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thorjeep 05-18-2005 11:01 PM

Speedo Gear Larger?
Changing my speedo gear in my d300 to go with my new lower gears. It is a 40t, and I know it has more teeth, but should the actual gear be larger than the old stock one? It fits snugly, though I would like confirmation that I have the correct gear before I drive it.

**DONOTDELETE** 05-19-2005 12:24 AM

Re: Speedo Gear Larger?
If it was larger, then it means you would have to replace the drive gear with a smaller one.

There is a limit on the range of speeds the D300 can go. The gear is the same size, but the teeth are different. The drive gear is cut in such a way that it will work with a fairly large range of slave gears (the one that you are replacing).

thorjeep 05-19-2005 09:55 AM

Re: Speedo Gear Larger?
Thanks DDawg, I think.

Let me explain. Changed gearing in axles, called up dealership to get a 40t speedometer gear to correct the difference in speedometer readings of the new axles. When I took the old gear out is was 1/2 the diameter of the new gear.

I would just like confrmation this is "How it is" vs, driving it and causing more damagethan the $12 the new gear cost. I have never changed speedometer gears, and concerned the dealership may have given me the wrong part.

**DONOTDELETE** 05-19-2005 02:09 PM

Re: Speedo Gear Larger?
That does not sound right...the gear needs to be the same physical size, otherwise it is not going to fit....unless I'm wrong about this. I changed the gear on mine and they were the same physical size, just different tooth count.

This is the slave gear that drives the speedo...hence, more teeth means it will turn slower and give you a slower speed indication. Less teeth means it turns faster. Typically, when you go to larger tires without changing gears, you need a lower tooth count. (it gets confusing sometimes)

The only reason you would want to go to a larger (more teeth) is if you went to smaller tires but did not change gears. If you changed gears to get your rpm's back to where they belong then the stock gear should be about right. In other words, the gear tells the speedo how fast the driveshaft is turning. If you go to larger tires, the driveshaft turns slower for a given speed (with 32" tires, on a stock CJ, you will indicate about 10% slower than your really going). Change your gears to 4.10 with those 32 or 33" tires, and your driveshaft is now back to turning about the same amount for a given speed. Hence, no change in speedo gear neede.

Clear as mud...right?

thorjeep 05-19-2005 03:33 PM

Re: Speedo Gear Larger?
Yep, clear as Guiness! [img]/ubbthreads/images/graemlins/40BEER.gif[/img]

I looked up my tire size and ratio on Terry Howe's speedo gear calculator. I just spoke to the local dealership parts dept, and they said it can be a larger diameter gear if teeth were added. Haven't driven it yet though. Will update when I do.

WILL 05-19-2005 04:22 PM

Re: Speedo Gear Larger?
I haven't worked on a dana 300 but I think I read somewhere that the part that holds the speedometer gear has four positions it can be put in to account for the different diamater gears.

TiminMb 05-19-2005 06:34 PM

Re: Speedo Gear Larger?
Will is right. The gears do vary in size. They have a neat setup where you rotate an eccentric disk to accomodate the different diameter gears. I changed mine when I switched gear ratios as well. But I sure didn't double the size of the gear.

thorjeep 05-20-2005 11:37 AM

Re: Speedo Gear Larger?
Well it worked fine speed seems correct, though I haven't verified I have it exact.

FYI: The new speedo gear just drops in, no adjustments necessary.

MarineOpLaw 05-20-2005 01:37 PM

Re: Speedo Gear Larger?
$12 bucks!!! Local stealership quoted me $27 for a new speedo gear! Grrrr....

RickB 05-20-2005 02:19 PM

Re: Speedo Gear Larger?
I paid $24 for mine at the local stealership...and that was with our club's discount.

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