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MG MGB Technical - gearbox oil

HI!
I would like to change the gearbox oil in my 1964 MGB (3 synchro manual, no OD) and I wonder which oil I should use. The owner’s manual says 20x50 same as engine oil and so does my Haynes manual. However my mechanic friend says it seems odd.
What do you think ?

Thanks for your help

Jaypee
JPR ROUDEIX

Use 20/50, I queried this & The MGB Hive confirmed it (& they would know!)
Pat Gregory

Absolutely correct - the gearbox uses the same oil as the engine - not only 20/50, 10/40 is also recommended by the factory manual (as is 20/40 and 10/50 but they are pretty rare oils) for all temperatures above 10 degrees Fahrenheit.
Chris at Octarine Services

trust the Driver's Handbook (more so than Haynes too)
Nigel Atkins

JPR-
20W/50 is the right stuff. However, be warned that you shouldn't use synthetic oil in the transmission. It's so good at reducing friction that it'll interfere with the action of the synchro rings (baulk rings).
Stephen Strange

Interesting thought Steve - where do you get that from? Synthetic and semi synthetic are actually recommended for Ford type 9 boxes.

I have never had issues with synchromesh when using synthetics and personally use Comma 75W/90 semi synthetic in all my own cars including the OD one.
Chris at Octarine Services

Heres another one for the pot. I used the 20/50 Trans oil specified for Minis etc with transmission in the sump and immediately had problems with Overdrive slip, not with synchro. Changed to Penrite 30 and all is well again. Now done many miloes with no further trouble.

Jim
jim soutar

FWIW I have been told that the viscosity enhancers in normal motor oil shear down quickly when used in a gearbox. I tried some synthetics in mine and the syncro action seemed a little weak. I have since switched to RedLine MTL and have been quite pleased. I called RedLine and explained to them that I have an MGB with overdrive transmission and they seemed familiar and this is the product they recommended.
Rob Edwards

Jaypee - I use 20/50 in mine.

A couple of months ago, Auchan were selling Elf 20/50, 5 litres for 16€ with a 1 litre top-up 'bottle' gratuit, so I bought some in anticipation. I'll be doing the job this week.

In the winter I use any good 15/40 in the engine.
John Bilham

I think the gearbox and diff oils should be changed after x number of years (you decide what x equals) and these are forgotten about, even checking the levels at services isn't done by many

as already mentioned if engine oil is used in the gearbox it probably needs changing a little more frequently that gear oil

I'm all for fully synthetic oils (most that say they are aren't truly anyway) but it might depend on how badly worn the gearbox is already

I used modern synthetic oils that also covered a range that went thinner (i.e. 75w-90 in diff) in engine, g/box and engine and there was a decrease in power loss to the rear wheels when it went on the rollers

the engine oil wasn't a success (Mobil 1 0w-40) so I bought the last of the Mobil 15w-50 but I think Mobil 1 might just be a bit too thin nowadays (I used to use it in my previous MGs 15+ years ago with no problems) so I'm now going to use Mobil 1 10w-60 as recommended by Daniel and someone else confirm that after some mileage use the Mobil 1 10w-60 tested within the 50 range so so more of a thick 50 than thin 60

a mate uses 10w-40 Castrol Magnatec all year round in his modified Marina engined Spridget without problems

for the diff I use fully synthetics Castrol Syntrax Longlife 75W-90 (GL-5 spec) or Mobilube 1 SHC 75W-90 (GL-5 spec)


Nigel Atkins

Chris-
The best petroleum-based oil for the B Series engine of an MGB is Castrol XL 20W/50, while the best synthetic oil is Mobil 1 15W/50. I use the former in my transmission and the latter in my engine. Why do I not use the less expensive Castrol in my engine? Simple: most of the wear that takes place in an engine occurs during the warm-up period because the oil is too thick to flow easily. Once the engine gets up to operating temperature, the oil flows freely and does its job outstandingly well. The Mobil 1 synthetic oil flows just as well when it is cold as it does when it is hot. It also does not thin out at high temperatures, which is a serious plus in an engine that has been modified for higher power output. Why do I not use Mobil 1 in my transmission? Because the baulk rings (synchro rings) of the transmission require a certain amount of friction in order to perform their function properly, so it seems to shift a bit better with the Castrol petroleum-based oil, and the sliding annular clutch (conical clutch) of the Overdrive unit does not try to slip as it does when filled with the super-slick Mobil 1.
Stephen Strange

