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windy81



Member Since: 14 Mar 2018
Location: North Wales
Posts: 75

Wales 1993 Defender 90 200 Tdi HT Montpellier Red
LT230 Transfer box speedo gears - Your experiences ?

My original 1.4 LT230 Transfer box got rebuilt along with the gearbox engine at the same time by a reputable company a while back.

Whist doing this i got them to install the 1.2 gearing into the Transfer box which they then installed the largest Red 23t (i think it's 23t, not sure) speedo gear to compensate for the speedo reading high before the rebuild.

Thing is , I can't go any higher than the Red 23t gear but it's still reading too high, even with the 235/85 R16 tyres.

Speedo is reading 40mph @ 30mph (measured using GPS) thats a 33% higher !
So at 60mph it's reading 80mph!. It's massively out.

I would have thought the Red speedo gear would have sorted this. Am i missing something ? What are your experiences ?

Only thing i can do, which i don't want to is install a TD5 speedo with the Ashcrofts speed corrector.

Post #758144 12th Feb 2019 1:11pm
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Hufflepuff



Member Since: 25 Oct 2014
Location: Hampshire
Posts: 295

England 2005 Defender 90 Td5 XS CSW Tonga Green

Hmm that's odd. I had the Ashcroft 1.4 -> 1.2 ratio change put into my transfer box (by a garage), and as far as I know the speedo gearing wasn't changed - and it still reads fine.

I thought/assumed the speed reading came off the back of the transfer box - ie. the speed with which the prop-shafts are rotating, which is independent of the gearbox/transfer box gearing.

Was your speedo reading correctly before the change? No changed made to the differential ratios? 2005 Td5 90 XS
1989 V8 110 CSW

Post #758151 12th Feb 2019 1:24pm
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windy81



Member Since: 14 Mar 2018
Location: North Wales
Posts: 75

Wales 1993 Defender 90 200 Tdi HT Montpellier Red

The speedo was reading high before which is why i asked for a bigger speedo gear. The diffs are standard 1.54.

I have got it right though haven't I ? I mean if i put in a smaller Blue gear, the speedo would read even higher wouldn't it ?

I'm beginning to think the Speedo unit itself might be at fault. Might have to test that out

Thanks Huff,

Post #758155 12th Feb 2019 1:31pm
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Martin
Site Admin


Member Since: 02 Apr 2007
Location: Hook Norton
Posts: 4805

United Kingdom 2015 Defender 90 Puma 2.2 XS CSW Montalcino Red

For 235/85R16 tyres (or 265/75R16) you want the blue gear FRC3310 (20 teeth).

You've gone the wrong way with the number of teeth Smile

Edit: https://www.defender2.net/forum/topic39592.html?highlight=frc3310  1988 90 Td5 NAS soft top Cool
2015 D90 XS SW Mr. Green
2006 D110 CSW (Dad's)

Post #758160 12th Feb 2019 1:43pm
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windy81



Member Since: 14 Mar 2018
Location: North Wales
Posts: 75

Wales 1993 Defender 90 200 Tdi HT Montpellier Red

hmm ok, I'll order one and see, i must admit i cannot see how that can be though.

Maybe the logic is different with a worm gear arrangement.

I'm thinking larger driven gear on a push bike is slower, smaller gear is faster ?

Anyway thanks, i'll report back when I've installed the Blue Gear.

Post #758164 12th Feb 2019 2:13pm
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LandRoverAnorak



Member Since: 17 Jul 2011
Location: Surrey
Posts: 6394

United Kingdom 2013 Defender 110 Puma 2.2 USW Orkney Grey

Your logic is backwards. For any given speed and speedo reading, smaller tyres rotate faster than bigger ones and visa versa. The drive wheel compensates for that variation rather than vehicle speed. Darren

2013 Defender 110 USW XS
2013 Discovery 4 XS

"You came in that thing? You're braver than I thought!" - Princess Leia

MY 110 USW BUILD THREAD - MY 200tdi 90 BUILD THREAD

Instagram: @landroveranorak

Post #758169 12th Feb 2019 2:36pm
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windy81



Member Since: 14 Mar 2018
Location: North Wales
Posts: 75

Wales 1993 Defender 90 200 Tdi HT Montpellier Red

Aha.... that moment when the penny drops is a nice feeling. Yes you are right !

