time to play name that noise!
 

Recently my truck has started making noise while accelerating up to around 35-40 mph and its getting worse, also driving through deep water the other day seemed to make it worse the followig day. the noise is a squeaking / rubbing noise that sounds like two metla parts of some sort rubbing against each other that changes with rpm. Im thinking its the clutch but hoping its not, I sprayed some wd-40 on the driveshaft u joints the other day (no not to fix the problem) I figured if one of the u joints had lost its grease somehow then a spray of lube would make the noise go away for a little while anyway. So from this I learned its not the u joints, also the noise only happens when the clutch is fully engaged (foot not pushing the clutch pedal). My truck is a 1988 F-250 diesel with a 7.3 non-turbo, 5 speed and 4x4. also this is hapening under normal driving with the 4x4 disengaged at the transfercase and at the hubs (you can freely spin the front driveshaft with the truck parked and the tranny in gear).
Thanks for any help!

WD40 is not a lubricant, its a penetrant. WD40 removes moisture from whatever you are spraying. You need to grease those ujoints back up because you could have potentially dried them out. If they have zerk fittings then throw a grease gun on there, otherwise it might suffice to spray some white lithium grease where you sprayed wd40.

As for the noise, not really sure. Are you sure its coming from the drivetrain? Check your pinion nut where the rear driveshaft attaches to the rear rear differential (you have to remove the driveshaft). Also regrease the slip yoke on the transfer case. Lastly, if you have a 2 piece driveshaft, grease the slip yoke at the center of the shaft also. Hope that helps.

Well im no mechanic but I know enough to know it has to be coming from some part of the drivetrain because it only occurs when the truck is moving, and with the windows down it is clear the sound is coming from under the truck, not necesarily the engine compartment. I will try to lube the slip yoke today, as for the pinoin nut, that sounds like a weekend project. but it sounds like what ever is making the noise is very loose, so loose that you could freely move it with your hands, which no part of the driveshaft can do.

Well the pinion nut is known for becoming loose and the driveshaft is super easy to remove. And also, you can't lube the slip yoke unless you remove the driveshaft either. You might now want to drive your truck too much if your pinion nut is loose...

Im thinking it is thepinion nut now, last night i stuck my head out the window to listen to the noise as i took off, and it was definately coming from the back of the truck, definately not in the trans or even the front u joint. Im pretty excited just knowing its not the clutch. I noticed too that I could only hear the noise when the engine was under load (accelerating or going up hill). I have never removed a drive shaft, though it seems easy enough, just undo the bolts on the rear u-joint and slip it out of the trans tail shaft right? will I need any special tools?
Thanks

You're driveshaft might be a bit different from mine (mine is a 2 piece shaft) but it shouldn't require any special tools. Just undo the bolts at the rear diff and let the rear end of the shaft rest on the ground. Tighten the pinion nut (its big... like 1 1/4" ish) and throw the driveshaft back on. Good luck man.

The only way to properly check those u-joints on the driveshaft are to remove it. So when you remove to check pinion nut, check those u-joints. Make sure they move in all axis' freely. If you have a slip yoke on the t-case side a small amount of trans fluid may leak out. Use some grease on the inside of the yoke before you replace everything.
I'm betting on u-joints as your noise.

You can't spray anything on a u-joint and expect it to quiet down. First, they're sealed. Anything you spray on them won't get to where it needs lubrication. And Chris is right - WD-40 is no lubricant.

If you really want to find out if it's your u-joints, and I would be surprised if it's not, then jack up the rear of the truck. Crawl under it and check for play at each u-joint in the rear driveshaft. If there is any play, the joint is bad and needs to be replaced.

u-joint could be dry.

replace it/them.

One tip about removing the driveshaft. You need to mark the driveshaft and put it back in exactly in the same position. The drive shaft is balanced, at least the one on my 90 F150 was. I put mine back in without marking it and had to move it's position several times to stop it from vibrating while driving. Just use a grease pencil or punch.

Jim

I had the same pickup and a similar sound it was the speed sensor ring in the rear end broke for some reason and eventually took some teeth off of the ring and pinion. Hope thats not your problem.

ok, I knew I never should have mentioned the whole wd-40 thing, everyone is totally missing the point, I know that an aresol sprayed on penetrating lubricant could never do the job of grease, the point was not to fix the problem but to identify it. wd-40 stops squeaks, so I knew if the squeak went away, it was time to replace the u-joints with new ones full of grease and of course no wd-40.
Now that we cleared that up, I have grabbed the drive shaft a few times in the past week and tugged and turned it in all directions to check it for play but it seems like both ends are pretty solid, but that was with all 4 wheels on the ground, anyhow I plan on taking the shaft down this weekend to check the pinion nut, and I should be able to tell at that time if they need to be replaced.

Like Andy said, it's very hard to tell if you have bad u-joints FOR SURE without removing the driveshaft. You need to remove it and rotate each of the u-joints in all directions, making sure there is little-to-no resistance against any of the motions. If your u-joints were bad and making noise the WD40 would not make a difference because the u-joints are completely sealed (they have to be or else they would spray all of the grease all over when the driveshaft starts to spin).

In all of the commotion about using WD40 on your u-joints I overlooked them as a possibility for your noise. I have officially changed my vote to u-joints although I still think it is definitely possible that your pinion nut is loose, so check it anyways. Good luck man.

just a quick funny about checking u-joints while the truck is sitting on all fours. Friend of mine asks me to help with his truck says making clanking sound. I tell him its u-joints. he says no i played with drive shaft and it tight. I ask if wheels were touching ground he says yes doesnt matter does it. i laughed and jack the truck up pull the drive line and the while i was pulling it out of tail shaft it pretty much became a 2 piece DS. sry to ramble. but i have a question? you said you have been driving it in deep water right? well deep enough to get into breather tube? if tube is still atacthed? it will take 2 hrs (includes 12 pack)hours to pull drive shaft replace 2 u-joints lube drive shaft, pull pumkin cover inspect reseal and refill, and tighten pinnion nut. so just do it and save your self money in the long run. i recomed using dana u-joints as well dont go cheap there 43-52$ a each. ok im done

just a quick funny about checking u-joints while the truck is sitting on all fours. Friend of mine asks me to help with his truck says making clanking sound. I tell him its u-joints. he says no i played with drive shaft and it tight. I ask if wheels were touching ground he says yes doesnt matter does it. i laughed and jack the truck up pull the drive line and the while i was pulling it out of tail shaft it pretty much became a 2 piece DS. sry to ramble. but i have a question? you said you have been driving it in deep water right? well deep enough to get into breather tube? if tube is still atacthed? it will take 2 hrs (includes 12 pack) to pull drive shaft replace 2 u-joints lube drive shaft, pull pumkin cover inspect reseal and refill, and tighten pinnion nut. so just do it and save your self money in the long run. i recomed using dana u-joints as well dont go cheap there 43-52$ a each. ok im done