Speedometer is off

[kboucher]

Hi,

My speedo is off by 10 mph and am having trouble trying to figure out all the info on replacing the gear in the tranny to fix this.

I just bought what I think to be a stock 1983 CJ7 with the AMC 258 i6 / 4.2l and 5 speed tranny - T-5 and just put on 33x12.5x15 on the jeep.

How do I determine the gear in it now?
Where is it located on this tranny?

Any help - pictures - insight would be of a great help as I did buy a new Speedometer but now in doing research I think its this gearing issues.

Thanks

 

[Old Dog]

The gear is located in the Transfer Case , just look for the cable going in.
4wd and quadratec use to have charts to which gear you needed by cross referencing your gear ratio and tire size. Do you know your gear ratio?
The hard part is finding a gear for a cj.

 

[Turbogus]

X2 and especially a big X2 on CJ's but, as for me that's part of a CJ's charm that, and the puddle in my drip pan

 

[PaRenegade]

As was said, the speedo gear is located on the side of the Transfer Case . Pictured is the Dana 300 case. You remove the cable from it, then the bolt and clamp. There is a housing with a big o-ring that holds the gear. Pull that out and the gear will probably come out with it. Count the teeth to find out what you have. There are 2 housings used. One is for 21-25 tooth gears only, the other has 3 positions that allow you to use all the higher count gears, by group 26-31,32-38, 39-45. You want a "long shaft" gear for the Jeep/Dodge to fit a Dana 300 . See about the middle of the page or pick it at the top.
Also, if your ordering one from them, order a new o-ring and gear seal too. They're cheap.
Speedometer Gear, Speedometer Gears, Ford, GM, Dodge 700R4
Here's the calculator to find out what tooth count you need.
Speedometer Calibration Program - Method 1

And here's some pics of when I replaced mine.

 

[kboucher]

Man you are the bomb, thanks for all this information and I will get going on it.

Again, THANKS

 

[Old Dog]

Good to know where to find one. I looked everywhere, finally found what I needed on fleabay.

 

[kboucher]

How do I find out the differential gear ratio and Revolution per mile (it talks about modern one not mine which is 1983) asked for in the calc table?

 

[PaRenegade]

The diff. gear ratio is what's in your Jeep now. If you don't know get a piece of tape and jack up the rearend. Crawl under it and put a pc. of tape on the driveshaft at 6 o'clock and the tire at 6 o'clock. Rotate the tire 1 complete revolution while counting how many time the drive shaft turns. Your choices will most likely be 2.73, 3.07, 3.31, 3.54, 3.73, 4.1, 4.56.

As for the revolutions, I just used 1000. Or you may find the number on your speedo itself. There's an algorithm at the bottom to calc. it but you need to know your "drive" gear tooth count and that's hard to find out unless you have the cover plate off your Transfer Case . This whole calculation may not put your speedo dead on. It may be off a mph or two due to the variable of tire wear, but this is why cops have to give some calibration flex too. Speedos nowadays use adjustable sensors and are more accurate. Older ones never were dead on, from what I've read.