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MG TD TF 1500 - TD Speedo 4.3 Modifications

Can anyone confirm that the correct TPM for a TD with a 4.3 rear end on 165 15 radials is 1342 or is 1350 more accurate? I’ve seen figures of 1350 & even 1375 in the archive.

Carl Cederstrand says ‘The chronometric (flat face) speedometer has a single worm gear on the end of its input shaft. This worm engages a 25 tooth pinion which in turn advances a 64 tooth ratchet. One turn of the 25 tooth pinion advances the 64 tooth ratchet wheel one tooth. One full turn of the ratchet wheel will then advance the first number on the odometer by one digit. Accordingly, it takes 25 x 64 or 1600 revolutions of the input shaft to advance the odometer reading one mile’. This figure is correct for the standard TD.

Reason I ask is that having had success stripping the mechanism to replace the odometer & trip meter strips I’m now wondering whether I can replace the relevant gears to ensure both counters correctly record the distance traveled. I’ve seen that my odometer & trip meter have 64 tooth ratchets – the numeral is stamped on the odometer gear – so a pair of gears with 53.68 teeth (rounded to 54) would produce approximately 1342 TPM. This figure of 53.68 is arrived at by dividing 1342 by 25. By multiplying 54 by 25 the actual figure is 1350. I assume the difference between 1342 & 1350 is attributed to the use of radials as opposed to cross ply tyres & that if I fitted a pair of 54 toothed ratchet gears, as Carl’s statement implies, both odometer & tripmeter would then record accurately?

I do realize that gearboxes are available to make this correction but if the same result can be achieved by simply replacing a pair of ratchet gears then that’s what I’d prefer to do.

I’m also wondering whether I could approach either Speedograph Lichfield, APT, Vintage Restorations , Nisonger or one of the other suppliers & ask them to supply me with the correct gears to also alter the chronometric mechanism to reflect the new 4.3 rear end? Here I’m on shaky ground as I’m yet to get my head around which gear or gears would need to be changed to ensure the speedo recorded the correct speed. Does anyone know if anybody else has been down this DIY road? As I said above I'm not interested in fitting a gearbox to correct the error. Cheers
Peter TD 5801


P Hehir

Hi Peter,

Speedo graph Richfield rebuilt the speedo from my TF and of all the repair shops and suppliers I used whilst restoring the car they were the best. Following their instructions I had to push the car so the rear wheels turned exactly six times (I think it was six) and at the same time count the number of revolutions the speedo cable made. I had to fix a cardboard pointer to the end of the cable to do this accurately. Speedograph were able to calculate the TPM for my car, fitted with a 5 speed gear box, from these figures. I forget what they charged for the rebuild but it was around £60. It came back after two weeks looking like new, the needle is rock steady and checking with my Garmin sat Nav shows perfect accuracy. They explained that the speedo from a TF can be internally calibrated but some from older cars cannot. They do have a range of external gearboxes with differing ratios to set up older speedos. I would email them they are very approachable. I almost forgot they also made up a cable with a Ford and a MG end.

Cheers

Jan
J Targosz

Thanks Jan. I understand the whys & wherefores associated with providing the TPM. As I said I'm not interested in an external gearbox. I'm still keen to source those 54 tooth ratchet gears as I just love the challenge of doing this stuff myself. It keeps me young. Maybe someone has a pair of 54 tooth ratchet gears that they're prepared to part with. Or it might come down to having them milled on a CMC machine.

I will get around to contacting the suppliers I mentioned but I'm keen to hear from the hands on types on this site first. From my scouring of the archive it seems nobody has gone solo down this road before, except maybe for Hugh. But I live in hope. Cheers
Peter TD 5801
P Hehir

I've not yet had my first cup of coffee, so my mind isn't tuned in for higher math. But let me give this a try. You are correct with the reduction of the the original TD/5.125's 1600 TPI to 1342 based upon 4.3 vs. 5.125. However, what you are missing is the tire factor. Not radial vs. cross ply, but size. The 1600 TPI was based upon 5.50-15 tires. The 165-15 radials are closer to 5.90-15. (5.5+15+5.5)/(5.9+15+5.9)=.97; .97*1342=1302. We need someone to supply the circumference of an old fashioned 5.50/15 tire. My new Michelin 165R/15 xzx has a circumference of 79.25 inches. That's an aspect ratio of about 79, i.e., 165/79R15.