Steven,
I don't know if it was what was meant but Chris referring to gear oils (to GL4 spec for g/box I'd guess), he may have been also meant semi and full synthetic engine oil in the g/box too

Chris suggests different colour oils so that you can tell which oil is leaking from where (as if a MG would leak)

of course the use of the word synthetic was widen to include synthetic-ish oils hence semi-blends

we can't get Mobil 1 Motorsport 15w-50 in the UK anymore other than old stock

is there any proof that says a synthetic(ish) engine oil like say Mobil 1 is bad for the g/box and or o/d?

I found to my cost that Mobilube 1 SHC 75W-90 (fully synthetic-ish?) was once specified for a Ford Type-9 g/box but they then changed their minds

however in my Ford Type-9 g/box I use Castrol Syntrans Multivehicle 75W-90 Fully Synthetic(ish) MTF which is GL-4, it's the GL-5 spec that seems to be the hang up with g/boxes but GL-5 has been fine for r/axle for many years

Chris,
my Ford Type-9 gearbox had Comma semi 75/90 but after the oil had been in for two years I swapped to the full synthetic(ish) in a warm April and although the Comma oil was only 2 years old so not that worn the fully synthetic(ish) gave me instantly better gear changes and that was not being able to siphon change all of it
Nigel Atkins

In my view the use of synthetic & semi synthetic oils in the engine is a waste of money - the oil needs changing every 3000 miles for good engine life - you just don't get the benefits - use the cheapest oil and change it often.

The gearbox does not need the additive package of engine oil so I use a specific gear oil of the same weight - here the extended life of the synthetics is useful and worth the extra expense.

Yes - GL4 spec not GL5, the latter is not safe with bronze found in the MG gearbox.
Chris at Octarine Services

Nigel-
Proof? I found that Mobil 1 synthetic reduces friction so well that it interfered with the ability of my synchro rings (baulk rings) to make smooth shifts and caused the sliding annular clutch (conical clutch) in my Overdrive to slip. That's why I went back to Castrol's petroleum-based XL 20W/50 oil.

Chris-
Perhaps synthetic oils are outrageously expensive in the UK, but over here the improvement in fuel economy resulting from the reduction in friction usually covers its higher cost. I know that such conditions in the UK are milder, but our winters can be quite cold, with temperatures well below 0 degrees Fahrenheit (17 degrees Celsius) at night and occasionally during the day as well, so synthetic's ability to flow well at such low temperatures is a definite plus for engine life. Our summers can be very hot (yesterday it hit 105 degrees Fahrenheit (40.6 degrees Celsius) in out nation's capitol), so the synthetic's resistance to thinning out when running hard under summer conditions is also a plus. On this side of the pond we find that it's cheaper to use a more expensive grade of oil that it is to rebuild a worn engine (presuming, of course, that you can still find a competent machine shop). Engine rebuilding over here is so ridiculously expensive that you can rebuild and pay to ship an engine to the USA and still have an easily competitive price. I must agree with you about changing oil frequently. I also agree that GL4 is sufficient for a gearbox, but only if it doesn't have an Overdrive paired with it. The additives in the engine oil helps keep the passageways in the Overdrive clear, although this does mean checking as well as possibly removing and cleaning the filter screen regularly.
Stephen Strange

