Re: GL-4 vs. GL-5 ?

["Jim Adney" <jadney@vwtype3.org>]

Listees:

Since we were getting a variety of opinions on the GL-4 vs GL-5 debate, I 
emailed Bob Hoover. Here is his response:


> Dear Jim, et al
> 
> Volkswagen used to use BRONZE syncho rings.  Bronze is an alloy of copper and
> TIN.
> 
> In one of their many 'improvements' Volkswagen went to a cheaper BRASS 
> synchro ring.  Brass is an alloy of copper and ZINC.
> 
> Unfortunately, in trying to save a penny or so per synchro, VW decided to use an
> alloy of brass that contained a significant percentage of aluminum.
> 
> Then along came GL-5 tranny lube, which contained a new anti-oxidant, 
> supposed to allow you to extend the replacement period of the oil, which was
> fine for differentials and steel gears and even for the older BRONZE synchros
> but pure hell on those new, improved, save-a-penny aluminum-copper-zinc
> synchros.  
> 
> Bottom line:  GL-5 caused the newer synchros to 'honey-comb.'   I don't 
> recall the half-page explanation but GL-5 attacked the zinc in the synchros and
> they would break.  So VW issued a Service Bulletin telling all of their dealers
> to NOT use GL5 on transmissions manufactured after a given date (about 1967, as
> I recall... which I don't, all that clearly).
> 
> So use GL-4.  Or make sure your tranny is rebuilt using the old style BRONZE
> sychros.
> 
> I've never paid much attention to this problem because I've still got most of a
> 37 gal drum of  GL-4 tranny lube, plus a box full of old synchro rings. 
> (Replacement of the synchros is a relatively minor chore, compared to replacing
> a gear set.)
>
> You'll have to answer the synthentic lubricant question yourself.  When I run
> out of tranny lube eight or ten years from now, I might look into the use of
> synthetics but having no need to do so, it is a non-issue to me.  Sorry I can't
> be of more help.
> 
> -Bob Hoover

-
Jim Adney
jadney@vwtype3.org
Madison, WI 53711-3054
USA

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