[T3] Brake Calipers

[Dave Hall]

I suppose the shape of the piston retaining plate allowed the pad to act a
bit like the leading edge of the shoe, but not over its whole width. 

Since both calipers wore similarly, I'm inclined to think there could be
something else at work.  I've not had problems like that with the original
calipers on any of my Type 3s.  In the event, they use the more common pads,
and don't get a lot of use, so I'm inclined to not worry over much.

Silicone brake fluid is available in the UK.  Around $50 for a US quart inc
shipping.  How much is needed?  Also available in litres and smaller sizes.
I see a 191 litre drum is around 1/3 the price per litre.  I don't think I
know 200 others who want some!

Maybe if/when I restore the Variant it will be a good move.


Dave.
UK VW Type 3&4 Club
===================

-----Original Message-----
From: type3-vwtype3.org-bounces at lists.vwtype3.org
[mailto:type3-vwtype3.org-bounces at lists.vwtype3.org] On Behalf Of Jim Adney
Sent: 12 August 2011 18:29
To: type3 at vwtype3.org
Subject: Re: [T3] Brake Calipers

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?

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

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