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MG MGB Technical - Gearbox choices Overdrive it is!

So I have eventually made a decision on which box, nearly, for the new project. I have eliminated 5 speed and going to use overdrive!

So today's question, I have a number of 4 synchro boxes, early and late. I understand the earlier overdrive black label is the one to go for, but is the later box an improvement on the earlier box. I know about the different speedo gears.

Many thanks in advance for your expert opinions.

Colin
Colin Parkinson

There is no significant difference between the early and late gearboxes.

Most parts are common between them, the laygear thrust washers on the later box are keyed to the case and bronze faced on the gear side so they do not wear like the free to rotate washers of the early box. So in that respect I would opt for the later box. It can also be serviced for oil level entirely from underneath the car which saves cutting fingers on the edge of the access hole when getting at the dipstick and the danger of getting oil on the carpets!

The internals of the early and late OD units are also mostly the same, the big advantage of the early unit is that the sunwheel thrust bush is more robust, in the later unit it is just a bronze washer glued to the case and is prone to breaking up with consequent damage to the casing.
Chris at Octarine Services

Interesting ,I have a box here, a later screw in level bung box which has 3.138 1st gear the same as the v8 box, it's 4 cyl non od box that came with a heap of others from wrecks in the us, looks as though it's never been apart--Is it a one off modded box or are there others out there, as mentioned it just came from a wreck and looks untouched really
box no. 6387
William Revit

Not sure it is an MGB box - I think similar boxes may have been used in other BMC cars with the 1800 engine.
Chris at Octarine Services

Wouldn't mind trying to id this box if anyone knows about the numbering on it
This is on the top near the sidecover
Actually looks like I might have made a boo boo with the number before--it's

IQ 6381


William Revit

On the shifter housing lh side


William Revit

Sidecover


William Revit

extension housing (upside down)


William Revit

Have a look on the casing between the gearbox mounting pads - there may be a date stamped there.
Chris at Octarine Services

Will, I have checked the part numbers on my old microfiche, 22B369 not listed, but side cover 22B309 is the 4 synchro side cover for an mgb, and also listed for the Austin 3 litre.

Does that help you?

Colin
Colin Parkinson

22B369 is the standard rear extension on non overdrive gearboxes.

BMC bolted various standard parts together to make gearboxes for different applications.

The fact that those castings are there does not indicate the application, but the first gear ratio suggests to me that it was paired to a high axle ratio and the fact it is a late main casing suggests possibly that it originated from a van, maybe an 1800cc Sherpa.
Chris at Octarine Services

The 3 litre came with 2 final drive options, 3.9, BTC 849 and 3.545 BTC 855 ( Automatic).

An overdrive option as well.

I cannot find any reference to actual gear ratios or any photos of the actual gearbox.

What about MGC?

Colin
Colin Parkinson

The 3-litre gearbox casing is identical to the MGC, but uses a different remote.

I don’t know about the ratios.
Dave O'Neill 2

It's not MGC, they had dipsticks and were 3.44 same as a B
It came with a heap of identical looking gearboxes from wrecks,Useless interesting feature is you can get 9 boxes in a cubic metre pallet box, the guy said one was a close ratio and that's the only reason i checked them all out -this was the only different one, not close ratio but different to the others
It bolted straight up to my B series s/c engine and that's what it's intended use is,
everything on the outside looks identical to an MGB box.
Does that -1Q-6381 mean anything date wise
I'm starting to think it might have v8 gears with a modded input shaft--or maybe the factory v8 input shaft is the same length/cofiguration as the 4---don't know, I must admit I've never had a factory v8 box out, engine yep but never had the need to remove a box
I'll have a look for that date Chris
It's no big deal just interesting, I'll run it like it is and if it fails we'll find out then
The only diff. between 4 and 8 gearsets is the input shaft and cluster ,the gears on the mainshaft are identical so it must just be a ratio change between the input and cluster, I've been told (only possibly true)that the v8 input gear and the front gear on the cluster have teeth at a slightly less helical angle to reduce the load on the input shaft bearing--------??

No date stamped between the mountings there anywhere but found this casting mark on the bottom of the bell near the jiggle pin --?



