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The handbrake on my GT has never worked very well, even with the clevis on the handbrake cable adjusted to its tightest setting. I did some research online, particularly on TR7/TR8 forums (as these cars share the same Lockheed drum brakes), and it seems in many cases poor handbrake function is actually caused by a problem with the brake shoe self-adjusters, which, er, don't...
There are a number of steps to making the self-adjusters work properly.
Firstly, they need to be installed correctly. Figure F4 in the J-H WSM is completely wrong - the self adjuster pins should be inserted from inside to outside, such that the pin flange is on the inside face of the brake shoe web. The two self adjuster levers also sit on the inside face of the shoe web, with a small shim washer between the self adjuster lever and the brake shoe web. The upper lever also has a spring between the adjuster pin flange and the lever itself. On the other side of the brake shoe web i.e. the outer side, a thicker washer should be placed over the upper adjuster pin, and then a circlip. The lower adjuster pin only has a circlip.
Secondly, the mating surfaces of the self adjuster levers and the brake shoe web should be rubbed down so they're completely smooth, and lubricated with high temperature grease. Check that both levers move smoothly across the face of the brake shoe web before reinstalling the brake shoe.
Thirdly, make sure the serrated teeth on each self adjuster lever are free of rust, I used a wirebrush. If they are worn, it may be necessary to gently sharpen each serration with a hacksaw blade. I didn't have to do this. Apparently, the geometry of the teeth is such that the lower adjuster lever can only adjust in one direction, so you may need to use a magnifying glass to make sure you're sharpening the teeth correctly.
Fourthly, disconnect the handbrake clevises on both sides before installing the brake shoes and checking the brake shoe adjustment. Pulling up the handbrake 4-5 times does NOT adjust the self adjusters, as is stated in the Haynes Vauxhall Magnum workshop manual (and repeated elsewhere). Connecting the handbrake actually stops the self adjusters working during the brake set up procedure. Pushing hard on the brake pedal, with the handbrake clevises disconnected, is what makes the self adjusters adjust. If everything has been assembled correctly, and the self adjuster levers can move freely, you should be able to hear the self adjusters click when you depress the brake pedal. If this doesn't work, the self adjusters can sometimes be persuaded to adjust by reversing quickly, and stamping on the brakes. But if you do this, of course, you won't be able to hear the self adjusters adjust.
Finally, once the self adjusters have adjusted you can reattach the handbrake clevises and adjust the left hand clevis so that the handbrake functions properly.
Using the above steps, I now have a working handbrake. It only took me 2 months to work it out...
I hope this is helpful for others having the same issues that I did.
Best wishes,
Nige
Last edited on 08-15-2017 07:43 pm by NigelK