Same thing happened to me. New slave cyl did not have the range of movement that the old slave did. I machined a longer plastic cup to fit in the rod cup to fix it.

Samba thread here
http://www.thesamba.com/vw/forum/viewtopic.php?t=299013&highlight=clutch+slave

My adventures, including chewing off throw out arm ( oh the grief I got for doing that), here
https://shufti.wordpress.com/2014/06/21/vanagon-syncro-clutch-slave-cylinder-replacement-adventure/

Alistair

> On May 2, 2015, at 9:02 AM, Craig Cowan <phishman068@GMAIL.COM> wrote:
> 
> I recently went through the same thing and there's an obvious line in your statement that stands out to me, they just replaced the slave cylinder. 
> 
> It has just come to my attention that some of the slave cylinders in one of the "good german brands" do not have a long enough rod, therefore their travel occurs mostly internally. Crap. 
> In other words, your clutch isn't fully disengaging as a result of a part that's engineered wrong and sold as a replacement. 
> In my case i machined a brass spaced that extended the throw by about 1cm and it made a huge difference. 
> 
> Watch the clutch lever on the transmission actuate while someone pushes the pedal, make sure it's moving plenty. 
> 
> -craig
> 
> 
>> On May 2, 2015, at 11:21 AM, Wes Neuenschwander <wes.neuenschwander@COMCAST.NET> wrote:
>> 
>> I have a '91 Westy with a fairly new/rebuilt engine (Go Westy) and
>> transmission, now with about 40,000 miles on the combo.  The last few years
>> I've pretty much 'archived' the vehicle, keeping it in the garage except for
>> occasional road trips.  I took it into my local VW 'go-to' shop in Seattle
>> (Fine Tuning Performance - absolutely outstanding service on the vehicle for
>> the last 20 or so years!) for routine service (oil change, coolant flush and
>> change, replace brake and clutch fluid) and during the post-service test
>> drive owner/head guru Chris noticed difficulty in engaging the van in
>> reverse.
>> 
>> 
>> 
>> He thought the problem was most likely a failure in the clutch hydraulics
>> that was preventing the clutch from completely disengaging (and since
>> reverse has no syncro, the 'grinding' noise would only occur in reverse).
>> They replaced the clutch slave cylinder (the master was replaced a couple of
>> years previously), but the problem persisted.  Next step was a clutch job,
>> including replacing the idler bearing.  Unfortunately, it's still grinding
>> when engaging reverse.  Huge bummer, especially as we were planning on
>> heading out for a fishing/camping trip to a remote area in NE Washington
>> next week!
>> 
>> 
>> 
>> If anyone has *any* ideas what could be causing this - persistent, and now
>> mystifying - problem, you suggestions would be *much* appreciated!!
>> 
>> 
>> 
>> -Wes