How do you fix a speedometer on an 88 f-150 and will this fix the odometer and trip meter?

Answer 1

Fixing SpeedometerI have a '90 F-150 with a 300 inline 6 and manual 4-spd manual transmission. Our speedometer didn't work and here's what we did.

The speedometer cable drives the speedometer and the odometer/trip meter. Fixing one should take care of the others.

The speedometer cable runs from the back of the dash down to the tail of the transmission. There is a bolt (7/16 head) holding the cable assembly to the side of the transmission tail. Clean off all the dirt, then remove the bolt and twist/pull the assembly out of the tranny. Check the gear on the end. The teeth should not be excessively worn. If the gear looks OK, carefully place the round end of the gear in a electric drill and run it backwards while someone is watching the speedometer. This simulates the truck moving. If the speedometer works, the problem may be the gear inside the transmission.

If you can, take a flashlight and look in the hole the gear came out of (we had plenty of space...it's a truck). You'll see another gear inside. It should be straight across the gears. If it is worn curved, the two gears may not mesh and the speedometer won't register any movement, which was our problem. Note the color of the gear. You'll need to know it when you buy the new one, and they're not available at local parts houses, only the dealer. Dealer said these wear out before the more easily accessible side gear. Go figure...

To change the inside gear (plastic, about $15 at the dealer), you have to remove the driveshaft. Before removal, you may want to drain some oil out of the tranny (drain is on the side near the bottom of the main tranny body). We had our back wheels on ramps, so we didn't have any oil come out. If the truck is level, be ready for oil coming from the tranny if you don't drain some. Remove the two bolts holding the transmission mount to the transmission tail. Jack up the transmission body so that the tail is just clear of the mount. Remove the four bolts holding the tail assembly to the main body of the transmission. Carefully remove the tail to the rear.

The gear is held on with a C-ring. Buy special pliers to remove it. It will save you loads of time. We spent an hour trying to remove the ring before we broke down and spent $23 on the pliers. Took about 1 minute with the right tool. With the C-ring removed, slide the gear off to the rear. As you start sliding it, watch for the ball bearing that fits in a hole on the shaft. It's what holds the gear from spinning on the shaft.

Install your new gear by holding the ball bearing in its hole and sliding the groove in the new gear over the ball bearing.

You may want to replace the driveshaft seal in the tail, since it is out and accessible. Reinstall the tail, using RTV after cleaning the mating surfaces. Drop the tranny back onto the mount, reinstall the bolts holding the tail to the mount and put in your driveshaft. Reinstall the speedometer cable/gear to the tail. Add oil if you drained any. Fill plug is above the drain on the same side.

Took quite a while, but speedometer works great now. .