MG-Cars.info

Welcome to our Site for MG, Triumph and Austin-Healey Car Information.

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB Technical - Rear differential leaking

I enjoy driving my 1978 MGB but have no technical know-how. I leave that to a British car specialist, who does whatever the car needs every spring. The problem is that he's rather far away, so for small things during the year I'll go to a local shop.

I needed a bracket repair for the exhaust system, so I went to Mr. Tire. Of course they found other stuff when they were poking around, including an oil leak (no kidding).

They showed me a "wet" rear differential and said it's leaking. I've noticed nothing on the garage floor ever, not even oil.

If it's possible to give this type of advice over the internet, I'd appreciate it. Can this wait till next spring for the specialist to look at? I drive the car once a week without problems.

Thanks.

Bob






Bob Meyer

Bob,
well what a coincidence, I was just about to put up a thread on the Midget and Sprite technical forum on diff oil

yes it can wait

you might have a leak on your diff or it might just be weeps and blow off from over filling

I've changed my diff oil 6 times in the last eight years and only this last time I have I not overfilled

it's so easy to overfill as it's difficult to see when you're just at below the filler hole and the overfilled oil will run out so slowly that if you're like me you'll replace the filler plug before the oil has finally stopped very slowly dripping out

until this last change I've had oil covering the back plate of the axle

changing the diff oil is often overlooked, the workshop manual doesn't give a period for changing but I'd recommend every 3-5 years for mineral oil but longer if using synthetic oil

I's strongly you ask for a thorough change of diff oil and replacing with Mobil Mobilube 1 SHC 75w-90 (the subject of my thread) as it will help your diff and might help keep your axle dryer
Nigel Atkins

Bob,

The leak won't hurt anything as long as you don't run it low on oil. It might be worth having the oil level checked. Sounds like it doesn't leak much if it is not showing on the garage floor.

If I were a cynic, I could suggest they put the oil there. That makes it an easy fix for them. Once a quickie shop told my mother she needed new rear brakes. This was two weeks after a reputable shop had replaced the rear brakes.

Is the leak from the driveshaft input, from the back of the diff, or from outboard by the wheels?

I advise strongly against letting Mr. Tire mess with anything other than the simple rear cover gasket. If they try to put a front seal in it, and don't understand it, they could easily do some serious damage.

Charley
C R Huff

good point about checking the level of oil and I must admit I was only thinking of the oil being on the rear cover or from the vent
Nigel Atkins

If there are no oil drops on the garage floor then the leak (if it's there at all) is very small. Just drive and enjoy. But if work does need doing, find someone in your area who has some knowledge of this type of vehicle. The average tyre shop man knows absolutely nothing about them.
Mike Howlett

You can take your car to any local garage and have them put it up on a lift and check the differential oil level properly. If it's even close to full, don't worry about it. The proper oil is GL-4 80W90 gear oil. RAY
rjm RAY

"If there are no oil drops on the garage floor then the leak (if it's there at all) is very small"

...or very big!
Dave O'Neill 2

sorry I'm not doing well with my words today my last sentence of my first post should have read -
>>I'd recommend you ask for a thorough change of diff oil and replacing with Mobil Mobilube 1 SHC 75w-90 (the subject of my thread) as it will help your diff and might help keep your axle dryer


Mobilube is a GL5 spec but GL5 is considered fine for use in diffs

over here for many years now if you ask for 80w90 you'll generally be given a GL5 product, even the Heritage range that is sold specifically for our cars

originally mineral EP90 would have went in Bs but oils have moved on a bit in nearly 50 years

oils, always a subject of debate

a link to (UK) info about Mobilube - http://www.mobil.co.uk/UK-English-LCW/heavydutyoils_products_transmission_mobilube-1-shc-75w90.aspx

shouldn't that dog be tucked up in the glove box?
Nigel Atkins

Keep checking the level. When I first got my roadster it had a damp diff, no drips on the garage floor, but the level was fine. Not long after I was out one day when it started whining - no oil! It must have been losing it, somehow, in such a way as not to drip when parked.

