Hmmmmmmmmmm Speedo neaeds a tweakette.....

[Hybrid_From_Hell]

Right,

Just got in from the workshop after a major refit, ..............

now have a set of ashcroft Pinned and ARbed 24 spline diffs with 4.11:1s...Thanks Dave !

Oh what a difference, the Eales pulls now like a train in every gear, even with the 34 simexs on 5th is USEABLE but I haven't found the rev limiter in every gear yet, botty bottomed out so to speak

However, .........on the way home from testing up the A3, I passed a mate (without knowing) he said - "yikes you were moving" , erm, my speedo I remember on the A3 was showing about 65 mph....

Done a few calcs (same progaram as the one I used to recalc the gearing) and I reckon the speedo is probably about 22-24% out.

So, question is HOW can this be rejigged to ensure is closer to accurate ?

Does it HAVE to be the speedo that is recalibrated, or can it be done with the nylon gear in the gearbox, if so how and what are the options ?

Nige Eales 4.5 V8 & 4.11s = V Happy Bunny

[LR90]

Done a few calcs (same progaram as the one I used to recalc the gearing) and I reckon the speedo is probably about 22-24% out.

Seems odd. Bigger wheels will make the speedo read slow while the 4.11's will compensate.

For the same engine rpm you should be doing about 5% more MPH than a stock 90 with 3.54s and 205r16s (ie original fitment). Of course the original speedo may not be terribly accurate

[Bull Bar Cowboy]

I suspect that you have the 750/16 gear in there ............. using the calulators we both have.,try and work the % backwards and see if the standard 205 gear might do it ..............from memory there were only 2 options.

If recal is required then it might be time to get an electroic speedo and sender from Merlin of Demon ?

I think i may have the 205 gear in the workshop .... I'll look later ......... I know that ones red and the other is blue, cant remember which is wot .... so to speak.

Oh...... BTW ...............just dont mention Roll Cages ......... been at it all day with nothing really to show other than getting the Main hoop chassis mounts ready to weld.

Ian

[LR90]

Will read about 5% under with a 110 (7.50) gear.

I'd err on the over reading and use a 205 gear, makes your mpg look worse but less likely to find yourself speeding (a topical topic).

[BogMonster]

Erm

Maybe I am being thick here (no need to answer that bit ) but surely the lower ratio diffs will make the speedo over-read not under-read???

The diff ratio is lower thus the propshafts and transfer box will be spinning faster for any given road speed, therefore so will the speedo drive so the speedo will indicate higher for any given road speed than before, will it not?

Approx 16.1% difference in the diff gearing (gearing down)

Approx 6.25% difference with the tyre diameter compared to a 7.50 (gearing up)

So about a 10% overall net difference (over-reading compared to std vehicle)

Most older Defender speedos I have calibrated either with GPS or against a measured mile over-read by about 8-10%.

....so if there is a 7.50 speedo drive fitted it should end up being way over-reading shouldn't it?

Have you got a GPS? The speed reading from those is very accurate, I calibrated mine (yellow eTrex) against the measured mile the police use here for the same purpose and it was something like 0.2% different which I was quite chuffed with

Edited to correct my calculations before somebody else does

Edited December 17, 2005 by BogBuster

[Hybrid_From_Hell]

Er

Righty ho,

Think some time soon I get a mate to drive at 40 indicators, 50 indicators, 60 indictaors, and my passenger with a tippex and paper and pen....

Then I can see whats what, maybe it not as far out as I think, hadn't thought of the 4.11s helping out the 34 tyres....

I'll let you know

Nige

[western]

This might help you find the correct speedo drive gear---------------------

90/110 speedo drive gears

frc3310 blue----------20 teeth

frc3311 green--------21

frc3312 yellow--------22

frc3313 red-----------24

Discovery 1 [200Tdi/V8]

frc3310 blue----------20----diesel

frc9339----------------23----[see note]

frc3310 blue----------20----V8 efi

frc9339----------------23----V8 twin carb

Note frc9339 diesel for gulf states vehicles,no colour code listed, auto trans Tdi vehicles

my 200Tdi 110 runs a blue 20t frc3310 on 255/85r16 tyres, speedo is nearly spot on with my gps- less than 4 mph difference, hope that helps

Edited December 17, 2005 by western

[darthdicky]

Nige, borrow a GPS - it's so much easier than following a mate etc. You can see what speed you're doing for whatever's shown on your speedo and so on.

I think mine works out about GPS 60mph at an indicated speedo 63mph which is pretty good.

Richard

[Guest diesel_jim]

I had 4.1:1's on my 90 until recently, along with 300Tdi,R380 and 1.2:1 transfer box. using the blue speedo gear, mine read under speed (by about 20mph),

overall "feel" of the gearing was is felt about 1/2 a gear under what it used to. good with 35" simex's though.

[Hybrid_From_Hell]

Ralph,

cheers for the options, any idea which one a std 1985 V8 90 would be as a reference ?

Nige

[western]

Ralph,

cheers for the options, any idea which one a std 1985 V8 90 would be as a reference ?

Nige

EPC tells me ----------

A 90 on 205 x 16 tyres is fitted with a 22 teeth Yellow gear FRC3312

A 90 with 3.5 V8 twin carbs & LT77S is fitted with a 24 teeth Red gear FRC3313

Hope that helps

[Bush65]

This might help you find the correct speedo drive gear---------------------

90/110 speedo drive gears

frc3310 blue----------20 teeth

frc3311 green--------21

frc3312 yellow--------22

frc3313 red-----------24

Discovery 1 [200Tdi/V8]

frc3310 blue----------20----diesel

frc9339----------------23----[see note]

frc3310 blue----------20----V8 efi

frc9339----------------23----V8 twin carb

Note frc9339 diesel for gulf states vehicles,no colour code listed, auto trans Tdi vehicles

my 200Tdi 110 runs a blue 20t frc3310 on 255/85r16 tyres, speedo is nearly spot on with my gps- less than 4 mph difference, hope that helps

Interesting. Some good info to keep in mind.

