Tech Tips:
Gearbox Oil (3)

From: Laurence McCracken [lmccrack(at)bigpond.net.au]
Sent: Monday, May 29, 2006 11:22 AM
To: HillmanCars@yahoogroups.com
Subject: [HillmanCars] Gearbox oil

Hi Guys,
I am confused with the oil for the manual gearbox in my Gazelle (it's in and works wonderfully well thanks to Graham & Peter), I have read all the posts regarding this subject but I can't seem to bring myself to draining the oil and filling the box with motor oil, can anyone tell me why it needs engine oil rather than gear oil?


From: Jan Eyerman [jan.eyerman(at)usa.net]
Sent: Monday, May 29, 2006 12:20 PM
To: HillmanCars@yahoogroups.com
Subject: Re: [HillmanCars] Gearbox oil

I could say "because Rootes designed it that way".  But that would be begging the issue.  In a Rootes (Hillman) gearbox, the gears are only partly submerged in the oil.  The spining gears then splash the oil up onto the other gears in the gearbox.  If the oil is too thick, it can't splash high enough to lubricate everything up there - leading to early failure of internal gearbox parts.  In addition, since everything was designed for "thin" oil, when the weather gets cold, it becomes almost impossible to shift the gearbox.

Solution?  Use straight 20 weight or 30 weight engine oil.  This should not upset you as automatic transmissions use very thin oil and Chrysler Valiants with manual transmissions use automatic transmission fluid (which is even thinner than engine oil).

Soooo, keep your Hillman happy with a diet of engine oil (20 or 30 weight) in the transmission.  There are at least 100 cars on the list running with it now and I have been doing it since 1955!!!  I have only had one manual transmission failure (out of 100+ Rootes cars) - and that was due to all of the oil leaking out.

Jan Eyerman

From: Armadillo Technical Services [1dillo(at)bellsouth.net]
Sent: Monday, May 29, 2006 12:23 PM
To: HillmanCars@yahoogroups.com
Subject: Re: [HillmanCars] Gearbox oil


Here is the straight dope.  This is the text of a message from December 2, 2002.

"        The reason 90 wt is bad for a standard gearbox is because unlike American transmissions that have 1/4" or larger holes in the gears for oil passages, Rootes used tiny holes.  Consequently, a thick as molasses oil does not 'even' pass thru the holes at low temperatures and transmissions literally run dry.

        Laycock Overdrives are designed with controlled orifices as well: 30 wt passes thru them and 90 wt WHEN HOT will too.  However, there is a pump: again, it is designed to pump 30 wt oil when cold and hot, and not a thick differential gear lube, especially when it is cold.

        I have seen both standard and overdrive transmissions that have run literally forever using both a light engine oil and a gear lube.  I have also seen several transmissions that failed in service with blued parts from overheating, and they were full to the top with 90 weight goo.  I have never seen a failure caused by using the correct lube. 30wt.  Non-D works for me...

Jim Leach    Pacific Tiger Club    Seattle  "

Martin DeWitt
1960 Minx IIIA Deluxe Convertible
1962 Minx IIIC Deluxe

From: Laurie [lmccrack(at)bigpond.net.au]
Sent: Monday, May 29, 2006 4:32 PM
To: HillmanCars@yahoogroups.com
Subject: Re: [HillmanCars] Gearbox oil

Thanks Jan,
The oil will be changed tomorrow

From: Graham Robinson [grhusky(at)optusnet.com.au]
Sent: Monday, May 29, 2006 5:37 PM
To: HillmanCars@yahoogroups.com
Subject: Re: [HillmanCars] Gearbox oil

Heavier than engine oil makes the synchros work easier and in some cases the synchro sliders and cirlcips can jam up with the heavier grade thus causing some to drop or fall out of gear later on.
In Overdrives Laycock used external oil balance pipes and in later version moulded in the casing to redistribute this light oil as the planetary gears threw it out so much the whole internal gears etc. would go very BLUE and eventually weld together rendering the overdrive effect useless but will still operate as a straight gearbox.  Some early versions were released with this external oil balance pipe and was subject to a Sunbeam Service bulletin to have it fitted because of this internal heating problem.

From: Tigerootes(at)aol.com
Sent: Tuesday, May 30, 2006 2:03 AM
To: HillmanCars@yahoogroups.com
Subject: [HillmanCars] Re: Gearbox oil

       Unlike American transmissions whose gears and other components have large drilled holes in them to distribute oil, Rootes transmission parts have tiny holes.  Thick, viscous "gearbox oil" doesn't easily pass thru the small holes, especially at low temperatures.  If you use too "thick" an oil, the gearbox essentially runs dry as if there was no oil in it.  I have seen several failed Rootes gearboxes with parts that have turned blue from overheating and every one had 90 weight gear oil in them.
Jim Leach    Pacific Tiger Club     Seattle
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