I'm more for thorough oil changes and good oil, get it as hot as possible and leave to drain as long as possible

thorough changes with cheap oil every 3k-miles would work too but at least once I think the extra heat capabilities of Mobil 1 has helped when with my previous Spridget I lost a coolant hose and had to drive home forgetting the short way also involved a steep 30 mph road with speed camera so everyone went 25 mph up the steep hill and this was before hitting the duals with roundabouts and traffic lights, the engine was very hot when I got home, I lifted bonnet and left the oil filler cap off, didn't smell too good and I guessed I'd lost the HG, next day I replaced the hose and topped up the long-life coolant and thought I'd see how the car went, no HGF, so later I done a thorough oil and filter change and the car was fine, I believe (no proof of course) the Mobil helped

when I was running the engine in on my present midget I can't remember how many oil changes I done for the first 2k miles but it was a good few, then on to 6 monthly changes which was around an average of 3-4k miles using Halfords Classic 20w/50 mineral or Castrol XL 20w/50 mineral

but as a lot of those changes can be at roadside (not public road of course) in uncertain weather they're not for me as I get older, fatter and lots more joint problems so I'm for thorough annual changes now using synthetic(ish) Mobil 1 as I used to do tens of thousands of miles in my previous MGs and other classics and moderns on annual changes of Mobil 1 (after running-in using frequent/regular mineral oil changes)

a couple of 660cc turbo Jap cars required 3 months/3k miles engine oil changes and at least one of them required semi-synthetic (I'd guess both) and they were done on the dot

ETA: Steven I don't (and can't) doubt your experience I just wondered if you'd seen anything written down anywhere for me to reference to
Nigel Atkins

Nigel-
If you want some form of documentation, I can only point you to the archives of this website. The subject has come up from time to time, and there have been contributors who have found that synthetic oils do have definite advantages in specific applications. As I recall, I'm not the only person to ever mention synchro ring (baulk ring) and slipping Overdrive problems when using synthetic oil.
Stephen Strange

Stephen,
(sorry I keep forgetting to check the spelling of your name and then run out of editing time to alter when I notice)

you've reminded me one of the reasons I tried 0w-40 in the engine was because two winters ago (and last) we actually had sustained very cold weather in winter that we hadn't seen for the previous 20 years and it was almost record cold in some places so my Midget was sluggish to start that winter with mineral 20w/50

as I put earlier the Mobil 1 0w-40 synthetic(ish) along with (different) 75w-90 fully synthetic(ish) oils in the g/box and diff cut the mechanical drag to improve performance (which includes mpg but I very rarely check mpg)

figures for 2012 from the weather station 3 miles from me and we're in a generally mild location-

Air Temperatures (2012):
The Highest Maximum: 28.9 C on 19th August
The Lowest Maximum: 0.1 C on 8th February
The Highest Minimum: 17.1 C on 18th August
The Lowest Minimum: -13.0 C on 11th February

this will surprise some in the UK -
No. of days without sunshine 2012: 80 (so 285 days with some sunshine, many in winter)

Days with (2012):
Thunder: 5
Hail <5mm: 6
Hail >/=5mm: 0
Snow or snow & rain: 7
Snow lying: 11
Fog: 23
Air Frost: 35

(note only 11 days of snow lying and 35 days of frost in a bad winter too, not as bad as this winter though)

UK weather depends on where the Jet Stream goes, locally 2012 was the wettest year for Northampton since 1880 yet 2011 was the the driest year locally since 1921

so far in 2013 locally we've had -7.6C to 29.5C and -
Snow or snow & rain : 32 days
Snow lying: 28 days
Fog: 10 days
Air Frost: 56 days
Duration of Air Frost: 338 hrs

back more directly to cars -
when I had a Rover 3.5 V8 engine reconditioned properly about 15+ years ago IIRC for around the same sort of money (or was it less?) I could have had a new crated 5.3 Chevy engine delivered, I doubt if that's changed but Chris would know better and more about it than me
Nigel Atkins

"I have since switched to RedLine MTL and have been quite pleased. I called RedLine and explained to them that I have an MGB with overdrive transmission and they seemed familiar and this is the product they recommended."

