XK120 brake bleeding torture

I replaced all the brake cylinders, shoes, rebuilt the M/C. There are no leaks. I have spent all day bleeding the brakes using a pneumatic bleeder and the air bubbles just never stop. I’ve gone around the car 6 times, checked for leaks - none, and cannot get the air out. I tried the old fashioned way of having someone pump the brake pedal slowly but that didn’t work either. I’ve looked at the archives on the subject but no help. Any ideas? Also another question…I want to turn the engine without starting it to lubricate the cylinders and check oil pressure since the car has been sitting a while. All wiring is disconnected and Rob told me how to hook it up and I did so. But, since I do not yet have a battery dedicated to the car, I tried using my truck and jumper cables and it appears that it would not provide enough power because the starter spins up but not fast enough to engage. Am I right that it’s just a matter of not enough juice? Thx.

Gbeck - if the starter is spinning up, but not engaging, then this usually shows that the mechanism which moves the starter shaft, with the toothed gear that is meant to engage the flywheel, is failing - not sure which starter you have, but if there is an external solenoid, mounted on the starter, with the fork arm that moves the starter shaft, this is what would not be working - Tex.

Hi and thanks. It is the original starter and worked fine a few months ago when I started it for a few minutes. It just isn’t spinning fast enough for the gear to retract and engage with the flywheel. It may well have gone bad I suppose but before I spend the money on a new high torque one I thought I’d try everything else. The solenoid is also original but when I push the button nothing happens. If I put an ohm meter across either the battery or starter cable connectors and the small terminal that goes to the starter button on the dash, there is no reading. Am I right that if it is working that there should be a reading? Thx for the help.

Brakes - try pumping the pedal vigorously 5-10 times to force all the air to the wheel cylinders. Then put a clear hose on the nearest bleeder nipple and the other end in a clear jar with some fluid already in it. Open the bleeder a quarter turn and pump the pedal until you see fluid coming through the hose, and no bubbles. Close the bleeder. Check your fluid level in the supply reservoir, you don’t want to let it run out or get down to the master cylinder level. Do the same procedure with the other front, and then the two rears.

Starter - You need a battery in the car; jumpers don’t carry enough current through the jaws to run the starter. Then if the big rubber button doesn’t work at all your solenoid is probably shot.

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That’s what I figured on the starter. As for the brakes, I will tray your suggestion again tomorrow and let you know. Thanks.

Gbeck - make sure that if you want to check a circuit, with an OHM meter, that you have the battery disconnected - if you have your meter set to check volts, then yes, with the battery connected, you can test for volts traveling from the starter button to the starter solenoid - if you measure the volts at the battery terminals, meter set to approx. 20 volt DC range, let’s say you get a reading of 12.8 volts - now with one meter lead on the wire from the starter button, and the other meter lead on a bolt on the engine block (with the meter still set as it was when measuring at the battery terminals), when someone pushes the starter button momentarily, you should see approximately the same volts you read before - if the reading is low, then the volts are being drawn down by the bad solenoid/starter circuit - Tex.

I forgot to mention your clear hose should reach to the bottom of the jar, submerged in the fluid, so no air will be sucked back in when the pedal is released.


Air is also sucked back in around the threads of the bleed nipple once it is opened. Remove all the nipples and wrap teflon tape around them then re bleed, the teflon will fill in the gap between the threads.

Well, I am ready to give up! When I open the wheel bleeder screws, fluid never “flows” out. It barely comes out with all the bubbles. No matter how many times I bleed them, there is never a flow of fluid. Before I hooked up the lines to the M/C I blew out the lines and they were clear. Looks like I’ll just have to spend a few hundred to flatbed it a hundred miles to let a mechanic do it.

The old school method of bleeding brakes…ideally you need a helper…start at bleed nipple furthest from fluid reservois…tube on nipple into a jar…open nipple press pedal down and hold it down…close nipple…Release pedal…repeat till no bubbles…move to next nipple…never have a nipple open when you let the pedal up…if no helper hold pedal down with a piece of timber wedged on pedal…Steve

Tried that 6 times now. There is obviously a bad seal or blockage somewhere so I have to decide whether I want to take the M/C out and start all over (and replacing that M/C is insane!) or bite the bullet and have the car trailered 100 miles to the mechanic. No doubt it will be several hundred dollars to have it done. Honestly, I’m ready to sell the car.

If u want to lube the cylinders then just pull the plugs and squirt in some oil and turn over by hand…dont forget if you turn it over on the starter the fuel pump will be pumping fuel and wash the bores…re you bleeding yes l read that youve done it 6 times…but is that as i detailed above or just by pumping…as i said never let the brake pedal up if a nipple is open…Steve

I agree: that suggests something is wrong with the master cylinder.

Besides teflon tape on the bleeder screw threads that Morris recommends, I’ve also installed pieces of 3/4 inch shrink wrap to further limit air from re-entering around the bleeder screws.

Below: The cut pieces of shrink wrap before heating.

Below: The shrink wrap after heating and shrinking.

Two other bleeding tips: 1) Position the bleed jar above the bleeder screws to force the air out of the bleeder hose and through the bleed jar. 2) Each time your assistant pumps the brake pedal to the floor, close the bleeder screw. Open the bleeder screw at the same time your assistant depresses the brake pedal.

It can be particularly difficult to remove all the air from the tandem master cylinder XK120s. Especially so for the front brakes in my experience.

It’s just me but yesterday I had a friend pump while I did the correct proceed as you said. I’ve bled brakes on several other British cars that I have and never had this problem. I’m using a pneumatic bleeder now and almost no fluid comes out of the bleeders.

That’s the way I was doing it yesterday and today I am using the pneumatic bleeder but almost no fluid is coming out of the bleeder screw.

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Is this a tandem master cylinder? Also, was the master cylinder recently rebuilt and reinstalled?

Just to add my dos centavos here. I do know that if the actuator rod fitting into the master cylinder does not have any play when the pedal is a rest then the fluid is blocked by the internal valve.
Pat H

Yes it’s the original master cylinder and I did replace all the seals. I just took out the front bleeder and pressed on the pedal and no fluid comes out. I suspect the M/C is bad.

That’s something I hadn’t thought of. It’s the original M/C and I did replace all the seals. The plunger was not readjusted from when I took the M/C out so would it be different now? There is NO fluid coming out of the bleeders. Man, taking the M/C out is a killer but I guess it’s the only thing that’s left.