A new form of e-brake failure

[Paul Heneghan]

Hello Kneale,

I'm going to try a piston from a spare caliper tonight and see if the
self-adjusting mech in that is any better.

You're right about the thread on the central rod - I couldn't find anything
to fit it.  I have a special nut (from a suspension strut I think) that I
have crushed slightly with a hydraulic press and I can drive that on to the
threaded rod.  It cross threads, but the rod is much harder than the nut.  I
tried (like you) levering directly on the threaded bit of the rod using two
large screwdrivers, but I only hurt myself when the screwdrivers slipped!

I'll publish anything I find out.

Paul

> -----Original Message-----
> From:	Kneale Brownson [SMTP:knotnook at traverse.com]
> Sent:	Tuesday, August 28, 2001 6:00 PM
> To:	Paul Heneghan; 'quattro at audifans.com'
> Subject:	Re: A new form of e-brake failure
> 
> Paul,  from looking at the piston in the '86 5Ktq rear caliper I took 
> apart, it appears that the  captive "nut" inside the piston is somehow 
> pressed in place on the older design and efforts to turn the piston when 
> the threaded rod in the cylinder and/or the "nut" are corroded result in 
> the "nut" and captivating assembly somehow detaching from the inside of
> the 
> piston.  In the newer cars (like my '91 200), the part that's threaded
> onto 
> the rod in the cylinder is held in place with an internal snapring.   I'd 
> guess your piston has reached the failed status.
> 
> BTW, on your website write-up of rear brake caliper disassembly, you 
> suggest removing the threaded rod by applying a nut to provide a perch for
> 
> levering the rod out.  The threads on this rod are not any sort of
> standard 
> metric thread.  I took it to a thorough metric fastener supply house and 
> they could find no commercially-available nut to match that thread.  I've 
> extracted the rod by persistent levering from two sides at once with
> heavy 
> screwdrivers and sort of alternating a bit of extra pressure from side to 
> side.  The far end of the rod is machined quite closely to fit into the 
> cavity for it.
> 
> 
> 


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