Speedometer

Technical questions and answers
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Geoff
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Speedometer

Post by Geoff »

Stupid question time. Can anyone tell me if/confirm that the speedometer for the Stage 1 with the 1376 turns per mile figure on it is the same speedo as for the standard Series 3 109, ie part number PRC1775 in the Parts Book and now apparently superceded by RTC5035, which is marketed here as also for the 88 with 7.50x16 tyres? It's an 'academic' question - I don't need one, although I have a spare one and I suppose it would be useful to know all its applications should I ever decide to sell it. I'm confused because I have also seen the figure of 1408 turns per mile quoted as correct for the 88 with 7.50x16 tyres. I've never bought a new speedo and (mercifully) not given any thought before to their Land Rover part numbers. I guess I just assumed the 1376 (mine are Jaeger) was unique to the Stage 1, but the lack of separate part numbers in the Parts Book seems to suggest otherwise. The question arose on another forum and I'm now very confused. Does the different rear diff ratio in the Stage 1 make a difference and, if so, is that compensated by any of the different speedo worm gear, pinion and cable for the Stage 1, which are shown in the Parts Book? map?
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map1275
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Re: Speedometer

Post by map1275 »

In the KPH version, all 109 with the same tyres use the same speedo.
Had my original fitment gauge fixed. Have a new replacement as a spare and have used ones from concurrent Series III.
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Geoff
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Re: Speedometer

Post by Geoff »

Thanks map (thought you'd know) That settles it as I thought - I had been labouring under a misapprehension (couldn't remember the number on my old Series 3 109 2.25 - probably never took any notice of it back then as long as it worked)
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firemanshort
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Re: Speedometer

Post by firemanshort »

I thought that the regular Series 3 with the 4.7 differential had a different speedometer than the Stage One with the 3.54 differential.
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firemanshort
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Re: Speedometer

Post by firemanshort »

Ok - the parts book does not differentiate with Stage One or Regular Series 3 - just tire size and wheel base. Odd.
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Glen
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Re: Speedometer

Post by Glen »

Stage 1 speedos are identical to any other series 3 (just like all the other standard series 3 parts that are paraded around eBay as something special such as bulkheads and bumpers) on 7.50 tyres. As stage 1’s are often higher spec vehicles though (in the UK at least) they are often fitted with the posh speedo with trip counter, and maybe even with the green illumination cap riveted inside if it’s really fancy (county?), either of which would probably give it a different part number to the basic series 3 variant but the turns per mile (tpm) is the same.

Earlier series LWB use the 1408 tpm clock so that’s where that number comes from (definitely the earlier clocks without the warning lights but it would be too easy to assume that was the change point). The 1 ton models with 9.00 tyres have a lower number again due to the tyres.

For km clocks the number (rev/km) is divided by 1.6 as they have a 20 tooth drive wheel in the clock instead of a 32 tooth. British MOD clocks are unusual too as they are km clocks with MPH on an inner scale - km clocks don’t usually have duel units.

As for the stage 1 gearing being different due to the diffs, this is adjusted in the gearbox using a unique set of speedo drive gears with a 0.6:1 ratio. I don’t know about the 101 but all other versions of LT95 along with the series transfer box use the same ratio, I think it’s 0.4545:1 or something which is why if someone fits a complete Range Rover gearbox the speedo will underread by about 32%. The gears aren’t that hard to change if your speedo is wrong and the diff won’t need reshimming.
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Geoff
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Re: Speedometer

Post by Geoff »

What about if a complete LT95 gearbox from a 110 is fitted to a Stage One?
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map1275
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Re: Speedometer

Post by map1275 »

What about it?

Same questions I would ask for any modification approval, as vague verbal digressions aren't useful. Precisely which 110 and what have you done to prove the donor vehicle internals, ie the speedo pinion and drive are the same as needed for the recipient vehicle? Precisely ID the gearbox as per the serial number, confirm it with the 110 parts book and what the 110 parts list identifies as the pinion bits. They may well be the same but speculation isn't proof. There's certainly variation in 110 LT95s and the first 110 is almost fourty years old and typically well played with.
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Geoff
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Re: Speedometer

Post by Geoff »

My question followed on from Glen saying, "... if someone fits a complete Range Rover gearbox the speedo will underread by about 32%."

Both my Stage Ones have replacement 110 LT95 gearboxes fitted by previous owners.

The green one's serial number is 17C00198A. It was almost certainly new when fitted at the same time as a new engine in 1985 at Studley Castle by the British Motor Industry Heritage Trust who owned the vehicle at the time. The original Jaeger 1376 speedometer has always recorded the vehicle's speed perfectly accurately, as recorded against other devices, during the 24 years that I have owned it, so I assumed that whatever alteration was required to the speedo gears in the gearbox had been done when it was fitted.

My limestone Stage One's gearbox serial number is 13C02817A. I have no information when, where or by whom it was fitted, of from where it was sourced. When I purchased the vehicle 10 years ago the non-original unbranded speedometer was underreading badly. None of a new cable, correct (for a Stage One) pinion drive, or a used Jaeger 1376 speedometer made any appreciable difference. I found a NOS Genuine Stage One worm gear on ebay but in the event have not fitted it. Instead I had the unbranded speedo recalibrated to 1000 turns per mile which I believed matched the speedo on the early V8 110 with the LT95. This was nearly 8 years ago and I just dimly remember that I had difficulty ascertaining that figure, so I am not certain now that it is the correct figure. Speedograph Richfield in Nottingham who did the recalibration said the speedo was a Smiths one, though the name did not appear on the face, nor any turns per mile figure, just MADE IN UK. The speedometer now overreads slightly more than I would like but as I believe it may provide some unconscious safety margin when negotiating the speed cameras that are ubiquitous in this country I have lived with it. With hindsight, I should have done the proper calculations with the vehicle that Speedograph Richfield advise and had the speedo recalibrated accurately to suit it, but as that would have involved asking another person to assist I didn't bother.

