clunking drivetrain (1 Viewer)

[spdracr58]

So I found this online and seems pretty accurate.
Noise: Clunking when depressing the throttle pedal (takeoff)
Cause: Worn U-joints; worn spider gears; worn axle splines; excessive gear backlash; loose yoke splines; worn slip yoke splines

I have gone under and checked the driveline and it seems good along with the U-joints. I did this by placing the vehicle in neutral and trying to rotate the driveshaft. It is able to move ever so slightly then stops. This started to present itself after I rotated the tires and had the starter realigned by a shop. It has the SBC conversion with a Turbo 350 tranny, but then to a stock fj40 transfer case. 1974 fj if that makes a difference. I am fearing that it is the transmission / transfer case or the rear axel. is there anything I can check under the car that may show this. It is only audible when I accelerate, is definitely coming from the rear of the vehicle, and is not the exhaust banging around, and is getting worse.

 

[shawnfj40]

Yes you can lay under it after chocking all 4 wheels and have someone get in the truck and hold the brake with the truck running shift back and forth until you can repeat the "clunk" you are going to have to reproduce the noise in able to find the source. Plan "b" is to just start taking this apart until you find it. What I have seen with the V8 conversions is the transfer case getting loose from the trany and causing a really noticable thunk.

 

[ozcrusier]

Jack the back end off the ground with good wheel chocks stick it in first gear and turn the diff backward and forward to see how much backlash you have in the diffs. Then move forward and spin the tail shaft as above to feel the gearbox this should indicate where the major play is but don't sweat it as these are tough old trucks so drive accordingly until your ready to rebuild.

 

[Cleg]

I had noise like you are describing that was coming from a worn spline on the output shaft of the transmission.
The driven gear in the t-fer case was loose on that spline.
The spline teeth were worn almost to points allowing for a small amount of rotation of the gear, maybe only 2 or 3 degrees?.

Checking for slop in the drivetrain from underneath with the truck not running didn't show where the problem was.
The amount of play didn't seem like enough to be the cause of the loud clunking noise but that was it.

That said, if your problem developed quickly, it seems unlikely that the spline is worn.

If you eliminate all other possibilities, it may be possible to see what is going on in there by taking off the PTO gear cover plate and the input gear cover. I never took anything off of the transfer case while it was in the truck so can't tell for sure.

Good luck.

 

[allan man]

[QUOTE=" transfer case getting loose from the trany and causing a really noticable thunk.[/QUOTE]

X2

 

[spdracr58]

I went underneath and checked what I could and everything seems snug. When the car is parked, in neutral with the tires chalked I can rotate the rear driveshaft about 2-3 degrees and I hear a clunk in the transmission. I went by a local transmission shop and they quoted me $2,000 to rebuild my turbo350 transmission, or $1,400 for a bench rebuild. I can buy a brand new one for that amount. Looks like I may pull the tranny and transfer case and see what is causing such a raucous.