Thread: Speedo difference fitting a defender transfer box to Disco????

Hi there,

This thread may be of use.

Cheers,

Phil

None provided you use the drive gear from the original box.

John

It's more to do with what the std tyres were on the vehicle the TC came from - remember the speedo drive is at the rear end of the TC- defenders come standard with 32's, Disco's 29's. In that other thread, it makes more sense when you remember that Gulf states Disco's (and the carby V8 RR) were issued 32's.

29's -- 20 teeth
so
(30 -- 21 ?)
(31 -- 22 ?)

32's -- 23 teeth

I know this is very rough, but try a red frc3313 - at 24 teeth it may be spot on for 33 inch tyres.

Hi

Being somewhat sad when I was jiggling about with CWPs, T Box Ratios, Tyres and such like I found I had a 90 that was hopelessly over geared

1st was ok, 2nd too, 3rd er ...lardy...4th Yaaaaaaaawn, and 5th unusable.

As such being sad I managed to get hold of some program from a R&D engineering mate which I have tweaked and now use for myself and others.

If you post up

your tyre CIRCUMFERENCE, both now and standard
T Box type (Ratio) Now / std
Axle ratio
Primary gearbox type

I can run it through the program, what is good is to send me the "Factory fresh" settings for the above, and then what you have know, I can then post up a PDF of this which shows RPM vs Spped, all 5 gears high and low at varying set points, this way I found that at something like 4500 RPM in 5th I would be doing - wait for it - 137 MPH just a "Tad" over geared

Also bear in mind that changing the T Box ratio ONLY affect raod driving ( High Box) as ALL LT230s have the same Low range of 3.321:1, to change both High and Low you have to chnage the CWPs, ratios about are 3.54 (std) 3.8 4.1 4.7 4.75 4.88 (V early 80 inch), and there is also a range of T Boxs - see www.ashcroft-transmission.co.uk for model numbers and ratios.

If I can help with the calcs post up

Nige

Thanks Kam Diff Nige,

Current set up is: diff ratio 3.54
standard t/case 1.222
new tyre circumference approx 2619mm or 103 inches
old tyre circumference approx 2393mm or 94.2 inches
gearbox is zf 4 spd auto

Proposals are : 1. keeping above figures with diff ratio changed to 4.11

2. Keeping above figures with transfer case change to 1.4 (approx)

As i explained in original post, am happy with the low range reduction it still has now, so mainly interested in bringing the high range gearing back to assist with towing/fuel economy.

My figures are I think in high range the figures work out about the same for the above two proposals, but if you have a program which can confirm this, it would be great. thanks.

Tyre diameter change affect on speed is:
(33" - 29")/29" = 0.1379 a 13.79% increase in speed at same engine revs and gear.

Alternatively 33"/29" = 1.1379 so 13.79% increase.

Transfer high ratio change affect on speed is:
1.222 to 1.41 = 1.222/1.41 = 0.8667. So speed is 13.33% ((1.000 - 0.8667) x 100) slower.

Difference between 13.8% and 13.3% is insignificant for our purposes.

Here you go,

Happy studying !

Nige