I'm planning on driving to Columbus this week and I put a 2.76 gear into my car. I decided to get the correct speedo gear for the transmission, which happens to be a 26 tooth gear. I clocked the gear to the 26-31 position on the tranny and everything seemed fine.

The speedometer was fairly correct but was reading about 6 MPH high based on the speed app on my phone. After about 20 miles it began reading much higher and was bouncing. When I was driving at 70 MPH the speedo would be bouncing between 85 and 95.

I pulled the dash apart, disconnected the cable at the tranny and pulled the speedo cable out. It was a little oily but I went ahead and cleaned the cable housing with brake clean, blew it out with compressed air, and then oiled the cable with a graphite/oil lube.

I still had the same problem so I pulled the speed gear from the tranny. I could see that the plastic gear had not been tight against the gear in the tranny. It is still usable but the center of it is slightly worn away around its entire circumference.

So the question is this. How do you know when you have the plastic speedo gear clocked tightly, but not too tightly, against the gear in the trans?

Thanks

On the advice of a Chrysler Tech buddy I decided to clock the speedo gear a little closer to the trans gear. We'll see what happens.

Here is the speedo gear after about 75 miles.

Well that didn't work. I went from a 59 tooth for the 3.91 down to a 26 tooth for the 2.76 and I think that my 46 year old speedo just doesn't like it. After all the cable is now spinning at twice the speed that it was.

I'll probably pull the cluster this winter and send it off for an overhaul.

It's a standard cluster in a '72 Cuda.

hi cd, they didn't make a 59 tooth gear. I think you had a 39 tooth with 3.91 . what size tires are on the car. I think you need a 28 tooth gear. ronnie

spin the cluster with the inner cable & a reverseable drill (CCW) to try & pin it down to a cable/cluster issue or a speedo gear issue (I think the first one). then with that sorted out if the speedo reads 6% too fast get a plastic gear with 6% more teeth & as you know clock the adapter on the side of the trans to the right tooth # cast on the face (several groupings to choose from iirc). best is to get a junk inner cable & cut a piece of it & use it to spin up the speedo that way, to elim or confirm it is the housing or the cable.

The adapter has three clock positions and each position covers a range of pinion tooth counts which are shown on the adapter face. The hash mark on the adapter lines up with the raised dot on the tailhousing. When the retainer is bolted on there is no adjustment left.

No, it is not spinning faster at all.
The speedometer and cable are spinning at the same speed, that why the speedo will read correctly with a different rear gear and speedo gear. For the speedo to read 60mph with any rear gear ratio the cable spins the same speed, we change the speedo gear to get it at that correct speed.

The transmission/driveshaft was spinning way faster with the 3.91 now it is spinning much slower with the 2.76. Just like your tach when in drive, same vehicle speed and different RPM,

Here's my thinking ... the numbers show you the range but within that quadrant you have to adjust to the actual get you're putting in. So in the case of your 26 tooth gear you should be right at the bottom end of that quadrant - first line lined up with the dot.

Also, do you have the gear matched to your tire size as well as the rear ratio ??

There used to be a calculator where you entered your rear tire hight and your rear end gear ratio....it told you what speedo pinion you needed.

I used it when I had my wagon and it worked out very close. Wish I knew where that calculator was.

Right you are. It's actually 37 teeth but there's a big a$$ 59 on it. I bought that one from A and A as well but had more luck.

I went to the chart last week. 2.76 gear and 28" tire = 26 tooth gear.

I had it clocked at the 26-31 position.

Cable is MORE than lubed.

Instrument specialties this winter, I would imagine.

$150-$200 to rebuild the speedo
$50ish to install a voltmeter
$50ish to restore the fuel gauge if it's bad.
4-6 weeks.