My experience with the instrument rebuilders is that they are loath to sell you parts. They'll be happy to have you pay them to install them in your instrument. Bud
Bud Krueger

Bud I mentioned radial v cross ply because of the obvious size difference which will clearly have an impact on TPM. Be nice to compare the height of the wall. As it happens I have an original Dunlop cross ply on my spare. If someone can suggest exactly where & how to measure it I'll post the result. Cheers
Peter TD 5801
P Hehir

The circumference of the inflated tire is the critical parameter. Just wrap a tape measure around the middle of the tread. What size is the tire? Bud
Bud Krueger

What I thought was a Dunlop is actually an Olympic Tubeless Airtite cross ply. It's been on the car since 1969 when I bought it & has never been on the road. The other 4 were Michelins. It's a 5.60 15. The circumference in the middle of the tread is 6' 9.89" (208 cm). Cheers
Peter TD 5801
P Hehir

I believe the OEM tire was a 5.50-15. I surmise that the 1600 TPM is based upon that size. A 5.60 has a larger circumference than a 5.50. All of the tire size calculators that I can find insist upon having the aspect ratio as a parameter to compute the circumference. My 165R15 xrx compute to being an aspect ratio of 79 (probably 80). Bud
Bud Krueger

Anyone have a pair of 54 tooth ratchet gears they'd be willing to part with? I can swap a pair of 61 tooth or a pair of 64 tooth gears. Or $ if that's what it takes. Cheers
Peter TD 5801
P Hehir

Peter,
I think you are going the wrong way about correcting your speedo. You are missing out on several issues.
As Bud has mentioned the circumference of the tyre inflated at the correct pressure is critical but not just that.These speedos are not really accurate.
These speedos are not linear over the whole range and show a dip in accuracy around 50 ... 60 MPH. When I design a corrector gearbox (which I know is not an option for you), I ask for a set of readings of GPS vs indicated speed.
A typical set of values in MPH which I recently received from someone on here after a ratio change is as follows:
GPS Speedo
30 20
40 28
50 32
60 42


If you plot this on a spread sheet you can see the dip.
If a 1.5 correction is chosen you get this:
GPS Speedo
30 30
40 42
50 48
60 63
It would slightly under-read at 50MPH and over-read at 40/60MPH.


If a 1.42 ratio is chosen you get this:
GPS Speedo
30 28
40 39.76
50 45.4
60 59.64
Fairly accurate at 46/60 MPH but look at what happens at 50MPH!

The speedo would be out by 4.6MPH which is not on!
Correcting the speed amplifies the problem so you have to choose the right compromise as in the 1.5 correction above.

The needle in the speedo does not know (or care!)where the correction takes place. Is it from the wheel you want to change or is it from a corrector gearbox?
I would wait until you have the car on the road with a proper set of readings and go from there.
Using the GPS to set up the speedo is by far the easiest way and most accurate way to proceed without getting bogged down im mathematics where you have too many unknowns in the equation. I doubt that what you are attempting will be successful.

Regards
Declan
Declan Burns

Hi Declan. Thanks for your thoughts. There are two issues that I'm addressing here. One is the speedo reading & the other is the odometer/tripmeter. With the 54 tooth ratchet gears, I'm attempting to correct the mileage traveled. With my 4.3 diff & driving on radials the 54 tooth ratchet gears will achieve this.

The other issue is the speedo. The ratchet gears I'm seeking do not have any impact on the speed reading whatsoever because the odometer/tripmeter gearing is completely separate! The ratchet gears do not correct the speedo readings, nor do I think that they will. I wonder whether any of the professionals even bother to address the mileage error when adjusting the speedo? I suspect not.

My research now suggests that the problem of the speedo reading accurately can be achieved with the addition of weights to the balance wheel & that this MAY have to be done professionally. I realise even when this is done using the generally accepted figure of 1350 TMP for a 4.3, there will still be some errors throughout the speed range. But I can live with that as I'll be using the tacho to monitor speed in the various gears. Cheers
Peter TD 5801
P Hehir

Peter,

In response to your initial question. "Can anyone confirm that the correct TPM for a TD with a 4.3 rear end on 165 15 radials is 1342 or is 1350 more accurate? I’ve seen figures of 1350 & even 1375 in the archive."

According to my calculations the TPM for 165 15 tyres and an axle ratio of 4.3, is 1374.69. This assumes a cable drive of 5/13 (S), my car had a 6/15 (T) which is incorrect for a 5.125 axle.