William Revit

The factory V8 has a smaller diameter pilot bearing and shaft than the 4-cylinder. The 4-cylinder version can be used in the V8 box if it is machined down, with the 4-cylinder laygear (and apparently the 1st gear cluster, although the invoice doesn't show that). Mine was rebuilt like that by the PO 25 years and 100k ago due to the non-availability of V8 parts.

According to sundry sources MGCs had two gear sets with the second having 1st gear the same as the 3-litre and both different to the V8, and a 4-synch casing different to the 4-cylinder. With this one having 1st the same as the V8 I'd say an engine larger than 1800cc is implied, unless the axle ratio compensated for it by being higher ... or should that be lower ...

Whilst the 4-cylinder didn't get the side level/fill casing until late in 74 the V8 had it from the outset i.e. late 72, but always had OD of course.
paulh4

1st 3.111
2nd 1.926
3rd 1.306
4th 1
Rev 3.422

Are these the ratios in the mystery box?
Chris at Octarine Services

A possible Chris---what box is that

When i was checking these boxes ,i marked the top of the input shaft and got 3 full turns and then down to about 5 o'clock for the others and this one went to 3 turns plus just after 1 o'clock so took it to be the 3.138 v8 ratio----------------maybe not though
Didn't check the other gears
Didn't really want to pull it out again now, but could wind the engine over I guess to check
There were different ratios in later C's as well but 1st gear was 2.9ish (less than 3)

The numbers you have there are very possible, interested to know what box that is-------
Cheers
Happy New Year
William Revit

Austin Marina - a USA model of the UK Morris Marina

They were built up to 1975 and it is my guess that the casting date in the circle is week 38 of 1975.

The car used the 1800 B series engine and an axle ratio of 3.636.

It is not unusual to find bits of Marina engines etc put into MGBs as many are interchangeable if not exactly the same.
Chris at Octarine Services

Sounds positive Chris
I'm going to have to do an acurate check then by the looks of it
It could be a marina box with MGB gearchanger if they were different
It definately came out of a rubber nose B as did the rest of the boxes, but aparently the car itself had heaps of mods done to it and a bit of a racer so could be from anything--The car died from an engine bay fire which seems to be a common fault stateside
Thanks for your effort finding the info, I'll check it out tomorrow
William Revit

I thought the Marina used a gearbox similar to the midget 1500/Triumph?
Dave O'Neill 2

I had one new in the early 70s and thought I read somewhere it was based on a VW box. Sundry online sources say it was the same as the Triumph Toledo and Spitfire/Midget 1500 as above. One of those sources says Australia had a locally-sourced 3-speed box from Borg-Warner which was basically a 4-speed with 1st blanked off as the 'perceived' torque made such a low gear unnecessary. That was a 120hp 2600cc six-cylinder, which given how my 1300 felt in excess of 80mph sounds scary. That one did apparently have rear radius arms 'in an attempt' to improve handling...

Funnily enough in my 1300 I rarely used 1st as it pulled well from a standstill in 2nd and saved a gearchange. Had the original clutch and gearbox when I sold it 65k later. In fact despite the reputation of BL the only parts I had to replace - bar tyres and a battery - in 6 years were a front damper and an interior light-bulb. Body was really good too, the only slight signs of any rot were over the headlights where the Zeibart process was missed.
paulh4

The Australian Morris Marina, at least in 4 cylinder form, used a Triumph gearbox.
When I asked a former BMC (Australia) executive why they didn't use the excellent MGB 4 synchro gearbox, his reply was a brief "cost".

For engines, I seem to recall, again in Australia, they used the E-series OHC engines in 1500cc four cylinder and 2250cc six cylinder versions.
The A and B series engines were not fitted to the Marina here. So, perhaps the gearboxes fitted in the UK were different as well? But I suspect, Triumph.

