Oil levels again ! 1934 RP

[morrisminor]

Hi all, 
Looking in the handbook 1095 it says gearbox needs 2/3 pint to fill, what you do guys recommend as I remember seeing articles about putting less in, likewise with the rear axle ?

[Dave Mann]

Here's my article.      <!-- @page { margin: 2cm } P { margin-bottom: 0.21cm } H3 { margin-bottom: 0.21cm } H3.ctl { font-family: "Mangal" } -->
4 speed gearbox oil level
Whenever I get a new gearbox of unknown provenance, I take the lid off, drain it and if it looks OK refill it and give it a spin test at 500 RPM on my lathe for about half an hour. I then drain it and examine the drained oil for debris, if there is non and it didn't make an unwanted noises it is put into stock.
I was given a 4 speed synchromesh box this week and remembered that there is some question over the amount of oil that is required in these boxes and carried out a oil level test:
¼ of a pint - the oil level is barely up to the gear level with only a few drops being thrown up - too low
½ pint - at this level I needed the top on the box to prevent oil being thrown all over my bench.
2/3 pint gives 2” of oil in box measured above the drain plug
3/4 pint gives 21/2” of oil in box measured above the drain plug and 15/8” below the top of the oil filler hole
1 pint gives 3” of oil in box measured above the drain plug and 7/8” below the top of the oil filler hole
11/4 pint gives 31/4”” of oil in box measured above the drain plug and level with the bottom of the oil filler hole.
The measurements were taken with the gearbox top off on the end of the lathe bed, see photo, the brake drum allows me to put some load on with a piece of 3” x 2”, very difficult in the car.
Then I borrowed my mate's RP saloon handbook 1095A from which I quote on page 15;
Monthly attention

1. examine the oil level in the gearbox which should contain 2/3 of a pint or measure 2” to 2/12” deep.
   

Then I looked at The Austin Seven Book sixth revised edition by Nicholson page 64, from which I quote:
The gearbox should carry a little over two thirds of a pint which will give a depth of rather more than 2 inches.
On the nearside of the gearbox you will find a plug 2K 8648. When the plug is removed the level of oil in the box can be verified. It should rise to where the base of the plug rests when in position. When refilling the gearbox simply pour in oil until it overflows at the inspection hole.
Finally the Pitman's book of the Austin Seven And Eight third edition reprinted 1951 page 16 from which I quote:
Remove the combined level & filler plug, if this has not already been done and fill up with a pint and a half of new oil which is in readiness. This should give an oil level up to the bottom of the thread in the plug hole.
If you follow Nicholson's advice , until it overflows the inspection hole the first & third motion shaft bearings will be flooded (see drawing) and I wouldn't be surprised if return scroll is overwhelmed and oil found it's way into the clutch. I like Nicholson's 'a little over two thirds of a pint' (how little?) and Pitman has found that the Austin recommended oil quantity of 2/3 of a pint needed to be increased to 11/2 pints for some reason that is lost in the mists of time.
I leave it up to you to decide how little over two thirds of a pint you put in your gearbox.

[Mark McKibbin]

Using Dave's numbers I have added a couple of lines to the drawing, the drawing was not straight so had to make the lines go accordingly.

[Tony Griffiths]

Thanks the empirical experiment, Dave - most interesting. If the lowest gear in the train that runs continuously is one-third to half-submerged - as I suspect it would be with the 1/2 pint level - that would be sufficient to lubricate all box (as Dave's workshop walls and floors attest...). It would also give the lowest power loss - if you fancy a bit of competition use. Oddly, many machine-tool gearboxes use a relatively thin hydraulic oil, Shell Tellus, for example.