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MG Midget and Sprite Technical - so how noisy should a rib-case gearbox be?

A 'how long is a piece of string question'

Gearbox on my 1275 midget was suffering from lack of synchromesh on 3rd gear. Otherwise the gearbox was fine. So around 7 years ago I took the gearbox out for a rebuild. I replaced 3rd gear as the friction material that the synchro ring works against was damaged along with bearings and seals.

After 7 long years the car s finally running again. Gearbox works well but does seem noisy - this may just be down to me driving modern cars for too long.

Fist has the usual whine. 2nd and 3rd are fine under load but whine on the overrun. Is this normal? It's so long since Ive driven the car that I'm can't remember what it was like. 4th is quite both under load and on the overrun.

I've double checked that the gearbox is fun of oil. This is my first gearbox rebuild so concerned I may have screwed up along the way.

Any thoughts greatly appreciated.

Bob
Rob Storer

I've used both smooth and rib case boxes over the years and the latter whines slightly under load, but should not do so on overrun. First on either normally wails like a banshee, but indirects are quiet on smooth and whine a bit on ribs. I would take a look at layshaft thrust washers.

Les
L B Rose

If the gears and bearings are in good condition, there shouldn’t be any noticeable whining or wailing.
Dave O'Neill 2

Thanks guys, confirmed what i thought. Engine an gearbox out again. Layshaft makes sense as it's fine in 4th.
Rob Storer

The scraping noise in 4th in the 1971 Ribcase when coasting downhill always bothered me. I had the original rebuilt a couple of times when the car was fairly new and even installed a new one in 1977 that I bought in the UK. I found that running 75W-90 synthetic seemed to quiet it down some and provided a longer service life. At 200,000mi, I installed the Rivergate Datsun and it has been much quieter.
Glenn Mallory

Mine has whined in the indirect gears for years. It was a new unit I bought from the factory. I rebuilt it a couple of years ago with new bearings throughout, I also replaced the layshaft again with new bearings and carefully checked the endfloat was within tolerance. I had a nos laygear and replaced that as well. The anti rattle on the gearstick was also new. The result? The noise has not changed! It also 'growls' slightly on the overrun in top when its really hot. Its not as noisy as a straight cut box but I have got used to it now.
Bob Beaumont

Rob
I think there are probably two issues. Firstly, you say you replaced 3rd gear. Assuming the laygear and shaft are orginal then a new gear is meshing against a worn gear which may produce the whine. However, the layshaft has a hard time and probably needs replacing, together with its needle roller bearings. The laygear itself may be worn and need replacing - a worn layshaft will make it worse and worse. Top gear will be quieter because it is direct and does not stress the laygear so much. While stripped, it is generally recommended to change the synchronizer rings.
Bill Bretherton

My newly rebuilt ribcase whines in 2nd and 3rd. Normal straight cut whine in 1st and I think fairly quiet in top. I say think because it was difficult to hear it over the noise of the diff! Diff is currently at Hardy getting rebuilt. Box was done at Heathrow at great expense! Both box and diff were new to me so I had not heard them previously.
John Payne

Glenn put "I found that running 75W-90 synthetic seemed to quiet it down some and provided a longer service life."

Coming from someone that puts hundreds of thousands of miles on the car I think provides some proof of the benefits of using a good quality gear oil against engine oil in the gearbox. BL confirmed the use of gear oil in all the MG gearboxes in the 70s too.
Nigel Atkins

I’m using a 20/50 oil specially designed for the Mini and it’s shared engine and gearbox.
So it’s ok to use a modern semi or full synthetic gear oil? I thought it was engine oil only?
John Payne

John,
don't get too tied up with semi and full synthetic (mostly theses are used as marketing terms) a good oil is a good oil.

A good quality Mini 20w/50 oil is a good choice for the gearbox for the reason you mention - and if it's a different colour to your engine oil you will be able to identify which oil is leaking a fraction faster (unless the two oils mix in together on the floor!). :)

Yes it is fine to use a modern good gear oil, mineral GL4 if you're a worrier, full-fat, devil may care fully-synthetic GL5 if you want to worry others.

Some people use a straight 30 grade engine oil instead of 20w/50 as that's what was used in the good old days (not usually Spridget owners).

Many will say it makes no or little odds which you choose and of course that is correct but depends on your use of the car and your oil, and overall classic car ownership, beliefs.

The Midget 1500 specifies gear oil.

You'll find loads on this subject in the Archives here and other models Archives with me usually a lone supporter of gear oils (and GL5).

