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Re: Brake MC pushrod length

On  6 Jul 98 at 9:03, Toby Basiliko wrote:

> Jim,
> 	Since I've never had to mess w/ a VW dual MC, I'm speaking from
> experience with other dual-circuit cars...  
> 	I thought that the most important thing about the pushrod length (on a
> Datsun Roadster, it's set with shims behind the MC!) was that the
> plunger was allowed to return to the top of the cylinder, allowing it to
> open the ports to the reservoir.  A "long" pushrod would cause all sorts
> of fluid flow problems, but a slightly short one would just increase
> pedal travel a bit.  Way short, of course, is also bad...
> 	Am I way off base with this?  Somehow, it doesn't seem to be as crucial
> as, say, main bearing clearances...

You are exactly right about letting the MC up to the end of its 
stroke and all the problems that will come about if you don't.  The 
1mm free play insures this.

The trouble comes about when someone adjusts the pushrod length AND 
the pedal position so that they still have 1mm of free play, but they 
now have less stroke available for the pedal.  This works fine as 
long as everything is okay, but if one of the tandem system fails, 
then suddenly more stroke is needed and the driver finds himself 
slamming the backside of the pedal into the kickplate with very 
little braking effect.  It would be quite unexpected, and would mean 
total loss of braking, at least until the driver thought to pump the 
pedal again.

Pumping should help, but the delay that ensued might cause an
accident that might otherwise have been avoided.  Remember, we are
already talking about a car that is down one set of brakes so it
probably needs all the braking time it can get. 

Jim Adney, jadney@vwtype3.org
Madison, Wisconsin, USA

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