cornish rattler

cornish rattler

Well-Known Member
Hi guys
I am useless trying to convert gearing into math's, atm my current 1970 S2a is fitted with below
1 200tdi engine.
2 A suffix F original gearbox
3 Defender 3.54 diff's
4 looking at fitting an O/D
Can someone please help me with what the overall gearing would be with this setup, I am toying with the idea of fitting an Ashcroft transmission with the same engine, diff's and O/D fitted so again looking for the overall gearing with this setup aswell.

I have had a 1961 swb fitted with an Ashcroft transmission, std 4.7-1 diff's and O/D before but on a motorway it always felt like it needed another gear as it was quite noisy in there, hope this helps :)
 
cornish rattler said:
Hi guys
I am useless trying to convert gearing into math's, atm my current 1970 S2a is fitted with below
1 200tdi engine.
2 A suffix F original gearbox
3 Defender 3.54 diff's
4 looking at fitting an O/D
Can someone please help me with what the overall gearing would be with this setup, I am toying with the idea of fitting an Ashcroft transmission with the same engine, diff's and O/D fitted so again looking for the overall gearing with this setup aswell.

I have had a 1961 swb fitted with an Ashcroft transmission, std 4.7-1 diff's and O/D before but on a motorway it always felt like it needed another gear as it was quite noisy in there, hope this helps :)
Click to expand...
Post up the size of the tyres and wheel set up you are planning to use.

(There are several calculators for this kind of thing on the interweb but I'm happy to work it out for you so you have a comparison and perhaps will then believe in the power of the Stretch! Power / torque calculations for specific gradients can also be calculated which is what manufacturers will be doing so you get a better idea of driveability - however - I don't have the time to dig out all of that information so the simple calculations I am prepared to make are assuming the engine will be able to turn the drive line at the prescribed rpm for every conceivable condition {very unrealistic})
 
Hello.

I have a Series 3, 200tdi, 3.54 diffs, Fairey Overdrive and 205 r16 tyres and the ratios seem pretty good to me. 60mph is about 2100-2200rpm which is comfortable. It will do 70, but the wind noise just makes it pointless so I just sit behind the wagons....

The 2a gearbox seems to be slightly different gearing, at least according to the Ashcroft calculator, but 4th is still 1:1.

I previously had 7.50 tyres and while this made first gear more usable and dropped the revs on the motorway it put 30mph in the gap between 3rd and 4th gear which meant you either had too many revs on 3rd or labouring in 4th. This is why i switched back to 205s, plus I think it gives the half shafts an easier life.

Generally if I don't use the overdrive at speeds less than 50mph and I don't feel like I am over revving the engine, its probably doing about 2100rpm at 50mph.

If you are interested in any specific speeds, acceleration or combinations please let me know.

Ric
 
Stretch said:
Post up the size of the tyres and wheel set up you are planning to use.

(There are several calculators for this kind of thing on the interweb but I'm happy to work it out for you so you have a comparison and perhaps will then believe in the power of the Stretch! Power / torque calculations for specific gradients can also be calculated which is what manufacturers will be doing so you get a better idea of driveability - however - I don't have the time to dig out all of that information so the simple calculations I am prepared to make are assuming the engine will be able to turn the drive line at the prescribed rpm for every conceivable condition {very unrealistic})
Click to expand...
Sorry yeah they are 750X16
 
ricyoung said:
Hello.

I have a Series 3, 200tdi, 3.54 diffs, Fairey Overdrive and 205 r16 tyres and the ratios seem pretty good to me. 60mph is about 2100-2200rpm which is comfortable. It will do 70, but the wind noise just makes it pointless so I just sit behind the wagons....

The 2a gearbox seems to be slightly different gearing, at least according to the Ashcroft calculator, but 4th is still 1:1.

I previously had 7.50 tyres and while this made first gear more usable and dropped the revs on the motorway it put 30mph in the gap between 3rd and 4th gear which meant you either had too many revs on 3rd or labouring in 4th. This is why i switched back to 205s, plus I think it gives the half shafts an easier life.

Generally if I don't use the overdrive at speeds less than 50mph and I don't feel like I am over revving the engine, its probably doing about 2100rpm at 50mph.

If you are interested in any specific speeds, acceleration or combinations please let me know.

Ric
Click to expand...

