Yo Justin,
#1 suspect is lack of cable lubrication.
Lubrication; This is for a Stang, but similar "...Cable function depends hugely on lubrication and plenty of it. When lubrication becomes lean, cables bind and deteriorate, which only makes the problem worse. If the cable has deteriorated to where it is frayed anywhere along its length, it's time to replace the entire cable assembly. Frayed speedometer cables damage the inside of the sheath to create two sources of binding. This is why entire cable assembly replacement is so important to smooth speedometer operation. Here's the transmission end... Here's the transmission end of a speedometer cable, which takes a #N751 o-ring and the appropriate speedometer drive gear, chosen depending on the transmission and rear axle gear. New cables are already equipped with the o-ring. The barber pole pathway carries transmission lubrication to the drive gear.When you install a new speedometer cable or service an old one, generously lubricate the cable with a mixture of transmission fluid and lightweight lithium grease. Mix up a modest *** of lithium grease and transmission fluid in the palm of your hand and run the cable through it. You can also use speedometer cable lubricant for this purpose. Run the cable back and forth until saturated with ****. Then, slip it into the cable sheath..."
Cable & Speedometer Head "... Speedometers get into trouble when cables bind or magnetic heads cease due to the absence of lubrication. Like the humble car clock, speedometers need periodic maintenance, too. The spinning speedometer head needs occasional lubrication (speedometer-head lubricant). Pull the cluster out, disconnect the cable, and feed modest doses of lubricant into the head once a year. Don't overdo it. While you're at it, pull the speedometer cable out and bathe it in white grease and a low-viscosity engine oil. This combination will keep it happy for thousands of miles..." MIESK5 NOTE; Some Speedo ends (at Speedo) are held on by a plastic clip: place Index finger on Metal Tube & thumb on plastic ring flat surface; Press Flat Surface of clip & Pull Cable from Speedo (Ford calls the speedo end the Head; or screwed on:Turn the cable end counterclockwise to disconnect. You may need an open end wrench. This is by Chilton for an 85 Bronco; 1.Remove the instrument cluster as previously described. Remove the lens and the mask from the cluster. 3.Disconnect the speedometer cable. 4.Remove the speedometer attaching screws and remove the unit. To install: 5.Position the speedometer to the pack plate and install the two attaching screws. 6.Examine the square drive hole for sufficient lubrication. If required, apply a 3/16 inch dab of lubricant (B5AZ-19581-A or equivalent) in the drive hole. 7.Reconnect the speedometer cable. Total Cable replacement; 1.Reach up behind the cluster and disconnect the cable by depressing the quick disconnect tab and pulling the cable away. 2.Remove the cable from the casing. If the cable is broken, raise the vehicle on a hoist and disconnect the cable from the transmission. 3.Remove the cable from the casing. 4.To remove the casing from the vehicle, pull it through the floor pan. 5.To replace the cable, slide the new cable into the casing and connect it at the transmission. 6.Route the cable through the floor pan and position the grommet in its groove in the floor. 7.Push the cable onto the speedometer head..."
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Cable Depiction in Xfer Case Tail Housing
Removal tips;
Put the clear plastic lens back on the cluster and take out the 4 screws in the WHITE plastic, just outside the lens. IIRC, they're T20.
If you remove the 4 screws from the HVAC panel, you'll be able to turn it to release the wiring & cables. The cable sleeves clip to the white frame, and when they're released, you can unhook the cable ends from the levers.
speedo cable could keep you from getting the cluster out far enough to get at the connectors. Look under the Bronco & make sure all the slack is pushed forward, then pull it up by the brake pedal & try again at pulling the cluster out. To release the speedo cable from the cluster, push the large white plastic collar down, then back.
The cable end locks automatically when you push it into the back of the speedo
