Speedo calibration vs rear end or transmission

[chuck1006]

My 100-6 came with the correct style speedo that reads 1020 on the faceplate. I sent it to Mo MA for refurb but the speed reads way high. I called Mo Ma and she sent me a calibration test of cable to wheel turns which came out with a value of 1600. She said she didn't have any records of speedos having calibrations that high but APT Electronics said 1600 was common for Smiths gauges. Either way, I guess I need to get mine regeared or find a correct gauge. Anyone know if this 1600 is Ok for a 1959 100-6? It runs and accelerates good but I do not have the overdrive installed in it which I wouldn't think affects the speedo calibration. Any ideas? Anyone know where to get it regeared if I need to?

 

[HealeyRick]

Nisonger can regear your speedo: https://www.nisonger.com/
Contact them and they will give you a formula to count the number of turns of the speedo cable over a certain distance that will allow them to correctly calibrate your speedo to whatever rear end ratio you're running. I've heard nothing but good things about MoMA. I'm surprised she doesn't over this service.

Happy Healeying,
Rick

 

[Michael Oritt]

After I got finished changing everything around from stock with a 3.5 rearend and a Toyota 5 speed box I had a local guy near BWI airport--"Safety Check"--make a converter box which lives in back of the dash, driving directly off of the transmission output and connected to the speedo head by a short length of speedo cable. He simply measured the number to turns of the speedo cable in a certain distance, resorted to a calculator and came up with a reduction ratio, then built the box for about $200. I did not have to pull the speedo head itself.

 

[chuck1006]

HealeyRick,
After I did the post today, I talked to Nisonger and they said the differential between 1020 and 1600 could not be regeared. You would need to change out the entire core. So, I need to find a gauge closer to 1600 or just get the speed needle adjusted which Mo Ma would do for me and forget about the odometer being correct. I will probably do that and keep my eye open for a speedo closer to 1600. Since my acceleration is good, I don't want to mess with my gearing and I don't want to spend $200 on a converter.

 

[Bruce Bowker]

Curious but what would they charge to adjust just the needle? I have done this myself on many gauges. Not at all difficult.
If their price is very reasonable I would have them do it but if it is high, think about doing it yourself.

 

[chuck1006]

Bruce,
They would do it for free since I already spent $125 with them to have it refurbished. I would still have shipping boths ways though. I've seen some instructions for changing the needle and it seems like it would be easy to the spring if not careful. Do you have instructions?

 

[ThomP]

Something is fishy here. The whole story doesn't seem quite right. My Smiths speedo is marked 1000. 1000 turns to the mile. I have the standard 3.89 rear end. If I were to take the calibrated 1600 speedo and apply the correct rear end ratio it would be 6.37! Wow wow wow! What was this speedo for? A tractor? I find it hard to believe the output from a 100-6 transmission speedo take off would differ so greatly from a BJ8. I haven't seen 100s of Smiths speedos, but the numbers I have seen are all in the 800 to 1200 rev per mile region.

Why doesn't the number on the faceplate match the calibrated number? I would have expected MoMa to have called and asked you about that. I think something is still slipping/sticking in your speedo, or there's a tractor speedo in your 100-6.

One other thought; 1600 turns per mile is very close to 1000 turns per kilometer. Could this be a KPH speedo and when you're doing 100, you're only going 62 MPH? If this were a KPH speedo the 1020 would be 1020 revs per kilometer. The real calibration number would have been ~1645 revolutions per mile.

 

[chuck1006]

I don't know ThomP,
I just did the 52'9.5" calibration check tonight and it came out with 16 cable turns which would equal the 1600 test I did before with the fornula Mo Ma gave me. The only thing I can think is the overdrive that came with the car but in a box has a different ratio than where the cable is installed in the transmission. I know Moss sells different cables for with or without overdrive but I thought it was only for the cable length difference. Maybe if I installed the overdrive (need more parts to do that) and ran the cable to it things would be OK. Maybe speedos were different for overdrive vs w/out. I will try to read the stamping on the rear end this weekend. maybe the gears were changed out. The speedo says MPH on it but maybe the faceplate was changed. I don't know..I am totally stumped. /ubbthreads/images/graemlins/confused.gif Dave, Keoke or Andrew....any ideas???

 

[AndrewMawson]

Chuck,

Two things:

First absolutely determine what the speedo is currently set to. If you have (or have a friend with) a lathe, rig up a drive at known rpm, and using a stop watch check the trip, the oddometer and the mph. This way you can work out how many revs = 1 mile for the two sets of digits and see if it really is a '1600' instrument.

Second: pop off to https://www.jdo1.com/page10.html where John Ostick has a page on calculating the required calibration number. There is a second page hot linked but hidden if you hit the 'Both Driven Wheels' tag in the middle of the page.

When you have the two sets of data then you can 'size' your problem. Good luck. /ubbthreads/images/graemlins/england.gif

 

[ThomP]

OK, So, you're saying your car provides 1600 turns to the mile at the speedo cable AND you have a 1600 turns to the mile speedo. The odometer should read accurately. If you have MoMa calibrate the indicated speed correctly, you should be all set. The part of this story that is still "fishy" is the 1020 on the face plate of the speedo not matching the 1600 calibration. Perhaps, someone, somewhere, long ago, swapped the faceplated for cosmetic reasons and it is just a "confusion factor" here.

Concerning the speedo cable; I noticed in the Moss catalog that there are different speedo pinions for overdrive and non overdrive units. These are separate items from the cable itself and would have an affect on the cable speed. You should not be concerned, because your current speedo configuration matches the car.

 

[chuck1006]

ThomP,
I didn't say the speedo was 1600. I said the faceplate says 1020 and I would assume that is correct. When Mo Ma refurbished it, they didn't calibrate it. I told them it was reading way high but they didn't have me check the cable turns until I got it back and called them. Maybe the 1020 speedo is correct for the overdrive I have that isn't installed yet. I will use a spare cable with it an see if there is a difference between the number of drive turns vs cable turns with it vs the gearbox in the car.

 

[ThomP]

I thought you said, in your inital post, that MoMa said it calibrated to 1600 turns...

"I called Mo Ma and she sent me a calibration test of cable to wheel turns which came out with a value of 1600"

The 1020 on the face of your speedo comes very close to the 1000 on my overdrive BJ8.

 

[chuck1006]

Hi ThomP,
The 'calibration test of cable turns to wheel turns which came out with a value of 1600' is done without the speedo. You remove the cable from the speedo and put a tape flag on the end then roll or drive the car a distance and count the cable turns. The number of cable turns for the distance traveled is then converted to number of cable turns per mile. That should be close to the speedo calibration. So hopefully when I install my overdrive, the pinion on it will turn the cable to match my speedo. Right now the cable turns by being attached to the gear box is 1600 per mile and the speedo reads 1020.

 

[chuck1006]

OK. I think I found it. I measured the cable turns per shaft turns of the overdrive (out of car) and the gear box I am running with. The number of cable turns of the overdrive is less per shaft turn to the ratio that would give me in the 1020 range that the speedo has. My next step is to get the overdrive installed and I have no idea what shape it is in.