So I bought a forklift today, weighs about 8,000 lbs, and have it on a 2,000 lb trailer. Drove it about 100 miles home. The last leg is a nice long highway grade, so Im all smiles pulling it at about 72 mph in 6th with about 26 to 28 Lbs of boost up, and life is just great. This is like a 3 mile grade like this, but EGT's are good so I just hold it there. Then I get off at my exit, and am accelerating through the gears pulling a light grade on a back road, and I hear this really loud "chirp" and the whole truck jerks, like something in the drivetrain grabbed something. Then, again about 20 seconds later, this is a really ugly sound and feeling through the whole rig, so now I am sure I am not making it home. I drop from 5th to 4th thinking it was something with 5th, but then it happens again, and now starts repeating every 5 seconds. It would only do this with a fair amount of torque and speed. Wouldnt do it going slow with even decent torque, and woudlnt do it at speed without any torque. So I get it home and pull it in the garage and take off the PTO cover access plate on the transmissions to drain the trans oil and look in there. Oil looks great, and the gears look totally amazing. Like they were new. 123,000 miles on it.

Take the driveshaft out, and u joints are great.
Jack up the rear and turn the pinion yoke by hand and wheels turn smooth and quiet. Everything seems great ???

So what the heck could it be ?? Anybody else have this problem ??
Input shaft bearing? Center bearing, output shaft bearing ??? Or maybe in the transfer case ?????

 

clutch maybe?

 

Since u have the driveshafts off already, just take the t-case off and rotate it by hand to see if u feel any binding. But it could also be the clutch slipping and thats why u get that jerking because it slips then grabs hard again.

 

did you try running light without the trailer? It sounds like a clutch problem but I would check for something binding on my trailer too. a lot of weight with that fork lift! A binding wheel bearing or brake on the trailer might cause that too. Good luck.

 

I think you broke the center of the clutch disc. That's how mine felt/sounded when it broke.

 

What he said. Dad pulled the hub out of his, pulling a BIG load. He said the tranny shifted differnt for a couple more weeks, before it finlly came apart.

 

Sounds like a broken tooth on the rear end to me... that would be easier to check than the clutch.

 

Its absolutely nothing at all to do with the clutch, that’s for sure. The chirp/bang is positively instant, literally a .01 second, and the shock through the drivetrain is like a gunshot. Trans idling in neutral is quiet, trans in gear and clutch depressed is quiet. Clutch applies and disengages exactly like it should. Very strange indeed, don’t get me wrong, I dont know what it is right now, but I am certain its not the clutch.

T-Case looks ok inside, although I am shocked at the slack in the chain??? Is it really supposed to be that sloppy ?? There is at least an inch of catenary in lower length of chain with the top pulled tight. Of course that doesnt matter, since its not turning in 2wd, but just curious on that since I have it out and apart.


I have to pull the diff cover and have a look. Could be a broken tooth, as JKM says, and its lying in the bottom of the pumpkin and when conditions are just right, its gets entrained in the oil and makes a pass through the gearset That would be ugly.


I originally, and probably still do mostly suspect a bearing on the verge of seizing in the transmission. I have read about the rear output bearing not getting enough oil with the standard 5 quarts, and it failing under heavy and prolonged loading....

Harbor, funny thing is that at first I did think maybe something was going awry with electric trailer brakes, like a instantaneous short from the light circuit right to the brake circuit, and thus appliing full trailer brakes for a split second, but I observed the trailer closely and also kept my hand on the gearshift lever to feel it resonate up through the lever. Didnt seem to be the case.


Well, I'll keep taking things apart until I find some carnage...... Not the normal way I like to troubleshoot, but this is bizarre.


Kp

 

Does it do it in 4 wheel. I just went through some fun with the snap ring in the transfer case breaking. It would not make the noise in 4 wheel. But take it out and it would move all the gears back in the transfer case. And make a bad grinding noise.

 

Any updates on your truck? Im curious too know what you find out.

 

my truck, which to me seems to lack power, is doing that up steep grades with no load. have to floor the truck to get up this hill and has done it about 4 times now in first. have had my tc replaced 4 times in last year so i took truck to tranny shop yesterday. we went for a ride and he heard the noise. tried the climb in 4x4 and no noise. guess tranny guy is off the hook and i have to find another mech. thats what i woild suggest, try it in 4x4

 

i'm thinking the chirp was ur tires. Have u taken the mainshaft out of the t-case yet? maybe the shift fork in there was letting the chain engage. Other then that I'd say the rear diff.