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MG MGB Technical - Oil grade for Trans and O/D

Changed the transmission oil in our 79 LE with O/D, with 20/50 Castrol GTX as book recomends , however notice, it takes a little longer to engage. Am thinking it must be a little too heavy. Will replace with 10/40, as the old oil had probabley thinned out over the years. Previously the engagement was almost instant. Any thoughts on this. I am sure the old oil had never been changed.
Kim Rutherford.
K Rutherford

I have a '73 B with a '76 O/D transmission. This transmission has a side fill rather than the top dipstick arrangement. My manual always said to fill an O/D box with engine oil.

I was having trouble with mine being slow to engage and even slower to disengage for a long time. About 2 years ago, I had my clutch replaced by a local MG shop that has been in business for a long time and inquired about the O/D problem while they were changing the clutch.

The local shop recommended and then refilled my O/D box with EP90 saying that later MGB boxes with a SIDE FILL take EP 90 rather than engine oil and were designed that way. I was skeptical because I had always read that engine oil was the ONLY lube for an O/D box. I also have never seen a shop manual or owner's manual for a later model to know for sure.

The only thing I can say is that the change made my O/D work perfectly and it has been working perfectly for 2 years now. And I drive it all the time.

Others on the board may be able to contribute more information on this subject and I still have reservations about the use of EP90. But it works well in my car with no obvious bad effects so far...
Richard Smith

The reason for not using ep90 is that it has sulfur as an extreme pressure additive, and Sulphur attacks the brass synchro rings.

GL4 gear oils do not have sulphur.

I ran 1 guart gl4 and the rest Mercon III in my overdrive trans and it shifted and ran like a charm. I figure a gear oil is better for gears than an engine oil.

Barry
Barry Parkinson

Here is a link to Quantum Mechanics, John Esposito, who recommends 30 wt non detergent in the MGB overdrive.
http://www.quantumechanics.com/categories.php?op=newindex&catid=11
I just bought one of his rebuilt units and plan to follow his guidance.
Dennis
D F Sexton

Interesting test, I wonder why John didn't test 20W-50 oil that most MGB owners use? Dennis, does John recommend any specific brand of oil, it's very difficult to find a quality non detergent oil. A few days ago I changed my OD oil and used 20W-50 Castrol to refill. That is what was in it and I noted no difference in operation. No problems with the OD I changed the oil and dropped the sump to try stopping the filter/gasket from leaking.

Clifton
Clifton Gordon

My thoughts were that the old oil had sheared over time thus was thinner. I run 30 non detergent in our Healey BJ7, am leaning towards that for the B.
Thanks,
Kim Rutherford.
K Rutherford

Clifton, no brand is specified, but the installation instructions also say that if one lives in a hot climate 40 wt (non detergent) is also ok.
Dennis
D F Sexton

Have drained the 20/50 I put in the transmission and O/D and refilled it with 30 non detergent oil, as per quantumechanics recomendations. Seems to engage a lot faster, but can't help but think it was more positive with the old oil that had probabley been in since new.
I am not really sure just what is normal, should it be almost instant? In my Healey engagementof the O/D is very fast. I am happy with it, just like to hear other opinions.
Thanks,
Kim Rutherford.
K Rutherford

Mine works well with 30 weight non-detergent oil....Castrol do make this oil, but it's hard to find in most accessory shops..they can usuall order it and it's cheap.
My box hated 20/50...didn't work well at all....very slow to engage.
P J KELLY

I wonder if there is a difference in rebuilt overdrive internal parts compared to OE overdrives that have never been rebuilt? I have no problems with sluggish or rough shifting in/out with 20w-50 Castrol. To my knowledge my overdrive has not been rebuilt.

Clifton
Clifton Gordon

I agree with Clifton. My 1980 LE overdrive has not been rebuilt and the 20/50 allows smooth, quick and positive performance.

