Hybrid_From_Hell Posted December 17, 2005 Share Posted December 17, 2005 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 Quote Link to comment Share on other sites More sharing options...
LR90 Posted December 17, 2005 Share Posted December 17, 2005 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 Quote Link to comment Share on other sites More sharing options...
Bull Bar Cowboy Posted December 17, 2005 Share Posted December 17, 2005 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 Quote Link to comment Share on other sites More sharing options...
LR90 Posted December 17, 2005 Share Posted December 17, 2005 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). Quote Link to comment Share on other sites More sharing options...
BogMonster Posted December 17, 2005 Share Posted December 17, 2005 (edited) 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 Quote Link to comment Share on other sites More sharing options...
Hybrid_From_Hell Posted December 17, 2005 Author Share Posted December 17, 2005 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 Quote Link to comment Share on other sites More sharing options...
western Posted December 17, 2005 Share Posted December 17, 2005 (edited) 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 Quote Link to comment Share on other sites More sharing options...
darthdicky Posted December 17, 2005 Share Posted December 17, 2005 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 Quote Link to comment Share on other sites More sharing options...
Guest diesel_jim Posted December 18, 2005 Share Posted December 18, 2005 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. Quote Link to comment Share on other sites More sharing options...
Hybrid_From_Hell Posted December 18, 2005 Author Share Posted December 18, 2005 Ralph, cheers for the options, any idea which one a std 1985 V8 90 would be as a reference ? Nige Quote Link to comment Share on other sites More sharing options...
western Posted December 18, 2005 Share Posted December 18, 2005 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 Quote Link to comment Share on other sites More sharing options...
Bush65 Posted December 18, 2005 Share Posted December 18, 2005 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. Quote Link to comment Share on other sites More sharing options...
LR90 Posted December 18, 2005 Share Posted December 18, 2005 Tony, that info of Ralph's should go into tech archive. Very usefull. Quote Link to comment Share on other sites More sharing options...
western Posted December 18, 2005 Share Posted December 18, 2005 (edited) 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 Quote Link to comment Share on other sites More sharing options...
simonb Posted December 19, 2005 Share Posted December 19, 2005 (edited) 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 Quote Link to comment Share on other sites More sharing options...
Bush65 Posted December 19, 2005 Share Posted December 19, 2005 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. Quote Link to comment Share on other sites More sharing options...
02GF74 Posted December 19, 2005 Share Posted December 19, 2005 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. Quote Link to comment Share on other sites More sharing options...
Bush65 Posted December 19, 2005 Share Posted December 19, 2005 ...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). Quote Link to comment Share on other sites More sharing options...
Hybrid_From_Hell Posted December 19, 2005 Author Share Posted December 19, 2005 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 Quote Link to comment Share on other sites More sharing options...
Zed Posted December 19, 2005 Share Posted December 19, 2005 I use my GPS for accurate speed reading Quote Link to comment Share on other sites More sharing options...
Bull Bar Cowboy Posted December 19, 2005 Share Posted December 19, 2005 HmmmmHave 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 Quote Link to comment Share on other sites More sharing options...
Mark90 Posted December 19, 2005 Share Posted December 19, 2005 But it's still way more accurate than any thing fitted by LR Quote Link to comment Share on other sites More sharing options...
Turbocharger Posted December 19, 2005 Share Posted December 19, 2005 [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 Quote Link to comment Share on other sites More sharing options...
Hybrid_From_Hell Posted December 19, 2005 Author Share Posted December 19, 2005 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 Quote Link to comment Share on other sites More sharing options...
white90 Posted December 19, 2005 Share Posted December 19, 2005 (edited) 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 Quote Link to comment Share on other sites More sharing options...
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