I'm working on a dead speedometer problem on a 1991 4X4 F150 4.9L M5OD. I pulled the instrument cluster and Speedometer cable out and both checked out OK. An extensive search for speedo problems in this forum pointed towards the Vehicle Speed Sensor (VSS) driven gear and the drive gear inside the t-case tailhousing.

It seems my VSS pinion gear is OK (gears still look intact) so I suspect the drive gear inside the t-case tailhousing needs replacement? The only problem is...I need a bit of tutorial to tackle this job...or is it a projecct for a professional tranny shop? I appreciate any advice you can throw my way...

Thanks in advance.

 

Broken speedo cable? Did you pull the cable off at the transmission end to inspect the gear on the cable?

 

Thanks. I already pulled out the cluster and the speedo cable, connected them together and spun the t-case end of the cable with my fingers and the speedometer seemed to worked fine. It jumped up everytime I turned the cable so I'm assuming my speedometer and cable are both ok. No binding or anything like that. The only suspect left is the "internal" t-case gear that drives the cable gear unless I'm missing something else.

Is it too difficult to get inside the t-case to check the speedo gear in there? Should I bring the truck to a tranny shop? I'd like to give it a shot but I can't seem to find any references online and I sure hate to tear into it blind-folded. Anyone with experienced advice?

 

look at the inside of the speedometer gear at the trany. On m truck, the gear was stripped on the inside where the square cable goes in, so I dipped the cable into some 5 minute epoxy and let it dry inside the gear and it works perfectly now, just be carefull not to use too much and while it is drying give the gear a turn with your hand evey couple of minutes so it doesn't stick the hole mess together.

 

Thanks! I'll check it out this weekend and let you know.

 

Checked it out this morning by chucking a drill to the tip of the speedo cable and vss pinion gear and the speedo cable, vss, and pinion gear connections are solid. My speedometer worked smoothly with the drill. While under the truck (with engine off, tranny in reverse, parking brakes engaged) I stuck my finger into the transfer case opening for the speedo pinion gear to check the "drive gear" inside the transfer case. I was surprised that I was able to spin the gear freely with my fingers. I'm guessing the gear is only suppose to spin when the vehicle is driving? The gears also "felt" kinda worn out. I getting more convinced that the "drive gear" inside the transfer case is the culprit here. I checked out the Borg Warner 1356 transfer case section in my Haynes manual but it doesn't have any specific info on how to replace the speedo drive gear. Front and rear output shaft oil seal replacement is all they cover. I'm guessing from my inspection of the t-case, remove driveshaft, drain t-case fluid, remove t-case rear cover bolts...then remove rear cover? Has anyone done this procedure before? Thanks.

 

Im having the same problem, i pulled out that gear that connects to the cable and thats all fine, although it was kinda tight at first but it works fine i even replaced the whole cable, still nothing. im thinking its the gear inside the TC, how could we get to that gear?

 

It is quite simple to access the drive gear for the speedometer.
remove the drive shaft, remove the tailpiece housing... it’s just four bolts and some sealant when you put it back on. Torque is 36 to 40 ft/lbs or so.

once inside, you will see your gear and it is fairly simple to remove. There is a ball under the gear that is set in a detent in the shaft. To access the ball, there is a clip forward if the gear that keeps it from sliding forward. Remove that clip with a pick and you should be able to slide the plastic gear forward, firmly by hand. Use a magnet to catch/withdraw the ball from the detent under the gear. Once the ball is removed, the gear will slide aft off the shaft!!!

This is covered under BW1356 rebuild videos you can find on YouTube. Really not a lot you can mess up, but be carful with the plastic gear, teeth will chip if you pry on it.

 

It is simple to access the gear, i detailed it under the last comment on this thread. Let me know if you understand or need help. I just had a couple apart.

Really unnecessary to take it to a tranny shop, but they could easily access it for you. The gear should only spin with the output shaft, as you suggested. Possibly the gear is cracked if it is spinning, or the detent ball is missing.

 

i am thinking he got it fixed 11 years ago, rite before he stopped posting here.