When I am driving and let off the gas, there is a knocking under the gear shift that I have located in my opinion, and it is the prop shaft. It seems to be much worse in a particular gear, between 25-45mph. I crawled under and grabbed on to the shaft where it comes out of the trans or transfer case (I am very new at all of this and am still learning parts, but it is whatever the shaft connects to with what I think are U-joints??) and there is about an inch of play in the shaft when engine is off and in park.
Can anyone help guide me in a direction so I can learn more and get the needed parts/instructions, and get to work. Does this sound like a problem in the shaft itself, the joints, or something far more sinister inside of the trans? The fact that the knocking is much worse in a certain gear scares me, but my trans isn't slipping and acting funny when I drive/press gas, just when I left off completely and that shaft knocks once or twice.
Thanks everybody for all the advice on this forum. I am really looking forward to learning all about these great trucks and nursing my Disco back to full health.

97 Disco
134,122

 

A little bit of play is normal. Is there any play where the driveshaft goes into the transfer case? Have you checked or changed your transfer case and diff fluid. My 98D1 was real noisy untill i changed all the oils then it quieted down considerably. You should have grease fittings on your Ujoints try greasing them real good and see what happens.

 

Sounds like you need a driveshaft rebuild. The UJ's are probably shot. When was the last time you greased your UJ's? Are you doing it at regular intervals? Also I would stop driving it until one of the guru's on here chimes in. If it is your driveshaft about to fail you could do serious damage to your truck. I believe there is a write up in the how to section at the top of the forum page. If not just do a search. There was a good thread on this not long ago with pics and everything. Antichrist is the man you need to talk to about driveshafts. He has forgotten more than I will ever know about them. He also knows part numbers. Good luck!

 

Thanks guys. As far as maintenance up til now, I have no idea. I just bought this truck a few days ago, knowing it was going to need immediate attention. I am new to all of this, but am anxious to learn and nurse this truck back to 100%. I am assuming the worst as far as how well it was taken care of before me, and am just trying to diagnose the major problems at this point.

LONGHAUL- I don't think there is any play at the transfer case, it is all at the other end (assuming that I am identifying parts correctly.) For idiots sake (mine), let's say that the front bumper is NORTH and the rear is the SOUTH. I am calling the unit at the north end of the drive shaft the transfer case...is that correct? Is the transfer case the bulbous part of the axle? The play is at the South end of the shaft, I believe it to be connected to the transmission? Am I right so far?

Okay, I just went and crawled underneath to double check what I was typing and now I CAN'T get the shaft to budge at all. It is in park just like it was when I last tested it, the only difference is that the truck is hot from being recently driven. Could that cause a change in diagnostics? Right now, nothing under there feels loose, and it is a little to dark to check for grease on grease fittings, which I will do in the morning.

DISCOMEDIC- Do the front and rear drive shaft run off of the same transmission gearing? My question is really this...if it were a trans problem rather than shaft/diff problem, wouldn't I be noticing the same symptoms in the rear? I intend to not drive unless absolutely necessary, with is one more 13 mile round trip tomorrow to pick something up, then it is all Honda and motorcycle until I figure this out. I will search that thread and hopefully there is some info in there that helps me figure out what is in need of repair......let's hope it is JUST a shaft.

How do I test U-joints?

 

I am fairly new to all this myself so I am learning as well. I read almost every thread on here in the disco section though. I don't want to start telling you things that are wrong. I just know that the DII's have driveshaft issues and have to be rebuilt with greasable UJ's. Like I said before, some of the guys on here only found out their UJ's were bad by pulling the shaft. Not sure on the gearing question. My DI was making the same noise and I rebuilt it recently and no more problem. Mine had been neglected so the UJ's failed. Sorry I can't be of more help. Hang in there, some of the other guys know way more than I do and can help you. Good luck!

FYI: the "North end" bulbous thing on the shaft is the front differential, there is a rear one also. The "South end" is the transfer case (or T-case) and yes it is attached to the transmission.

 

Thank you...this is the exact clarification that I needed. I will read up and try to diagnose the problem and report back.

thanks guys.

 

Easiest way to know if it's the propshaft is lock the center diff, remove the propshaft and see if the vibration is gone.

 

So are you saying that I should lock it inside with the gear shift and then remove the shaft entirely, and drive it?

 

the transfer case is in the middle bolted to the back of your transmission, (you may think it's one unit)

At the "north & south" ends are your front & rear differentials.

The driveshafts (front or rear) connect the transfer case to the differentials.

At the ends of each driveshaft are your "U"joints, allowing the differentials to move up or down w/o binding the shafts.

Peek into the center of all your ujoints to see if there's a "nub" in the cross, that's your grease fitting (called a zerk).

You hope there's one on each ujoint, those need to be greased at least once a year, probably twice.

It's not unusual to have a little rotational play going into the differentials, but holding the fittings front and rear of EACH ujoint, there should be NO play, (the joint should move freely with no binding, squeeking, or play.)

You'll have to jack up at least one wheel front and rear to rotate the driveshaft by hand. The truck will have to be in neutral (after jacking up)on level ground. PUT JACKSTANDS UNDER IT!

luck,greg

 

This is great information. I can't wait until I have some daylight to get under there and look for all of these parts/potential problems.

The thread with pics looks super helpful, too....thanks for recommending it DiscoMedic