Defender 90 speedo over-reading

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smthack

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Im looking for some thoughts or advice about what to do about a problem with my recently aquired Defender 90 td (constructive comments only please :D )

I've long suspected that the speedo was over-reading by the way I was holding up HGVs on the motorway even when travelling at warp-speed 65mph. After some tests with my satnav, it turns out that the speedo is over-reading by around 33% at any speed. I bought the landy with 205/75/16 tyres (snow + ice remoulds) and have wanted to change themfor something a bit more useful for my part of the world. My thought was to go for something with a bigger rolling radius to correct the optamistic speedo, but even if I go for the biggest Goodrich seems to ffer (285/75/16) I'm still only increasing the radius by 20-something% plus going way outside the "standard" sizes.

So my reckoning is that something is either wrong with the speedo drive, the speedo or the cable. I've got no real reason to doubt the speedo itself, and the needle sits steady at any speed. What can I check or does anybody have other suggestions as to how best to go forward?
 
it could quite possibly have the wrong speedo drive in it,I've just changed the transfer box in my 90 for one out of a disco ,and i had the same problem,i think there are 3 different colours of speedo drive and these reflect the speeds,although i cannot be certain, you need one with 22 teeth which i think is cream in colour,the others are blue and red.
 
As luck would have it I've just taken delivery of a 200tdi 90 (in france), changed the std size dia rubber to 750 r 16's and took it for a run to visually calibrate the speedo against the gps, and it now reads spot on!!:), all I have to do is keep an eye on the kph inner ring until I get used to the speedo readings.
 
Thanks for the suggestions. There's a definite possibility that the speedo drive has been changed at some time in it's past so I'll go take a look at that. Right enough I did see something on another forum taking about the colour coding. Cheers!
 
on the larger wheel sets such as 33 12.50 u have to put a diffrent ratio speado into the dash. my rover came with this high ratio fitted and when came to fitting standard road wheels it over read. easy enough to find a low ratio speedo and even simpler to fit.
 
when i recently swopped my transfer box for one out of a disco ,the colour of the speedo drive i used was cream (think it used to be yellow) this registers spot on with a sat nav and with the speed indicator down the road ,i run 235/85/16 tyres , i hope this helps .
 
Mine is totally stock with original tire size and the speedo reads 10 km/h over all the time. Doesn't matter what speed I drive. Where can I purchase ratio gear to compensate for that ?
 
it seems to me that its pretty standard for speedo's to over-read on most cars, I know what speed I'm doing regardless ofwhat the clock says cos I've used a gps to calibrate it. The number of cars that I pass on the motorway (in a V8 disco - my other drive) is unbeliveable. I bet they all think "look at that tosser speeding" when they are only doing 65.
 
Weird. I've got 265's on both my 300Tdi's and one reads 10 mph over at 50mph and the other is spot on when compared to my GPS. So with stock tires both my speedos would have been out, it's just chance that the bigger tires on one took up the error. On the other with 20% overread error, seems likely that the stock speedo drive gears were changed out at some point by previous owners. Will have a look...
 
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Can someone explain this in more details?
Do you need to change the cable is it part of the cable or is it in the box and can it just be changed with nothing else?
My GPS reads 40 when Speedo reading 50...I'd like it right....its defo down to the 200tdi conversion done in past....its also means its putting more miles on and prob done less than it reads!! :)
 
Rossy said:
Can someone explain this in more details?
Do you need to change the cable is it part of the cable or is it in the box and can it just be changed with nothing else?
My GPS reads 40 when Speedo reading 50...I'd like it right....its defo down to the 200tdi conversion done in past....its also means its putting more miles on and prob done less than it reads!! :)
Click to expand...
there are a few different ratio speedo drives that are pushed in to the output housing ,frc3310 the blue one is for the larger tyre
 
Sorry "output housing" this on the gearbox? can any be pushed in?
Also how, do you remove the cable and is it obvious to pull out whats in to push in a differant one?
Sorry, just never had to mess in past with speedo...
 
Rossy said:
Sorry "output housing" this on the gearbox? can any be pushed in?
Also how, do you remove the cable and is it obvious to pull out whats in to push in a differant one?
Sorry, just never had to mess in past with speedo...
Click to expand...
behind the hand brake on the t/box ,theres a choice of drives depending on tyre size
 
My Speedo is pretty good for accuracy but the odometer is reads under by almost 30 % ,
No ideas how that works ??!
 
My last 110 on 33)12.5s was spot on with a Discovery transfer box.

My current one that's standard over-read about 10% or so with standard wheels. Was perfect with 33s and now has 35s and upto about 40mph, it's spot on but starts to underread a little from then on so about 60-80mph, it's under-reading by about 5-10mph


33s seems to make most read right though going by my own and others I've been in that have had GPS showing a read out too
 
Rossy said:
Sorry "output housing" this on the gearbox? can any be pushed in?
Also how, do you remove the cable and is it obvious to pull out whats in to push in a differant one?
Sorry, just never had to mess in past with speedo...
Click to expand...
Its easy to do but awkward, its a little nylon thing. All you need to do is undo one bolt on the transfer box that holds in a fork which holds the gear in and swap the gear. I went from a blue one to a red one (I think) as mine was overreading. It is perfect now.
 
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