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Getting pretty far off topic here, but before this gets too far out of
hand, I have to point out that the standard gearbox is not just splash
lubicated. Every Austin A-series and B-series gearbox has a helical
screw oil pump on the mainshaft immediately aft of the center main
bearing. This pushes oil into a coaxial bore hole in the mainshaft
to lubicate bronze bushings inside of 2nd and 3rd gears as well as oiling
the needle bearing between input gear and front of the mainshaft.
This is what allows the car to be flat towed without disconnecting the
propshaft (among other things). There is an exensive description on
overall gearbox lubrication on my web site.<br><br>
Barney Gaylord -
<a href="http://mgaguru.com/" eudora="autourl">http://mgaguru.com<br><br>
<br>
</a>At 01:16 PM 1/18/2019, Max Heim via Mgs wrote:<br>
<blockquote type=cite class=cite cite="">There are flame wars on this
subject on the MGB Experience forum…<br><br>
But here's my logic:<br><br>
The factory manuals specify "engine oil" for both overdrive and
non-overdrive transmissions.<br><br>
If you analyze that recommendation, you would conclude that the key
characteristic they are concerned about is viscosity. Analysis
follows:<br><br>
Transmission oil does not have to deal with combustion blow-by or high
heat, so it doesn't need detergents or protection from thermal breakdown.
And my personal take on it (though this is apparently highly
controversial) is that for transmission oil it is better to use a
single-grade oil, as multi-grade oils break down into the single-grade
stock over time, and one does not change the transmission oil very often
compared to engine oil (or ever, IME). It's not that multi-grade would
hurt; it is that its benefits, if any, won't last, and the single-grade
base stock is equivalent to the lightest grade in the rating; i.e. 20W50
breaks down into 20W.<br><br>
But some people will fly off the handle at the suggestion that 20W50 is
not ideal. Their logic goes something like this: “the manual says
"engine oil" for the transmission; for my climate it recommends
20W50 engine oil for the engine, therefore 20W50 is the only correct oil
for the transmission. I believe it is only the later model MGs that
have this particular recommendation (20W50) in the drivers
handbook.<br><br>
Anyway, backing up a paragraph or two, to my mind there is a significant
difference between the standard transmission, which uses oil for splash
lubrication only, and the OD transmission, which uses oil as hydraulic
fluid with a planetary gearset, much like an automatic transmission.
Automatic transmissions are extremely sensitive to viscosity — I don't
think you would have much luck with 90W gear oil in an auto
trans.<br><br>
So that is my thinking behind my suggestion. Are you sure the article you
read was specifically about OD?<br>
--<br>
Max Heim<br>
'66 MGB</blockquote><br><br>
<blockquote type=cite class=cite cite="">
<blockquote type=cite class=cite cite="">On Jan 18, 2019, at 8:22 AM,
Jack Wheeler
<<a href="mailto:jwheeler1947@yahoo.com">jwheeler1947@yahoo.com</a>
> wrote:<br><br>
Hi Max. No, I'm not sure, but it is something I am looking in
to. I have used straight 50 Wt. motor oil for years, and it has
always worked fine. Based on the article I saw recently in the Tech
Issue of "MG Driver" magazine (starting on page 46) I switched
to EP 85/90 GL-4 gear oil. I couldn't find straight 90 Wt., so I
used the closest GL-4 oil I could find, which was 85/90. So do you
think this change could be causing my overdrive not to engage. If
so, then someone ought to advise "MG Driver" magazine about the
error in their article. Thanks.<br>
<br>
Jack</blockquote></blockquote><br><br>
<blockquote type=cite class=cite cite="">
<blockquote type=cite class=cite cite="">On Thursday, January 17, 2019,
11:58:16 PM EST, Max Heim via Mgs
<<a href="mailto:mgs@autox.team.net">mgs@autox.team.net</a>> wrote:
<br>
<br>
Are you sure it isn't the gear oil?<br><br>
The factory has always called for engine oil. There has been a lot of
ridiculous debate over precisely what grade of engine oil (personally, I
don’t think it matters, but let’s not start that), but there is
certainly a large difference in viscosity between say 20W50, and 85W90.
The overdrive, unlike the rest of the transmission, uses oil in a
hydraulic function, not just as splash lubrication, so viscosity is
probably very important.<br>
--<br>
Max Heim<br>
<a href="mailto:mvheim@sonic.net">mvheim@sonic.net</a></blockquote>
</blockquote><br><br>
<blockquote type=cite class=cite cite="">
<blockquote type=cite class=cite cite="">
<blockquote type=cite class=cite cite="">On Jan 17, 2019, at 11:13 AM,
Jack Wheeler via Mgs
<<a href="mailto:mgs@autox.team.net">mgs@autox.team.net</a>>
wrote:<br><br>
Does anyone have a good exploded diagram of the overdrive unit used in a
1971 MGB, that you could send to me? I am particularly interested
in the pump assembly. I changed the oil in my gearbox this week,
using EP 85/90 GL-4 gear oil, as recommended in a recent article in the
MG Driver magazine.<br><br>
While the car was up in the air, I noticed a leak around the plug which
holds the pump assembly in place. So, I removed the pump, careful
to keep all the pieces in the order in which they came out. I
cleaned everything up, and reinstalled the pump assembly and plug (part
number 466-315 in the Moss catalog), with a new gasket. I thought I
had all of the pieces of the pump assembly (items 62-66 in the Moss
diagram) in the right order when I reinstalled it, but when I took the
car out for a test drive, the overdrive would not engage.<br><br>
In addition to trying to keep the pieces in the order in which they came
out, I also used the exploded diagram in the Moss catalog (Page 41) as a
guide. The Moss diagram, however, is different than my overdrive
unit. Moss says their diagram is for cars from 1968 to 1980, but
apparently, some things were changed during that time frame. I
can't believe the engineers would let anything go unchanged for 12
years! It looks like the plunger (Moss part number 466-305) shown
in the Moss catalog diagram has a roller on the end of it. My
plunger does not have a roller on the end of it. Maybe this will
give you a lead to which diagram I am looking for.<br><br>
So, that leaves me looking for a good exploded diagram of the unit used
in a 1971 model. Can anyone help with that, or does anyone have any
suggestions as to what I might have done to make the overdrive not work,
when it has always worked fine. Thanks.<br><br>
Jack Wheeler</blockquote></blockquote></blockquote></body>
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