This is the GL4 gear oil I recommend having used it and others on here recommending it especially for use in the cold or colder parts of the UK - Castrol Syntrans Multivehicle 75W-90 Fully Synthetic MTF. - https://www.opieoils.co.uk/p-739-castrol-syntrans-multivehicle-75w-90-fully-synthetic-car-gearbox-oil.aspx

No point you thinking of changing your gearbox oil until it's service oil change, if you believe in such a thing - the MGB using engine oil in gearbox and overdrive specifies oil change at 24-months or 24k-miles whichever is sooner. Gear oil would be longer lasting.

Having posted about oil the obligatory oil viscosity chart below - and mention of the good book for good measure - I'm going against what's in the Driver's Handbook for the A-series Spridgets - where my horse hair shirt!



Nigel Atkins

Bill,

I think you've hit the nail on the head. I changed 3rd gear and the layshaft needle bearings but not the shaft and lay gear.

Time to pull the gearbox out and rebuild it correctly.
Rob Storer

Cheers Nigel, good info. As it’s a ‘new’ box I’ll probably change the oil after a thousand miles to get rid of any rebuild crud. The GL4 you recommend sounds like the stuff I use in my type 9 so would be handy to use the same. It’s easy enough to change the oil (unlike in the Type 9!) so might give it a go.
John Payne

John, put a drain plug in your type 9. There's even a nice flat circular place to drill and tap it!
GuyW

John,
as Rob is sorted, thread drift, yes it probably will be the same stuff, I used to use in my Type 9 box (but now, according to some, I'm going to destroy the box as I switched to a GL5 'fully synthetic', getting the opportunity would be nice).

It's also recommended for MX-5s especially those in Scotland.

I have done a good few partial syphons on my T9 and I wished I'd put a drain hole and plug in.

Below is Willy's prefered position.






Nigel Atkins

Position on Arie's T9 (which is is in much better condition than the reconditioned boxed I paid for).



Nigel Atkins

Had a drain plug fitted virtually from the start, getting the oil out isn’t the problem, it’s getting it in I find a bore! The standard box has a nice angled filling point that lines up with a nice big hole in the tunnel so you can fill it from topsides. With the type 9 I have to crawl around underneath with a big oil syringe job and I end up with oil everywhere!
John Payne

John,
I've got an access hole in the passenger's side footwell with the trim cut around it and a grommet but it's still a stretch and fiddle checking the level and topping up but much better than crawling around underneath, especially with a box that leaks.



Nigel Atkins

I use a squeezy oil bottle fitted with a long delivery tube. The awkward bit is properly checking the oil level with that bit of bent wire!
GuyW

Nigel
You stated that BL confirmed the use of gear oil in its MG gearboxes in the 70's. Do you have evdence of this? My understandng is that engine oil MUST be used in the ribcase. AIUI it is designed to use lower viscosity oil especially for the synchros. It may also be that various clearances are too tight for a thicker oil as well. Although 30 weight was specified originally, that is before multigrade was in common use and I would have thought 20-50 (which behaves as a 20 weight when cold, rising to 50 when warm) is OK. But NOT gear oil. This may initially quieten the gearbox but will ultimately lead to more rapid wear.

It may be that a 10-40 or even 0-30 is better as it will circulate more readily when cold - I don't know. This all applies to the ribcase box only.
Bill Bretherton

Bill,
yes, I'll sort it, I'm used to having to provide evidence, my wife has to see something with her own eyes to believe me. It'd also be interesting to see evidence of engine oil MUST be used.

Even the good book only puts "recommended lubricants" and it has a range of weights of multigrade engine oils for the carbs yet SU specify a straight 20.

Pure speculation on my part but I think 'recommendations' and 'musts' varied over the years depending on requirements, advancements, to cover build mistakes, changes in manufacture, rationalisation and commercial tie-up. Bit like the varying torque setting for the same parts and fixings over decades.

Nigel Atkins

I know there was a service bulletin issued for the MGB, but I don't know about Spridgets.
Dave O'Neill 2

Bill,
also see Glenn's post of 25 May 2020 at 03:02:56 -
"The scraping noise in 4th in the 1971 Ribcase when coasting downhill always bothered me. I had the original rebuilt a couple of times when the car was fairly new and even [-]installed a new one in 1977 that I bought in the UK. I found that running 75W-90 synthetic seemed to quiet it down some and provided a longer service life. At 200,000mi,[-] I installed the Rivergate Datsun and it has been much quieter."

Now what we need to know from Glenn is -
the mileage that the new 1977 ribcase covered before the Datsun installation and how much of this mileage was with use of 75W-90 to give "longer service life".

