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Post by minimuis on Jul 25, 2016 19:41:06 GMT
Hi. I am new here. And I have a question about the speedo drive gears in an automatic. I have recently bought a mini clubman estate, with a 1275cc austin metro engine and gearbox fitted. And it is an automatic  . The issue I am having, is that the speedometer reads 17~18% to low. It seems to me that when the previous owner did the engine conversion, he did not change the speedo drive gears to the correct ones for the mini speedometer. Now for my question: what are the correct speedo drive gears for my min? And what gears should be in the metro box from the factory? The diff is a 3.27, the speedometer in the mini is a 1280 turns per mile one, and it has 13" wheels with 175/50/13 tires. I hope you can shed some light on this! regards minimuis |
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Post by mra-minis on Jul 26, 2016 8:58:26 GMT
I can be contacted on martin@kmprecisionengineering.com The speedo gears you have are possibly correct for your transmission and wheel size, however I would suggest getting your speedo re-calibrated as a far simpler option, if you remove the speedo drive gears it will be easier to take your engine out to put it all together, ie find all the bits etc... With the correct tools to refit the forward clutch and the auxiliary pump... www.ebay.co.uk/itm/Classic-Mini-Automatic-TOOL-Forward-Clutch-Retainer-18G1097-AP2-APII-/322201061331?hash=item4b04ae07d3:g:vs0AAOSwxN5WZGM~(shameless plug) Then you can simply remove the auxiliary pump and change the gears in car, however it still will not read right and I take you back to my first point, that it is best to get the speedo head re-calibrated. |
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Post by minimuis on Jul 26, 2016 21:00:19 GMT
Do I understand correctly that you have to remove the auxiliary oil pump and forward clutch to change the speedo drive gears? Or at least for changing the worm-wheel?
The mini is currently on the road, so taking thing apart for seeing whats in there is not an option. hence the question what gears should be in a metro. With a bit of luck only the pinion gear needs changing. I believe that can be done without taking things apart.
If this is not the case, a speedo re-calibration might be in order!
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Post by mra-minis on Jul 26, 2016 23:00:16 GMT
I can be contacted on martin@kmprecisionengineering.com Not quite, the auxiliary pump has to come off, the forward clutch (using the tool mentioned above no shame... ) can be held in place whilst you strip out the auxiliary pump. the one gear in the speedo bush housing can be taken off but you still need the pump/pinion gear removed to change the speed, but as above you will not get it right, maybe closer but not right. QUOTE With a bit of luck only the pinion gear needs changing. I believe that can be done without taking things apart. If this is not the case, a speedo re-calibration might be in order! QUOTE nope you need to change both together as they are different tooth form DP's A re-calibration is certainly the best and easiest way. |
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Post by richard1 on Jul 26, 2016 23:33:16 GMT
I'm guessing this applies to me as well, but I really don't want to pull apart that pump/disc unit.
I have not yet tested the odometer or speedometer, but are all of them the same?
I have a speedometer from a manual transmission saloon that probably had 12" wheels, a 92 SPI engine/auto transmission from a saloon that probably had 12" wheels. But I have 10" 165/70 R10 tires.
How far off is it likely to be and is there any solution other than taking apart the transmission.
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Post by mra-minis on Jul 27, 2016 0:20:30 GMT
I can be contacted on martin@kmprecisionengineering.com
It could be a fair way off, i'll look through the part numbers and see what I can "organise" to see what final drive unit goes with which speedo gears, I don't think it will tell me the TPM of the speedo but if ti does all the better.
Richard in your case you could also get your speedometer re-calibrated, this is the part in the dash.
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Post by richard1 on Jul 27, 2016 11:35:15 GMT
I did not take this speedometer apart, but on all the others I have, and the odometer is geared directly, while the speed is magnetic. I thought calibration was on the speed part, either re-magnetizing the bar or adjusting the tension spring.
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Post by limby2000 on Jul 27, 2016 19:33:29 GMT
I think were all in that boat too Richard, my mini thirty which was once a 998 now has a 1275 box from a 93 sprite although i have my original 998 clock,s. Wont know till its all running. There is a firm called speedy cables, you mark your tyre, move the wheel over so many revolutions, measure the distance, then send your speedo assembly to them and they calibrate it. Dont suppose its cheap but looks better than sticker overlays on the speedo.