To paraphrase: "Well they would say that, wouldn't they?"
Paul Hunt

Thanks for your help, I will use Elf 20x50 whis is relatively cheap and easily available in this country
Jaypee
JPR ROUDEIX

Jaypee,
get the existing oil as hot as possible and leave to drain for as long as possible

careful on the refill as it's easy to overfill which you don't want better to under fill and carefully top up a little each time until it's full

you can compare the oil to the new to see how much service it might have done and based on this you may want to change the oil again in 3-5 years time

check level at services and top up as required

I do the same change for the diff, easy and cheap to do and for some cars it's a very rare event, even checking the level is unknown

good luck, your car will be the better for it and you'll known when it was last done for certain
Nigel Atkins

The gearbox oil change period for these boxes is every 24,000 miles or every 24 months whichever comes first,A.T
andy tilney

well done AT, thanks

for some reason I thought it was 36k-miles/3 years and being realistic allowed more makes sense at 24

I think I have been reminded before but forgot again, doubt I'll remember now again but who knows I might
Nigel Atkins

>To paraphrase: "Well they would say that, wouldn't they?"

They could have recommended any one of their products, but that was the one they specified.
Rob Edwards

Again, they would, wouldn't they!
Paul Hunt

Hi Paul, err.... depends what you mean.

>they would, wouldn't they!
Pick the product from their portfolio best suited to the application? Certainly. At least one would hope so.

>they would, wouldn't they!
Pick "Manual Transmission Lubricant" (MTL) for a manual transmission? Not necessarily -- they also make MT90 which is a 90-wt gear lube without EP additives for manual transmissions (GL-4, I think that would make it). But they knew what an LH overdrive is and picked MTL over MT90.

>they would, wouldn't they!
Recommend their own product?
Of course, it's absurd to think they wouldn't. ;-)

The point I was making was the second....
Rob Edwards

The point is, anyone with something to sell will almost always recommend one of their products, regardless of whether it is better or worse than anything else. One can only hope that they *would* sell you a product that was least worst, and not the most expensive.

I've never found any need to use anything other than the engine oil for the 4-cylinder, or the gear oil for the roadster, as recommended by the factory.

It should be noted that many years ago my son said his ambition was to be as cynical as me.
Paul Hunt

I wonder what the factory would recommend for the cars if they were being manufactured today - the current range of oils were not available then.
Chris at Octarine Services

Chris, didn't you post on your site that, when you visited the present owners of the Laycock De Normanville tooling, that they said the OD units could be run on anything from ATF to 90W? I've been running non-detergent 30 weight oil, in my Black Label OD, for over two years at the advice of an OD re-builder here in the states. He claimed that all of the oils he tested produced exceedingly high pressures or foamed and caused engagment/disengagment problems. I have to admit that after installing the non-detergent oil, the transmission shifts much easier and the performance of the OD unit is a lot crisper. RAY
rjm RAY

Well the V8 (with a very similar gearbox) did not use 20/50 and (to boot) most of our gearboxes are now quite elderly.
Time for a rethink?
Roger W

I don't recall reading too many problems with failed MGB gearbox/overdrive units using the factory-recommended lubricants.
John Bilham

Ray, yes and the person who told me that was an original employee of Laycock.

I use ATF as a flush and clean lubricant in gearboxes and it certainly shifts a lot of grime out of the average gearbox - OD or non OD.

But since many oil companies now produce specific manual transmission lubricants I see nothing wrong in using them instead of the 40 year old factory recommended oil.

I can't imagine you get much foaming with ATF - it is designed to work in auto boxes using much the same mechanism as the OD.

There is no need for the detergent package of engine oils when used in the gearbox and I do wonder if the original factory spec was one of keep things simple by using just one oil in the gearbox & engine - after all the Mini, 1100, Allegro, 1800 etc. were forced to do just that!

John, there are many common failures in the MGB box - mainly the layshaft & bearings - I wonder whether they would be better protected with a synthetic transmission oil.

