<VV> Finding manual transmission oil locally?

Hugo Miller hugo at aruncoaches.co.uk
Sun Jun 30 13:05:30 EDT 2019

Here is what I wrote - You will not find the word 'diff' or 
'differential' anywhere in my post;

"As a general rule, synchromesh transmissions run best on ATF. What you 
want to avoid is hypoid oil, as this will allow the synchro cones to 
slip & slide without biting. I have known commercial ZF transmissions 
become almost underiveable when filled with hypoid oil.
The problem is that in the good old days, we had hypoid gear oils and 
we had EP (extreme pressure) gear oils. So you had EP 90, which was good 
for synchro transmissions, and Hypoid 90, which was not. The two were 
quite different.
But today, through the magic of modern chemistry, we see EP/hypoid 
oils, which serve both functions. I would avoid these and use ATF or EP 
90 if you can find it.
I'm not up to speed with the GL numbers - Google will tell you more 
than I can. Just steer clear of anything with 'hypoid' on the label."

  The reason I omitted to mention differentials was that we were talking 
about synchromesh gearboxes. I was trying to explain in general terms 
why hypoid oils, and that includes modern EP/Hypoid oils, are unsuitable 
for synchromesh gearboxes. This is not 'bad advice' as you claim - it is 
perfectly sound, and the effects of diregarding it can be quite 
  One would hope that the original poster is aware that his car shares 
the oil between gearbox and axle, so would treat my advice about gearbox 
oils accordingly, although it does pose something of a conundrum. On 
balance, I would be more inclined to put EP oil in a differential than 
to put Hypoid oil in a synchro box, but neither is ideal.

On 2019-06-30 17:48, FrankDuVal via VirtualVairs wrote:
> Hugo, you say "but I wasn't actually suggesting putting ATF in a
> diff."  But you did!
> By not knowing the transmission and differential on manual
> transmission Corvairs share fluid.
> Since PG Corvairs have separate fluid, you can run GL5 in their
> differentials with no problem.
> Just adding this email in for the archives to make sure no one
> follows the bad advice in the future.
> I've shared bad information in the past also.... You have now joined
> the club. ggg
> Frank DuVal
> On 6/30/2019 10:36 AM, Hugo Miller via VirtualVairs wrote:
>> Thank you, but I wasn't actually suggesting putting ATF in a diff. I 
>> went to some lengths to explain that (hypoid) crown wheel & pinion 
>> gears (ring & pinion if you prefer) require a different oil from the 
>> standard Extreme Pressure stuff, and I explained why hypoid oil was 
>> unsuitable for synchro cones. It has less to do with the oil attacking 
>> the soft metals (in fact I've never seen a sybchro cone corroded in 
>> this fashion) and everything to do with making the cones slide over 
>> one another instead of biting, which can literally make a vehicle 
>> un-driveable, on commercial gearboxes anyway.
>> But I've already said all that - the confusion arose because my car 
>> has separate oil for gearbox and transmission and I didn't realise 
>> that a 4 speed shared trans oil while a PG didn't. Not that this 
>> affects the validity of my arguments of course.
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