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Author Topic: Rear Brakes Question  (Read 2307 times)

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Lizzie Zoom

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Rear Brakes Question
« on: 19 January 2022, 12:22:29 »

As you may have noted from my other thread a major service I have just carried out, where I have yet again adjusted both the handbrake cable and rear brakes,  out of interest I am wondering why we have to adjust both together?

As the handbrake cable is a separate adjustment to the rear shoes, why is it not advisable to just adjust the handbrake cable to achieve the optimum "5 clicks"?

I have faithfully followed the guide on every Omega I have owned, but although to some it may be a stupid question, what is the technical answer please. ??? ??? ;)
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YZ250

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Re: Rear Brakes Question
« Reply #1 on: 19 January 2022, 12:48:26 »

When you adjust the star wheel to the point that it's just backed off a tad from binding the hub, you know that when you pull on the handbrake it should pull evenly on both hubs. If one star wheel is out and one is in, the cable will go tight on the closer side, requiring a mighty pull on the handbrake to get the other side to grip, and this upsets the mot man due to insufficient braking force.  ;D. If they are both equal, the handbrake cable should stop both wheels on the roller equally, which just leaves the handbrake cable adjustment to reduce any slack.
Hope that's what you meant anyway.  :y
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Lizzie Zoom

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Re: Rear Brakes Question
« Reply #2 on: 19 January 2022, 12:59:04 »

When you adjust the star wheel to the point that it's just backed off a tad from binding the hub, you know that when you pull on the handbrake it should pull evenly on both hubs. If one star wheel is out and one is in, the cable will go tight on the closer side, requiring a mighty pull on the handbrake to get the other side to grip, and this upsets the mot man due to insufficient braking force.  ;D. If they are both equal, the handbrake cable should stop both wheels on the roller equally, which just leaves the handbrake cable adjustment to reduce any slack.
Hope that's what you meant anyway.  :y

Yes, thanks YZ250, that is what I wanted to know, and now I do! ;D :y :y

I have wondered that for years!! ::) ;)
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Andy B

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Re: Rear Brakes Question
« Reply #3 on: 19 January 2022, 14:17:11 »

which raise the question of why you use it on an auto?  ::) ::)  ;)
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Nick W

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Re: Rear Brakes Question
« Reply #4 on: 19 January 2022, 14:25:02 »

which raise the question of why you use it on an auto?  ::) ::) ;)


Because you know just how weak the park lock mechanism in the gearbox is?
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dave the builder

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Re: Rear Brakes Question
« Reply #5 on: 19 January 2022, 14:26:37 »

which raise the question of why you use it on an auto?  ::) ::)  ;)
???
The "park brake/handbrake" is also the "emergency brake" in the event of rapid brake fluid loss .
selecting P at 100 err I mean 70 won't end well for the gearbox  :P

My handbrake is 3 clicks ,TIS says 7 IIRC , I know why too ,but never had an issue at 3 clicks in 20+ years of Carltons and the Omega .

I'm a rebel  :D 
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Doctor Gollum

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Re: Rear Brakes Question
« Reply #6 on: 19 January 2022, 15:03:45 »

Each hub is a separate system. Adjusting just the lever does nothing to allow for wear/binding discrepancies across the axle.

Also if you adjust the lever cable first, then you may not be able to correctly adjust the shoes. The operating lever should always be the last adjustment on any such mechanism.

3-5 clicks is the accepted optimum range as it is enough to ensure application but not too much to allow for stretch and future adjustment. The Omega handbrake mechanism is NOT self adjusting.
« Last Edit: 19 January 2022, 15:05:40 by Doctor Gollum »
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Lizzie Zoom

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Re: Rear Brakes Question
« Reply #7 on: 19 January 2022, 15:09:08 »

Each hub is a separate system. Adjusting just the lever does nothing to allow for wear/binding discrepancies across the axle.

Also if you adjust the lever cable first, then you may not be able to correctly adjust the shoes. The operating lever should always be the last adjustment on any such mechanism.

3-5 clicks is the accepted optimum range as it is enough to ensure application but not too much to allow for stretch and future adjustment. The Omega handbrake mechanism is NOT self adjusting.

It still makes me wonder why Vauxhall (and perhaps other manufacturers) did not design the system to automatically adjust the handbrake cable / rear pads together. ::) ::)

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Nick W

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Re: Rear Brakes Question
« Reply #8 on: 19 January 2022, 15:24:53 »

Each hub is a separate system. Adjusting just the lever does nothing to allow for wear/binding discrepancies across the axle.

Also if you adjust the lever cable first, then you may not be able to correctly adjust the shoes. The operating lever should always be the last adjustment on any such mechanism.

3-5 clicks is the accepted optimum range as it is enough to ensure application but not too much to allow for stretch and future adjustment. The Omega handbrake mechanism is NOT self adjusting.