I seem to remember that I sent you a spreadsheet of REVS vs MPH. I have made a newer version which includes the TPM information. It includes a Load factor parameter, this is the reduction of the rolling circumference, due to the overall weight of the car. I can forward the file to you if you are interested.


John


J Scragg

Thanks John. I do recall receiving the spreadsheet though I did struggle to understand it. Working backwards from your figure of 1375, with the pinion of 25 teeth being constant, given that 64 teeth on the ratchet gear produce a TPM of 1600 - which is not in dispute - I arrive at the figure of 55 teeth on the ratchet gear, which is as near as dammit to the 54 tooth gear that I'm seeking.

My math is as follows: 64 x 1375 divided by 1600 = 55. However as the original TPM of 1600 was computed on the original cross ply tyres, not on radials with the smaller circumference & with a 5.125 ratio, where does this leave us? As maths was a subject that I struggled with at school I’m not pontificating here, but genuinely seeking confirmation that a ratchet gear with 54 or 55 teeth will produce accurate odometer & tripmeter readings using radials with a 4.3 diff. Cheers
Peter TD 5801
P Hehir

Found it. See http://www.automobile-catalog.com/tire/1952/1695215/mg_td.html . The 5.50-15 tire diameter is 24.9 in., which *pi= 78.23in. circumference. If the 165R15 radial is 79.25 in. the tire factor would be 78.23/79.25. So the TPM would be 1600*(4.30/5.125)*(78.23/79.25)=1325 TPM.


Bud Krueger

Declan, in Peter's case he is dealing with a chronometric speedometer which, due to the nature of the gear driven mechanism, should be linear throughout its range. This obviously is not the case with a magnetic speedometer which relies on the balance between a spinning magnetic field and a hairspring.
Hugh Pite
H.D. Pite

Whoops, I reversed my field. The tire factor has to be the new circumference relative to the OEM circumference, i.e., 165R15/5.50-15, being (79.25/78.23)=1.013. So, the TPM would be 1600*(4.3/5.125)*(79.25/78.23)=1360 TPM. Except that you intend to change a ratio inside of the speedometer to account for the factor of 0.85. That means that the 64 tooth gear would be replaced by a 54.4 tooth gear. Bud
Bud Krueger

Thanks Hugh,
I know the chronometric speedos operate differently but I have no idea on their accuracy and have no experience with them.
Thanks for the info.
It would still be interesting to see what the deviation is compared to a GPS.

Regards
Declan
Declan Burns

Peter

See if you can beg, borrow, steal a HUD when you have the car on the road. In fact unless you are concerned regarding inaccuracies in the mileage traveled reading I would buy a HUD and use it whilst driving it might save you a "BLUEY". I went thru the exercise you are attempting to achieve with the TF it was all too hard with the TC gearbox and diff ratio exchange as well as attempting to source gearing for the task.

Graeme
G Evans

Agree it's vital Graeme to know what speed you're doing especially with speed cameras all over the place now. Not giving up on this exercise though. The speedo now moves smoothly when driven by my variable speed electric drill, the 30 mph contact has been successfully shifted to indicate 69 mph, the necessary wiring is connected to the unused trafficator light & the odometer & trip meter wheels now look 'as new'. Had some great advice from John at Vintage Restorations & also from Hugh Pite who confirms, among other things, that chronos are linear throughout their operation & so I guess would be more accurate than the magnetic versions fitted to the later TD & TF. See Hugh's post above.

Does anyone have a pair of 54 or 55 tooth ratchet gears in good nick for sale or swap? Cheers
Peter TD 5801
P Hehir

I was right the first time. The ratio is the original to the new, i.e., 5.50-15/165R15, as 78.23"/79.25"=.987. So the total factor is .828:1. The gear would want to be .828*64=53 teeth. Sorry about the error about error. Bud
Bud Krueger

Maths, ratios & factors aside, what I’m trying to resolve is this. The TPM figures of 1325, 1342, 1350, 1360 & 1375 have all been used at some point in this discussion or elsewhere in relation to a TD on 165 15 radials with a 4.3 diff. Clearly they can’t all be correct.. The question that I posed to open this thread is:

What is the correct TPM for a TD on 165 15 radials with a 4.3 diff?