Don't all of these have the same 3.54:1 diff ratio stock?

So the different numbers of teeth could be explained by different tyre rolling radii.

I was not aware that Disco's had that much (15%) difference in stock tyre rolling radius.

[LR90]

Tony, that info of Ralph's should go into tech archive. Very usefull.

[western]

Tony, that info of Ralph's should go into tech archive. Very usefull.

It's in the 'Tech Archive' already

Speedo drive gears

Edited December 18, 2005 by western

[simonb]

Correct, diff ratio is the same at 3.54 but Discos have 1.2 ratio transfer vs 1.41 for all Tdi. V8 and 2.5 Petrol have 1.6 ratio transfers (red gear), so its all to do with tyre and diff ratio. Not sure what the green one was ever used for... FRC9339 is Disco auto which may have different transfer ratio, anyone know?

Edited December 19, 2005 by simonb

[Bush65]

Correct, diff ratio is the same at 3.54 but Discos have 1.2 ratio transfer vs 1.41 for all Tdi. V8 and 2.5 Petrol have 1.6 ratio transfers (red gear), so its all to do with tyre and diff ratio. Not sure what the green one was ever used for... FRC9339 is Disco auto which may have different transfer ratio, anyone know?

The transfer ratio does not make any difference to the speedo drive because it on the rear output shaft.

[02GF74]

Oh what a difference, the Eales pulls now like a train in every gear, even with the 34 simexs on 5th is USEABLE but I haven't found the rev limiter in every gear yet, botty bottomed out so to speak

From the description of your driving style, I'd suggest you should get the speedo to read correctly pronto.

There are 2 or 3 compaines that recalibrate speedos; it involves remagnetising the disc for correct mph and gearing for the odometer.

mini gearboxes that fit to speedo cable are available but I am not sure if there is one for your application.

you can get aftermarket speedos that can be set but they run of a signal from the gearbox i.e. not mechanical.

Another option is to mark on the glass the new mph readings or get a new rear face printed (you need to be careful when refitting the needle to be sure it is in the same place I think)

Or do what I do, make a mental calculation.

It just occured to me to print out a small table - shown speed/actual speed and pin next to the speedo; I am sure in no time you will be able to remember them (now why haven't I doen that to mine?)

re: calibration; most car speedos under read.

On any motor way you have posts 100 m apart. Find a straight length of motorway, M1 is good for this - drive at constant speed and count the posts in a given time then work out you true speed.

[Bush65]

...mini gearboxes that fit to speedo cable are available but I am not sure if there is one for your application...

I have used a couple of these with different ratios to suit tyre sizes on my rangie and they work well, but I had to have custom speedo cables made to suit the drive on the gearbox.

AFAIK there is a good selection of ratios).

[Hybrid_From_Hell]

Hmmmm

Have just been playing with my very cheap Tom Tom sat nav.......and it has a MPH function YIPPEEEEE

Will try it later ....when I go for the MOT

Also, my transfer box LT230 being a genuine V8 is a 1.1923 :1

Nige

[Zed]

I use my GPS for accurate speed reading

[Bull Bar Cowboy]

Hmmmm

Have just been playing with my very cheap Tom Tom sat nav.......and it has a MPH function YIPPEEEEE

Nige

[Pedantic Mode On] Remember that with regard to speed, the GPS does not take a 3D view of the world, it just calculates speed as the time taken to travel between fix updates (i.e. it assumes a straight line). So if you are traveling down or up hill then Mr Pythagoras has some effect and the speed indicated will be slightly inaccurate. However, depending on the auto update period that is set on the GPS unit you may need to travel quite fast for the inaccuracy to be noticeable. [Pedantic Mode Off]

The above statement is not completely true of all the units but is true of many. Those that do take account of a 3D view (i.e. the speed calculation takes into account topography) are still a bit iffy as height calculation on many of the affordable models is not that good. Also you would need differential GPS to ensure the offset accuracy

Ian

[Mark90]

But it's still way more accurate than any thing fitted by LR

[Turbocharger]

[Pendant Mode On] So if you are traveling down or up hill then Mr Pythagoras has some effect and the speed indicated will be slightly inaccurate.

But on a 1 in 8 hill, the difference is only 2.8%...

I've found major flaws with the altitude calculation anyway, especially when the unit is using less than 6 satellites, so you'd probably be better off without the correction anyway!

JB

[Hybrid_From_Hell]

Well, just got back clutching new MOT (Jeez, thats a shambles with the new electroinic MOT process ) certificate, and tested the MPH / sat Nav GPS thingumy on the way there.

Its more than close enough for me, so job done, guess thinking this a simpler way, if I have been trying to get the 90s gearing back to standard via diff CW & P changes, wghich I have done via a excel program, then if I have done that then the speedo should be correct anyway DOH

Anyway, legal for another year, so AWDCs Broxhead boxing day 'drive around day' on the 27th dec is a definate ! B)

Nige

[white90]

RE:

Nige Eales 4.5 V8 & 4.11s = V Happy Bunny

the A3 was showing about 65 mph....

it that your top speed?

blimey 300BHP for that.....

A TDI will do 80+ on a flat motorway..

Nige you need to take that poor asthmatic V8 out and fit an oil burner...

Edited December 19, 2005 by white90