This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.

Jul 13, 2009
HELP!!!!! Drive line issue

The Truck is a '77 FJ40 with its original 2F, trans and Tcase. SOA and 33's daily driver.

Ok heres the scenario:

Driving and all of a sudden a very odd whop whop whop sound and a lot of vibration can be felt through the gear shifter. Pull over nothing visual find the 4 bolts for the rear drive shaft at the pinion have backed off slightly, u joints all feel good. Get in figure move it to identify the problem and its gone.

Get home tighten loose bolts and grease all joints.

Go for a drive around the block, nothing

Go for another drive, everything is good and then a sudden BANG. Pull over nothing visual. Move the truck again to see if issue can be found and nothing.

Their might be a bit more noise out of the tcase now when driving (hard to tell over all the other usual cruiser noise, but something sounds off)

Anyways get it home, drain the tranny oil its all good about a year old still looks like new,

Tcase oil was changed at the same time 3 small chunks maybe .03 x .03 x .03 inch in size on the drain plug magnet, oil has a very metal flake look to it. (dumped and filled when found)

Rear diff, oil is a bit milky, dump and fill, no metal in it at all.

Thats everything as I have it right now.

I'm thinking Tcase is buggered? but I don't know and I'm at a loss as to how best to go about figuring out whats going on.

So I ask for Help.
Last edited:
The easiest thing to check are the u-joints. Make sure they're OK before proceeding.
U joints all seem good, no movement they feel good, they were all replaced 2/3 years ago. U joints where my first thought also, but not finding any play in them.
I once knew someone who put the wrong gear ratio in the front axle. When driving in the right condition it would do something like you mention.
I have had the truck for 5 years now and wheeled often gear ratio is not an issue, and its in 2wheel drive with front hubs unlocked. Thanks though.

Screwed around with it some more seems to be more noise in 3rd and 4th gear then in 1st or 2nd and its a different noise then the truck has made in the past.... so I'm thinking its tranny or Tcase, was thinking of opening up the covers on them both and seeing what I can see.
Might be too easy but you don't have a tire separating do you?
Might be too easy but you don't have a tire separating do you?

I havent seen any signs that would make me think of a tire being the issue (not that I would have even thought of that) will take a close look at all tires just to be safe. though I don't see how that would explain the loud bang when driving and then nothing?
I had an old 9" Ford differential make a loud BANG. Did not realize it was the differential at the time. Had more noise, but only at speed. It was hard to figure out where it came from. Discovered it was a spider gear that broke, but not enough to completely take the rear end out of commission.

But, if the noise is in a certain gear, and not at a certain speed, that suggests it's the transmission. Synchros operating OK?
Pulled the pto cover off the tcase, used a bore scope, got two teeth mostly gone off the one gear, I think odds are thats my problem..... looking at the haynes book it looks like its the highspeed output thats missing teeth.....
Last edited:
Huston we have a problem

Hmmmm I think I found my problem.

Gear is the high speed output.

Shaft is the Idler shaft

Users who are viewing this thread

Top Bottom