[T3] Brake Calipers & Pistons

[William Jahn]

 I always wondered why when VW first began using front disc brakes it was a
two opposed piston design. It may be because of the front suspension
design. There is one member on Samba who did a write up on rebuilding VW
calipers stating later 411 and type 4 didn't have the compensation
mechanism.

 The other frustrating issue is the lack of new calipers for the late 72
and all 73 type 3 . Certainly it's the result of these being the end of
production where the earlier type 3's you can buy new off brand calipers as
well as many older Fords and GMC ext.

 I worked as a tech for Ford for decades. When I started it was at gas
stations and small shops that repaired different makes of american designed
cars and trucks. I only recall a few makes that used opposed piston
calipers and had two pistons per side and the caliper was mounted trailing
yet higher up above the center of the spindle. Most had one much larger
piston on the inside. This design was much the same on all makes.

On Tue, Aug 16, 2022 at 5:58 AM Jim Adney <jadney at vwtype3.org> wrote:

> On 15 Aug 2022 at 12:17, Stephen Unsworth wrote:
>
> > Here in the UK we can usually get Calipers Remanufactured by Budweg in
> > Denmark. These come with New Stainless Steel Pistons. The New Stainless
> > Stainless Steel Pistons are also available separately.
>
> I believe the stainless steel pistons are rather commonly available, but
> they
> are not the solution they might seem. They are not particularly expensive,
> but they are a lot cheaper than OE pistons. The OE pistons are hard chrome
> plated on their outside sealing surface. While spots of rust do
> occasionally
> occur on the leading edge of the piston, it's not common and it's not the
> cause of frozen pistons.
>
> Frozen pistons are caused by rust in the cylinder bore of the caliper,
> which
> takes up space until it clamps down on the piston within. Stainless steel
> pistons do not cure this, so they do not have the advantage that we might
> assume, but they are better than unplated aftermarket pistons.
>
> My main objection to this is that the stainless steel pistons do not have
> the
> OE compensating mechanism inside, which pushes the piston forward to its
> desired position after it's been pushed back by flexing of the spindle
> during
> hard cornering. Admittedly, this is a minor problem, but VW thought it was
> worth paying a bit extra for, so I like to see that mechanism left
> functional.
>
> I believe the stainless pistons are "open front", so in order to install
> them, the
> pin in the OE caliper must be broken out. This means that the caliper can
> never be restored to original condition. I see this a lot in calipers that
> have
> been rebuilt by commercial rebuilders.
>
> Many years ago, I found a set of early OE pistons where the mechanism
> inside the piston was retained by circlips. I removed the circlips and the
> mechanisms and drove with those calipers that way for a few months. For
> the record, I could not tell any difference, but I still suspect that it
> might be
> noticable during spirited driving, when the flexing loads on the spindle
> are
> larger. It's also worth mentioning that VW increased the diameter of the
> spindle by 2 mm in mid '68, which also reduced any flex in their later
> cars.
>
> What might happen if that mechanism is missing? After a hard corner, you
> might find that your next application of the brake pedal required a much
> longer, and unexpected, stroke.
>
> So, I prefer to keep that mechanism intact and functioning in my own cars
> and in the calipers I rebuild for others. It's not always possible, but I
> do insist
> that both calipers be in the same condition.
>
> It's worth asking if other automakers use this feature in their brakes. I
> know
> that it was used in the VW Type 3 and Type 4, and in the VW/Porsche
> 914/4. VW Beetles and Buses did not get it. My experience is limited, but
> I
> can tell you that Mercedes did not use it, but I've been told that Toyota
> did
> (does?) use it.
>
> --
> *******************************
> Jim Adney, jadney at vwtype3.org
> Madison, Wisconsin, USA
> *******************************
>
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