In my case it was the cover gasket, so a relatively easy fix. The pinion oil seal is a quite different proposition, whoever does that has to be very careful when retightening the pinion nut or they can ruin the collapsible spacer on the pinion shaft. The book recommends doing it to torque, but practical advice is to mark the relative positions of the flange, nut and shaft, refit the flange in its original position, and retighten the nut to the same position.
Paul Hunt

Thanks everyone for the advice. Have a good weekend. Bob
Bob Meyer

Not unusual to have oil weeping from the either of the dif plugs. They are BSP taper plugs and need to be screwed in tight, even then they tend to weep. If you change the oil put some non setting thread seal on the drain plug and some PTFE tape on the filler/level plug. Check that the breather isn't blocked. When you fill or top up with the rear end jacked up, put oil in so you can get your pinky wet through the hole then lower the car (remove finger first!) with a container under the dif and leave till it stops dripping.
Allan Reeling

GL5 gear oil has a very high sulfur content which can attack the bronze thrust washers in the differential. GL4 does not. I experienced the same problem when I first purchased my B as Paul described. The rear axle was quite noisy and it turned out to have leaked all of its oil out past the pinion seal. The case hardening had been worn off of the surfaces of the ring and pinion gears making them extremely loud. I drove the car this way for two years before acquiring a spare rear axle. If you use synthetic oil, it should last the life of the car. Most large truck manufacturers, in the US, will warranty a manual transmission for 300,000 miles if synthetic oil is used from the start. RAY
rjm RAY

it's considered that GL5 doesn't get warm enough in the diff to cause problems

whereas the g/box it's considered does get hot enough for GL5 to possibly cause problems

as I put 80w90 sold for quite a while is GL5

also of course it's as much about the contents and make up of the oil as its spec grading

I've been using GL5 in the diff of my Midget for 7 years and tens of thousands of miles, I've changed the oil 6 times and never seen anything in the oil that came out, the loud diff whine that I had when I got the car has now gone

you could put that down to the frequency of oil changes or the current use of Mobilube or a combination of both
Nigel Atkins

Nigel, that loud whine was probably due to a total loss of oil at some point. I can't understand why you deem it necessary to change your differential oil so often. I've owned my '67 B for over forty two years and have only changed the differential oil twice in all that time. Every seal and bearing in it are factory original. It's as quiet today as the day that I got the car. RAY
rjm RAY

I can't say what caused the whine as it was with the car when I got it, personally I didn't think it was that loud but a mechanic did

the first change of oils is what I do with any car I get and don't fully know the history of, after that it was circumstances at the times but as it's so cheap and easy why not, I done a few more changes to see what bits if any came out with the old oil

plus I wanted to try out different oils, moving on to Castrol Syntrax Longlife 75W-90 (synthetic) but I'd always meant to try the Mobilube so after two years of Castrol I moved on to Mobilube and now wished I'd used it from the start

I'll not change the Mobilube for 3-5 years as I'm settled with it

I've changed 'filled for life' components before, what life do they mean though the oil or the car's, the manufacturers didn't expect their cars to be around in 20 years time let alone 50 with the same oil

someone on here put that they had a diff whine and (IIRC) annual changes of (I guess mineral) diff oil got rid of it which prompted me to think my synthetic diff oil had been in two years so time to try Mobilube

oil change are good for the engine and gearbox so why not occasionally for the diff

I expect my car to be able to be driven in a spirited way when I want to and I expect the whole car to preform well, most classic owners accept a mediocre mechanical standard because they rarely drive their classics

they also don't get tio drive other good mechanical examples of their model to compare against so don't know how well their car could or should go

Nigel Atkins

ETA: obviously I don't include those that have owned their cars 42 years

but unless you drive other good mechanical examples you might lose track of where your car should be running wise

parts of my car are 41 years old but I only know the last 7 years of their history so I may be having to make up for previous abuse and lack of care, or not, I don't know so am more cautious than if I owned the car from new

I didn't intend to change the diff oil so often but I don't regret it other than as I say perhaps putting Mobilube in after the first two changes to fully flush any bits, crud and old oil out
Nigel Atkins

Nigel, nothing wrong with being too cautious with a car that you have very little history on. When I'm brought a vehicle, with no known history, I assume that very little maintenance has been done to the car over its lifetime. When I first went looking for my car, I must have looked at at least a hundred cars before deciding that they were all driven into the ground by their previous owners. The one that I finally purchased and still have to this very day, was just taken in on a trade for a VW. My friend, who was the dealer's service manager, called me up and told me about the car and what great condition it was in. I was skeptical even when he told me it was a one owner car and that the owner had received it as a Christmas present in '67. I went to the dealership that afternoon and was amazed to find the car in excellent shape including the original leather interior that the car still has to this day. I put $50 down as a deposit and later learned that three different people tried to purchase the car that afternoon. On another note, when you have a whine coming from your rear differential, it indicates that the case hardening has been worn off the surfaces of the ring and pinion gear faces due to being run with little or no lubricant. In the olden days, shady auto salesmen would add sawdust to the differential to quiet the gear noise. RAY
rjm RAY

well done on finding your car, my experience of buying cars is usually the opposite but then I do get bored after looking at only a few examples

