Dismantling the Lockheed brake master cylinder
"I've been bleeding the brakes for hours and still can't get a pedal".
The early Scimitar (SE4/5/5A) is particularly tricky to bleed for several reasons; the pipe from the master cylinder to the servo is higher than the fluid level in the reservoir, it is a single line system, and the rear wheel cylinders have only one bleed point, on the left-hand side.
The best way to bleed the brakes is to use a fast-bleed system. If you're working alone it also pays to use an extra-long bleed pipe so that you can watch the purge process from the seat. Keeping the handbrake on will reduce the amount of air that could be in the system by reducing the volume held in the rear wheel cylinders.
You do not need to have the engine running.
Firstly, try to get the air out of the line to the servo, and the servo itself, by slackening the outlet pipe from the servo and pumping the pedal until the air bubbles stop, keeping the reservoir full to the top. Re-tighten the outlet pipe.
Then bleed the right-hand front, opening the bleed screw a full turn, giving 4 full pedal pumps, top up the reservoir, and carry on until no more air bubbles are rising up the purge pipe.
Bleed the left-hand front in the same way.
Bleed the left-hand rear, and put plenty of fluid through it. Remember that you're purging air through a single length of pipe that runs almost the full length and full width of the car.
Pump the pedal several times to compress any remaining air into single bubbles, then bleed the right front, left front, and left rear again.
By now, you should be close to getting a reasonable pedal. Carry on bleeding all 3 points until the air stops coming out. It can take a long time if you are on your own.
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This can be a puzzle at first; the fluid in the master cylinder needs frequent topping-up, but there is no sign of fluid leakage from any of the calipers, wheel cylinders, pipe joints, or the master cylinder.
It's being burnt in number 3 cylinder. You might occasionally catch a glimpse of a burst of white smoke out of the right-hand tailpipe if you're lucky. Undo the vacuum pipe that connects the servo to the inlet manifold by number 3 and you might just find some traces of brake fluid inside it. You might also find that number 3 spark plug is a bit cleaner than the others, depending on how much fluid has been lost.
The cure is to overhaul the servo using a hydraulic seal kit.
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(SE4/5/5A Girling cylinders )
Two distinct problems occur when trying to remove the brake master cylinder. The first is getting the bottom nut undone, and the second is getting the master cylinder to actually come free. The second problem can also occur when removing the clutch master cylinder.
The first problem has an obvious solution - remove the clutch master cylinder and you can get a spanner on to the bottom nut. However, since removing the clutch master cylinder might entail two doses of a sticking cylinder, and since I abhor undoing perfectly good assemblies for no reason, let's try an alternate approach. It is just possible to get the bottom nut turning with a deep 13mm 1/4" drive socket on the end of a universal joint. On the SE5A of mine which I've just finished this very job (some Christmas this is turning out to be), I had a Lockheed servo, and after spending ages fiddling the bottom nut off, I found that the servo had to be removed anyway to get clearance to pull the master cylinder free of the pedal-box studs, so I suggest you remove the servo first of all, and then getting the bottom nut undone will be easy. (Doh !)
Problem two I have encountered frequently. The master cylinder sticks to the studs and will not budge. Whatever you do, do not try and lever it out with a screwdriver. Although you can get a purchase on the top lug, the bottom lug is hidden, and if the master cylinder is aluminium, you can expect to snap the bottom lug off. I have found that the trick is to firstly use a hot-air gun to put some heat into the bulhead lugs, but more importantly, try to get the dust cover off the master cylinder inside the footwell, and spray some WD40 around the cylinder end. Then, using a 15" long piece of steel rod, start tapping on alternate sides of the master cylinder in the footwell. Keep putting small burst of heat into the bulhead lugs with a hot-air gun, and get penetrating oil onto the threads. (You will find a photo of the special tools I use in the Wreck to a Runner project)
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Most of the Lockheed cylinder is straightforward to strip and re-assemble, if you follow the workshop manual. But it has one bland section describing how you undo the large nut, and then remove the pressure differential piston assembly. When I came to this on a recent overhaul I was stumped for a few minutes, because the piston assembly stubbornly refused to come out of the bore. It would push down against the spring until it bottomed out, but when released it seemed to come up against a stop, and wouldn't even blow out with compressed air.
I solved the problem with a very stiff piece of wire, about .75 mm diameter. I clamped it in a vice with no more than 1 mm protuding, and turned that end over to form a right-angled hook. This was then pushed down the bore between the spring and the steel wall, turned through 90 degrees, and the piston popped out.
The reason for it sticking was probably the fact that I was dismantling a brand new cylinder, and the seals were so good that they formed a vacuum that held the far end of the piston in the machined chamber.
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