1275 diff ratio?

[LINEARAUDIO]

Hallo, not posted before, so I hope I'm in the right place!
I'm trying to do some calculations re speedo readings, and would find it jolly useful to know what the standard 1275 Marina diff ratio is. Also, does the 1.8 have a different ratio? Many thanks, Pete

[MarinaCoupe]

Hi Linearaudio

All 1275 saloons & coupes ran 4.11:1 rear axles, some commercials also used this ratio and others 4.55:1.

1.7/1.8s all used 3.63:1.

[Kilroy]

Hey Chris.

Does this mean that some of the 4.1 diffs had the same stud pattern as the 3.63's.?
My commercials use the larger pcd - did the 1275 saloons have the same pcd as my 1700's then.?

Cheers.

[MarinaCoupe]

Hi Kilroy.

1.3 saloons/coupes/estates all shared the 3.75" pcd with the 1.7 & 1.8s - so yes.

7cwt & 440 commercials also used the 3.75" pcd in the UK.

It was only the 10cwt or 575 commercials that used the bigger pcd.

[locost_bryan]

It was only the 10cwt or 575 commercials that used the bigger pcd.

Is that the MGB 4x114.? PCD? What power would that diff/axle handle, and what diff ratios can it take? Any MGB ratio?

I suspect that only the 575 van and pickup came to NZ. If they have a stronger axle, that can take MGB gears, then that could be an upgrade option. Are the front uprights and hubs the same as the cars (just with a different stud spacing)? More wheels available here for MGBs than Marinas/TR7s.

Bryan
Auckland NZ

[Kilroy]

Yes - I believe the 575 rear axle can take the mgb diff, and it is the same stud pattern.
Mind you - thats only a 3.9 at best probably.
I will have a couple of spare 575 rear ends soon.
Not sure they would fit in your mailbox though...

Kilroy

[MarinaCoupe]

The 575 axle is the same as the early MGB axle (so called "Banjo Axle"), also Austin A55/ A60 / MGA. It is different from later MGB axles. As Kilroy says the best ratio available is 3.9:1.

These things are fairly bullet proof, the UK Marlin trials cars use them even now, as did the original works UK rally cars, partly for strength but also for the standard ratio of 4.55:1.

The front hubs share the same basic design as the 3.75" ones and they all share the same wheel bearings.

[Number 63]

The Ital 1.3 models had a 3.89 Diff ratio which made them much more useable day-to-day.

[locost_bryan]

Interesting. Was the 3.9 MG ratio actually the 3.89 mentioned for the Ital? Curious that the Aussie Marina 4's with a Borg Warner axle had the same ratio. Just coincidence, or was the early MGB axle a Borg Warner design?

[MarinaCoupe]

locost-bryan,

The MG 3.9:1 ratio was for a completely different axle, the MGB/MGA/A60 'banjo axle'. This axle was only used in 10cwt & 575 Marina commercials. It will not fit into the standard Marina back axle. Similar axle ratios pop up but are not neccessarily interchangeable, probably 90% of all European car diff ratios are in a band between 3.25:1 and 4.6:1.

Let's talk about axle families as the best way to identify what might be swappable.

Family one
Standard Marina or Ital with 3.75 PCD wheel stud spacing - Saloons, Coupes, estates and 7cwt/440 commercials - these commercials don't seem to have been exported to Aus or NZ. Other cars using the same diff include Triumph Spitfire 1500, Triumph Dolomite 1300/1500/1850 (not Sprint). Ratios vary from 3.27:1 to 4.55:1.

