18 replies to this topic

[dklawson]

Go back to my February 19th post above. I explain one method to figure the TPM number and I provided you a link to Speedy Cable's method for how to determine TPM.

[james962]

No I need to to work out what gauge to purchase that has the right TPM to work with my set up as my engine was only put in about 2 weeks ago and I really don't want to take it out again anytime soon..

I know:

Tyre size - 175/50/13
Diff ratio - 3.444:1
Gearbox type - Standard

So I need to work out me worm and pinion ratio in order to know war gauges will work with all my current setup?

Aren't you working this out the wrong way round? Surely you have the speedo, and your need to find the correct worm and pinion to suit, rather than change your clocks to suit this ratio?

Have a look on the clock face (or here http://www.guess-wor...Tech/speedo.htm or as Doug has explain above to find the TPM of your speedo.

Once you have this, you know the drop gears are 1:1 (or ask Minispeed as they rebuilt your engine), you have a 3.44 diff, and you know the tyre size, so again use the guessworks calculator to find the correct worm and pinion combination. Once you know this, take out the rad, undo an engine mount, jack the engine up a bit and change the two gears.

Yes it is a pain to change the speedo gears, but the better solution.



As a side note, I would recommend against getting Speedy Cables etc to recalibrate your speedo. Purely for the fact that this does not "cure" where the problem is (which is the worm/pinion combo). I personally have just fitted a central speedo from the 3 clock side set up. Used the calculator to get the correct ratio whilst I rebuilt the engine, fitted everything and guess what..........the speedo is wrong. I can only assume that someone has had the speedo recalibrated at a earlier date. I therefore have to change my speedo drives again, but this time with the engine in the car. Maybe when I do the job in a month or so, I do a "guide" which could become a FAQ/sticky to aid others??

Edited by james962, 21 February 2013 - 01:27 PM.

[dklawson]

I am not an advocate for modifying the speedometer. It is not a simple process. The analog needle is one thing... relatively easy to change. The odometer is not. It is a worm and pinion arrangement along with a "pawl" with a given number of teeth. You have to fit the right combination of those three mechanical bits to get the odometer to read as you want it to and that will not be cheap.

An alternative is a ratio box. I have mentioned these before but no one seems to pursue them. They are a small mechanical device about the size of a pack of cigarettes. The cable goes in one side from the gearbox and through properly selected internal gearing the output is the correct TPM you need to support the gauge you have. Over here these cost between $100 and $150 depending on the type you buy. Add to that the cost of a new speedometer cable which must be modified (cut) to fit the gearbox in the middle. To order these you still need to know the TPM your car's drive system produces and the TPM calibration of the speedo you are trying to match. The benefit of the ratio box is you don't have to open the transmission and/or pay a lot to modify the gauge.

[Elliskwleisk]

Managed to work out what I need, thanks for all your help guys