IIRC Glenn had his Midget from new(?), 1971(?), and has covered 300k-miles(?) in it - that's only an average of just over 6k-miles a year though, practically a show-only car, I used to do more than that taking mine back for repair! :).
Nigel Atkins

Dave,
where were you yesterday, you were needed in the Downing Street garden, supposedly "forensic" political journalists and they were so stuck in their ways that they missed two obvious questions that most of the rest of us saw. That's the trouble with being wedded to something too strongly.
Nigel Atkins

It always is controversial when the topic of gear oil comes up - so I will just note what I use :-

Penrite GB30 Gearbox oil.
The can notes for use where originally 20/50 engine oil was specified.

It's the oil listed as 'preferred' when you use their oil selector.
They also list as an alternative a 75-85W fully synthetic.


https://www.penriteoil.com.au/product-selector?by=Quick%20Search#/recommendations
richard b

Well that is absolutely terrible of Penrite to state good old (but it won't be as the old formula oil) straight 30 and then have the audacity to put a 75w-80, and a 'fully-synthetic' at that!, as an alternative! There must be a mistake in their database and website! I'll get Willy on to this.

Rich this is the problem with buying Aussie made oil for a British car, the heat must have frazzled their computer programs.
Nigel Atkins

Nothing wrong with synthetic Nigel. It outperforms mineral in all respects, apart from price. I think an American truck did something like 400,000 miles on synthetic and, when they stripped the engine, it was like new virtually.
Bill Bretherton

Bill,
I'm joking, I'm all for 'fully-synthetic','semi-synthetic' and particularly genuine real fully synthetic oils.

IIRC they done similar for the Mercedes 659cc turbo engine in the smart cars, over 100k-miles and the engine was still within factory build tolerances - this of course was before Mercedes joined the race to the bottom and ruined the Swatch idea and introduced Mercedes late-century lower build and finish quality. I tried to deal with Daimler-Benz when they first set up the smart UK HQ in Milton Keynes (year 2000) but the corporate rot had already set in.

Then going to a Mercedes dealership workshop, with a smart, was a further eye-opener, not that I didn't already know about English dealerships.

I used Mobil 1 in my classics engines and was told by others it would ruin my engines, rot my teeth and steal my good looks - whilst the cars were moved on I've kept my teeth and looks. I noted the others that told me this often done less miles a year in their classics than, at the time, I'd do inmine in a matter of weeks.

I've got my evidence, although Dave has preempted some of my cautious evidence caveat that I give being an even-handed, open-minded type of person, as he's seen it all before with oil beliefs on the B-side.

Still very interested in seeing your evidence though that engine oil must be used in the ribcase.
Nigel Atkins

The ‘never use gear oil in the BMC gearbox’ might have come about because about the only gear oil available would have been 90 weight or more. The modern 75/90 I use in my Ford box seems much thinner.
John Payne

Nigel
I can't find specific wording that tells you not to use gear oil, it is something I have stored in my brain from the past. But the specified oil is engine oil so that's good enough for me. We'd need the original design parameters I guess. At least I didn't make up some stoopid tale about Barnard Castle!
Bill Bretherton

I understood that the issue with some grades of gear oil (GL5 perhaps) tended to "eat" the yellow metal parts like the synchro cones in gearboxes. Whatever that really means.
GuyW

Bill,
no worries just having a bit of fun today to take my mind off my joints aching, now I know at least I've made it to old bones.

I heard it was Castle Barnard - bloody useless "forensic" political jurnos so focussed on asking their repeated question to get the same repeated answer they missed the two blindingly (unless driving to Barnard Castle) obvious questions to ask.

I'll put up my stuff later (Dave, you spoiler).
Nigel Atkins

Bill,
yeah hands up, another total brain fart on my part, I didn't mean to put 'all' (I was having trouble with my eyes, I've been for a drive since and they're OK now) as Dave put it was for the MGB/BGT.

I was interested to see if you had anything.

A BL / Austin MG Technical Service Bulletin (75-D-5) from USA dated April 1975 -
"Will Service Personnel please note that Hypoid
SAE 90 oil has now been approved for use in the
gearbox On MG vehicles.
ThiS supersedes the previous specification calling
for engine oil, and is suitable for vehicles equipped
with or without overdrive."

http://www.spridgetguru.com/TSBs/TSB_no75d5.pdf

At the time the 1500 that already used gear oil would have been over there - but - IIRC, and this brings tears to my eyes, I think I was told they didn't update the good book with this. However an interesting TSB 73-A-12 seems to be just a promotion for Quaker State Oils, so I wonder about vested interests and commercial agreements to perhaps continue recommending certain oils and/or makes and types.

