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MGB MGB tranny oil?

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R6MGS

R6MGS

Yoda
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So I took the B in for an oil spray and had them change the diff and tranny fluid while it was in. I later noticed that even after I gave them the manual which specified 20W50 motor oil for the tranny they used a heavier weight(75W90...i think) synthetic gear oil for both the tranny and the diff. I later asked about this and they said the synthetic gear oil is better and alot of MGB owners have been using it in place of the regular motor oil.
Any thoughts?? This is new to me.
 
Get that stuff outa there & don't take your car back to them again!

Oh, do you have "alot of MGB owners" in your area?

Oh, change it at their expense!!
 
Thanks
The place that did it was my normal mechanic for my normal cars....He's usually pretty good. There are like 5 or 6 other MGB that get serviced there, and apparently they've been using it....He said that the synthetic stuff doesn't eat the syncro's like the older gear oil used it. Iunno, I guess it's time to bring it back in....
 
Yep, this is a issue that comes up from time to time, these transmisions are designed to run on motor oil not gear oil. A trip over to Quantum Mechanics' website to show you what gear oil does to a tranny is time well spent.
John actually recommends SAE30WT.
 
If it's an overdrive gearbox then I agree, get that stuff out of there. If it's a non-OD box then it won't really hurt, providing the gear oil they used is safe for bronze parts.
 
There is nothing wrong with using 75W90 gear oil in an OD transmission. 75W90 is NOT heavier than 20W50. 75W90 gear oil has the same viscoity as 20W50 motor oil. Gear oil and motor oil are rated differently and hence the reason for the different viscosity valves. Volvo, who put over 400,000 OD units in the their cars specified everything from motor oil to gear oil and finally ATF, so obviously the OD unit is not particular.
 
Thanks for the additional input.
It not O/D so that shouldn't be an issue here. I also googled it and found out that most TR's, 1500 Midgets, T-series, and V8 MGB all recommend gear oil. I can't really see why a regular MGB gearbox should be that much different than any of those, this stuff is suppose to be safe for bronze parts, so I think it's gunna stay and we'll see what happens.
 
US$0.02
The original specification for the Overdrive was a 30W Non-detergent motor oil.
If it is a non-overdrive transmission it probably would be better with the synthetic gear oil as far as oil shear strength. And it will coat the parts better, too.
However, I do not think the Overdrives work any better with the thicker oils. I have used Mobil 1 in my overdrives for so long I can't remember if it was 10W30 or 10W40 that I used. But I do know they worked better and more reliably once I made the switch from standard oil. However, it is easier to get RedLine synthetic now than it was back then, so I think I will check with them for a more appropriate oil.
Interesting on the Volvo info, though. My GLH Turbo 5-speed manual originally used Dexron, which is a synthetic ATF. (The old Type F was originally a castor bean based oil.)
C Ya,
Mark
 
Well, my '79 MGB that I bought new came across the ocean with Castrol 20W50 in it! & all I've ever done is change it occassionally & I have a little over 120,000 on the car - with no major repairs!! & when the service technician went over the car with me back in 1979, he said Castrol 20W50 in engine & trans, auto trans fluid in Zenith dashpot & 90wt in rear end.

I don't see any reason to use anything else & that's what I put in every car!

Why would anybody want to do something different from what the factory manual says?
 
Mr Autoist, you are asking an open ended question.

Modern improvements in chemistry, and metallurgy..

Instead of hylomar anymore, all I use is Permatex "The Right Stuff". Look at all the European auto manufacturers recommendations for Oil today. They are all using a synthetic...

And antifreeze formulations have improved remarkably over the last couple of decades.

Time marches on, and hopefully progress is progressing..
 
I agree, that's a question that can't be answered definitively. Yes, it's safe to use the manufacturer's specified lubricant, and yes huge improvements have been made in lubricants since these parts were in production. The problem is that there has been no research worth of notice into what type of modern lubricant is truly the best for these parts. Therefore, you take your chances that whatever you decide to substitute will actually work as well as what was originally used. Considering the specific nature of certain required chemicals and compounds within various lubricants such as gear and motor oils, I feel much safer using exactly what the manufacturer specified, or at least the next best thing.

That said, Castrol 20W-50 is the only lubricant that I know of which has been used extensively in place of 30W-ND and produced equal performance and longevity.
 
If that's the case, the Castrol 20W50 you get today isn't the old Castrol 20W50 of 30 years ago....so, by contining to use it in its new form, you're getting modern technology.
 
Ah, see that's where investigation involving chemicals, oil, etc. comes into play. Now we all know(or should know) that the API, in response to EPA requests lowered the ZDDP level in engine oils several years ago. Basically doing away with ZDDP in all oils graded SI. So it does take a little curiousity to find which oils, brake fluid, antifreeze, etc. are to be used today.

As you said the oils, etc. aren't the same as they were 30 years ago. Some are better, some aren't.
 
The zinc issue doesn't apply so much to use in gearboxes. Yes Castrol has modified its formulas over the years but the reformulations have been very slow, and the gearboxes using it are still holding up well and performing as they should. If you aren't comfortable with the newer formulas, you can always go back to 30W-ND.
 
exactly Steve, what I was trying to get across. Is that there is no "forever" constant when it comes to lubricants, fluids, etc.. As it applies to cars that are anywhere from 30-70 years old... Gotta use investigation and common sense..
Some times experimentation is helpful also..
 
RonMacPherson said:
exactly Steve, what I was trying to get across. Is that there is no "forever" constant when it comes to lubricants, fluids, etc.. As it applies to cars that are anywhere from 30-70 years old... Gotta use investigation and common sense..
Some times experimentation is helpful also..
Click to expand...
Still, that ha nothing do do with putting 90wt in a transmission that originally required whatever oil you used in the engine!
 
Ah, flyguy(retired). But it does. Common Sense.

Most people, I would hope, when told that the oil in their differential is not going to be the same as what the factory installed would do a little investigating and make the selection of what lubricant to use..

Common Sense...

Oh, have you seen the youtube by Thomas Paine on "common sense".? Interesting, but political.
 
Somewhere there exists a factory B/L TSB that discusses the merits of engine oil vs gear oil in an MGB gearbox. In fact, I think (I know) it's in a set of TSB literature that I sold to Tony last year.

:laugh:
 
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