[Healeys] Russ Thompson

[Harold Manifold]

Mike,
 
I am new to the Healey world but I am an engineer with an automotive
background who recently had a BN4 transmission with an overdrive completely
rebuilt. I could not find a consistent answer on the recommended oil for the
transmission. The original Healey manuals are not consistent either, the
shop manual recommends 20W50 and the Healey service bulletins from the day
recommend 30W. Coming up with the right oil is further complicated by the
design of a Healey transmission which is two different transmissions with a
common oil system. One transmission is a traditional gear type with syncro
rings that are not compatible with the additives in modern gear lubricants
and the other is a hydraulic pump. I am sure there will be much disagreement
but these are the steps I went through to select the oil I would use:
 
1. The additives had to be compatible with brass and other soft metals used
in older transmissions.
2. The oil should be designed to work with gears and have some level of EP
protection. Note very few engine oils meet gear oil specifications.
3. The oil should have a viscosity similar 30W engine oil which was
recommended in an Austin Service bulletin in 1960 replacing 20W50.
 
The oil that best fits all of these requirements is a 70W-90 GL4 gear oil.
Red Line MT-90 meets this specification as does Pennzoil Synthetic 70W-90
GL4. I picked the Pennzoil as it costs less than the Red Line but both
should work well. Do not use a GL5 as the additives are not compatible with
brass. I looked into why Austin switched their recommended oil from 20W50 to
30W and concluded it was for a lower viscosity at lower temperatures i.e.
when the transmission is cold. Viscosity is another important consideration.
70W-90 GL4 has the same viscosity as 30W engine oil above 35 degrees C and a
better low temperature viscosity. The only downside I have seen with
Pennzoil Synthetic 70W-90 GL4 is that it can get through even the smallest
openings and cracks and the transmission may leak a little more but that is
evidence the oil is getting every where it should. I have heard Red Line
MT-90 doesn't leak as much as the Pennzoil.
 
For those that may doubt the viscosity claims please note that engine oils
and gears oils are classified differently and should be compared by looking
at the numbers on the can. See the attached viscosity curve.
 
I trust this helps but I want to emphasize this is the oil I use and I
recommend you reach your own conclusion.
 
Harold
 
 

  _____  

From: Healeys [mailto:healeys-bounces at autox.team.net] On Behalf Of Michael
MacLean
Sent: Tuesday, August 08, 2017 5:47 PM
To: Healey List
Subject: [Healeys] Russ Thompson


     Through a reference from the list I am having Russ Thompson in
Northridge, California rebuild my BN2 transmission.  It is a low mileage
(10,000 mi. approx) transmission, but I wanted to be able to put it in and
not have to take it back out again.  Good thing I took this precaution.
Russ found the overdrive stuck and would never have worked.  Today he showed
me the accumulator piston.  The smaller center piston was scored from dirt
or crap in the oil.  Russ replaced it with a one piece piston from a Triumph
overdrive.  There was a huge spring below it.  Anyone heard of this?  He
said engagement will be real positive now.  Even with the low mileage, the
number 2 synchro was toast and will be replaced.  The other two were fine
and will be re-used.  All the gears showed very little sign of wear.  The
reverse gear had some surface rust on the teeth, but that can be blasted and
it will be fine.  Getting closer to having the drive train is the car.
     I know I am going to start a discussion, but Russ recommends using 40wt
motor oil for the transmission.  Anyone know what weight Redline MTL is?

Mike MacLean

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