how the hadbrake works and why it will fail

[newbster]

just had to replace a rear caliper because the handbrake was sticking on, also chewed up the disc and pad.

I'm a little ocd on finding out how thing work and why they failed

anyways, the new caliper was a non exchange unit, so thought i's try and pull the old one apart.



not too difficult really.

the lever that the cable hooks into is connected to the shaft at the left end, where my finger is.




shaft rotates, and the plate stays still, there are 3 ball bearings between the two parts, sitting in ramps, so when the shaft rotates it forces the two plates apart, this is what moves the brake piston

better photo of the inside's




now, you can see the shaft is all cruddy, this is the part that passes through the caliper body, the build up of rust causes the shaft to stick slightly, so the pads are being held in contact with the discs, a little.

two reasons for this, the shaft does not seem to have much passivation on it, so it will go rusty, and the movement of the shaft is in and out as well as rotation, i.e. when you put the hand brake on, the shaft moves in, this tends to pump water past the seals on the outside of the caliper, so guaranteeing corrosion

could it be repaired? yes, you can get overhaul kits for 25, but with the price of new calipers at around 45 , its not really worth it

 

[badger5]

interesting..
great post

thx for sharing

 

[JimS3]

Great info.

There are 'helper springs' available from VW /Audi for these calipers, don't know why they weren't fitted as standard. They were to some models.

Left and right are different part numbers:

7M0 615 295
7M0 615 296

 

[newbster]

yes, I forgot to say that the new caliper I bought had a helper spring fitted,
and annoyingly, the old caliper had the holes punched in the lever arm to be able to fit one, as JimS3 did
they should have been fitted as standard,

I think it was for the bigger vehicles with longer handbrake cables, needed a bit more help.

 

[A3_130]

Great little thread, handy to know how they work.

 

[newbster]

I can put up piccies of the rest of the mechanism, which explains why you have to screw the piston back in when fitting new pads,
if any body I interested

 

[Ian2012]

It's been a constant failure on Audi's for years i remember my old type 85 quattro's suffered the same problem, the solution at the time was to buy Ford Granada/Scorpio return springs which were much stronger. Add this to pile of crap design like rear wiper motors, door handles that break and freeze up in the winter.

 

[NE Marlon]

I've just had to replace both rear calipers for this very reason. Didn't realise the helper springs were such an advantage...

Something else for the shopping list!

 

[newbster]

here are the rest of the insides before they go in the bin

the piston


this is how it came out, not cleaned up, amazingly good condition

rest of the h/brake mechanism



its all held in the cage on the far left, I chopped the tabs off to get them out, the screwy bit engages with a threaded hollow rod in the piston, which all move forward when you apply the handbrake

close up of screwy thing engaged in piston




the threaded hollow rod in the piston is a friction fit in the piston, which allows it to rotate and adjust the handbrake for pad wear

simples

 

[Dani_B19]

Newbster where did you buy your caliper from?

 

[TomoUK]

I literally just has to have all this done on mine on Tuesday. Will be looking into some helper springs. Thanks for the post

 

[newbster]

I got the caliper through e bay, energizedcustoms
55 pounds delivered

it was delivered on next day, had new bolts for the sliders, looks to be a quality item, no complaints

give me 5 mins, i'll find the ebay item number

flea bay number 331134575975