The Marina was certainly a "parts bin special". My memory may be playing tricks on me, but I seem to recall reading at the time of their release in the UK, in a motoring magazine, that the suspension was derived from the Morris Minor!
T Aczel

One could equally say it was derived from the E-type as they all used torsion bar at the front and leaf springs at the rear. And what is a torsion bar if not a straight coil spring? It WAS basically old wine in a new bottle though, as was the MGB from the MGA and the TD, with suspension going back to the 1930s. The Marina was derided at the time, but not as much as the Allegro with its 'quartic' steering wheel, even though a number of performance cars subsequently received non-circular steering wheels. Both were perfectly adequate for what they were intended to be - a bread and butter car.
paulh4

Sorry guys---wrong
Chris is quite correct in saying the Austin Marina sold in the USA up to 1975 had the B series 1800 engine and box,they also had 1275 A series engines, there were a few of them here as well--I remember a '1800GT' up at the wreckers here --A friend here had a single carb us spec MGB and got the inlet manifold and twin SU carbs off it for his B--

Today I fitted up my degree wheel to the engine ,marked the tailshaft flange and in 1st gear got 3 complete turns plus 50degrees
So definately 3.138 1st gear in this box---
I'm just going to run it as is, it must have been modified at some stage of it's life is my guess---unless some info pops up that changes my mind
Thanks
willy
William Revit

Are you saying E types had leaf springs---

Aust. Marina--
https://www.tradeuniquecars.com.au/feature-cars/1910/morris-marina-aussie-originals

" A performance version shared the MGB’s ancient 1.8-litre B-series engine. "
William Revit

Willy

The UK Marina was available with either with 1275 A-series, or 1798 B-series, with either single or twin (TC) SUs. However, it didn't use the MGB gearbox.
Dave O'Neill 2

Thanks Dave--got it now
Guess it doesn't matter now i know i'm on 3.138:1, I'm half tempted to pull the thing out and just see what's been done to it --but my lazy half says just run it till i have to pull it out for some reason and find out then
It definately had the large 4cyl MGB spigot on the end ,so it's a bit of a mystery all up
William Revit

This was my brother's 1.8TC, which he owned around 1980.

Paul might recognise the setting, prior to the redevelopment of the town centre.

There are still a number of 1.5 diesel Marinas in Malta. They were built locally, by Car Assembly Ltd of Marsa.


Dave O'Neill 2

Reminds me of Homer Road and the Civic Hall car park, but doesn't look quite right from memory.

Was that the 1.5 Diesel frequently used in boats? Rather apt in a 'Marina', which the AA at launch (ho ho!) said 'handles like a boat'.
paulh4

Yes, it's the road which ran between the Library and the Civic Hall. The brick building to the left of the photo is the Library Theatre.
Dave O'Neill 2

Marinas handled like a boat for sure. Interestingly it didnt take too much to get them right. I built an (1800) engine for one entering in the local Lemons endurance series. (A perfect car for the series!) With a few of the usual changes to suspension settings the car now walks away from much more fancied opposition in the corners. Between corners it gets reeled back as we concentrated on relatively low stress reliability, opting for around 130 at the flywheel rather than going for broke. It lasted the distance well.
Paul Walbran

Just blew up pictures of a v8 and a 4cyl input shafts to compare
Both the same length from the bearing shoulder out to the end of the spline
The spigots are different with the v8 spigot being having a smaller od and shorter
Interestingly, from what I can see both appear to have the same number of gear teeth, but the v8 unit also appears to be a slightly larger diameter gear--maybe runs a tooth or two less on the cluster which would explain the gearing difference
I'm thinking now that the box I have has v8 gears (input/cluster) and has maybe had a sleeve fitted over the spigot or a hybrid shaft made with a 4 cyl end on it
I really want to pull it out for a look now
but it won't really make any diff. it is what it is---
willy
William Revit

Ah, off Homer Road, that explains it. I worked opposite there for a few years and saw Touchwood being built.

The Marina couldn't have been that bad if it didn't take much to put it right. I found the steering well balanced, going into a corner with a certain effort on the steering wheel if one wheel lost traction on ice or wet leaves the steering simply tightened and the car stayed on the same line. The problem was the lack weight in the back, but that affects many cars, and I never got stuck in it. Where we lived a few years ago BMWs couldn't get up and down the road on packed snow even though you almost needed a spirit-level to see the incline.

paulh4

This thread was discussed between 28/12/2019 and 03/01/2020

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