However it is such a tough old bird that it will soldier on for ages while gently chewing itself to bits inside!
Chris at Octarine Services

Chris et al,
That's my thinking as well -- engine oil might be "good enough", but it is obviously optimized for entirely different conditions than it encounters in a gearbox. There's no blowby and exhaust products to deal with, very little water so reduced need for acid control additives, and no fuel at all. What a gearbox does have is lots of sliding contact between gear teeth that (as I understand) tend to shear down the viscosity improvers. So now that products optimized for this specific application are available, why not use them??
Rob Edwards

I believe that we've run into a conundrum. The lubricants that assist the synchros in shifting aggravate the engagement of the OD contact materials. RAY
rjm RAY

"I wonder what the factory would recommend for the cars if they were being manufactured today - the current range of oils were not available then."

A perfectly valid wonder, but have there been any problems with the oils they *did* recommend? I think it would be common knowledge by now if they had.
Paul Hunt

As I said above - there ARE problems with wear in the MGB gearbox - the needle roller bearings on the layshaft, especially the front end, and on the nose of the mainshaft, in particular.

Chris at Octarine Services

when I get a chance (and if I remember) I'll try to get some info from the oil companies but when I've contacted them before they've usually replied to use the oil specified by the car manufacturer or it goes to a customer service department that doesn't deal with technical matters, however I did get one reply from Norway or somewhere like that that was very informative but it did take quite a while for each response
Nigel Atkins

Chris - thanks, I happily bow to your superior knowledge. I wonder if the wear is sometimes caused by owners not bothering to change the oil because of the 'difficulty' of doing it?

Trouble is, I drained the gearbox a couple of days ago, and now I'm really not sure what to put in it!

However, since it gets changed regularly I'll put 20/50 in for now, it's cheap enough if I decide to upgrade - and if I can decide what to upgrade to - after reading this thread.
John Bilham

>>I wonder if the wear is sometimes caused by owners not bothering to change the oil because of the 'difficulty' of doing it?<<
plus some don't even check the level for many, many years so it very doubtful they'd consider changing the oil until they found the level is low by which time any oil would probably be years passed it's best

I know the B is slightly more difficult to change than on the Spridgets but every 24k-mils/24 months doesn't seem over onerous or expensive
Nigel Atkins

see - http://medias.ina.com/medias/en!hp.tg.cat/tg_hr*ST4_1652077067

extract -

Pressure properties
and anti-wear additives


If the bearings are subjected to high loads or if the operating viscosity ν is less than the reference viscosity ν1, oils with anti-wear additives (type P to DIN 51 502) should be used.

Such oils are also necessary for rolling bearings with a substantial proportion of sliding contact (for example bearings with line contact)

These additives form boundary layers to reduce the harmful effects of metallic contact occurring at various areas (wear).

The suitability of these additives varies and is normally heavily dependent on temperature. Their effectiveness can only be assessed by means of testing in the rolling bearing (for example on our test rig FE8 to DIN 51 819).
Chris at Octarine Services

Just another thought - the V8 gearbox was essentially the same unit as the MGB and that specified an EP 90 weight oil - so clearly EP gear oil IS recommended by the factory - I leave it up to you to decide whether the additional protection of an EP gear oil is worthwhile in your gearbox ....
Chris at Octarine Services

If you decide to go with 90W oil, look for GL-4 rather than the current standard GL-5. GL-5 has a high level of sulfur which attacks brass and bronze components. RAY
rjm RAY

this is what I've got in my Ford Type-9 box and it improves the shifts

(GL-4) Castrol Syntrans Multivehicle 75W-90 Fully Synthetic MTF - http://www.opieoils.co.uk/p-739-castrol-syntrans-multivehicle-75w-90-fully-synthetic-mtf-replaces-smx-s-75w-85.aspx

Nigel Atkins

Nigel - we have the same in our LT77 - the OE1800 has EP 90. I shall bear Ray's advice in mind. FWIW the MG box feels as good as new
Roger W

I have to confess that in a senior moment last year I did top up my (20/50) gearbox with EP. It wasn't a lot, just a couple of good squirts from the bottle, but it was taking us on holiday later the same week, so I just thought, what the heck...
John Bilham