Does anyone have the answer? Cheers
Peter TD 5801
P Hehir

Just received a very informative & detailed email from Bud who walked me through the fairly involved set of maths. The long & the short of it is that the correct TPM figure is 1325. Cheers
Peter TD 5801
P Hehir

Peter,

Bud's method does not take into account the reduction in circumference due to the overall weight of the car, I call this the "load factor".
I have used his figures to calculate the TPM of the original factory spec i.e. 5.5 X 15 cross ply tyres and 5.125 axle ratio, the result is 1596.47 instead of 1600. I add a load factor until I obtain 1600, then use this load factor in the new calculation, i.e. 165 x 80 X 15 with a 4.33 axle, and get TPM of 1374.49

John


J Scragg

Yes, its called the rolling radius of the wheel and tyre, though like everything else varies with speed and temp.
Dave H
Dave Hill

Uh, Oh! I sense a nutty contest evolving, pecans. I'm not about to defend the values that I've used. I've accepted the 78.23" figure that I found through googling. The 79.25" figure was obtained by wrapping a measuring tape around one of my new 165R15 Michelin xzx tires while the car is on jackstands for the new crank seal project. Would someone mind measuring the distance covered on the ground by a 165R15 tire after 10 rotations?

Does anybody happen to know the exact ratio of the speedometer gears in the XPAG gearbox? That figure is significant in performing this arithmetic. It's easy to point out gross errors due to things like forgetting that the MGA gearset ratio is exactly 4.3:1, not 4.33. That brings John's figure down to 1364.97. It's amazing how precise we can be using approximate parametric values. Bud
Bud Krueger

Bud,

The 4.33 is a typo, in my spreadsheet it is indeed 4.30. Back to square one.

John
J Scragg

This is getting really interesting.. Maybe we again need to hear from someone who has provided a professional instrument firm with a TMP figure & a chronometric instrument that resulted in a perfectly accurate speedometer? I say chronometric because of their linear accuracy. It also crossed my mind that the 'load factor' that John mentions would alter depending on whether there is or isn't a passenger & hence affect the accuracy of the speedo? Those with mathematical brains - & here I exclude myself - may be able to produce a table that would enable the TMP to be seen at a glance, taking into account all relevant factors. Cheers
Peter TD 5801
P Hehir

I do recall someone in the archive who stated that a TPM of 1375 did produce a near perfect result. Cheers
Peter TD 5801
P Hehir

Lets remember that you can only change the gear by one full tooth.
The difference between 54 and 55 is 1.0185, say 1.02%. So any variation causing a correction of less than 1% or so (1/2 of 2%) is lost in the gearing.
So if 1375 were "perfect" for a 55T gear, the next "perfect" TPM (up and down) would be
around 1402 and 1348.

Jim B.
JA Benjamin

Jim as you no doubt know the 55 tooth ratchet gear only affects the odometer & tripmeter. Not sure that the relationship has yet been established between 1375 TPM & a 55 tooth gear. I'm keeping out of the maths though. I'll leave that to the boffins! Cheers
Peter TD 5801
P Hehir

This is getting ridiculous. The entire equation can be written with only one arbitrary variable, i.e., the rolling circumference of the tire. Everything else is determined by something that can be counted.

Peter tells me that inside of the speedometer are two gears that drive the odometer. I don't know what their tooth count is. One appears to have 55 teeth. At any rate, they are countable. One of these gears is being rotated by the speedometer cable.

The speedometer cable is attached to a gear in the gearbox. This gear is driven by another gear in the gearbox that turns at the rotational rate of the driveshaft. The ratio of these gears is fixed and is approximately 2.6:1. It is the ratio of the driveshaft revolutions to 1600 when traveling one mile. A figure commonly used for a TD is that in top gear it goes 14.4 MPH per 1,000 RPM. So 60 MPH is approximately 60/14.4=4,167 RPM. Therefore the gearbox speedometer gear ratio is about 4167/1600~2.6. But, this is a real number that can be measured (counted).

Next we have the rear end ratio. This also is a fixed number that can be measured by counting gear teeth. Our OEM figure for this is stated to be 5.125:1. It takes 5.125 turns of the driveshaft to spin the rear axle through one revolution.

The only thing left is the rolling circumference of the tire that is being rotated. It would appear that the MG engineers chose some measurement to make their system display 1.0 miles for this tire having traveled 1.0 miles.

Nothing else in this set of parameters is arbitrary, only the tire circumference that fits the bill. Everything else can be counted.