Chuck
Chuck Hassler

Our 79 LE is a 1 owner well looked after rust free car, low mileage, 50.000 miles, trans and O/D are OE according to the original owner. no explanation as to why with 20/50 oil engagement of the O/D was slow. However am going to stay with the status quo. Could be something internal in the O/D, that I don't know about.
Preformance car, no, but need the O/D for highway cruising, bought it for my wife and she is enjoying it. Have other cars with the LH overdrive, find they all have their own feel.
Kim R.
K Rutherford

I have to agree with Clifton as well. My 76B which I have owned for 5 years and was idle for the previous 6 years. I changed the oils before driving it. The transmission looked as if it had had a rebuild as it was fairly clean and seals looked newer, At any rate I changed front and rear seals and refilled with Castrol 20/50 and it shifts smoothly and engages rapidly and has never been a problem. fwiw.
Gil Price

Looking at the posts, it looks like no matter what anyone has put in the trans it works fine. Non detergent oil sounds fine, except that modernly that oil is cheap stock and not as good quality oil as used in premium detergent oil. The ep additives for valve train wear in a good motor oil are needed to protect the ball and roller bearings. The shear strength characteristics of better oil are also probably superior.

My question is why did the factory spec. motor oil?

Transmissions have a shearing effect on oil that you don't get nearly as much in an engine.

The Mini with the engine/trans combined sump reportedly had less engine oil life and engine lube probles with delayed oil changes because of this effect. Gear oils are specifically designed to resist this breakdown. The detergents designed to keep carbon in suspension, and the viscosity improvers to get the multi grade rating all detract from the long term strength of the oil.

Other than keeping sulfer out to protect the synchros, it appears to be an inappropriate specification. However, it appears the transmissions are very reliable with the specified lube.

The roller/needle and ball bearings and gear teeth are not categorically different than transmissions commonly used in the industry at that time by other manufacturers. The 60's and 70's Datsun/Nissan transmissions were virtual BMC clones early on, and later continued to use the same style synchros and general design. Datsun spec'd a GL4 oil for it's manual transmissions.

My belief is that the factory decided the 20/50 stuff worked good enuf. If they had spec'd gear oil someone sure as h-- would put 90 hi sulfer in, instead of the 80 gl4 lube. The 80 gl4 lube is probably a problem with the radial gears and band clutch of the overdrive. So then you would need to spec one type of oil for the overdrive and one for the 4 speed trans.
Just simpler to spec the 20-50.

My speculation and ruminations on this shifty subject.
Barry Parkinson

Hi Folks:

The prime issue is using multi-grade oils in high pressure(400 psi+)hydraulic systems. Multigrades contain detergents, which cause foaming (air bubbles) in the system. The foaming affects the life of the cone clutch because air bubbles cause chatter & heat. I have seen cases where hydraulic valve lifters (Olds V8/V6)crashing due to foam.

In any event, use the 30 W non-detergent oil, also known as "compressor oil"

Rich Boris 67 B roadster
Rich Boris

Rich, Agree with you about foaming, it is my opinion that was my problem in our particular car. O/D engaged quickly when cold but was slow when hot. However, whatever works for your car.Thanks to all for responding.
KIm Rutherford.
K Rutherford

Looking at the 67 handbook, the spec was for engine oil and was 40 grade for tropical and temperate climates down to 5°C. For winter 30 grade was specified. Out of interest, there were 8 brands suggested and 3 were straight grades.

Duckhams made their name, partly, in the 60's for overcoming oil foaming in the Mini. (For those not familiar the Mini was a new breed with a common engine and gearbox oil supply.)

Today, 2 things cross my mind. First, the box was designed and has survived with those oils in mind. Second, most oils today should be low foam as this problem has been around for 40 years so a low API spec engine oil (no friction modifiers or sulphur) should be fine.

Rich

Mine very well not have EP90 but a 90W gear oil instead. Like I have said, it works fine and shifting the gearbox is fine, even in very cold weather. And it's seen over 2 years of regular driving and engages and disengages fine.

