Classic Audi Technical Mech/Tech Suspension & Brakes » Adjusting B4 rear calipers

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Old 26-02-17, 08:43 PM   #11
Hanuman
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Take a look at the image I included earlier.

Top row. Empty piston.
2nd row- rotating nut assembly, which is assembled inside the piston (rotating part of the adjustment mechanism)
From my experience, this is where any corrosion starts affecting the handbrake adjustment, as the ball race no longer rotates freely. The whole assembly is rationed with the circlip.

3row- the rod. This is pushed outwards by the handbrake lever, against spring pressure. The rotating nut runs on this Rod. The rod assembly is retained in the calliper housing with the circlip. You need a very good set of circlip pliers, deep reach, narrow, which many diy pliers are not.

4th row-
Pin. It sits between the rod and the lever, located in dimples in each. It's only task is to translate rotating action of the lever into pressure on the base of the rod.

5th row-
Handbrake lever (calliper end). You can see the dimple for the pin.
As the lever rotates, it 'cams' the pin against the rod, which is spring loaded. The rod pushes out against the rotating nut, which due to mechanical action, is locked at this stage. Therefore, the piston pushes out. When the hand brake is released, the mechanical action is released. The nut is now free to rotate inside the piston. The piston is held out by hydraulic oil, the spring on the rod pushes the rod back. The rotating nut turns freely on the rod as it retracts. The piston position is now adjusted for wear in the brake material.

A few more pics from the stuff I'd worked on for the 'Toxic Toad'
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Scruffy callipers just removed-

Left is grubby, but functional, just. Right side is seized.


So, I started to strip the left while the right is being soaked in the hope that I can get the piston to turn.


Piston came out easily. It's not chromed like the callipers in my stock


The hand brake acts through a shaft on which the piston slowly worms its way out as the pads wear.
With some fairly narrow internal circlip pliers, you release the circlip, and the cage, spring and washer.
I use a 'nut' salvaged from a scrap piston to help pull the threaded shaft out;


And this is what you get; threaded shaft, through a keyed retaining plate. And in the other end of the shaft is the little rod which translates rotation of the hand brake lever in movement of the threaded shaft.


And now the piston internals. The 'nut' that I mentioned before is retained in the piston by a sandwich which includes a thrust bearing, spreader plate, waved spring washer, a second spreader plate, and finally the retaining circlip.
If the piston assembly is in good order, the 'nut' can be turned very easily.


I'm still making some assumption that the B4 calipers will have largely the same idea.


BiggRed kits supply a set of seals and boots-
Dust seals for the piston
Oil seals for the piston and handbrake lever
Dust boots (maybe) for the slider pins

It's not a bad thing to do, but it depends on your problem whether this will solve your problem.
The seal for the handbrake lever is a big problem if you cannot remove the internal components of the calliper. This seal is often compromised by wear and corrosion on the shaft of the handbrake lever.
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Last edited by Hanuman; 26-02-17 at 08:48 PM.
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Old 26-02-17, 08:50 PM   #12
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Actually-

If anyone has similar information about handbrake callipers, assembly, internal components, etc, it might be quite useful to have it all together in one place as an aid to future queries. What thinkest you lot?
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Old 26-02-17, 10:27 PM   #13
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Quote:
Originally Posted by Hanuman View Post
I'm still making some assumption that the B4 calipers will have largely the same idea.

If anyone has similar information about handbrake callipers, assembly, internal components, etc, it might be quite useful to have it all together in one place as an aid to future queries. What thinkest you lot?
I think it's a good assumption, and the above pics and details will help many.

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Old 26-02-17, 10:55 PM   #14
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Many thanks for the pics, gives me a good idea of the process and yes agree it would be good to have a rebuild guide for others to follow as I hear it's a common problem.
I will take some pics to upload whilst overhauling them to add to the thread
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Old 26-02-17, 11:28 PM   #15
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There is a little more to it, which I hadn't included, as I didn't get pics at the time, and I've been too busy with flying crap.

The handbrake lever sits in/supported by a split bush, which has a slot for the pin. As the bush is not a great engineering fit, and there is a seal at the top, the shaft can tip out of line when the handbrake cable is pulled. I believe this is where the seal fit is then compromised, and water/moisture may be able to track in.
In some refurbished calipers, this bush has been replaced with a plastic cup/sleeve. So it's worth checking first, before you dry out a set of calipers in the oven.(ask me how I know)
I packed the shaft with grease on one set of rebuilds, to see how it fairs. The standard split bush is readily available from SKF, but needs modifying for the purpose. I.e. No slot in the bush as supplied.

I will get around to doing more one day. Hopefully before cars are totally obsolete.
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