<VV> Manual Transaxle Oil

Hugo Miller hugo at aruncoaches.co.uk
Sat Sep 14 12:57:41 EDT 2019

That still leaves the circle to be squared in that synchromesh 
gearboxes do not like hypoid gear oils. The hypoid oils are designed to 
help gears slide against one another, which means that the synchro cones 
will slide instead of biting. I have known a commercial vehicle with a 
ZF gearbox be rendered practically un-driveable when they put hypoid oil 
in the gearbox. I would think that is a bigger problem than the risk of 
corrosion. ZF's suggestion was to use ATF, and that absolutely 
transformed the vehicle.
Also, hypoid and EP oils used to be two different animals. Many 
gearboxes of that era used EP90 in the gearbox, but never hypoid. Now, 
by the magic of modern chemistry, they seem to have combined both 
properties in one lubricant.
What the solution is I do not know. ATF is an EP oil which is suitable 
for the gearbox but not for the hypoid diff. Hypoid oil is good for the 
diff but might mess up the gear-change. If they had seperated the two, 
there would be no problem.
Having said all that, the Mini, when it was introduced, ran the whole 
lot - engine, gears and diff - on the engine oil alone, and they worked 
just fine. But I don't think they had hypoid diffs.

On 2019-09-14 16:54, edward szuch via VirtualVairs wrote:
> Just wanted to share some info on Corvair transaxle oil.  I know 
> there have
> been quite a few discussions on this but I couldn't remember all the
> details so I was checking around by phone and Google.  I ended up at 
> the
> penngrade.com site which was the old Brad Penn Co now under the D-A
> Lubricant Co.  I called the contact number and was eventually put in 
> touch
> with a Mr Ken Tiger (sp?).  He said he gave an engine oil 
> presentation at
> the Pittsburgh convention but no one had requested info on transaxles 
> with
> a hypoid differential.  This issue is the EP (extreme pressure) 
> package
> (lots of sulphur) added for the hypoid gears attacks the brass 
> synchronizer
> rings and can cause surface corrosion (pitting). Long story short, he
> recommended their PennGrade 1 80W90 Classic Multi-Purpose Gear Oil 
> which is
> a GL-4 rated oil.  Their part number is #7729 but will appear as a 
> #77296
> at Summit, Jegs, Amazon.  The '6 designating a quart bottle 
> container.
> Interesting point was that he asked me what the owner's manual said 
> and I
> checked mine (1966) and the shop manual and they both said 
> MIL-L-2105-B.
> This is a military spec and when he checked his resources, found
> information that said it was the same as API GL-4 and other resources
> saying it was an API GL-5.  However, some of the info from the API 
> GL-5 was
> from later documentation of the mil spec (2105-D, 1995) so his 
> conclusion
> was to stay conservative and go with the GL-4 oil.  This oil will not 
> harm
> yellow metal (brass synchros) and has a sufficient EP additive 
> package to
> work well with our hypoid differential gears.
> This oil does not have a limited slip additve (LS) so I'll have to 
> get some
> of that for the posi unit in my car.  He said there shouldn't be an 
> issue
> with adding it to their oil.  He suggested the GM additive so I'll 
> try that
> first.
> I bought my oil from Summit for $8.99/qt.  Amazon only sold by the 
> case and
> JEGS was selling the GL-5 version with an LS additive.
> Hope that helps someone considering a manual transaxle oil change.
> Gary Szuch
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