and can be accomplished either using a “pressure bleeder” or by simply air-pressurizing the reservoir (10-15psi?) and frequently checking the fluid level during the operation. (This pressure-method does not rely on sucking fluid back into the system through the air-leaking bleed screws.) A critical component is illustrated.

Once set-up with the system/reservoir pressurized, and something to catch the expelled fluid, (with NO brake-pedal operation at all), it’s a matter of abruptly opening one or more bleed screws, a full-turn, for a few seconds and then closing it/them. Check the fluid-level in the reservoir and repeat until the brake pedal firms-up.

Good luck

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That seems like a really good way to do it and I’ll try to figure out how to make one of those caps. I have been using a pneumatic bleeder hooked up to my compressor and while there is an incredible amount of air coming out, there is very little fluid.

One last thing you can try before removing the MC. As Rob Reilly recommends, loosen the front banjo bolt of the MC, and leave the front bleeders slightly open. Then have your assistant pump the brake pedal until fluid comes out of the banjo and begins making its way to the bleeders. Tighten the banjo bolt and then the bleeders.

I had to do this once after installing a rebuilt tandem MC. It seems there was air trapped in the MC that needed to be purged. After cleaning up the brake fluid mess, I was able to bleed the brakes and get a good pedal.

One thing that helped me bleeding a simple, yet impossible to get firm pedal in my Classic Cooper Mini: there seem to be sometimes bubbles in from of the piston that are quite impossible to get out. The solution was to forcefully jam the pedal with a broom and leave the system under pressure one day. The gas seems to be able to cavitate, under pressure through the seals of the cylinder, while the fluid does not.

I used this once and worked for the last bit of feel.

I’ll try that now then if it doesn’t work, out it comes and I’ll order a new one. Thx.

Inch and a half of movement is a little more than you need, which is I presume at the #8 pedal rather than the #7 yoke, but anyway good that you have something.
You could loosen the #44 brake light switch and see if it squirts out there.
I’ve also seen vacuum bleeding systems where they suck on the reservoir to pull all the air up.
Don’t lose heart; as you can see by the many responses, it is a simple system when all is right, and we’re all pulling for you.

Yes. That will certainly tell you if the MC is pumping. My guess is nothing will come out. I just can’t get over how great the JagLovers forums are. where else can you get so much professional advice for free. Charley Bishop-haven’t heard from u for a while. Have you gone AWOL?
Pat H

Yeah, this forum is incredible. It’s only about a half inch before the plunger hits…yes, fluid comes out of the brake light switch when i pump the pedal.

This is why I always bench bled master cylinders.

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One more…“before-you-take-it-apart”, check is to look in the reservoir while the pedal is being depressed. The fluid-level should only rise a fraction. Any larger rise indicates that one or both of the tilt-valves is leaking/not shutting closed …and fluid is not going into the system.
No shortage of experience/opinion here… .