Marina/Ital 1.7/1.8 - 3.63:1
Marina/Ital 1.3 - mostly 4.11:1 - except as listed below
Late Ital 1.3 - 3.89:1
Most UK Marina/Ital commercials - 4.11:1
Some Marina 7cwt/440 commercials 4.55:1
Triumph Spitfires -
Mk1, Mk2 & Mk3 - 4.11:1 (use with solid spacer)
MkIV - 3.89:1 (use with solid spacer) to mid 1973, actual change data not documented - (use with collapsible spacer)
MkIV from mid 1973, actual change data not documented - 1500 (use with collapsible spacer) - 3.89:1 OR 3.63:1 OR 3.27:1
Dolomites
1850 - Manual 3.63:1
1850 - Auto 3.27:1
1500 - 3.89:1
1300 - 4.1:1
Triumph TR7 - 4 Speed only
Manual - 3.63:1
Automatic 3.27:1

Family two
Marina or Ital 10cwt/575 commercials, the diffs are common with Early MGB (up to 1964 I think), all MGA, Austin A50s/55s/60s, J4 vans.
Ratios vary
4.875:1
4.55:1
4.3:1
4.1:1
3.9:1 MGB only

Other Axles

Aussie Borg Warner - don't know anything about them but I doubt whether any of the UK stuff above would fit. If Ford Australia used the same BW axle as has been suggested, try checking on an Aussie Ford forum.

Dolomite Sprint Axle
This has the same 3.75" PCD as standard Marina, but the Diff comes from a different Triumph family including Triumph TR3/TR4 I have not finished researching other big engined Triumphs to see what else the Diff was fitted in.
Dolomite Sprint - 3.45:1
Note - the Dolly Sprint axle is coil sprung, so will need all its' brackets cutting off and Marina spring saddles welding on - Martec has done this on his marina TC.

[locost_bryan]

Chris,

Dave Vizard wrote a Triumph tuning book in the early '70s "Tuning Standard Triumphs Over 1300cc". I stumbled across it as a pdf on a Triumph car club site. Looks like the 2000/2500 has the same diff as the TR4/5/6 and possibly the GT6/Vitesse. Presumably this is what the Dolomite Sprint diff was based on?

As far as the Aussie Borg Warner axle is concerned, there appear to have been two variants. Effectively "light" and "heavy" duty variants, going by the wheel bearings used. Same carrier and pinion, but different centres and half-shaft lengths.

The 4's had a model 68 with a 2-piece diff centre and a 3.89 ratio. This was also used in Aussie Escorts and Mk2 Cortina, Holden (Vauxhall) Viva, Toyota Corolla KE20-KE50, Datsun 1200 & 120Y, and early Holden Gemini (Vauxhall Chevette). The only other ratio I have seen for these is a 4.11.

The 6's had a model 68/70 with a 1-piece Salisbury diff centre and a 3.70 ratio. This was also fitted to Leyland P76, Ford Falcon (pre '96), Chrysler Valiant & Charger, some Holden Commodore (Vauxhall Carlton), Mitsubishi Galant/Sigma. Available ratios as high as 2.77, with 2.92, 3.23 and 3.45 most common. LSD centre is staright swap in, fairly common and cheap.

The Borg Warner axle would be rare as rocking horse poo in the UK.

Cheers,
Bryan.

[MARINAMAN480]

what about an mg midget diff would that fit as looking at my dads midget looks fairly similar??

[MarinaCoupe]

lee

I believe that the Midget diffs are the same as Austion A35, the standard Marina diffs heritage is through Triumph Spitfire, not Austin Morris.

[MARINAMAN480]

OK WAS JUST A THOUGHT AS IT LOOKS FAIRLY SIMILAR.

ON ANOTHER THOUGHT WOULD AN EARLY MGB AXLE BOLT STRAIGHT IN OR MODIFICATIONS NEEDED THINKING OF GOING DOWN THIS ROUTE FOR THE COUPE AS I HAVE TO KEEP TO PERIOD MODS FOR THE RALLYING I DO

[MarinaCoupe]

The works mod for the forest cars was the 10cwt van axle 4.55:1, bolts straight in and loads stronger than saloon axle. You'll rev the nuts off the car without a fifth gear or overdrive for road use. We can prove overdrive was used in period though.