Mike,
You have probably stepped in it by getting an oil discussion started again.
But to answer your question without adding my opinion to it, I believe
that when someone on the list contacted Red Line, they recommended
MT-90, which from memory is 40 wt. Check Red Line's website:
https://www.redlineoil.com/Products.aspx?pcid=7
They make a good argument for using a gear rated oil in a transmission
as Harold also outlines below. As he mentions and we have discussed
previously, it seems that the synthetic transmission oils do leak a bit
more.
Charlie
On 8/8/2017 11:24 PM, Harold Manifold wrote:
> 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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