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MG MGB Technical - trans oil

didnt know if tec or gen question but I just drained the trans and wondering if the hyp 90 pensol is ok to put in> I removed 3 qts from it. I read some where that if it had engine oil in it put it back that way, but i cant tell what type it is. thanks , DOUG
dd doug46chief

Hi Doug
If your gearbox is the standard 4 speed box - and not an overdrive equipped gearbox - most follow the factory recommendation and use a multi-viscosity engine oil

If you have an overdrive gearbox, most recommend a 30 wt single viscosity non-detergent engine oil

Some feel that a modern gear lubricant such as Redline MT90 or Redline MTL offer better properties

Lots of info in the archives

Let us know the year and type of gearbox you have and www can fine tune some assistance on your oil change
Best regards

Jeff
Jeff Delk

Jeff thanks, its a standard 4 sp on a 79 b. I thought it said 75/90 in the book?
dd doug46chief

after looking in the archives im more confused. I can get 20=50 wt or straight 30 but its probably detergent. Doug
dd doug46chief

Since it is a standard box, I would go with a multi-visc engine oil
The non-detergent seems only to be an issue for the overdrive gearbox. From what I have read, the non-detergent oil foams less and this is more important in an overdrive unit

I would think 20w50 would be fine
Jeff Delk

Doug. You need to obtain a copy of the factory workshop manual as it will contain much of the information you are seeking here. Also, you will have "the factory solution" in addition to various people's opinions.

The factory solution was to use engine oil in the engine and transmission and 90 weight gear oil in the rear end. Various people have, over the years, offered up their reasons for using something different than the factory recommendation. But, few of them have offered up any form of long term test series to support any claims of superiority of their choice over the factory choices. We do know that the factory choices were both determined to work well at the factory and have been field tested, for about 50 years by owners.

As to the overdrive transmission. I have used 20W-50 Castrol motor oil in my various overdrive transmissions since 1979 with no problems. The factory recommended that product and, according to the dealer, shipped the car with Castrol 20W-50 in the engine and gearbox.

Robert Bentley publishing does an excellent reprint of the factory workshop manual and includes the factory Driver's Handbook as part of the manual. Expensive? Maybe, but I have been using my current copies for over twelve years now which spreads the investment cost. Plus, it quickly answers a number of simple questions without having to wait for someone to reply on the internet--and, it gives me the factory solution.

Les
Les Bengtson

les i put the 20/50 in and its working good,thanks, Doug
dd doug46chief

Doug. That is a good thing and should serve you well.

Again, I point out, as an old man who has done such things for more than 40 years now, that the factory workshop manual is your primary reference. Everyone needs to own a primary reference.

I have done this thing, owning Little British Cars, for a long time. Many other people, who may have different opinions, have owned LBCs for quite a long time.

Thus, you have two references, as a relatively new owner. The first is the the factory information, a primary reference. The second is all of us, a secondary reference. We know what works for us, but that does not mean that what works for us is either ideal, nor may be the best possible solution. A few of us, like John Twist, Peter Burgess, and Chris Betson have a great deal of specialized expertise and years of accumulated knowledge. But, in the end, it is your car and you will have to make some decisions based on your best guess as to what/whom you decide to trust.

These are fairly robust cars and whether the difference between 30 weight motor oil in the tranny and 20W50 weight oil is not something that will make any form of difference is in doubt. Get a copy of the factory workshop manual and use it as your guide.

Les
Les Bengtson

Don't use hypoid (GL-5 oil) as there is a possibility that the antiwear additives can affect brass parts. The new additives are not so aggressive but why take a chance.

You can use 90 wt GL-4 gear oil. But my experience in a 3 synchro box is the second gear synchro doesn't work well.

I use Redline. I can't remember if MTL or MT90. I think it helped noise and synchro action.

If you use multigrade motor oil change it regularly as it will shear to lower viscosity due to the gears. You can use SAE 30 also. No need to go non-detergent for your box. I don't know if the newer SM/SN oils are as good for gears as the older SL etc. They've lowered the ZNDTP levels quite a lot. The ZNDTP is a great wear inhibitor.

Check the archives for other opinions including ATF.
Robert McCoy

Here is a link to a paper describing the differences between GL-4 and GL-5 gear oil. It is from a Corvair enthusiast but that aside there is a lot of good information.

Bottom line, keep GL-5 out of your gearbox, but you must use GL-5 in the differential. The article even discusses use of motor oil to some degree.

http://www.widman.biz/uploads/Transaxle_oil.pdf

Bob
Robert McCoy

I try to avoid using GL-5 in older car differentials because of the high sulfur content and the damage it can do to the brass thrust washers. GL-4 is still available and much more suited to use in our cars. I've been using it in the differential of my '67B for 40 years with no problems. No noises, clunks or seal leakage. Everything inside the rear axle is original. RAY
rjm RAY

Ray, thanks for the input on the differential. I've been using hypoid rated gear (nominally GL-5) oil in my banjo unit. As far as I know it is all original except replacement of the seal.

I think the only copper parts in the differential are the small pinion thrust washers. I suspect mine are in need of replacement. This could be due to the long-term effects of the GL-5 wear additive or age.

Also, the car was badly neglected by the previous owner.

Bob
Robert McCoy

Robert, you're correct in that the only copper components, in the differential, are the thrust washers. My banjo axle is extremely quiet and has no lost motion at all. The oil has only been changed 3 times in 45 years. RAY
rjm RAY

Mine is not quiet when the top is up. I get some noise on coast which means the drive pinion to ring gear is not properly set up. Plus there is some gear whine at high load. Likely the gears were damaged in a previous life. The car was pretty abused when I got it so all sorts of bad things could have happened to the differential.

Nothing has gotten worse since I've owned it and with Redline synthetic the gear whine at load is less.

I may try to check out the thrust washers one of these days.

These are actually pretty robust units. After all they've lasted 40 plus years.
Robert McCoy

I am want to harp on about this, but to my mind gears require gear oil. The V8 had the same gearbox but BL specified gear oil, I'd go with that!!
Allan Reeling

Allan, the Redline I in my gearbox is MT-90 a GL-4. For the differential I used Redline EP with the hypoid additive. This is a GL-5 oil. Ray has had good success with GL-4 oil in the differential.

You are right that in a differential you need gear oil. In the gearbox 20W50, 30W, ATF, and GL-4 hear oils have been used by various owners.
Robert McCoy

This thread was discussed between 20/02/2012 and 02/03/2012

MG MGB Technical index

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