So my question is academic but, as Glen touched upon the topic by mentioning the different Range Rover LT95, which I was aware of, and seemed knowledgeable on the subject, I thought I would ask out of interest. I am not at all an expert or knowledgeable about the matter and everything I have done has been based pretty much on guesswork.
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Geoff
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Re: Speedometer

Post by Geoff »

Further to my previous post and map's reply, the 110 Parts Catalogue (up to Aug '86) gives only one part number (FRC3162) for the worm gear for the V8 - 4 SPEED - GEARBOX (LT95) and one part number for its associated spindle (FRC3310) The Stage One's LT95's spindle is part number FRC2284. Both have 20 teeth. The Stage One worm gear is part number FRC2283. What actual difference there may be between the worm gears I don't know (or the spindles - they look slightly different, but possibly not significant)
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Glen
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Re: Speedomete

Post by Glen »

As you might have guessed mine had RRC gears in it so I don’t know details for the 110. As you say the part numbers are different for the 110 but it doesn’t list tooth counts or colours in the book so I don’t know how different they are. It is however not uncommon for gearboxes in some vehicles to have different gear sets available where the tooth count on the gear is the same but the worm is different, the gear profile has to match the worm so just because the tooth count is the same does not nesiserally make it interchangeable. I know VW colour code their gears presumably to help identify identical tooth counts but they then don’t bother to list the colours in the book. I seem to remember when I swapped the gears in my LT95 they were different colours too but I can’t now remember what they were or what the tooth count was - it was about 5 years ago.

On 90/110 (pre td5 when the speedo went electronic) they would change the drive gears rather than the clock for different tyre sizes but as with series this is usually only for the swb as the 110 basically only had 1 factory tyre size (7.50R16 and 235/85R16 are considered the same). That’s probably why the book only lists 1 pair of gears as it only covers 110’s and the V8 90 arrived at the same time the 5 speed LT85 was introduced. That said if the defender clock is the same ratio as a range rover which I think was 1000 turns per mile then the stock Range Rover drive gearing would work with a 90 on 205R16 tyres. It would then stand to reason that the gears fitted to the 110 (and 90’s with factory fitted 7.50 tyres) would be about 10% slower. That would mean they may only under read by about 20 % in a stage 1 and given the clock would have been calibrated to over read a bit anyway this may lessen this further.

Speedo accuracy and odometer accuracy are also not the same thing. The speedo can drift out due a faulty clock spring or magnet in the speedo head (gives a % error) or the needle can move on the spindle (an absolute error), all would make it read wrong with the correct gears. The odometer is however a direct gear drive so that should always read true unless the eccentric paw inside is sticking in which case it probably won’t log any miles but still show speed (though they can get a bit intermittent, especially on cars that don’t get used much). Assuming the numbers go round your best bet is to check it with a gps or the white sticks on the motorway which are every 100 m - the km number on the sticks are also on the driver location signs about every 500 m or so on the motorway (much easier to read!) - every 1.6 km you should clock a mile (that’s right, the measurement signs are metric even though it’s illegal to have metric speed limits in the UK and they often pretend it’s yards in the Highway Code).
Generally the odometer should be pretty accurate when it’s geared right but the speedo will probably then over read about 5…10% - I think that’s how they were originally set. It seems the faster you go the more it over reads (a % error) but some heads don’t over read much around 30 mph and may even under read a bit at 20 mph - check it with a gps on flat ground with no trees in the way.

If it turns out the speed is out by a fixed value you can reset them by taking the glass off and flicking the needle over the stop - you should then find it points at a little dot on the face of the clock slightly below the stop which is used to set it. If it’s not aligned you can hold the magnet cup on the back and twist the needle on its spindle until it’s aligned. If it’s still badly wrong then it’s probably got a magnet or spring issue and needs to be repaired.
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Geoff
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Re: Speedometer

Post by Geoff »

Thanks for your reply. This webpage lists 4 spindles of different colours, number of teeth, and part numbers for the 90/110 on different tyres:

https://www.land-rover-blog.co.uk/how-t ... and-rover/

The Stage One spindle (FRC2284) is pictured here:

https://www.ebay.co.uk/itm/261159853169 ... olid=10049

and here:

https://www.brit-car.co.uk/product.php/ ... series_111

The 110 spindle FRC3310 is pictured here:

https://www.johncraddockltd.co.uk/frc33 ... teeth.html

The one I replaced was white, and well worn (looked more like 2284 than 3310 - think I still have it somewhere, but that doesn't mean I can find it - I'm looking at a not very clear photo of it on the ground under the vehicle along with its housing, which was a bugger to remove!)

The percentages you mention describe pretty much exactly the way the speedometer in my Limestone Stage One was reading both before and after I had it recalibrated, also the overreading increasing with speed. The original underreading I found particularly dangerous as I found it very difficult to ignore and not let it encourage me to put my foot down, particularly in a vehicle I was not yet fully familiar with its engine performance. Since two speedometers behaved the same, I concluded the fault did not lie with them. I much prefer the speedometer on my other Stage One that reliably tells me my actual speed (I only wish its fuel gauge worked as well but you can't have everything!)

Interesting what you said about the odometer. I'm sure I tested that too against my GPS but it's years ago and I have forgotten the result, so I will repeat the experiment.
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