Speedo T-case gear slippage?

[csjr]

Gurus,
My speedo doesn't work any more. I've had it checked at a specialty gauge shop--all good. I replaced the original cable and inspected the T-case gear at the same time--all good. The speedo doesn't register properly and after a few minutes falls to zero and that's it. I'm thinking the T-case oil warms up and therefore causes slippage with the gear inside the T-case (not the one on the end of the speedo cable). Any way to fix this without dropping the case and doing surgery? If I do drop the case and do surgery, can anyone give me a head's up on what to look for and how to replace the internal speedo gear? If I leave the tranny and just pull the T-case, are there any bearings I need to worry about falling into the case when I seperate from the NP435, or is there just the spud shaft running through the adaptor? I put it all in the truck, but it's been so long now I can't remember. Any help would be greatly appreciated.
Chuck

 

[Broncobowsher]

The speedo gear is sandwiched when the rear yoke is tightened. If you can tighten the nut on the output shaft yoke a little that will probably tighten the sandwich and keep the gear spinning. Doubt any parts are needed

 

[Viperwolf1]

I rebuilt one tcase that had a bad speedo drive gear. It was one of the plastic ones that had slipped to the end of the steel core. I re-centered the plastic portion and it seemed to hold tight. I don't have an actual pic but it's similar to this. You can see it if you remove the speedo cable.

 

[csjr]

Hey, thanks guys. The speedo has worked fine in the past so I'm thinking the internal gear is OK. Viper-thanks for the pic. I need to lube my driveshafts up good before an upcoming mud outing, so I think I'll try tightening the yoke first before dropping the case and doing surgery. I may pull the cable to see if I can see the drive gear. If I can't then I'm sure it has slipped like the one you describe. Is it possible to just take off the tail housing of the T-case to maybe get at this gear without dropping the case? Thanks again.

 

[Viperwolf1]

Is it possible to just take off the tail housing of the T-case to maybe get at this gear without dropping the case? Thanks again.

Yes. Just have to be careful pulling it out so the 13 roller bearings don't drop out of the forward end of the output shaft. If they do you'll have to take the bottom cover off to get them out.

 

[deltarat]

How long has it been doing it? I rebuilt my T/C and my speedo acted crazy. It would register right and then go down to 20 or so and back to 50. After 50-100 miles it straighted out and has been working right ever since. I don't know the cause, but it corrected itself.

 

[csjr]

How long has it been doing it? I rebuilt my T/C and my speedo acted crazy. It would register right and then go down to 20 or so and back to 50. After 50-100 miles it straighted out and has been working right ever since. I don't know the cause, but it corrected itself.

Well, mine has acted like that in the recent past--I look down while going 50 and it shows 20, look down later it looks correct, etc. Finally it has decided not to fix itself, rather it just quit. It'll read correct for about 5 minutes and then down to zero. My thought is that if the yoke is a little loose and not "squeezing" the gear shaft (like in the photo) enough, then once the lube heats up it get in next to the shaft and then quits spinning. It could be the gear is slipping on the shaft. That'll require more work. Slacker gauge....

 

[iwlbcnu]

I wouldn't just tighten the yoke, that makes sense, but when I tried it, just a littel, could still spin the yoke by hand, it made the bearings heat up, so much in fact that when I tried to remove the speedo cable, it melted and pulled out. I had 2 doing this, on both the plastic gear had slid to one end, it seemed tight though. I pulled several extra cases i had and found two that still were centered and then set them up as stated in the Ford manual, both work great now. Some cases also have a steel gear instead of plastic.
I was able to pull both while in the truck and the 13 rollers stayed intact.