Greetings to all. In my 1974 F100 2WD, 390, C6, 9", I've been getting an occasional "clang" from the rear part of the truck from time to time. This almost always occurs when changing from forward to reverse, but it doesn't happen every time. Since I'm having to trouble shoot on my own, I parked next to my garage, opened the door, and shifted back and forth. The sound is a metallic "clang", sort of like if you hit a cast iron skillet with a metel spoon while it was resting on a hot pad (how's that for descriptive, eh?). It happens when I shift into reverse after driving forward (like backing into my driveway), and then when I shift into drive, it might do it again. And it doesn't do this every time. The truck has about 137,000 original miles, and as far as I know, nothing has been done to the axel. Engine and trans have about 25,000 since being rebuilt 6 1/2 years ago. This "clang" is only when shifting into gear (that I've noticed), and not driving down the road. U-joints all seem good and tight, and there is very little twist in the driveshaft, so the gears seem to be good. I know that a 9" is practically indestructable, so I'm a bit confused. I know that in the 60,000 miles I have put on this truck, I have never done any hard or extended towing, nor have I seriously overloaded the cargo capacity.
If anyone can offer some things to look for, I'd be most thankful. I have a really good local shop I can go to, but I want to go in with some ideas and knowledge, first.

Thanks to all,

Matt

 

From what you are describing, you have given a perfect example of bad u-joints. If its a mettalic echoing clank, its more'n likely u-joints. I've got quite a bit of "slack" in my 9in. rear, but it doesnt clank when shifting, just a dull thud. You say you checked the joints, did you do it in park where there was pressure on the driveshaft? Set the parking brake and put the trans in neutral and try it if not. Good luck,

 

I have the same problem. I put new U joints in it. Still makes the noise. Not sure if it's the reverse band or what. Oddly enough, the U joints that were in the truck were way too small. Some kind of muck hardened around the U joints that I had to chip away. If you figure out what the problem is, let me know. I was thinking about taking it to a shop. However, as stated on another thread, I may be looking for a new rear end all together anyway.

 

I've checked the U-joints in all kinds of ways; in park, in neutral, rotationally, laterally, longitudinally..... they seem fine, but since I've never handled bad U-joints, I'm just kind of shooting from the hip to see if they are bad or not. I'll probably replace them just for preventitive, if not necessary, maintainance. Had a roommate in college who broke a U-joint on his CJ-7, on the street, while going up a hill. Don't want to do the same.
I, also, thought it might be the reverse band in my transmission. But the sound, and granted I'm listening to it as an echo, comes from much further back. Also, the trans only has about 25,000 easy miles on it since it was rebuilt by a local shop. I need to get it serviced (fluid and filter change, and intermediate band adjusted) anyway.
My 9" is pretty tight (in neutral, can only turn the driveshaft a degree or two by hand), and I get the dull thud--always have.
U-joints could explain another thing I've noticed. At about 40 mph, I have a vibration. It's only in that speed range, is worse the colder the ambiant air temp is, and doesn't seem to happen if I have a load (600lbs). I know bad U-joints can cause a vibration/shimmy, but this almost seemed to come from the front end after I got new shocks on all corners, new king pins, new steering gear box, a new axel pivot bushing, and a new steering coupler (paid as much for all this as I did for the truck 13 years ago).
Thanks, gents, for the suggestions. Looks like it's time for some U-joints. If that doesn't do it, we'll see what next.

Matt

 

Well if u joints are clanking you will most likely feel some sort of play, but then again I have seen u joints cause the vibration you are describing without feeling loose or clanking. If they havent been replaced in the last 75,000 mi or so, I guess it wont hurt, but I wouldnt throw too much money at it until you can figure out what it really is.
good luck,

 

Have you chk the 9 ' 's backlash ?
or looked at the spider gears and lock pin.
also axle splines and axle bearings?

Just my $.02

Rich

 

Thanks for all the input, folks. Talked to the mechanic today, described the noise, and he's pretty confident it's the U-joints (and this guy isn't one to screw around just to raise the bill). I'm taking it in Friday morning (and NOT driving it until then, as the noise seems to be more frequent, 'course I could just be paranoid) to replace all three U-joints, which should be around $100, shouldn't be more than $150. If that doens't fix it, I'll know it's something else, and the U-joints should be good for many years to come. Wishful thinking, perhaps, but I'm pretty sure this will take care of it. They way it comes and goes, and isn't more pronounced in cornering, I'm pretty confident it's nothing in the 3rd member. I suppose that will be the next place to look, though, as the noise is definatly coming from that area, and doesn't seem to be from the almost-new transmission.

It seems to be adding some ticking now as I'm driving, particularly under load, hence my parking it until I have to drive it to the shop.

Thanks again, everyone, for adding your two-cents. Any other idea/possibilities still welcome, just incase this doesn't solve the noises.

Matt

 

It sure sounds like you have either worn spider gears or a bad carrier bearing in the rear end itself. If it ever starts to make a whiring noise when you are driving too its a carrier bearing and needs attention asap. If it is only just a clunk when putting it in gear it is probably nothing too serious.

 

The only noise is the metalic clang when going into gear, and some light ticking or clicking on occasion while driving. No whirring noises at all. And, if the carrier bearing or spider gears were an issue, wouldn't there be a lot more play in the gears, and a lot more twist in the driveshaft when trying to turn by hand? I'm very green on axels. Had an 82 Mustang that I suspect needed some rear end work, but that's been it. If I'm still getting unnatural sounds after the U-joint job, that's the next place to look.

Thanks for the info.

Matt

 

Do you have a 2 piece driveshaft? If you do, then you could try greasing the slip collar - the splines in there could have just enough slack to clang when you put it in gear, and the grease would possibly help this a bit.

 

If it's a constant metallic clicking/squeaking sound while accelerating or decelerating on compression and it is getting worse as you drive it I would bet 99% that it's the u-joints. If it's u-joints it should all but go away when you push in the clutch and coast. Until it gets real bad then it will be all the time.

 

Oh yeah and your spider gears shouldn't be doing anything when you are driving in a straight line so forget that theory unless it only happens when you go around corners.

If you can get drining straight with all the slack out of the drivetrain and then accelerate firmly and you start hearing it a lot then it's 99% u-joints.

My $.02

 

Thank you all so very much for your input on my noisy truck. I'm an extatic to report that after replacing all three U-joints (yes, it's a two-piece drive shaft), the noise is gone, and the ride is buttery-smooth (was getting a variable vibration at about 40mph, and didn't connect it to the noise until a couple days ago). Only $140, and the double checked the front end and checked lube level in diff.

Many thanks to Shane and John at Holland Alignment in Pittsburg, KS for the work. I have taken both trucks there for various things, and have been very pleased with the service. If you are in the area, I highly recommend them for all brake, suspension, steering, and like work. They even rebuilt the floors and front cab mounts in my 74 2WD a few years ago, out of 10 ga steel. They'll outlast the rest of the truck, and mostly likely me.

Matt

 

Glad to hear it!