English Diff Ratio's

[Adrian Southgate]

So I've got to a point where I need to make a decision on the diff but on checking them today I seem to have a bewildering range of ratio's. I assume that the numbers stamped into the crown wheel are part numbers and that a segment is the number of teeth on the pinion and another the crown wheel.

This being the case I have the following... 

That one is definitely 9-35 and I have a second one to match which needs new planet gears... Both have 69 part numbers so made in 1969?

That one is 11-39 and has a 71 part number and a large flange...

This is the one I have just taken out of the axle, looks much newer than the others but its a 10-39 and has a part number with no conspicuous date.

Now working from these numbers I would hazard a guess that the 10-39 is actually a 3.9:1 (3.89:1?)

That makes the 9-35 a 3.88:1 and the 11-39 a 3.54:1.

Bearing in mind i will be using a type 3 box and a 1630 xflow should I fit the 3.54:1?

[Adrian Southgate]

1600 (+ a bit) crossflow, type 3 4 speed.

I tried to run it through gearcalc but it doesn't give the type 3 as a specific on the ratio's list.

I was working on the principle that the 3.54:1 in a 1600 with a rocket or 2000e box was perfectly acceptable. I don't have either of those so for the moment will have to make do with a type 3. 

I agree that the 9-35 and the 10-39 are both actually 3.89:1 diffs and calling it a 3.88 was splitting hairs. :)

[Big Vern]

10-39 = 39/10 therefore 3.900  35/9 = 3.8888888889  MK2 Cortina's were 3.9 or 3.77 with a few Cortina estates having a 4.125 but yes to all intents and purposes they are both 3.9

Ford 4 speed boxes are 1:1 for 4th gear so its the rear axle ratio, type 3 (type c) is the wide ratio version of the GT/2000e box

The 3.54 works with the 4 speed

[Adrian Southgate]

Looks like its the 3.54 then :)   

That's actually the cleanest inside too with less 'mesh wear' than the others so i'll get that round to geartorque and get it checked.

I do have a full rebuild kit but the outer half shaft bearings seem in good condition so they'll be going back in. The inner ones i'll leave to the experts to check.

To be honest, 'doing the ton' was never critical but cruising RPM at 70mph is. If this set up gives me 70@3800 rpm will mean the secondary has just opened and that will give me the little nudge that makes excursions into lane 3 to pass things a lot safer.

[Big Vern]

the 69 or 71 only refers to the model year that design or part was intended for.  the 3.54: will give you the best fuel economy but the if your putting it in a Dutton, that's cancelled out by the aerodynamics, or rather lack of them :-)))) 

English ratio's are 4.44, 4.125, 3.9, 3.89, 3.77 & 3.54 any others such as 4.8 and 5.3 are custom rally jobs.

Most sort after and therefore expensive is the 4.44 & 4.125

Wouldn't bother fitting a 5 speed on an xflo they just don't have the torque for it.

[Jim (across the pond) Adamek]

Talk about the lack of aerodynamics, my Phaeton is probably the worst one on the road today.

[Adrian Southgate]

 full bodypan BV. The front aero on a legerra isn't as bad as some of the others. Got to work on the details but the white one is getting a 3/4 to full undertray.

4.44 and even the 4.125 are surely only good for sprinting on short twisties as they won't have any top end and you'll be screaming it at 70...

3.9 and 3.89 - I think thats what in CMV and with a 2 litre and the type 9 it works ok. I know if pushed it will hit three figures. To be honest I don't want a type 9 in this one as its going to be as close to 'original' as possible.

Project X has an MT75, thanks to Mr Adams - Project Y is going to be transverse, mid engine.

[Patrick Buchfink]

Project Y definitely sounds interesting! How to take another step forward in project Z then? An aircraft engine? Or will it be the flux compensator? -:)

[Adrian Southgate]

Project Z is a 2 litre pinto.... old school I know but there ya go...

[Big Vern]

an undertray isn't going to offer much with all the vents, grills, wheel arches and headlamp pods making it draggy. As for the 4.44 and 4.125 - depends what you call screaming? My mx5 has a 4.3 and that's still sub 5000 in 4th at 70mph.

[Adrian Southgate]

Trying to smooth the flow of air under the car isn't going to make it any worse than the tractor chassis already is.   

Ducting the air in the front and out of the bonnet is a start. I haven't worked out the square area of the modified front bumper vents yet so don't know what I am going to do with the rest of it as the bonnet grills are much smaller than the bumper vents. I might also tryout some sort of clear cover for those mental headlight pods like the E-type.

[Patrick Buchfink]

Is anyone driving the 5 speed Type 9 + 1600 crossflow?

My car was planed by the previous owner to be build with that setup including a 3:54 diff and 13" rims (don't know the correct wheel size at the moment). I decided to adopt this setup, since it will mainly be a touring Dutton.

Now that I've entered the values in a transmission calculator, I'm again hesitating. If I remember right it was something about 180 km/h = 111 mph on 6000 rpm 5th gear. I know that this might not be achievable due to missing power but this feels pretty much. What is the "top speed" of your Duttons?

[Big Vern]

The 1600 xflo just doesn't have the torque for the 5 speed.You'll be using 3rd and 4th most of the time.

140 brake 2.1 pinto engined melos with type b 4 speed and 3.77 diff = 106mph all out. The areodymamics prevented it going any faster.