Gearbox and overdrive oil change

[Goldie]

Does draining the oil from the gearbox also remove oil from the OD. How much oil should be replaced--3 qts? User manual says to use motor oil and I was thinking I would go with 20w50 which is listed as acceptable in the manual. I know the modern oils have different additives now than 50 years ago.

 

[Healey Nut]

In short no it doesnt , you need to remove both the gearbox oil drain plug and also that big round brass plug on the bottom of the OD . That will give you access to the OD filter screen to check its clean and drain the oil trapped in the OD .
You need either a spanner/hook wrench or a bigass set of channel locks /pipe wrench if your stuck to get it undone .

 

[trotti]

Does draining the oil from the gearbox also remove oil from the OD. How much oil should be replaced--3 qts? User manual says to use motor oil and I was thinking I would go with 20w50 which is listed as acceptable in the manual. I know the modern oils have different additives now than 50 years ago.

Just filled mine literally minutes ago - used 30w non-detergent oil. Couldn't find any at Autozone or O'Reilly so I just gave up and used Amazon. 3.75 quarts exactly (leave 8 oz behind in the fourth quart). Large crescent wrench works fine on the OD plug. I drained the tranny first and after that was "empty" pulled the OD plug. Lots of oil remains so you definitely need to drain both. Healey Nut also mentioned cleaning the filter screen and you should definitely take the extra few minutes to do so.

 

[blueskies]

Ditto on using 30 weight non-detergent oil. In Canada, Canadian Tire carries this oil in their own brand; not sure where to find it in the US.

 

[British_Recovery]

I use what the handbook recommends. The earlier cars call for the 30 non-detergent oil, and the later cars can use the 20w50 engine oil. The metallurgy of the synchros changed at some point, so the detergents may eat away at them in the early cars.
Bob

 

[fordtrucks4ever]

When I first got my Healey running the trans and od was empty. At the time it was hard to find much info on what to use. So I filled it with 90wt gear oil. For the next 20 years it seemed to work fine. Then I read horror stories about using the wrong oil in gearbox. It sat for several years not in use and the od quit engaging. So last fall I finally drained both and filled with 20W50 oil, same as in engine. I was surprised to find the minor drips from same didnt increase. but the od does shift smoother, without delay. I guess when you dont know any better, no damage will occur before your correct the problem.

 

[John Turney]

The SAE viscosity grades for gear oil and motor oil are different. A 90-grade gear oil is about the same viscosity as a 40-grade or 50-grade motor oil. The additives are different, and the gear oil may eat brass parts due to extreme pressure additives, but if it worked for you, then you're ok.

 

[DerekJ]

Interestingly, relating to Terry's comment above, Millers Oils in the UK list 'differential' type oils as being also suitable for classic gearboxes.
https://www.millersoils.co.uk/automotive/classic-gearbox-oil.asp

 

[pan]

I have found Penrite Classic Gearbox 40 weight oil to be perfect. I would avoid detergent oils.

 

[Goldie]

So I should drain the OD after the gearbox has been drained, then will filling the gearbox with replacement oil also find its way into the OD? Does the OD wrench sold by Moss work on the BJ8 OD? Its pretty pricey for something that doesn't seem to need to be changed very often.

 

[John Turney]

So I should drain the OD after the gearbox has been drained, then will filling the gearbox with replacement oil also find its way into the OD? ....

Yes.

 

[Healey Nut]

So I should drain the OD after the gearbox has been drained, then will filling the gearbox with replacement oil also find its way into the OD? Does the OD wrench sold by Moss work on the BJ8 OD? Its pretty pricey for something that doesn't seem to need to be changed very often.

Measure the diameter of the big brass plug with the notches on the outer edge . Go to your local bearing / belt supply house and ask the them for a spanner/hook wrench for the appropriate diameter . . Probably cost 1/2 of what Moss charges .

 

[trotti]

So I should drain the OD after the gearbox has been drained, then will filling the gearbox with replacement oil also find its way into the OD? Does the OD wrench sold by Moss work on the BJ8 OD? Its pretty pricey for something that doesn't seem to need to be changed very often.

Yup - single fill hole. I'm not sure about the OD for the BJ8, but if it's the same as mine, a large crescent wrench will do the trick for free. It's not torqued down too heavily and is well lubed so comes out without a fight/damage. It may mar the paint, but I believe that's inevitable.

 

[Jim 58 BN6]

Measure the diameter of the big brass plug with the notches on the outer edge . Go to your local bearing / belt supply house and ask the them for a spanner/hook wrench for the appropriate diameter . . Probably cost 1/2 of what Moss charges .

You might check Mc Master-Carr for spanner wrenches as well (for my British friends, I'm not being redundant - it's American for a special type of "spanner").

They sometimes have specialty tools at reasonable prices, plus all kinds of hardware and materials.

Jim

 

[crya]

Sorry for the old bump but what size is the hex wrench to fit into the main gearbox drain plug? I can't seem to find the answer to that one. Just handy to have that info before I crawl under the car only to learn I don't have the proper tool. Thanks.

 

[dcarlg]

Maybe 7/16 square?
I ground down a cheap 1/2" extension to fit into the plug.