[T3] Brake Calipers

[Jim Adney]

On 12 Aug 2011 at 16:10, Dave Hall wrote:

> I think most VWs after the Type 3s got aome sort of brake proportioning
> valve.  Type 4s had a prssure limiting valve on the rear, and our 74 Camper
> did, plus all the watercooled VWs we've had since.

I'm betting that Type 4s got the same proportioning valve that 914/4s 
got. It just send a fixed fraction of the front circuit pressure to 
the rear brakes. I have one of those on my shelf if anyone wants one.

> I appreciated that the piston retaining plate isn't the full thickness of
> the step in the piston.  The proper VW pads have a cork (?) layer on the
> back which I presume allows an amount of variation in the pressure across
> the pad. 

It's not cork, it's much stiffer than that, and only the best pads 
got it at all. Most aftermarket pads don't bother, and they still 
work fine. My understanding is that that back layer is a high 
hystersis material which eliminates squeal.

> I suppose the flexibility of the steel backing just makes sure the
> greater circumference of the outer area of the disc doesn't wear the
> pad more than on the inner area.   

I think that's why the cutout is oriented at the 20 deg angle. I 
don't understand why this works, but it seems to.

> Pretty careful engineering work by the brake designers, with the
> anti-run-out compensation mechanism in the caliper too. 

That compensation mechanism is a real puzzle. AFAIK, it was only used 
on VW Type 3s, Type 4s, and 914/4s. If it had real value, you'd think 
Mercedes, Porsche, and BMW would also have done this, but they 
didn't. In the end, that mechanism makes our calipers MUCH harder to 
get apart, and most rebuilders break off the inside pins to disable 
that mechanism. Nevertheless, so far I have stuck with putting them 
back together the way VW engineered them.

> The uneven wear I find is more to do with the inner and outer pads, and the
> last set wore out the inner pads while the outer were still only about
> half-worn (I think it was that way).  I concede this may not have anything
> to do with the step.  

Seems unlikely that this would have anything to do with the lack of 
the step. Uneven wear is usually a sign of sticking pistons. Did you 
bother with silicone brake fluid? Can you even buy it over there?

-- 
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Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA
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