If someone will tell me the ratio of these gears in the odometer and the ratio of these speedometer gears in the gearbox, I can tell you what the reference tire rolling circumference was. And, none of it is higher math. Not a partial differential hyperfunction in the lot. Bud
Bud Krueger

I can state that there are two ratchet gears in the speedo. One drives the odometer & the other the tripmeter. Each of these gears has 64 teeth (not 55) in a standard TD i.e. one that is fitted with a 5.125:1 ratio diff. They are visible at the ends of each set of wheels. Pic attached. Cheers
Peter TD 5801


P Hehir

Pic 2 Ratchet gears in the foreground.


P Hehir

So the gears at the end of the number wheels have 64 teeth. Is that correct? How many teeth are on the gear that turns this ratchet gear? Is that gear directly connected to the speedometer cable? Or, are there intermediary gears?

Looks as if I need to relocate the Jaeger website.

Bud
Bud Krueger

Yep. I mentioned this in the initial post. Check out the top of the thread. Also have another look at Carl's crown wheel & pinion article which is where I lifted the following quote from. Pretty sure you have a copy on your site.

'Carl Cederstrand says ‘The chronometric (flat face) speedometer has a single worm gear on the end of its input shaft. This worm engages a 25 tooth pinion which in turn advances a 64 tooth ratchet. One turn of the 25 tooth pinion advances the 64 tooth ratchet wheel one tooth. One full turn of the ratchet wheel will then advance the first number on the odometer by one digit. Accordingly, it takes 25 x 64 or 1600 revolutions of the input shaft to advance the odometer reading one mile’.

Sorry that I can't provide any more detailed info. The pinion & gears that Carl refers to are clearly shown in the pics above. Once you pull a speedo apart all is revealed. :-) Cheers
Peter TD 5801
P Hehir

The same system is used in the later, magnetic speedometers. See Anthony Rhodes' "Repairing Jaeger and Smiths Speedometers". So we then believe the 1600 revolution figure for the speedometer cable to 1.0 mile digit.

Only thing left is the speedometer cable to drive shaft gearing. Anybody have a gearbox apart who can count the gears on the Speedometer Gear (OEM Part #168100) and the Speedometer Pinion (OEM Part #AAA5435)?

Was this where the factory had a separate gear set for cars with the 4.875:1 differential?

Bingo!! AKD834 Section R, MARK II SUPPLEMENT 10 M.G. midget (Series "TD"). Under Chassis is listed:
Pinion-speedometer Part #X24441
Gear-speedometer Part #X24440
Rear axle assembly- ratio 9/49

These parts changed at Chassis #12285, the 9/49 is a 5.44:1 differential.
Then it became:
Pinion-speedometer Part #X17212
Gear-speedometer Part #X24442
Rear axle assembly-ratio 8/39
8/39 is the 4.875

So, it looks as if the gearbox speedometer gears were changed to correct the speedometer/odometer when the rear end gears changed.

I suspect that these parts were fitted to TFs.

Can anybody count the gears on these parts? Tom Lange?
Bud
Bud Krueger

Bud I'm aware of the 5.125, the 4.875 & the 4.3 as well as the 3.9. Where does the 5.44 that you mention come from? Cheers
Peter TD 5801
P Hehir

It's listed in the AKD834 MKII Supplement. I'm guessing that it might be optional for hill climbing competition.
I'll open a thread to see if anyone can add more light. Bud
Bud Krueger

Bud, I had a look at a bunch of later TD speedometers and found a couple with 1525 tpm while the rest had 1600 tpm. The 1600 is for a 5.125 diff ratio and if you do the arithmetic the 1525 corresponds to a 4.875 diff ratio. So maybe there were two solutions to the diff ratio change - either change the speedometer gearing in the gearbox or change the speedometer calibration (which would be easier).
Hugh Pite


H.D. Pite

Thanks, Hugh. An interesting conundrum. Could only be one or the other. Or, was only the speedometer face changed without an internal change? I'm curious about what the TF Service Parts List shows for a TF's gearbox.
Bud
Bud Krueger

Bud, the TF Service Parts list only shows one set of speedo gears. They are: 168210 for the gear and X17260 for the pinion the ratio is quoted as 6/15. This is the only set of speedo gears shown in the parts list altho' the list shows 3 diff ratios of 5.125, 4.875 and 4.555.
The TF speedos I have all show 1525 TPM which corresponds to the 4.875 diff ratio. The other diff ratios were special orde.
Hugh Pite
H.D. Pite

I'd really like to bring the discussion back to my original question. What is the correct TPM for a TD on radials with a 4.3? I think Bud says 1325 while John says 1375 (approx).