It still makes me wonder why Vauxhall (and perhaps other manufacturers) did not design the system to automatically adjust the handbrake cable / rear pads together. ::) ::)


I've never seen a system which does that. Adjusting the shoes so that they just contact the drum, and then making the cable tension keep them there has been the procedure for decades.  Stretching the cable can be a direct result of adjusting it without first  ensuring the rest of the system is in spec.


What's under your car is the basic layout for a drum type handbrake. The more sophisticated complicated ones use a separate cable and adjuster for each brake. They don't work any better.
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Andy B

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Re: Rear Brakes Question
« Reply #9 on: 19 January 2022, 15:36:51 »

.....
The "park brake/handbrake" is also the "emergency brake" in the event of rapid brake fluid loss .
selecting P at 100 err I mean 70 won't end well for the gearbox  :P
 .....

so why wear it out using it when you don't need to  ::) ::)
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Doctor Gollum

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Re: Rear Brakes Question
« Reply #10 on: 19 January 2022, 15:42:12 »

Each hub is a separate system. Adjusting just the lever does nothing to allow for wear/binding discrepancies across the axle.

Also if you adjust the lever cable first, then you may not be able to correctly adjust the shoes. The operating lever should always be the last adjustment on any such mechanism.

3-5 clicks is the accepted optimum range as it is enough to ensure application but not too much to allow for stretch and future adjustment. The Omega handbrake mechanism is NOT self adjusting.

It still makes me wonder why Vauxhall (and perhaps other manufacturers) did not design the system to automatically adjust the handbrake cable / rear pads together. ::) ::)
They are separate and independent systems.

The hydraulic caliper/cab service brake is self adjusting by design.

Brake shoes are a bit more mechanical in how they apply force. In a service applicantion these have a self adjusting element to allow for the significant increase in friction material wear. In parking/emergency brake applications these are almost never self adjusting.

BMW and Mercedes have both been long term users of rear discs with the parking brake being contained within the hub drum of the disc brake. The Omega is no different in this regard.

Using the service brake caliper/pad is at first glance a simpler arrangement. The reality is the polar opposite. The mechanism to actuate the parking brake is a screw mechanism behind the piston and these can fail/bind, also the mechanical versions are prone to releasing as the pads and discs cool. Electrical versions use a motor to drive the mechanism to apply the piston which over applies itself in order to allow for cooling, but eventually this strips the gears within it and they fail. Usually when applied.
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dave the builder

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Re: Rear Brakes Question
« Reply #11 on: 19 January 2022, 15:48:23 »

.....
The "park brake/handbrake" is also the "emergency brake" in the event of rapid brake fluid loss .
selecting P at 100 err I mean 70 won't end well for the gearbox  :P
 .....

so why wear it out using it when you don't need to  ::) ::)
Using it stops the cable (which is plastic lined) and mechanisms from seizing .
Also , in the event of someone crashing into the Omega while it's parked (which has happened to me many times  >:( ) it puts less strain on the park pawl
Failure of the pawl could see 2 ton of Vauxhall's finest opel rust on it's merry way down the road
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Marks DTM Calib

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Re: Rear Brakes Question
« Reply #12 on: 19 January 2022, 16:41:54 »

Each hub is a separate system. Adjusting just the lever does nothing to allow for wear/binding discrepancies across the axle.

Also if you adjust the lever cable first, then you may not be able to correctly adjust the shoes. The operating lever should always be the last adjustment on any such mechanism.

3-5 clicks is the accepted optimum range as it is enough to ensure application but not too much to allow for stretch and future adjustment. The Omega handbrake mechanism is NOT self adjusting.

It still makes me wonder why Vauxhall (and perhaps other manufacturers) did not design the system to automatically adjust the handbrake cable / rear pads together. ::) ::)

Its an ATE system, used by loads of manufacturers at the time, very common for larger cars with rear wheel drive and discs.

The basics are this

The handbrake cable must be adjusted such that there is a little slack with the handbrake released, there should be no tension at the operating lever at the rear of the rear brake backplate and the return spring must return the actuating lever to its end stop. This ensures that the brake actuating lever is set to give complete travel.

The shoes are then setup to match the drums (very slight rub on rotation).

The handbrake cable it self shoudl rarely need any adjustment unless its replaced or has stretched following fitment of new.

Rear shoes should only need adjustment for wear.  :y

The trick has always been to use the handbrake and slightly apply it for a few seconds when driving at low speed every month or so, this keeps the drum faces clean and helps to stop it seizing up.
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cam.in.head

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Re: Rear Brakes Question
« Reply #13 on: 19 January 2022, 17:09:11 »

exactly as above.
also to note is that if the handbrake seems to go out of adjustment regularly its worth checking that the cable is not gradually pulling itself through the outer retaining brackets on the rear lower arms.they are only a wound/ bent piece of steel and they can easily 'open up' over the years.especially as they thin with age and rust.
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Andy B

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Re: Rear Brakes Question
« Reply #14 on: 19 January 2022, 17:18:05 »

which raise the question of why you use it on an auto?  ::) ::) ;)


Because you know just how weak the park lock mechanism in the gearbox is?

I've yet to break a pawl on an auto box in 30+ years ....  ;)
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