Unlike K. Rutherford, with 20-50 mine was only slightly sluggish to engage but was EXTREMELY slow on disengagement - I've driven as far as 2-3 miles before disengagement.

Since my shop specifically stated to me that the sidefill gearboxes and O/D's were designed to use 90 wt., can someone check the owner's manual for a '76 or later and see what the owner's manual actually says to use?

K Rutherford, do you have the ORGINAL (not a reprint) owner's manual for your car? I am specifically asking for the original manual because I do have the original owner's manual fro my '73 and the wiring diagram in the back is unlike ANY wiring diagram in either Haynes or Bentley's. And it matches my car perfectly. So I know there are indeed differences and the oil recommendations may be different as well.

Richard Smith

Richard S,
All I have is the original drivers handbook that came with the car. On page 83 is the Lubrication Chart, which states for the gearbox, use the same oil as selected for the engine. Went out today and drove 200 miles, with the 30 non detergent it works well but is not as good as before I drained the old oil out.
Have Haynes and Bentley only. Am going to email the MG Owners Club in the UK, our car club is a member and get their opinion from their Tech Dept.
Kim R.
K Rutherford

Richard,
Have dug out the Complete Official MGB Handbook 1975-1980 by Bentley, which they say comprises the official Drivers hand book and the workshop manual, and they state on page 73 that SAE 90 Hypoid oil is suitable for use in the gearbox, with or without overdrive! Adding any old oil should be thoroughly drained before Hypoid oil is added.
Kim R.
K Rutherford

A little care might be needed here. My original BMC handbook (1964 printing for the MK1 cars) clearly only references SAE 90 E.P. for the steering rack and rear axle, conditions down to -10F.

For the "engine, gearbox, oilcan (?) and carbureters" eight oils were specifically recommended, three multi-grades - Shell X multigrade 10W/30, Filtrate 10W/30 Multigrade and Esso Extra Motor Oil 20W/30*.

The remaining five were BO Energol Visco-static, Sternol Multiplic (spelling correct), Duckham's Q.5500, Castrol Castrolite* and Mobiloil Special.

In both cases of *, in temps below -12C (10F) SAE 10W/30 should be substituted.

Approval was also given to "Duckham's Q 20-50, BP Viscostatic 'Longlife' oil and to monograde or single-viscosity lubricants" supplied by companies on the Specifically recommended list.

This differs from the material in Rich's handbook mentioned above. I imagine that oils were evolving, companies coming and going over the production life of the B.

However, I think it is important to distinguish between primary and secondary sources of information.

Regards
Roger
Roger T

To All,

Thanks for checking into your sources. It seems that the jury is still out on EP90 vs. 20-50 engine oil. In particular:

"Have dug out the Complete Official MGB Handbook 1975-1980 by Bentley, which they say comprises the official Drivers hand book and the workshop manual, and they state on page 73 that SAE 90 Hypoid oil is suitable for use in the gearbox, with or without overdrive! Adding any old oil should be thoroughly drained before Hypoid oil is added."

For Roger T.

The whole issue revolves around late model gearboxes and O/D's. And my shop distinguishes between the late and early gearboxes by the position of the oil filler on the gearbox. Early models (like my orginal '73 gearbox) have the oil filler on the top, accessible through the tunnel from inside the car. Later models (like my current gearbox and O/D form '76) have the oil filler on the side and cannot be accessed from the interior of the car - only from underneath.
Richard Smith

My 1979 MGB Driver's Handbook says to use the same oil selected for engine. For the engine it says "Use a well known brand of oil to ..... quality, with a viscosity band spanning the temperature range of your locality".

I rarely drove it in the winter so was Castol 20w/50 for the engine & tranny. The overdrive always engaged & disengaged satisfactorily.
Carl Floyd

Should have checked the filter in the O/D, however have now done that, and to my surprise found it clean, had bought a new one so installed it. Refilled the trans with 30 non detergent. Seems to work OK now.
Kim R.







K Rutherford

This thread was discussed between 16/07/2005 and 28/07/2005

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