'26 gearbox oil

I have recently received some information from our contributor Robert Brims. For many thousands of miles he has used a gearbox oil with an I.S.O. rating of 1000; a steam cylinder oil with an S.A.E. rating of over 250. I have always thought you should use 600W steam cylinder but this is obviously a little on the thin side as I have experienced difficulties in making clean changes with my Dodge. As we know, these gearboxes have straight cut gears and can sometimes be a challenge.

Obviously, having purchased 20 litres of 600W I really didn't want to buy another 20 litres of 1000 so I chose to experiment. I added 4.5 ml of STP gearbox oil additive and to my delight, I now have a smooth clean change up and down through the gears. No more embarrassing crunches and the edge has been taken off the (admittedly worn) transmission noise.

My sincere thanks to Bob for help and advise.

Ray.

Interesting. I am dubious about this practice. When the gearbox is cold, the oil will be so viscous it won't easily get between the gear and the shaft it runs on. Thus lubrication will be significantly reduced for the first 20 or 30 miles of more, until the gearbox warms up. Gearboxes are lubricated by splash, and with thick oil there won't be much splash when the oil is cold. Gearboxes in good condition warm up by convection from the engine plus heat generated by motion and stirring of the oil.

I prefer to use thinner oil (90W-150) and work at silent gear changes in my technique. And keep an empty fridge box on the floor under the car to catch the drips.

Ref technique. I used to fear changing down and leave it until I was nearly stopped. Hopeless. Once I realised it needed revs to change, I found it easy to change early with a good footfull of revs. Don't be shy, give a good push on the throttle when double de-clutching down.

I use Morris oils, their 600w "straight mineral gear oil" is rated 250 S.A.E . The gears are only engaged in 1ST , 2 ND and revese not 3rd .The thick oil (I believe up to 1923 grease was added to make it even thicker) helps to slow down the gears when changing up and down as well as lubricating them

This subject has been beaten to death on this forum. It is correct to use at least 600 wt. steam cylinder oil, which is supposed to be lard based. STP is not good. A better way to thicken SC oil is by blending in tubes of grease with a mixer, no moly lube. Hypoid oil is not good, something about the way gears rub as they engage.

Is it really possible to downshift one of these? I can get clean up-shifts but just cannot seem to ever get downshift. Maybe I'm just not bringing up the revs enough...

I wound up dumping in some 00 grease to thicken up the oil.

It's a LOT cheaper than 600W too........

Is it really possible to downshift one of these? I can get clean up-shifts but just cannot seem to ever get downshift. Maybe I'm just not bringing up the revs enough...

Yes Mike. You will probably remember I missed a downshift when we drove through Derby. (Nun Street, where the Plating works explosion threat caused a mass evacuation the other day!!! - seen my post?) :eek: I gave it quite a lot of revs but the cogs would not play ball. Since thickening the oil a bit I have been able to change down easily without having to rev the nuts off!

Some boxes are worse than others and yes technique comes into it but I have been driving cars with crash boxes for 40 years so I think I might have got the hang of it by now.

The reason you should not use HP oil is that it contains sulphur which attacks any brass or bronze components. I'm sure adding grease would be fine but being soap based it can cause foaming. I had the STP to hand; it is the correct gearbox type and a relatively small amount has made a big difference. However, I would be inclined to agree with Robert B that ideally a thicker oil - 1000 W SC - would be ideal but for now I'm content with the way it is.

Gundog you made a very pertinent point that top gear is not meshing - it is direct drive if I remember?

Thank you guys for your responses.

Ray