Yeah 3.54 diff's are new to me as regards 2a's as all me previous 2a's / 3's had std gearbox's and O/D's fitted with the exception of my last 2a that was fitted with an Ashcroft transmission and O/D and std diff's and for town work I just used the O/D as a splitter box and as a 5th gear on a motorway but if I buy an Ashcroft transmission I am worried that 1st gear would be too high if I had my light duty trailer on but think the Ashcroft trans would be right for motorway work with the O/D and 3,54 diff's fitted
 
This site does break it all down better but still doesn't give me an out right figure with an Ashcroft trans, 3,54 diff's and O/D fitted but I do understand that the Ashcroft trans was designed to do away with the want of O/D and 3.54 diff's in a std S2a / S3 so was hoping someone with a better head than me could work it out for me :)
 
Hi Cornish,

You might have done this already, but if not, why not give the boys at Ashcroft a call and discuss what you need?.

Cheers
 
cornish rattler said:
Hi guys
I am useless trying to convert gearing into math's, atm my current 1970 S2a is fitted with below
1 200tdi engine.
2 A suffix F original gearbox
3 Defender 3.54 diff's
4 looking at fitting an O/D
Can someone please help me with what the overall gearing would be with this setup, I am toying with the idea of fitting an Ashcroft transmission with the same engine, diff's and O/D fitted so again looking for the overall gearing with this setup aswell.

I have had a 1961 swb fitted with an Ashcroft transmission, std 4.7-1 diff's and O/D before but on a motorway it always felt like it needed another gear as it was quite noisy in there, hope this helps :)
Click to expand...

I'd say it'd be massively over geared tbh.

Your current setup, 2500rpm should be about 57mph on 31" tall tyres.

Adding any of the OD's or Ashcroft high range, 2500rpm would be 71-75mph. But I think a Tdi simply wouldn't pull it on anything other than flat ground. Which means you'll likely have to run a gear lower a lot of the time.

For reference:

Stock Defender on 265/75R16 tyres - 2500rpm in top = 57mph
Stock Disco 1 on 235/75R16 tres - 2500rpm in top = 60mph
 
300bhp/ton said:
Stock Defender on 265/75R16 tyres - 2500rpm in top = 57mph
Stock Disco 1 on 235/75R16 tres - 2500rpm in top = 60mph
Click to expand...

Not wishing to start a p**ing match here, For information only.
I have a spreadsheet to work this out, Which I have cross referenced with the ashcroft ratio calc.
I get 61 MPH for the fender and 67MPH for the D1.

How did you get your figures?

Cheers
 
neilly said:
Not wishing to start a p**ing match here, For information only.
I have a spreadsheet to work this out, Which I have cross referenced with the ashcroft ratio calc.
I get 61 MPH for the fender and 67MPH for the D1.

How did you get your figures?

Cheers
Click to expand...
My own spreadsheet. Tyre size will affect results, as in how are you getting to this size. Plus there could be small changes in 5th gear, as there have been more than one.

Disco
Tyres 29" tall
Diff 3.54:1
High Range 1.22:1
5th 0.83:1 (Think this is an LT77 ratio, iirc there is a slightly taller variant and an R380 is likely different too).


=SUM((RPM*Tyre Diamater)/(Diff Ratio*5th Gear*High Range*336))
 
@300bhp/ton

Yeah it will be the 5th doing it, as I used an R380 (0.77 5th gear )in my calcs, mainly because both of mine have that fitted.

Strangely, Ashcroft only seem to list the 0.77 for the LT77 as well.

Cheers
 
I think there have been a number of different ratio's for 5th gear. Pretty sure LR has used both of them over the years. Although the shorter one probably in the 2.5TD days...

I think the number I'm using is what I think is in my TR7, which is what I originally created my gearing spreadsheet for.

My brother has an F reg Ninety with a 200Tdi swapped in. I think the mph per rpm tally more closely with that, so suspect it might have a different 5th gear to latter vehicles.
 
300bhp/ton said:
I'd say it'd be massively over geared tbh.

Your current setup, 2500rpm should be about 57mph on 31" tall tyres.

Adding any of the OD's or Ashcroft high range, 2500rpm would be 71-75mph. But I think a Tdi simply wouldn't pull it on anything other than flat ground. Which means you'll likely have to run a gear lower a lot of the time.

For reference:

Stock Defender on 265/75R16 tyres - 2500rpm in top = 57mph
Stock Disco 1 on 235/75R16 tres - 2500rpm in top = 60mph
Click to expand...

Yeah I think 1st gear would be like 2nd was in my last setup so should be ok using 1st with just 2a up to say a light load towing the trailer but would have to be careful with it any heavier, would probably have to use 3rd low box but its quite rare that I need to tow anything heavy so think I will be ok :)
 
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