Maths aside, it seems the most practical way to answer this question is to hear from owners of an early TD, with a chronometric mechanism, who have provided a professional instrument firm with a TPM figure that resulted in an accurate speedo & for that person to tell us all just what that figure is. Cheers
Peter TD 5801
P Hehir

Many thanks, Hugh. I think that lets us fill in the blanks. The 168210 gear and X17260 are the identical part numbers as in AKD834 for the TD.

It would appear that the TF's 4.875 is handled via the 1525 TPM in the speedometer.

That 6/15 ratio is an invaluable piece of information. It allows us to work backward to determine the OEM figure for the tire rolling circumference.

Thanks again. Bud
Bud Krueger

This last thread from Hugh is great. It clarifies the change from 1600 to 1525 TPM (Turns Per Mile) on the TF speedometer to correct for the 4.875 rear end ratio. So, the 64 tooth gear around the ratchet wheel would be changed to a gear wheel of 61 teeth. It turns out the figure of 61 teeth is 64*(1525/1600) and is the rounded value of 64*(4.875/5.125)=60.87.

If one wanted to correct a TD speedometer to compensate for a 4.3 differential via this method it could be done. The change would require a ratchet wheel containing 54 teeth. THat's from rounding 64*(4.3/5.125)=53.70. The new TPM number would be 1342, 1600*(4.3/5.125)=1342.44. This would be for an OEM 5.50-15 tire.

I'll work on the radial tire circumference factor. Bud
Bud Krueger

The gearbox speedometer gear ratio is 15:6, or 2.5:1. This is the ratio of driveshaft turns to speedometer cable turns. So a speedometer cable turning at 1600 TPM would be the result of a driveshaft turning at 4000 TPM, or RPM, i.e., 1600*2.5. This driveshaft 4000 RPM would be reduced by the differential ratio of 5.125:1 to rotate the rear axle. This would make the rear axle spin at 4000/5.125 = 780.5 RPM as would a tire attached to that axle. The circumference of the tire to cover 1 mile in 780.5 revolutions would be 5280 (ft/mile)* 12 (in./ft.) * 780.5 = 81.179 inches. Round it to 81.2 inches. So that is the rolling circumference of the standard OEM 5.50-15 tire used by the M.G. engineers in their speedometer calibrations.

The measured, unloaded, circumference of a 165R15 Michelin xzx was measured at 79.25 inches. The correction factor for tires is (standard)/(test). In this case that's 81.2/79.25=1.025. This factor can be used to multiply the TPM figure or the ratchet wheel teeth figure. For a 1600 speedometer the new TPM figure would be 1600*1.025=1640 TPM. The correct ratchet wheel would have 64*1.025=66 teeth.

If this radial tire is used in conjunction with a set of 4.3 differential gears it would have a TPM factor of 1600*(4.3/5.125)*1.025=1376. (John hit it.)
The correct ratchet wheel would need 64 * (4.3/5.125) * 1.025= 55 teeth.

So, there are two factors that give you the corrections for the odometer. One is for the drive train, i.e., the rear end gearing. It's simply the (new ratio)/5.125. The other factor is the tire factor, that's the ratio of the circumference of the standard (81.2") to the new tire's circumference.

These are both simple multipliers. Bud
Bud Krueger

Thanks Bud, attached is a screenshot of the tool I used.

John


J Scragg

Thanks Bud & John. So the answer to my question is 1376 TPM & the ratchet gear should have 55 teeth. I hope others also find this info useful. The icing on the cake would be to have an early TD owner with the 4.3 conversion confirm that they provided 1376 TPM to their instrument workshop & now have an accurate chronometric speedo. Cheers
Peter TD 5801
P Hehir

Lonnie Cook has shared some data found in AKD804, Service Parts List for TFs. It's the source of some of the data seen in John's tool above.

The TF was certainly flexible. Its alternative crown wheel and pinion sets included a set of speedometer gear and pinions for each rear end ratio.

CW&P of 9/41 ratio (4.555) speedometer set=5/15 (2.60).
CW&P of 8/41 ratio (5.125) speedometer set=6/14 (2.33).
CW&P of 8/39 ratio (4.875) speedometer set=6/15 (2.50).

John, could you please send me a copy of your tool that I could print out? I can't quite read all of yours from the image. Thanks, Bud
Bud Krueger

This thread was discussed between 12/11/2017 and 17/11/2017

MG TD TF 1500 index

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