Speedo in op on 4 speed OD trans.

[airkiller]

Ok, I have a different problem know on the 74 Duster. I just got the car runnig after a 8.75 rear end upgrade from the styock 7.25. That went ok and I have very little problem with the conversion. But here is the rub. During the test drive I noticed that my speedo was ready way high, like on the order of 30 40 miles high. When I installed the manual trans during the resto, I notice about 10 miles differnet from when the 904 came out and had not realy bothered with worring about it. But know I have to do some thing. I have a 833 OD trans driving a 8.75 rearend with 15 wheels. What speedo gear do I need. I try to adjust mine that is currently installed and it will not work the speedo when set in eithe rof the 2 positions marked. I have to rotate it a whole nother 980 degrees just to get the gears to mesh and then It reads way high. Can one one give me some pointers.

 

[67Dart273]

You must be misunderstanding how those work, or are mis-counting the gear teeth. there is not "one of two positions marked." There is only one position that covers the RANGE of gear teeth that you have installed.

Here:

http://www.forabodiesonly.com/mopar/showthread.php?t=143956&highlight=speedo

http://www.forabodiesonly.com/mopar/showthread.php?t=137442&highlight=speedometer


I believe where the arrow in the diagram points to "6' clock" there is a bump to act as a pointer. Note in the diagram it says, 32-38. This means that if you have a 32, 36, or 38 tooth gear, you point the plug in that manner.

http://www.yearone.com/pco/1_0210/full.asp?page=395

 

[805moparkid]

as 67 said each notch is for a given number of teeth on the gear, so how ever many teeth are on the gear you set it to that notch...

now when you change the rear end ratio and how tall the tire (not rim size) it will change the needed number of teeth on the gear to correct the speedo

 

[airkiller]

So I take it that for any given pinion gear there is only one location where the gear will mesh with the trans shaft and that is the ratio you have. I have P225/60R 15 tires and they are approx. 25.5" in Dia. and the rear end is set up with 355 gears. What speedo gear pinion do you think I need?

 

[805moparkid]

So I take it that for any given pinion gear there is only one location where the gear will mesh with the trans shaft and that is the ratio you have. I have P225/60R 15 tires and they are approx. 25.5" in Dia. and the rear end is set up with 355 gears. What speedo gear pinion do you think I need?

the rear end ratio has nothing to do with what slots you put that thing in at... its the number of teeth on the gear that is in the transmission...

 

[airkiller]

Do I not have to select a speedo pinion with a tooth count that is consitent with the gearing of the car and wheel dia?

 

[805moparkid]

Do I not have to select a speedo pinion with a tooth count that is consitent with the gearing of the car and wheel dia?

no you do but you were making it sound like you were adjusting it for the number of teeth on the ring gear... lol

somebody has the chart that breaks down for a given tire size and ratio what color/tooth speedo gear you need

 

[yellowdartdave]

Does this help ??.....

225/60 is the same as an F60x15

You need a 36 tooth gear.

 

[67Dart273]

So I take it that for any given pinion gear there is only one location where the gear will mesh with the trans shaft and that is the ratio you have.

That's right

I have P225/60R 15 tires and they are approx. 25.5" in Dia. and the rear end is set up with 355 gears. What speedo gear pinion do you think I need?

Here's a chart from year one:

http://www.yearone.com/pco/1_0210/full.asp?page=395

It shows you need a 36 toot speedo gear

Believe me, this is easy stuff. Mopar is the only manufacturer, that I know of, with easily swappable gears like this, because of the eccentric plug. Ferds/ GM have a press-on gear on the trans mainshaft, which will support one, maybe two different speedo gears, then you have to tear down the trans and press on a different speedo gear. !!! PITA !!!