As I understand it now, for every 360 degree revolution of the speedo gear, Red turns it 23teeth along and the Blue 20teeth,
Hence why the Blue is slower.

Tell ya i still get Gross and Net wrong...... Thanks guys, it's been doing me head in. Sorted!

Blue gear is ordered and one more problem solved.

I'll have 2 red gears and 1 yellow gear up for grabs if anyone wants/needs them.

Post #758176 12th Feb 2019 2:53pm
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Martin
Site Admin


Member Since: 02 Apr 2007
Location: Hook Norton
Posts: 4805

United Kingdom 2015 Defender 90 Puma 2.2 XS CSW Montalcino Red

Think of the rear propshaft, which is effectively what the speedo drive gear connects to directly.

Imagine with "normal" wheels and tyres. To drive a mile the prop will do a certain number of turns (for argument's sake call it 1000). The speedo drive cable does (say) 50 turns by using a 20 tooth drive gear.

Now imagine fitting bigger tyres with twice the circumference; each turn of the wheel goes twice as far. So the prop only needs to turn 500 times to cover the mile. With the same drive gear as above, the speedo drive cable does only 25 turns - and shows half speed/distance covered.

So in the example above we need to double the number of turns of the speedo drive cable (or pulse generator) to still show 1 mile covered. We would do this by fitting a speedo drive gear with HALF the number of teeth. 10 teeth gives 50 turns of the speedo drive cable.

Getting back to the Defender, going bigger with tyres means the distance covered per turn of the wheel is greater, so the prop turns slower at the same speed, the speedo drive is slower and it needs speeding up. So fewer teeth Smile  1988 90 Td5 NAS soft top Cool
2015 D90 XS SW Mr. Green
2006 D110 CSW (Dad's)

Post #758178 12th Feb 2019 3:06pm
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windy81



Member Since: 14 Mar 2018
Location: North Wales
Posts: 75

Wales 1993 Defender 90 200 Tdi HT Montpellier Red

Aha but my problem is my speedo is reading much higher.

Reducing the teeth will make it faster.... but i want it to go slower.

In fear of sounding stupid, have you missed that my speedo was reading too high ?
It's reading 40mph when i'm actually doing 30mph according to my GPS ?

I want to slow the speedo down 33% roughly and from your analogy less teeth = faster ?

Post #758184 12th Feb 2019 3:53pm
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Martin
Site Admin


Member Since: 02 Apr 2007
Location: Hook Norton
Posts: 4805

United Kingdom 2015 Defender 90 Puma 2.2 XS CSW Montalcino Red

Was the speedo reading high even before you had all the transfer box done?  1988 90 Td5 NAS soft top Cool
2015 D90 XS SW Mr. Green
2006 D110 CSW (Dad's)

Post #758185 12th Feb 2019 3:54pm
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windy81



Member Since: 14 Mar 2018
Location: North Wales
Posts: 75

Wales 1993 Defender 90 200 Tdi HT Montpellier Red

yes, the previous tyres were 275's or something close to that, it's reading higher now, i assume because the 235/85's i have are smaller.

Is it worth taking a known good Speedo out of a friends 200tdi and testing it in mine to see?

Damn, i've just ordered a blue cog anorl....

Post #758187 12th Feb 2019 4:02pm
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Martin
Site Admin


Member Since: 02 Apr 2007
Location: Hook Norton
Posts: 4805

United Kingdom 2015 Defender 90 Puma 2.2 XS CSW Montalcino Red

Yes swap the speedos over to check it isn't a speedo issue  1988 90 Td5 NAS soft top Cool
2015 D90 XS SW Mr. Green
2006 D110 CSW (Dad's)

Post #758188 12th Feb 2019 4:04pm
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