differential questions
 

first off, this applies to my 78 land cruiser. i am aware there is a cruiser section, but there are more people going through this section and i think this probably could apply to pickups as well...

last year my land cruiser starting making noises that sounded like it was coming from the rear end. it would only occur when i would be in gear, but off the gas pedal - kinda sounded like small engine brake on a semi or something similar. i parked it for the winter and now am trying to fix it, but i really don't know much about diffs. i probably should take it to a proper mechanic, but i like to learn and the satisfaction of doing stuff myself so here we are. before i tear into it, i figured i should at least try to get some suggestions as to what the possible problem could be. the flange area where the driveshaft mates to the diff has a lot of play. i can grab and shake the drive shaft a fair bit.

based on this, will i likely have to pull the rear end out? am i better just to replace rear end rather than finding and repairing the faulty part?

U joint

:guitar:

I don't know a ton about diffs but when mine went bad I had similar symptoms and my drveshaft had a lot of play also. My pinion bearing was shot and it ruined the seal as well so I had gear oil pouring out like it was cool.

My solution was to replace it and retrofit a brand new TRD e-locker but if you want just go to the junkyard and pick up a 3rd member for 200 bucks or so and replace it yourself. Diving into taking apart and repairing 3rd members is not for an ameteur for sure. However if your LC is as easy as my 4 Runner to swap rear ends it should be fun and you'll learn from it too.

i've changed a few ujoints in the past and i am confident that it's something else. when i shake the drive shaft, i can see the play in the differential flange and i can hear movement inside the carrier.

i actually do already have a pair of 4.10s in carriers ready to go, but with my current 3.70 ratio, it means that i would have to change the front as well (or just never use 4WD - no thanks).

also, i've heard that with land cruiser diffs, there are coarse and fine spline gears. is it obvious to the eye which is which?

If the U-joints are in good shape, the pinion bearings and preload are the next place to look.

when mine sounded like this and had play i had a chiped tooth. i would pull the trird and see if thats your problem

I have no experience with LC diffs but why not go 4.10 all around? Your problem does sound like what mine was. Bad pinion bearing

You can always drop the driveshaft and make sure the pinion nut is tight. Sometimes they back out. Unstake the nut, make sure it's tight and restake. But the bearing could be toast.

cuz in all likelihood this truck will be for sale after this fix and i don't want to do any more work than i have to.

I see... Well I've seen used 3rds at junkyards for 200 or less. The work shouldn't take you long either. That's not too bad I dont think

would that still make the noise i was hearing?

You need to take the companion flange off the pinion to see if its coarse or fine. I'll take a stab and say fine but thats just a guess.

Sounds like the nut has loosened off, bearings and maybe gears are probably done now. If you replace and tighen the nut you might get a little more life out of it... Please don't just to sell though.

pinion nut has loosened off. should i be replacing the nut and what size socket is needed? what are the odds that if i (replace and) tighten it that everything is good to go?

Well you could try. Its 27mm. Buy a new nut and torque and stake it properly (I think its about 110 or 130 ft lbs). I don't know for sure but it could be a crush type spacer in there in which case it won't last and you will have changed your gear patern.

after scouring the town looking for a 27mm socket and only finding 26s and 28s, I finally found a 27mm in a miscellaneous parts box. bought it, brought it home and the damn thing is too small. serves me right for not taking the nut with me i guess...

Pinion nut is probably a 30mm.

:guitar:

You could easily use a 28, or 30mm socket as well. That said, it would probably be cheapest to find another diff. Try EBI in Port Moody if you're stuck, they cater to Cruisers specifically.

off the top of my head i think originals might have been 32mm. its been 13 years since i've dealt with originals though.

Edit: that might have been 3 speed t-case nuts... get a 1/2" socket set. The new nut from toyota will be 27mm.

the old one is 30mm just like the new one

Thats odd, I just checked my spare diff and some used nuts I have on my tool box and they are all 27mm. I think the originals that were on my truck were bigger, posibly 30mm but that was more than 10 years ago that they were replace for the first time. Maybe toyota has some old stock kicking around still.