Series 2A/Stage1 speedo question

[65s2a]

What is the speedo cable drive ratio on a Stage1 V8? I have fitted 3.54:1 RR diffs in my S2A with 750 tyres (now love the gearing), and want to know if the speedo cable drive ratio on a stage1 V8 (that uses 3.54:1 diffs and has the same speedo format as S2A) is the same as S1, S2 & S3 (=2.25:1)
If it is the same, I'm thinking I could fit one of these speedos and it would read more correctly than the original SWB speedo that is expecting 4.7:1 diffs and 6.00 tyres? I would have to fit a S3 clip on speedo cable...
The original speedo does 1504 turns per mile, I need 1004 turns per KM or 600 turns per mile...which I hope is what the stage1 speedo does...any ideas? Thanks Les

[Lotz-A-Landies]

I don't think it is going to solve your problem as the Stage 1 V8 KPH speedo is marked 860 assuming this to be 860 turns per Km.

[isuzurover]

AS per Diana's post. Stage 1 ratios are completely different because it uses an RRC setup.

The easiest option would be to get your speedo recalibrated by Lionel Otto Instruments. I think there is even someone from there on this site???

[65s2a]

Thanks for the reply. I think I'm OK [or maybe I'm in space? :)]...I have been experimenting with a spare S2A speedo and by changing the magnetism in the rotor in the speedo I can get the reading to change by probably 20%...by using de-gaussing coil from TV tube to de-magnetize or if I over do it, using a powerful magnet to re-magnetize the rotor, I can lower the 860turns per KM to 600 turns per [mile] as the KM speedo would now read..? I'm encouraged !! (hope this activity isn't seen as wierd amongst LR owners) Cheers Les

[Lotz-A-Landies]

:confused: :confused:

Will that change the Odo or just the speedo?

Diana

[65s2a]

Good thought...ODO would still be wrong...:( I'm thinking how important would that be?

[Lotz-A-Landies]

Most automotive instrument people can add a little gearbox in the cable to convert between the speedo and the error.

I've not done the calculation, but you may find that the KPH speedo for a SIIa/SIIb forward control is almost the correction you need. (If you can find one.)

[65s2a]

Yeah, I've seen those...quite costly [in my S2A hobby world] but the main turn off with the ratio adaptors is I didn't get to improvise what may be reasonably available to me to solve my problem using research, collective knowledge and potentially innovative maby old school [or even silly] ideas...which for me is what makes the Series LR rebuild journey what it is...
I paid a farmer in out back NSW $100 twelve years ago for "Hillston" and it was absolutely stuffed, had an unfeasibly large water tank on top of it...sitting under a tree cos the clutch had blown up no doubt due to the weight that it had to carry, all the chassis stop rubbers had been worn to nothing and the chassis had cracked and warped...any sane person would have used some of the parts but for a more suitable restoration candidate...nope, I decided I needed to do this one up...wasn't looking for easy...lots of stories but back to the point, The ODO issue Diana rightly brought up is the only thing that may turn me away from tweaking a speedo to read correctly...sorry for the rant. Thanks Les

[TJWA]

Hi 65s2a. Did you end up carrying out a solution? I'm in the same boat here in a Series III. 3.54 Diffs and 7.50 tyres.

I'm thinking about calculating how many turns per kilometre are required then finding a speedo to suit from another vehicle that will accept the cable.

Are you sure you require 1004 turns per KM? My S3 SWB speedo is marked as 880, I would have thought that changing to 3.54 diffs and 7.5 tyres would LOWER the turns of your speedo per kilometre.

The speedo cable is spun at the final drive of the transfer case to the rear diff. If you have 3.54 diffs then it's going to take less turns of the shaft to travel a kilometre?

As the Stage 1 had 3.54 diffs I would have though it's speedo would be correct? Although my mental calculations would put it at 800 turns per kilometre not 860 as Lotz-A-Landies has quoted is written on the front of a Stage 1.

[HBWC]

this may help i know its for triumps and mg but the iner workings are the same
http://home.comcast.net/~rhodes/speedo.pdf

[65s2a]

OK here is what I found...I did also find the link to the article about Smiths/Jaeger speedos... was very usefull.