TSB 73-A-12 - http://www.spridgetguru.com/TSBs/TSB_no73a12.pdf
Nigel Atkins

I've got several magazine articles from the 1970s reporting on road tests of Midgets. They all say that the gearbox was noisy.
For instance, Motor tested a Mark 2 Midget and reported "In the lower ratios there was a certain amount of whine" (Motor, May 1964). Or from Autocar (February 1971) "...it is the gearbox that offends most clearly here. First gear... is very noisy on most examples we tried. 2nd and 3rd were only somewhat better. Or "Gearbox and transmission noise are very noticeable, especially in the intermediate gears (Sports Car World, April 1968). Bear in mind, these were new cars not 40-50 year olds!

I could cite more along the same lines. Methinks that a characteristic of the gearbox is that it is noisy. A quest for a silent Midget gearbox may be like a quest for the holy grail. That's the view that justifies my ceasing to worry about noise until something breaks!
Chris Hasluck

Thanks Nigel. Perhaps the jury (or some of it) is still out.
Bill Bretherton

I wonder if the same journos reported that the Morris Minor and Austin A40 gearboxes were noisy?
Dave O'Neill 2

In my earlier post I mentioned mine had whined and it was a brand new unit from the factory. I understand that BMC tried to reduce the noise by making the case in cast iron (More Healeys by Geoff Healey), apparently apart from the weight it made little difference. The later cars have more insulation certainly around the tunnel area and my RWA Midget I had in the late 70's was much quieter generally than the Frog.
Bob Beaumont

Bill we need more reports like Glenn's with combined higher mileage use over a long time.

I put (gulp) GL5 (yikes) gear oil in my T9 box!!!
Nigel Atkins

Bill,
I remember now what I was going to put.

The gearbox for the V8 MGB which wasn't much different to the 1800 yet it specified to use gear oil (engine oil for the 1800s, perhaps until that US technical bulletin(?) only in the US perhaps(?)).

The Rover/BL LT77 (and later 380) gearbox originally specified ATF which is very thin, see chart, too thin for the bearing manufacturer to guarantee their product or so I've read. They later went on to gear oil. Now some B V8 and RV8 owners are using and recommending our old friend Castrol Syntrans Multivehicle 75W-90 Fully Synthetic MTF, and preceding this the Castrol SMX (see my Type 9 oil threads for more history and details).

I can remember years back because engagement problems with first and second on those 5-speed boxes when cold owners using and suggesting ATF, engine oil and gear oil but now as I put some have found the benefits of the likes of Castrol Syntrans 75W-90 gear oil (GL4).

I of course would use the GL5 I use now and wait for my teeth to rot, lose of looks and gearbox to fall apart as will not doubt happen with my T9.
Nigel Atkins

Nigel
I think it needs a qualified engineering opinion. There must be a reason why engine oil was specified. I've rebuilt my ribcase so want to fill it with what's best for it!
Bill Bretherton

Bill,
opinion is one thing, and mechanics and mechanical engineers tend to be often very conservative, more inclined to their training, perhaps decades back, rather than always being able to keep with all modern developments.

Glenn has given real world running experience, using 75w-90 and getting a longer service life.

Do we read the following -
"[-]installed a new one in 1977 that I bought in the UK. I found that running 75W-90 synthetic seemed to quiet it down some and provided a longer service life. At 200,000mi,[-]"
- as the new one bought in the UK in 1977 lasted until 200k-miles (on the car's speedo?), when the Datsun 5-speed box was installed, I don't know.

But we can take -
"I found that running 75W-90 synthetic seemed to quiet it down some and provided a longer service life."
- as at least the opinion of a very long term owner who has put IIRC 300k-miles on the car so has a lot of road proven experience.