John, many years ago, I too had a senior moment. I was servicing my car and drained the 20W50 transmission oil I was using at the time and replaced it, by accident, with 90W. for the life of me, I couldn't figure out why the transmission had become so difficult to shift, especially when cold. It finally dawned on me that I had used 90w oil instead of the 20W50. After draining it out and putting back in the 20W50, all was back to normal. No good deed goes unpunished. RAY
rjm RAY

Roger,
IIRC the LT 5-speed boxes varied in their oil requirement and suggestions going back a bit so this is a story like Peyton Place (not that I know about that)
Nigel Atkins

Roger,
IIRC the LT 5-speed boxes varied in their oil requirement and suggestions going back a bit so this is a story like Peyton Place (not that I know about that)

I'm happy with fully synthetic(-ish) Castrol over the semi-synthetic Comma

a mate reckoned Comma was reclaimed oil from garages - and he wasn't joking
Nigel Atkins

I'm sure the contributors to this thread know this already, but for anyone else who doesn't, here's an aid to gearbox filling - the 14mm female/female copper elbow fits tight in the garden hose, and avoids any kinking where it enters the box.

After the initially filling, I left the job for a couple of hours to let the oil find its own level, so no need to top up from a bottle in a couple of days' time.


John Bilham

I've refilled mine from the footwell, for both top-fill and side-fill boxes, which needs a much shorter tube which drains quicker. Like the engine it has to be run and checked again, and overdrive boxes in particular drop more than an engine will. It needs to be run with OD in and out, and because it drops so much I didn't want to take it out so I jacked up one rear wheel with appropriate precautions and ran it that way. On one of the cars the drop in level was enough to make OD drift in and out instead of staying in, until topped up.
Paul Hunt

I have a grommet in the top of the gearbox tunnel, but it looks like I have to remove the centre console etc to access it, so I take the easy way out. The oil ran in ok (well over 3 litres), and drained quickly, it was over 30 deg in the garage.

However, reading your post, I will run it up - with appropriate precautions!
John Bilham

John,
be careful not to overfill, easier to add a little bit more if required

not that it matters but did you mean 15mm
Nigel Atkins

Nigel - Thanks, due to the design of our old French outbuildings I can walk around under the car without any problems, so after any topping up I just leave the filler plug out till it stops dripping (the car's on the level), then go down and refit the plug. I made the B's garage floor with removable panels the length of the car.

Metric pipe here goes up on even numbers, 10, 12, 14 etc, and a female 14 is just about 16mm externally, so is a tight fit in nominally 16mm hose.

Bizarrely, until recently many non-copper fittings here were in imperial - I've got quite a few old bits stamped, for example, 1/2", one was even stamped 5/4".
John Bilham

Not so bizarre, they do use BSP threads on brass fittings, they have different numbers, but they are still British Standard Pipe, sorry for being a geek.
john wright

John - what year is yours? My 73 and 75 have the rubber bung visible and accessible from the drivers footwell, between the rear edge of the console and the front of the heater surround, once the strip of tunnel carpet is pulled back.

You can also see the access point for Tom's Knob (he must have been a contortionist ...)


Paul Hunt

John,
I did wonder if 14mm might be used over there but thought as we'd here we'd swapped many years ago from 1/2" copper pipes to 15mm it'd be because 15mm was standard, silly me to think things would be that logical

Nigel Atkins

Paul - mine's a '77, and I've just been down to have a look from below. The bung is immediately above and between the filler and drain plugs, so I'm guessing in the same place as yours - could it really be anywhere else? - so a bit more accessible than it looks from below. What's left of Tom's knob is just in front of it.

Since I've had the car I've always thought that if I'm going to spill some oil I'd rather spill it in the engine bay!

I'll have a poke around tomorrow.
John Bilham

Paul - I can't access the bung without moving my console forward, so running the hose down from the engine compartment is quicker and easier for me.
John Bilham

OK, 77 and later console different then.
Paul Hunt

BTW, are you RHD or North American spec LHD?
Paul Hunt

Paul - North American spec LHD.
John Bilham

This thread was discussed between 20/07/2013 and 30/07/2013

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