FJ40 Transmission Output Shaft Nut Loose

[nazdackster]

1980 FJ40 4 speed, 2F: I'm replacing the seal between transmission and transfer, and while I was in there to remove the output shaft nut (the same shaft as transmission input - to separate the transfer, the back nut is loose, but staked in place. Anyone have any idea what effect that might have? It's supposed to be 90 ft*lb tight, then staked. Also, everything looks great inside, but I do notice a bit of backlash between input and output (to driveshaft) shafts. Once rolling, seems smooth, but clunking it back and forth by hand, it has to overcome some (slight) resistance before turning. How much backlash is too much? Input and output shafts have a little (guessing .005") radial play. Good? Could be too much by having that nut loose I suppose.

The transmission was tough to get out. After separating, I didn't have much clearance in the back to get the input shaft past the clutch stuff, so I mangled the clips on the fork raising, lowering, side to side trying to find a way to bring it back far enough... I think I have some new clips with my new clutch, but any tips on how to line this up when I put it back in? Get it close, then install the fork / clips once close, then bring it home? THANKS!

 

[Pin_Head]

A loose nut on the transmission output shaft would allow the transfer input gear to slide back and forth and wobble on the shaft. I'm having trouble understanding what you mean by the nut is loose, but it is staked. If you mean that there is clearance, but the nut won't turn because it is staked, the clearance is probably due to wear on the spacers.

The weak link with the 16 spline 4sp is wear on the output shaft splines. If they are excessively worn, this will allow backlash and allow gear lube to pump from the transfer into the transmission even if you replace the seal. Backlash in gears is normal, but wear on shafts and bearings is not. Since you have it out, this is a good time to tear the transfer case down and replace any worn parts, like the idler gear shaft and bearings, which is its weak link. There is no backlash spec, but there are specs for wear on components that contribute to backlash. Check the FSM for these specs and how to check them.

To get it back in, use a tranny jack or remove the tranny hump and suspend it from above with a shop crane or come along. You can also use the rope sling between the frame rails as shown in the FSM.

 

[nazdackster]

Yes, nut is staked and can rotate a little before binding on the stake, clearance is minimal, but enough to allow spacer to rotate. I'll check the splines for wear once I break the nut loose and remove transfer (tonight). Inside the trans and transfer looks really pretty with minimal (hardly detectable) wear. The fill plugs had maybe 1/2mm of metal powder on the magnets, and slight but visible traces of brass powder in the bottom of the drain pan. Pretty good I thought. I'll check what I can tonight... Thanks!

 

[Meadows]

Mine was loose too. See pics of my output shaft in link below. Not sure what caused it but this is what I found.

Link: https://forum.ih8mud.com/40-55-series-tech/294067-transmission-output-shaft-damage.html

 

[nazdackster]

Mine was loose too. See pics of my output shaft in link below. Not sure what caused it but this is what I found.

Link: https://forum.ih8mud.com/40-55-series-tech/294067-transmission-output-shaft-damage.html

Yep, mine looks like that, with an input gear to match. In 2 weeks I'm doing 500 miles offroad + 1000 highway miles. I need to get this fixed... Might try the PTO gear hack - put a PTO gear next to the bad input gear, weld them together after removing the teeth from the PTO gear, then shorten the spacer by an equal amount. Sounds good in theory, might have to... The rest of the transfer case looked really good inside, took it apart as far as I could without a press, I don't see any wear at all except a strange cut on the outside of the low speed gear and matching idler gear. Nothing rides there, so I'm not worried about it.