To summarise what I have learned...
S2A Speedo conveys TWO things, 1)Odometer, 2) Speed in either MPH or Kms

1) Odometer is determined by gears and ratios only.
Diff ratio[Originally 4.7:1 for S2A] & propshaft to speedo cable drive from gearbox drive ratio [2.2] & Turns per mile/kilometer gearing in the speedo [in the case of 88" SWB originally fitted with 600 or 650 tyres @ 1504 turns per mile (TPM) which is determined by A) the worm drive to ODO wheel gearing expressed as teeth on the gear that is driven by the worm, the choices for landrover [mostly 32] triumph and MG appear to be 20,25 and 32. Re-note that I have not seen anything but 32 tooth worm gears in either LR or Triumph speedos and although you may be able to acquire 20, 25 or 32 tooth worm driven gears, you probably cant get the worm drive with the right gearing. Since this confused me for a while, I will explain...the thing that spins concentrically with the cable drive, is the worm drive, documents dont seem to reference this when talking about worm drive ratios instead they reference the gear that is driven and that has X teeth however, the worm drive can only drive ONE of the worm gear teeth ratios either 20 or 25 or 32.
To get accurate ODO you simply need to have the correct gearing in the speedo to allow for i) tire/tyre size [turns per KM or mile], ii), diff ratio, gearbox propshaft to speedo ratio [2.2 for S2A], and turns per mile/kilomere gear settings [worm drive gear teeth and ODO wheel teeth in the speedo.

2) Speedo reading is completely separate from ODO reading and relates to turns of the speedo cable which directly spins a magnet in the close presence of an aluminium disk which is connected to a hair-spring and has the speedo needle attached to it. The magnet spinning near the aluminium disk creates eddy currents in the aluminium that resist the induced magnetisim causing the aliminium disk to move in opposition to the movement of the magnet which causes the speedo needle (which is attached to the aluminium disk) to move against the hair spring which attempts to keep the needle at Zero. To calibrate a speedo (not ODO), depends on MAGNETISM of the magnet that spins, pre-spring of the hair spring and the speedo may be calibrated at a certain speed and be less accurate at higher and/or lower speeds.
Important is the fact that for any given speedo needle setting, you can put behind it a 70MPH back plate or a 90 or a 120...so the calibration of the backplate is also relevant and important.

For my LR which has 7.50 tyres, and 3.54:diffs [ex RR] I calculate that I need 1052 TPM or 653 TPK at the speedo for my set up.
Remember for a speedo (NOT ODO) it doesn't matter if its TPM or TPK as long as your display [the print on the speedo face] matches. To put this another way, if you have a requirement (as I do) for a speedo with 1052 TPM, if I found a speedo with 1052 TPK on it...I would just imagine that the K's were Miles.

My calculations for ODO wheels are:
With 20 tooth worm gear (you probably won't have this but may get one from a triumph or MG?) you need 53 tooth ODO wheel.
With 25 tooth worm gear (etc) you need a 42 tooth ODO wheel
With 32 toothe worm gear (as all the Series LR's that I have seen have) you need 33 tooth ODO wheel.

For magnetisim level on the spining magnet...stay tuned!!

Side note: I could go to a specialist and pay money to get this stuff done...I'm not against paying the money (I may eventually end up doing this) but for me...part of the S2A restoration journey is figuring this stuff out with research and help from others...I love it and hope the above although incomplete may be useful.

[65s2a]

Calculations for S2A (hope these are correct)
diff ratio 3.54
prop shaft to speedo drive ratio 2.2
rear wheel to speedo drive ratio 1.609090909 (=3.54/2.2)
750*16 tyre TPM 654 from tyre data
750*16 tyre TPK 406
Speedo TPM 1,052 1,052 1,052 (=654 x 1.609etc)
Speedo TPK 653 653 653 (=406 x 1.609etc)
worm gear teeth 20 25 32
ODO drive wheel teeth K 33 26 20
ODO drive wheel teeth M 53 42 33
(worm gears x ODO gears = TPM or TPK for the ODO)

[TJWA]

I just purchased a VDO electronic speedo that is 100mm and measures up to 120km/h. It works off an inductive sensor or a hall effect sensor which I plan to set up on the handbrake drum. There are three ways to calibrate it. Drive for exactly 1km for it to self calibrate, enter a known pulse per kilometre value or enter a known speed while you can confirm you're at that speed.

Advantages: no more broken speedo cables, fits in original dash, no moving parts, basic electrics, easy and quick to calibrate when changing tyres or diff ratios

Disadvantages: Is not the original, some indicators within the original will have to be moved.

There is a photo of it and it's calibration instructions in my rebuild post in the SIII forum.

[Aaron IIA]

This same device could be used as a tachometer on a diesel vehicle. Do they come in a 1.5" or 2" guage, what ever the smaller standard size is?

Aaron.

[TJWA]

This same device could be used as a tachometer on a diesel vehicle. Do they come in a 1.5" or 2" guage, what ever the smaller standard size is?

Aaron.

Here's a link to the catalogue that Wolfman_TWP provided in my rebuild thread:

http://www.adelaideinstruments.com.au/uploads/vdo_automotive.pdf

http://www.aulro.com/afvb/series-3/78110-series-3-rebuild-new-post.html