Tallest axle ratio?

[slater]

So what's the tallest ratio live axle that I could easily source? I'm talking taller than 3.5:1 or so? It would help if its a narrow one but beggars cant be choosers. Doesnt need to handle much power.

[crockpot]

There's plenty of USA axles with ratios of 3.0 and less.
You don't say what it's for so anything else is a guess.
Are taller tyres an option?

[slater]

No, tyres are the reason I need it really. Somthing smaller and light weight would be ideal rather than a truck axle but I can put up with somthing atlas sized if needs be.

[nickwheeler]

Stock 2.0l Capri is 3.44 and will easily handle small-block V8 power. V6 cars had a 3.09 in basically the same casing.

They're not as cheap as they used to be though

[biturbo228]

Diffs from BMW turbodiesels can be as low as 2.47. Ford 7.5" rear ends (I think Sierras?) can be 2.29.

The lowest I think I've seen is the diffs in Haldex units which are 1.58.

[slater]

Yeh a Crapri atlas is my go too choice at the moment but its a bit overkill. I'd rather keep it lighter than that if I can find anything..

Sierra/BMW arnt a live axle 😉

[crogthomas]

Reliant Robin?
There seem to be ratios of 2.78:1 in some models......

[slater]

Reliant possibly a bit weak tbh.

What about MGB? 3.06 ratio avalible.. (answering my own questions now!)

[colnerov]

Mar 31, 2021 15:43:35 GMT slater said:

Reliant possibly a bit weak tbh.

What about MGB? 3.06 ratio avalible.. (answering my own questions now!)

Hi, That's a Salisbury type axle which is a bit heavy and to quote you "a bit overkill". SD1 V8 have a 3.08 but again a Salisbury type.

Colin

[vitesseefi]

Dolomite 1850 auto is 3.27. Early TR7 auto similar.

Might take a bit of finding these days.

Nick

[slater]

Mar 31, 2021 16:55:01 GMT colnerov said:

Mar 31, 2021 15:43:35 GMT slater said:

Reliant possibly a bit weak tbh.

What about MGB? 3.06 ratio avalible.. (answering my own questions now!)

Hi, That's a Salisbury type axle which is a bit heavy and to quote you "a bit overkill". SD1 V8 have a 3.08 but again a Salisbury type.

Colin

True. Seem cheap as chips tho and the 3.08 cwp seems to be avalible new from Moss.. Cheaper than a simlar Atlas setup I bet! Might be a bit wide I guess!

[vitesseefi]

Mar 31, 2021 20:40:38 GMT vitesseefi said:

Dolomite 1850 auto is 3.27. Early TR7 auto similar.

Might take a bit of finding these days.

Nick

Probably an equivalent Marina/Ital one too, likely 1800 auto.

Nick

[nickwheeler]

Mar 31, 2021 13:53:45 GMT slater said:

Yeh a Crapri atlas is my go too choice at the moment but its a bit overkill. I'd rather keep it lighter than that if I can find anything..

Sierra/BMW arnt a live axle 😉

English axles use a 3.54 diff in the bigger engined cars. They're getting very expensive now.

What car is it going in?

[Paul H]

If width is the main constraint after ratio, the rwd A series axles went to 3.7:1 (late Midget 1500, possibly Riley One-Point-Five?) in production form, and according to here, a 3.54:1 was available too:

performanceclassiccarparts.co.uk/bmc-axle-options.html

If the 3.54:1 CROWNwheel and pinion are available new, then the regular 4.5:1 or 4.2:1 donor axle would be pretty cheap as it's the 3.7 & 3.9 diffs that are in demand. From memory, the Spridget & A30 / A35 axle casings are narrower than the Morris Minor ones but not sure by how much.

[welshpug]

my e34 525 tds has a 2.65 but thats a diff not an axle, I think later vehicles don't tend to have as tall a ratio as the wheels got bigger.

[Dez]

You can get down to 2.5s in the American stuff like ford 9”. But they’re way big for your needs. A 8” much more lightweight but I don’t think goes below 2.7. Dead easy to narrow to any width with comparatively cheap off the shelf parts though.

For a only slightly lighter weight but narrower option you could use a scimitar axle, se5 is 54” and they accept jag gears so you can go as low as 2.7s with some parts swapping. Or 3.08 is a standard ratio in an auto iirc. They’re about comparable in heftyness to an atlas.

[slater]

Thanks guys, i think the MGB/C Salisbury looks like the ticket. Several ratios between 3 and 3.5, about the right width, strong enough, not massive money for a case at least and LSD etc available. Cant get my head around the exact variations yet but sure i will.

Scimitar too wide
Reliant too weak
Ford English too low ratio
Ford Atlas too expensive
American ford too big!
other BMC axles too low ratio and a bit weak

Makes sense to me anyway! Now I'm off to find if theres a gearbox better then a 6 speed Rx8

[Paul H]

Apr 2, 2021 11:03:47 GMT slater said:

Now I'm off to find if theres a gearbox better then a 6 speed Rx8

Better in what way? If you are wanting higher gearing, then the ZF box as used in a Corvette ZR1 & Lotus Carlton has a very long 6th. A friend is using one for a car he is building (bolted to the back of an engine of his own design & build), and the final gearing is in the region of 50mph per 1000rpm in 6th. Can't remember the diff ratio, but 6th is still a big step up from 5th. His one doesn't have an integral bellhousing (not sure if they are all like this though), so we've designed a bolt-on one which he has had cast, which would have needed to be done anyway to fit his engine.