I always recommend doing a 36k-mile service/check-up (plus a few other bits) on a car new to you

this took me years to learn and a lot of financial cost but I can't give the advice away, it's ignored and considered over the top

if my diff was worn then according to 'pub/internet' wisdom me using GL5 oils should have make thing worse not better, and I've had (like many others but they may not realise it) mineral GL5 oils in the diff for a number of years and the last two years at least GL5 synthetic

as I actually use my car I keep expecting the diff to exploded because of my poor choices of diff oil - I will report when that happens

I remember being told years ago my classics' engines would fall apart with the use of unleaded petrol and certainly if using Mobil 1 engine oil, usually by people who rarely used there classics

now we had the fad for ZDDPZZTop and the extreme worry of ethanol over here, again mainly by those that rarely drive their classics

what they should be concerned about is the p*ss poor quality of some modern parts but that doesn't matter some much on unused classics
Nigel Atkins

The only thing that GL5 would negatively affect is the bronze thrust washers. It would have no effect on the ring and pinion or the bearings which are made from hardened steel. The whine, being caused by the loss of case hardening from the face of the gear teeth, won't adversely lower the life of the gears. It only adds to the noise that's introduced into the cabin of the car. Your differential won't explode while using synthetic oils, just the opposite. Also, the use of unleaded fuels will only have an adverse effect on the exhaust valves and the seat area of the cylinder head. RAY
rjm RAY

It's usually putting gear oil in the gearbox of an MGB that people say is wrong - the sulphur damaging components, even though the V8 has always had gear oil specified. I've not heard of gear oil damaging diffs for the same reason, but it may well through inadequate cushioning, as diff oil should be used. Diff oil shouldn't be used in gearboxes, of course. An axle will whine for ever, you will fail before it does.

Some states in America have had E10 ethanol since the mid-70s, but a straw poll reports no adverse effects on MGBs. However problems with garden equipment like mowers and chainsaws not used over winter for long periods have been reported by some, but then others specifically state they haven't had problems with equipment and conditions like that. I doubt anyone here has seen E10 yet, oil companies have stated that they have no plans to introduce it as they can meet their statutory requirements for renewables purely through the sales of bio diesel - at the moment.

As far as ZDDP goes there are any number of enthusiast web sites claiming problems with low ZDDP oils in 'flat tappet' engines, and a pal had to have his cam and followers replaced only 20k after restoration, by the garage that also regularly serviced it. It was only after I asked what oil he used that he enquired and was told it was a 10W/40 to API SL which is a modern low ZDDP oil. Since high ZDDP oils are still commonly available and inexpensive it's no hardship to use them.

Similarly there are virtually no reports of unleaded fuel damaging valves and seats, especially from America which again has had it since the 70s - other than the tests the FBHVC initiated which involved new A-series engines run at maximum load for long periods. A bottle or so of Castrol Valvemaster a year is cheap enough insurance, and my roadster has shown no signs of valve clearances closing up despite several long journeys a year at motorway speeds.
Paul Hunt

RAY,
I was taking the micky out of the nay-sayers

I don't expect my diff to explode, as I put using Mobilube has lost the whine, perhaps it's just a coincidence or combined with my frequent diff oil changes but it's gone from being quietened to not there

the engines in my previous classics ran very well on Mobil 1 (particularly 15w50 when you used to be able to get it) and didn't fall apart from using unleaded petrol

my point was the scare stories put out and circulating exaggerating the issues

I don't go fully for the need for all classic engines for lots of ZDDP either as modern oils have packages of additives with ingredients that could balance out the need for high levels of ZDDP but the subject is too complex for me and oil companies don't give out full information about their products

I see it a bit like the food we eat, fads and fashions develop or spring up from nowhere, one day a food or element is good for you the next it's bad - unfortunately the only true test requires time which can make the results redundant because the effects take over - or not
Nigel Atkins

This discussion again!!!!' re; oils for axles (1800 and V8) , oil for MGB gearbox, oil for LT77 and R380, sulphur, bronze, brass, GL4, GL5, Synthetic!!! My head spins (cheaper than single malt, but nowhere near as enjoyable!)
There must be someone with the necessary expertise, out there who can put this dilemma to bed, once and for all…………….please!!
Allan Reeling

Alan,
if you don't like it just ignore it or "switch channel"

