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Cooper260z

What is the theory behind the brake adjustment?

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Hello again. I’m new to Z cars and trying to learn about how they work. 
 

I’ve done some Research and come to the conclusion that I probably adjusted the drums incorrectly when I replaced all the parts. I’ve been reading about how when properly adjusted the drums shouldn’t turn much at all? This contradicts how I’ve been adjusting drums on other cars so could someone explain why this is how it’s done? 
 

The new wheel cylinders I installed did not actuate the star wheel to adjust the brakes when I got them so I played around with them and got them to adjust the brakes by pulling the parking brake, but was worried that they’d adjust out so far that the drum would just get stuck, and if it gets stuck with the adjustment hole not at the star wheel then how are you supposed to get the drum off? 
And if the proper spec is for the shoes to be tight against the drum then how do the shoes not get wasted quickly by rubbing when you aren’t even touching the brakes?

 

I've found information on how people say to adjust the brakes, but not why that works, so I apologize if this has been discussed before but I couldn’t find it. And again, that process just goes against my previous experiences, so I’d love to know why these cars are different. 

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Posted (edited)

The parking brake adjustment mechanism is designed such that it will not tighten the drums so far that the shoes rub.  Pulling the handle moves the shoes, but the adjustment wheel only moves when the shoes get out far enough to get the arm over the next tooth on the wheel.  After it goes over the tooth the arm drops back enough, in to the valley between the teeth, to let the shoe fall back slightly.  The adjustment arm moves up and down in the valley between the teeth every time you pull the handle until the shoes wear enough to get over the top of the next one. 

If you have the mechanism working just crank way on the parking brake handle until the handle ends up in the same spot with each pull.  Over time you'll notice that the handle pull gets longer then suddenly it will get shorter as you pass over a tooth.

 

I rewrote this a few times, but that's the basics, I think.  It's a pretty cool mechanism.

Edited by Zed Head
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Are saying the star wheel and the hole don't line up, making them non-adjustable manually?

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@Mark Maras the hole will line up with the wheel, my worry was that I wouldn’t be able to rotate the drum to get it lined up If it got adjusted too tight 

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I couldn’t get the handbrake to adjust the shoes reliably, but I adjusted them manually so that if I put the wheel on and give it a quick spin it rotates for between a ¼ to ½ a revolution which I think is what some older forum posts suggested.
My handbrake still clicks about 5 times though and there is more drag on the drums than I would set if I was adjusting them on another car. is this an acceptable setting? I haven’t tried driving the car like this yet 

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When I adjusted mine after really cleaning up and greasing the E brake adjuster. I put one drum on leaving the other side off. I also had the E brake cable off. I turned the star adjuster until I could not get the next turn out of it. Like Zed said above - that last tooth. I then could still turn the wheel and using my thumb engage the E brake lever. It only mover a small amount to stop the wheel turn. I then removed that drum and repeated the process on the other side. After mounting the wheels which spin quite well, It now only takes 3 to 4 clicks for the E brake handle to firm up. Seemed to work well for me. 

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No, at least not for my adjustment. It is like Zed Head said above when I got to the point where I could not turn it anymore by hand it rests in the last notch. Thus backing off just enough to let the wheel spin. Don't force it! In fact, I was still able to pull the drum back off the shoes without "releasing" the adjuster. I did have to wiggle it some but it came off. When the drums are worn in they create a groove the shoe rides in, Then you have to release the tension to get over the edge of the groove. So make sure you don't have a groove first. There is a wear limit in the drum. When the have rotted in a field for 20 years then the rust holds them together and you have to beat them to get the drum off.

You can always just get it close testing the distance the E brake arm moves to where the movement gets less and less, Then, switch over to the auto adjustment by pulling the handle up. Just try to get the adjuster arm movement the same on both sides. Mine move >5mm

My thought was if you had one adjusted correctly and the other one not, the e-brake handle auto adjustment would not work right. The tight side would never let the loose side catch up. Then only one side would be properly adjusted and the weak side would do nothing. That is why I only had one drum on at a time when setting it up. To keep them even. This would also reduce regular pedal braking as the hydraulic side uses the same adjustment, just from the other side of the adjuster. 

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@Zed Head after reading what you said and looking at the mechanism multiple times, I understand how it should work now. When I Installed the new wheel cylinders, the adjustment arms that move the wheel did not contact the wheel at first. If I bend the arms so that they do contact the wheel do I run the risk of altering the point at which the arm will stop moving the wheel? Or as long as I’m bending the arm upwards to contact the wheel and not bending it inwards or outwards, will it still operate the way it should?
 

my dad keeps Instilling the fear in me that the shoes will just keep adjusting out until the drums seize and then I’m stuck somewhere 

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1 hour ago, Terrapin Z said:

No, at least not for my adjustment. It is like Zed Head said above when I got to the point where I could not turn it anymore by hand it rests in the last notch. Thus backing off just enough to let the wheel spin. Don't force it! In fact, I was still able to pull the drum back off the shoes without "releasing" the adjuster. I did have to wiggle it some but it came off. When the drums are worn in they create a groove the shoe rides in, Then you have to release the tension to get over the edge of the groove. So make sure you don't have a groove first. There is a wear limit in the drum. When the have rotted in a field for 20 years then the rust holds them together and you have to beat them to get the drum off.

You can always just get it close testing the distance the E brake arm moves to where the movement gets less and less, Then, switch over to the auto adjustment by pulling the handle up. Just try to get the adjuster arm movement the same on both sides. Mine move >5mm

My thought was if you had one adjusted correctly and the other one not, the e-brake handle auto adjustment would not work right. The tight side would never let the loose side catch up. Then only one side would be properly adjusted and the weak side would do nothing. That is why I only had one drum on at a time when setting it up. To keep them even. This would also reduce regular pedal braking as the hydraulic side uses the same adjustment, just from the other side of the adjuster. 

I believe the design of the Ebrake cable will prevent this. The one drum that is tighter will firm up first then the side that has more slack will continue to get pulled and possibly adjust until both sides have the same pressure on them. The cable slides in the middle through the yoke type piece to make this possible

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2 minutes ago, Patcon said:

I believe the design of the Ebrake cable will prevent this. The one drum that is tighter will firm up first then the side that has more slack will continue to get pulled and possibly adjust until both sides have the same pressure on them. The cable slides in the middle through the yoke type piece to make this possible

I agree that is plausible, I intended to lubricate the cable when I serviced the brakes, but with the RT mount it was near impossible to get up in there to remove the cable as it does not just unhook. A 50 year old cable and yoke might not slide like it used to to balance out when new. I should have serviced that when I had the diff out 5 years ago.

I can say that after using this technique the brakes do seem to work better. I made no other changes other then a re-bleed having replaced the springs on the front and rear. My brake handle never seemed to change after the 5 years of use. Yet now travels less than before. Could be a fluke I suppose.

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