|How To Change Your 700R4 Speedo Gears|
Written by: Mike Ervin
I wrote this page for the people who want to change there speedo gears but don't exactly know how. It is really pretty simple to do and besides if you are reading this it probably needs to be done. If your speedometer is off by much it is best to change them than risk getting a speeding ticket. Now with all that out of the way, let's get started.
If you have already seen my article on how to calibrate your speedometer for new rear end gears you have probably estimated what gears you need so I won't get into that here. Let's just concentrate on getting them changed over to the new ones. The first thing you need to do is jack up the truck and support it on some sturdy jack stands. Never ever work under your truck without it being supported. Then you need to remove the drive shaft. I suggest putting the transmission lever in (N) neutral, this will enable you to turn the driveshaft and make it easier to get at the bolts. Mark the rear u-joint and the pinion yoke so you can install it back in the same location, to keep it from being out of balance. You need to be prepared to catch the fluid that will come out of the transmission. Also I probably don't need to tell you this but, if you just drove your truck the fluid will be hot. Be careful. Remove the bolts and clamps at the universal joints at the rear. Now push the driveshaft toward the front of the truck to disengage the rear u-joint. Be careful and don't let the bearing caps come off the joint, you'll have a big mess if you do. Behind the caps are a bunch of needle bearings and grease and believe me you don't want these falling out. After you get the rear loose slide it toward the back of truck and pull the front yoke out of the transmission.
Here is a photo of all the parts you are required to remove from the tranny in order to change the speedo gears. You see the tailshaft housing at top, the sleeve at bottom right, drive gear at bottom left, and the driven gear at left. Also you see the rubber o-rings on the tailshaft housing and the sleeve. If these are damaged you will need to replace them to keep it from leaking.
First use a pair of pliers and remove the speedo cable
from the tail housing. At the same place the cable was attached there is a bolt that
holds the driven gear sleeve into the transmission. Remove it and pull the sleeve
out, again catch the fluid that comes out. Now take out the four bolts that hold the
tail housing to the transmission and remove it. Catch the fluid again. Again
there is another O-ring on the housing and if damaged replace it also.
What you see now is a metal sleeve on the output shaft. Up farther on the shaft is the plastic drive gear similar to the one below. Slide the sleeve off out of the way. The gear is held on with a small metal clip. You might have to turn the shaft to see the clip. The only way that I have found to remove the gear is to use an adjustable wrench or something similar and peck it off. While you are pecking on the gear you will have to press down on the clip with a screwdriver and the gear will slide past it and start coming off. It will take a little pecking but it will come off, believe me.
Re-assembly is the reverse of removal. I recommend changing the rubber o-rings on the tailshaft housing and the sleeve. Also it would be a good idea to change the little seal in the sleeve where the driven gear slides though. One more o-ring that I would change to save a headache later is the yoke seal. This is in the metal sleeve you slid off the output shaft earlier. Don't forget to remove the old driven gear and replace it with the new one if needed. Be sure you check the fluid level and add some if it needs it. Now you won't have to worry about speeding anymore. Yeah right!