I'm working on a dead speedometer problem on a 91 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. Thanks Steve!

https://www.f150online.com/forums/pr...989-4-9-a.html

It seems my VSS driven 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.

 

Try chucking up a cordless drill to the end of the cable where it goes into the tranny. Spinning the drill will result in some type of speed to show up on the cluster. If not, then keep going where you are headed. I haven't seen many "drive" gears go bad. A lot of broken speedo cables, or worn out "driven" gears. But anything can happen. Just make sure the speedo works, before you get too "deep".

 

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?

 

It's just behind the rear cover assy. Take off the four (or 5) bolts and it will come off. You'll lose about two teaspoons of fluid. The cover is sealed with rtv. I think there is a snap ring that holds the gear in place and it slides off the end of the shaft. Oh yeah, there is a ball bearing that holds it in place on the bottom side.

 

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

 

Checked it out this morning...

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.

 

Read my last post again. You don't need to drain anything. It is just behind the tailshaft extension.

 

Sorry but I'm not really sure which bolts you're referring to. The only bolts I see are the ones securing the back cover of the transfer case. No bolts around the "tailshaft extension". I took these photos this morning to help you see my transfer case setup:

Another view:


Which Tailshaft Extension bolts are you referring to?

 

Sorry, the photo's link did not work the first time...


Here's where the speedo cable hooks up:

 

My bad, that's a different case than I was thinking of. You're right. You will have to remove the case, stand it up so that the rear output is pointing up, unbolt the yoke, then split the case. Don't freak out if the bolts have aluminum chips on them. To save money, Ford didn't tap the bolt holes, they put self tapping bolts in there instead. Just take your time and be careful when you pry the two halves apart. Do not, I repeat, DO NOT attempt to take it apart still bolted to the transmission. Clean the surfaces and put black silicone on the sealing surface (one half only), and reassemble.


BTW, that is not a 13-56 Borg Warner case. That was the one I was thinking about. Not sure what that is. Unless it is a very early version of the 13-56. Get the numbers off the tag on the bottom and google search it. You might find an exploded diagram of it, or better yet, post them on here and I'll go to work and get the parts guy to print me out one. Best I could do would be to snail mail, or if you can get near a fax machine. Let me know.

 

Okay. I'll see what I can find online with the tag info. Thanks for the advice!