"there are more ways than one to skin a cat", "not everything is black or white"

and range of views and information is fine, pick the belief that suits you best, you don't have to stick with it you can change at any time and even change back to it if you want

unless oil experts own and regularly drive all the combinations of cars, g/boxes and oils over a long period of time and miles I don't think there'll ever be one answer (for each combination)

now, whiskey, a nasty drink, makes the drinker very tetchy :)
Nigel Atkins

Nigel, my experience with Mobil 1 goes back to the mid '70s. I was the head mechanic at a Mobil service station. The head office was running a program to introduce Mobil 1 to its customers. They included a free oil filter with every oil change. Since our clientele were locals who pretty much kept us in business, we monitored the cars's use of oil very closely. Almost every single vehicle used at least a quart of oil per week after being switched over to synthetic oil. When I tried it in my B, it used two quarts of oil! I believe that the early formula was bypassing the oil seals and escaping into the atmosphere. Over the years, I've seen where they have concentrated on this problem and that it is pretty much a thing of the past. As far as Ethanol in the fuel is concerned, I've replaced more than my share of collapsed or perished fuel lines due to breaking down by the Ethanol. I haven't written any scientific papers yet, nor am I likely to,but I know from experience what works and what doesn't. RAY
rjm RAY

RAY,
fair enough, I didn't start driving until 1977 and certainly couldn't have afforded Mobil 1 even if I'd know it existed then which I didn't

my first "classics", or more accurately over priced old cars, I got from the early 90s onwards, first was a BGT (1800)

I can't remember the weight grade of Mobil 1 back then but you could also get Mobil 1 'Motorsport' 15w50, and still could until recently

as far as the ethanol goes I was thinking of the UK where the maximum so far has been 5%

having experience new, off-the-reel 'classic' 1/4" fuel line from various suppliers in various locations over the country for the last 8 years I can tell you that my experience with modern made 'classic' 1/4" is that it was poorly made and nothing to do with ethanol, a lot of the time I was using a fuel that had zero ethanol, it was the p*ss poor quality of the rubber that would only last anything from days or just a couple of weeks to the last lot two years

I then swapped to use to modern made 6mm and have had no problems since

you've probably seen me moan about other p*ss poor rubber parts or components caused by tight fisted classic owners that rarely use their classics not prepared to pay more than the absolute minimum for parts so I won't repeat it here - whoops too late :)
Nigel Atkins

Nigel
Nowt to do with being "tetchy", and when it comes to the longevity of my painstakingly re-built mechanical parts, I'm sorry "belief" doesn't do it for me! Neither does trlal and error for that matter, both doomed to failure.

Our old handbooks and manuals gave us, chapter and verse, which lubricants to use and in which conditions to vary from the norm. Recommendations supplied by the manufacturer, who, presumably didn't desire premature demise of our engines and transmission.
THAT is all I want now!!!
Engine oil we are pretty well catered for with the "classic" products of Morris", Halfords etc.. But where is the "classic" oil for our old transmissions? Particularly the heavily stressed differential.

Allan Reeling

FOOT NOTE,
Smith & Allan sell a straight EP 90B which is the spec BL recommended for the GT V8 axle they also sell MTF 94 which is the spec recommended for LT77 AND R380 gearboxes.
Allan Reeling

Allan,
why continue a subject you're sick of(!!!???!!)

Others,
forgetting all the development in oils over the last 50 years as I was reminded multigrade engine oil was new to most owners in early 60s so originality may be monograde oil for some

I always take what the book recommends as a very good starting point, as many know I promote the use of the Driver's Handbook but I don't think all oils were recommended based on purely on engineering there'd also be commercial deals with oil companies and the oils would be for general use perhaps even compromised to keep within a general range of easily available oils at the time and use

your belief is not to use the modern oils without proof it is just a belief

I've done hundreds of thousands of miles in my classics using various modern oils and they've all run very well and haven't fell apart
Nigel Atkins

why continue a subject you're sick of(!!!??
Didn't say I was sick of it, just disappointed in the lack of difinity!
Allan Reeling

ah good, you're off the whiskey now then ;)

only a few years I thought I'll try an original oil in my diff to see if it would help with the whine so I asked for original diff oil for my Midget from a well known MG parts supplier (owner races/used to? MGs), I was given a bottle fully labelled up as Heritage (the 'official' parts company) it was 80w90 GL5 so obviously even Heritage had slightly moved on from the 1960s requirements
Nigel Atkins

This thread was discussed between 21/08/2014 and 30/08/2014

MG MGB Technical index

This thread is from the archives. Join the live MG MGB Technical BBS now