Even if you go for an engine oil it will be a different formulation to when engine oil was specified for the gearbox, just one example -
"DUCKHAMS Q 20W-50 is high quality engines oil formulated with the most modern additive technology." - https://www.duckhams.com/mal/product/20w-50-engine-oil/

Luckily for you I have stock of some genuine 1960s 20w-50 (darkish brown) engine oil I can let you have at a reasonable price, unmarked plastic can or it'd be three times the price. ;)

Each to their own (oil belief), no worries. :)
Nigel Atkins

Nigel
Glenn seems to have had the first new gearbox rebuilt twice and then needed another new box, up to 200,000, so it seems each box (including the two rebuilds) did about 50k each on average. We don't know at what mileage he started using gear oil. Sure, gear oil will make it quieter, so will sawdust! I repeat, we need to know the design parameters and why a thinner (engine) oil was specified. I doubt your 60's oil is better than a modern one in fact it's probably decomposed. But you were joking I assume ;-)
Bill Bretherton

Nobody has mentioned the phosphor bronze components in the A series gearbox. I thought gear oil was supposed to attack those components hence engine oil was recommended for a longer life (having said that I know a number of people who use gear oil and seem OK with it).
Chris Hasluck

Bill,
what makes you think 50k each for the rebuilds - are you doing statics for Dominic,

- "I had the original rebuilt a couple of times when the car was fairly new and even installed a new one in 1977..." - so the car was about 6 years old and the factory box had been rebuilt twice in 6 years from new, sounds 70s BL.

I did put we don't know what mileage, or time, Glenn started using 75w90.

Sawdust would improve some things for a while but probably not "provided a longer service life" as Glenn put.

The reason for original specification of oil may well have as much, if not more, to do with what was available at the time, keeping dealership servicing stocking requirements down and easier to administer and possibly commercial tie-ups.

A modern oil will be better than one from the 60s but the 60s oil would be to your belief the correct engineering specification so worth many times what the better quality oil would.

Of course I'm joking, but I bet my used oil (dark brown) would still possibly be better condition and quality that the oil in some (many?) other MGs and classics.

Let's be honest it doesn't really matter, to an extent, what oil you use so put in what makes you happy to your particular oil belief as the proof may not exist.
Nigel Atkins

Chris,
that was the GL4 to GL5 gear oil in the gearbox debate for years this has not been the case for some/many/most? of the more modern formula gear oils GL5s even.

GL5 widely accepted to be OK for the rear axle and sold as such for very many years.

But of course it depends again on your (oil) belief, some don't trust the oil blenders when they say it's safe to use their GL5 as it won't 'attack the yellow metals'.

If you don't believe it then why would you chose to use it, or if in doubt again stick with the old style stuff it will be good enough or more than good enough.
Nigel Atkins

Nigel
AIUI Glenn had, in effect, 4 gearboxes (including 2 rebuilds which should have replaced any worn parts) in 200,000 miles. That averages out to 50k per box. Of course one box could have done 75k and another 25k. Also, New Mexico is very hot most of the year so it may be that extreme conditions call for extreme measures i.e. a thicker oil.

It could be that the gears themselves would run happily with gear oil (the clue is in the name) but the helical gears, at least, don't seem to wear too badly. The straight cut gears i.e. first and reverse do wear so maybe gear oil would help them. But I'm not so sure about the needle roller bearings in the laygear and the first motion to third motion pilot bearing, which have a hard life. They might need a thinner oil to circulate better. Also the synchro rings are said to work better and for longer with engine oil.

As I've said, it needs a qualified engineering analysis to assess what the best oil is, not a matter of opinion. In the absence of that, why not stick to what the workshop manual specifies?
Bill Bretherton

I am with Bill on this. Changing to a different type of oil should only be done with appropriate qualified evidence. When I was racing using a straight cut box (which has less stress on the gears) I used engine oil with Molyslip additive. This was on the recommendation of ST. I never had a problem in 6 years of modsport although the laygear and third motion shaft needle bearings were renewed annually as a precaution.
The A series box was in production for many years. Oil technology developed in that time and Leyland as far as I know did not change the specification.
Bob Beaumont

I don't think you will get a qualified engineering analysis now and back in the day, as today, with large companies and small, things are often done more for convenience than improvement and mistakes were made and not always rectified.

Only last week one of my neighbours was telling me about LR in the 90s not accepting his company's advice on bearings (LR wouldn't accept their poor production finish on construction assembly). Though this is is the country of motorsport engineering too, I'm not sure I believe him as we all know German engineering has such high standards. Perhaps even Glenn is fake, I've only ever seen him post in threads I'm on.

There can even be more than one scientific conclusion let alone engineering, if human minds are involved then there's always going to be some element of opinion. Many years ago qualified people would have thought this virus was in the water, they would have been 'correct' for their time but things move on, more is discovered and learnt.

Perhaps in this uncertain world it is best to hold to certainties of the past.

I think for the majority of ribcase Spridgets the use and stress will be so little you could use almost anything - and the offer of my old oil would be a good one.
Nigel Atkins

This thread was discussed between 24/05/2020 and 28/05/2020

MG Midget and Sprite Technical index

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