Speedo reads wrong.

Topic: Speedo reads wrong. (Read 1002 times) previous topic - next topic

Speedo reads wrong.

July 26, 2006, 10:25:01 PM

I know absolutely nothing about transmitions, and verry little about cars in general, but I am slowly learning.

Anyway. My transmition died a couple months back and it was a pain to replace. A local shop did it, and they went rhough 3 different transmitions they had sent from junkyards before finding an OK one to use.

They got it in and everything seems to be running fine. My only problem is my Speedo has been reading wrong and I've been putting more miles on my car than I've been driving due to that.

I was wondering what I would have to do to get that to read right? I heard it was a gear that I could get replaced easy, but I need to know what gear to get and then where to get it.

(ps. I don't know if it matters, but I have a 87 LS (V6) with stock rear end.)

Thanks alot, Matt

Speedo reads wrong.

Reply #1 – July 26, 2006, 10:38:40 PM

if you look under the drivers side under the car, on the tail shaft of the transmission you'll see something sticking out of it, held in with a clip and like an 8mm bolt. it has a plug in it too. that is the vehicle speed sensor. you undo that bolt, pull out the clip slide the sensor out, and the gear is on the end. that gear comes off when you remove the retainer clip on it.

what car did the transmission come from? and if your cougar is a 3.8l im thinking its got 3.27s in the rear. the trans might have came from something with a 5.0 that had a 2.73 gear in the rear so its off. also up to 89 you have a 7 tooth drive gear, so if it was out of say an 88 mustang you need a 19 tooth gear. if it was out of say a 90 mustang its got the 8 tooth drive gear and you need the 21 tooth gear.

Speedo reads wrong.

Reply #2 – July 26, 2006, 10:38:44 PM

sounds like they never transfered your origional speedo gear from your stock tranny. Look under the car and find the tail of the tranny. You will see the speedo sensor sticking out. Take out the small bolt that holds the sensor in and put it out. Than you will see the gear.

Some ford dealers carry the gears for like 8-9 bucks. Or try online places. I'm not sure on the color you need. They will know, you can pop it in yourself its only a 5 min job. Should take you longer to put the car on ramps or jackstands than change it

Speedo reads wrong.

Reply #3 – July 26, 2006, 10:40:02 PM

Damm Nate you beat me to it.. lol

edit**

Now that I think about it. They would have had to have swapped the speedo gear, cause the speed sensor on the tbird/cougar fox is different than mustangs etc... So they just took the whole thing out speed sensor and gear and put in new tranny. I think Nate is onto something about it being the drive gear now..

Speedo reads wrong.

Reply #4 – July 26, 2006, 10:44:21 PM

Oh im getting pretty quick at getting it up on jackstands.. but hey, now that it moves, the ramps are a good idea :-p.

Thanks for the help guys, i'll try to figure out where the tranny came from.

(it could have been from another tbird/cougar tho.. they just didn't switch it.)

I was just thinking. Not trying to be annoying or anything. But the speedo reads fast, so that should be an indication on whether I need more or less teeth... anyway. Im going to go to a dealer and see what I can get out of them. Thanks alot

Speedo reads wrong.

Reply #5 – July 26, 2006, 11:32:55 PM

Find out what car the tranny came out of... or pop off the speed sensor, get a flashlight and shine the light into the hole. What color gear is in the tranny? If its like my t-5 it will be green or yellow. And What color gear is attached to the speed sensor.

To sum it up, you can't buy a speedo gear till you know for sure what drive gear you have 7 tooth or 8 tooth.

Speedo reads wrong.

Reply #6 – July 27, 2006, 12:00:20 AM

Ramps, Jackstands? Bah. I just layed on my back and crawled under the car to change mine;)

If your speedo is reading fast you need a gear with more teeth. The general rule of thumb is one tooth equals three mph. If your speedo is off by 9 mph you need a gear with 3 more teeth.