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Post by mra-minis on Jul 27, 2016 22:59:24 GMT
I can be contacted on martin@kmprecisionengineering.com See above Terry Anyone want to come and research on my microfiche is more than welcome |
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Post by limby2000 on Jul 28, 2016 14:11:56 GMT
Would any 1275 clocks work with my 1275 box?, sorry to dip into someone elses thread.
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Post by mra-minis on Jul 28, 2016 23:29:58 GMT
I can be contacted on martin@kmprecisionengineering.com
No, I think the later SPi auto Mini had a higher FDR and as such would have also had a correspondingly different speedo or speedo drive..
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Post by limby2000 on Jul 29, 2016 10:44:57 GMT
Great, nothing is ever simple (or cheap),lol.
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Post by mra-minis on Jul 29, 2016 11:41:16 GMT
Great, nothing is ever simple (or cheap),lol. Try running a machine shop  |
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Post by minimuis on Jul 29, 2016 19:41:09 GMT
I found some info on speedo drive gear part numbers. 22A1881 PINION, 17 teeth (off white nylon) 1965-82; 848 and 998 models with 10" wheels. DAM2905 PINION, 16 teeth (green nylon) 1982-84; 998 models with 10" wheels. TXD10006 PINION, 18 teeth (red nylon) 1984-92; 998 models with 12" wheels. TNB10003 PINION, 15 teeth (blue nylon) 1992 on; 1275 models with 12" wheels. 27H7713 GEAR, drive, 5 teeth (not paint coded) 1965-92; 848 and 998 models. TNB10006 GEAR, drive, 7 teeth (not paint coded) 1992 on; 1275 models. These are for automatic mini's. I could not find the metro one's. But it is a start . You could calculate the the ratio if you know what the gearing is for the auxiliary oil pump. Which drives the speedo gears. On manual mini's the speedo gears are driven by the output shaft. Which makes thing a little easier since there are online calculators for that.I can always mark the most used speeds on the speedometer with a marker pen. Who says it can't be simple and cheap!  |
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Post by mra-minis on Sept 20, 2016 11:31:35 GMT
I can be contacted on martin@kmprecisionengineering.com As the auxiliary pump gears are 1:1 they can be ignored for these calculations. As a rule of thumb if you changed the engine/transmission and speedo from one car to another the % difference would be approximately the difference between the 2 (if different) tyre sizes, so if you have 145-10 (standard ratio is 83%) and 175/50-13 The diameter is 83% of 145 x 2 +(10 x 25.4) = 494.7mm now this doesn't consider rolling radius which is when a weight is applied however as we will do the same to both we would be fairly close.. 50% of 175 x 2 + (13 x 25.4) = 505.2mm the percentage difference is calculated thus... 505.20-494.70=10.50 10.50/505.20=0.02 0.02 x 100 (%) = 2% Using basic theory about 2% A better method is to apply the rolling circumference of both tyre combinations with the vehicle weight, mark the tyre and the ground with chalk roll it forward till the mark touches the ground for one revolution and measure the distance traveled, substitute the 2 readings for the circumference for the 2 calculated diameters and hey presto The problems arise as you guys already know, is the different speedo heads and gear ratios and wheel & tyre combinations that can all have an effect on the speedo calibration. |
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Post by minimuis on Aug 24, 2019 22:20:15 GMT
Slight bump  ,
The speedo now reads correct!
I had to do some maintenance on the mini. New waterpump, radiator and the crank seal. So I thought I may as well try to fix the speedo issue. I found a spare transmission from an older mini with its speedo drive gears. 17/7 to be precise. With the spare transmission I could also see if the wormwheel could be removed without taking things apart. Which was the case, as long as the governor was horizontal to prevent it moving.
I calculated that I needed the 7 wormwheel and a 18 pinion. And I had an 18 pinion lying around. Swapping the wormwheel with the engine in situ was not a problem. The original metro gears I found were a 6 wormwheel (it seems it does exist) and a 17 pinion gear. If I had a 16 pinion, a 16/6 combo would also have worked with the 1242 tpm speedo. This gives a 1243 turns per mile. 18/7 gives 1289 turns per mile, which is best for my 1280 turns per mile speedo.
The speedo reeds about right, the mini stays cool and it still leaks oil. (probably the half moon seal, I see how that goes for now.)
I hope this can be of some use for someone else!
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. The issue I am having, is that the speedometer reads 17~18% to low. It seems to me that when the previous owner did the engine conversion, he did not change the speedo drive gears to the correct ones for the mini speedometer.
,