changed speedo gears

[ccrider]

i changed the speedometer gears on my th350 this morning, it only took about 1 hour. my speedometer has been off for 8 years and i thought it was going to be a big job so i didn't try it.anyone who's thinking of doing it , i can say it's an easy job- go for it!

 

[Keizer]

i changed the speedometer gears on my th350 this morning, it only took about 1 hour. my speedometer has been off for 8 years and i thought it was going to be a big job so i didn't try it.anyone who's thinking of doing it , i can say it's an easy job- go for it!

I will be doing this job too, since I changed the gears in my rear end. Do you have any step by step instructions? Photos?

 

[ccrider]

i first removed the driveshaft,then unscrewed the speedometer cable. i used a 1/2" wrench and removed the bolt and clamp for the driven gear and removed the gear. the o ring from the old driven gear is removed and installed on new gear and put in the housing. remove the 4 3/8" bolts for the tailhousing and remove.you'll see the drive gear on the output shaft.remove the retaining clip and change the drive gear and reinstall the retaining clip.i reused the o ring on the housing and installed a new oil seal on the rear of the housing.reinstall the cable and driveshaft, pretty easy. don't have a digital camera so no pics. i do have a th350 manual that has pics, so maybe that would help you before you start.

 

[Gary S]

It is easy if you follow ccrider's instructions. One more thing I might add is to keep a drain pan handy under the tailshaft when you remove it. Some trannys will have enough fluid in there to make a really big mess on your floor. It is easier to catch it in the pan than to wipe it up later.

 

[theflash]

It is easy if you follow ccrider's instructions. One more thing I might add is to keep a drain pan handy under the tailshaft when you remove it. Some trannys will have enough fluid in there to make a really big mess on your floor. It is easier to catch it in the pan than to wipe it up later.

+1 on that (found out the hard way)

CC how did you get the drive gear off the shaft? Both times I did this the gear was on pretty snug. I ended up using a big open end wrench that was just larger than the shaft to tap it off.

 

[JL8Jeff]

I need to change the speedo gear in my M21 as well. But are you supposed to change the drive gear on the output shaft as well as the plastic speedo gear? I thought I just needed to change the speedo gear to one with a different tooth count.

 

[Gary S]

I need to change the speedo gear in my M21 as well. But are you supposed to change the drive gear on the output shaft as well as the plastic speedo gear? I thought I just needed to change the speedo gear to one with a different tooth count.

If you need to change only 1 tooth, and that gear is available, all you need to do is change the driven gear on the outside. That takes only about 5 minutes once you are under the car.
The reason for changing the drive gear inside the tranny is when you make such a large change in gearing or tire size that there is no available driven gear to accomplish that much change. Once you are out of range on the driven gear, you need to change the drive gear too. Small changes can usually be done with just the outside gear.

 

[Twisted_Metal]

Gary is absolutely right. You need a speedometer calculator for your specific tranny, gears and rear tire size to figure out what combinations of the 2 gears to use.

If you don't know the gear inside, you will probably have to open it up to find out if you need 1 gear or both.

The TH350 is easy to change with it's removable tail housing. On my 200-4R you have to drain it and drop the pan to change the drive gear.

 

[slow80sc]

Here is a good calculator for you guys.....
http://www.tciauto.com/Products/TechInfo/speedo_gears.asp

 

[JL8Jeff]

That figures. I have no idea what's inside the transmission which is a 1964/65 Muncie M21. The rear is 3.55 with 245/60/15 tires and the speedometer is reading about 8-10 mph low at 60 mph. I was thinking it was a simple speedo cable gear change to correct it. I guess I need to make sure I know what's going on with those gears since I'll have the trans out shortly to do the clutch I can take care of it then.