1986 F-150 unidentified noise
 

My truck hasn't lived for about 3 1/2 years so this could be related to sitting up so long. When I get her on the road, I have a noise that begins around 45 -50 MPH. After it begins, it will do it at slower speeds. The noise ONLY happens when in gear and letting off the accelerator or coasting. If I push the clutch and / or take it out of gear, I do not have a noise. When I'm increasing speed, I do not have the noise. Whatever this is, I feel it slightly through the seat. (Yeah, I listen and feel my truck) Please help. I need her running but I don't want to mess her up and have to park her again.

Welcome to the forum, Lymira! :)

Hmmm... this will likely take a few guesses from members and is difficult over the Internet. A 1986 manual transmission has a hydraulic clutch, which offers no adjustment since the throw-out bearing is always in contact. Sometimes there is a slight squeal or chirping due to this. In my experience, this occurs when idling with the transmission in neutral and the clutch all the way out. If pressure is applied to the clutch pedal, the noise stops. The same happens when cruising with little strain on the drive train. While cruising, if you just touch the clutch pedal lightly, the noise stops. Also, at that point [cruising], if you accelerate [places stress on the drive train] the noise lessens or stops.

I do not feel anything through the seat, as you have mentioned. Normally, "feeling" something means a vibration due to reciprocating parts [i.e. u-joints, drive shaft, wheels out of balance or tires out of round, etc.]. Did the truck sit on the tires for the 3 1/2 year period? Could there be flat spots?

Does this sound anything like what you are experiencing?

Great description of this elusive, subtle "chirping" noise. I have heard it in my '85 when idling and it is exactly as you described it, going away with the slightest pressure on the clutch pedal. I'm glad to know what it is now!

The truck did sit on these tires while not running. I don't have noise while idle at all. It doesn't start until I'm up to speeds over 45 or so and let off the accelerator but stay in gear. After starting, it will do it at lower speeds. Pressing the clutch or out of gear stops the noise, or slowing to about 25 or less. My exhaust has broken loose from the muffler so the truck is loud and I can hear this over that.

Well, you're going to have to be a LOT more descriptive and specific as to what "the noise" actually sounds like; by virtue of feeling it, and experiencing it only with the driveline under load, that eliminates small things such as fan belts.

But this could be a lot of different things... my personal suspicion involves bearings in the rear end, but the "noise" in my mind is a bearing whine... and I have no idea if you're talking about a whine or a clunk or a chirp or what....

In any event, best for you to take it to a local shop and put it on a rack or dyno; sure, people here can ask questions and throw out ideas on what to maybe look at, but asking the Internet - people who can't hear and feel and see it themselves - for help is going to give you only so much help....

It's nothing quiet or faint. Metal on metal roaring. I can feel the roughness through the seat, but you are right. I'm out of work so I was looking for ideas that I could check. Thank you everyone for your help. I guess she sits a while longer.

Since I can't ask for help, moderator, can you tell me how to delete my thread?

You can ask for all the help you want, I'm not trying to discourage you, mostly trying to point out that noises are like smells - you need to describe them as best you can for people to get an idea of what you're experiencing.

Even with that, though, it's really hard for others by remote.

Maybe @Gary Lewis or one of the others can help...

You say it's not nearing whine, and this apparently began after having sat for 3 years... metal on metal... which makes me suspect something that is normally supposed to move (like brakes) is stuck... but only on deceleration? Hmmmm.....

I think you may have a worn out drive shaft. But, you haven't told us much about your truck so I'm not sure what kind of drive shaft you have. (I make it a habit to not respond to threads where people don't tell us more than we could possibly need to know about their truck, but Chris asked me to join.)

Anyway, if your drive shaft has a slip joint about 9" behind the transmission I'd bet that joint is worn out. I had that on one of my trucks and it came in much like you described - when coasting but not letting off completely.

If your shaft has the slip joint, try pushing it sideways or up/down. If it deflects at all then you need to pull the shaft off and pull the slip joint off to check the splines.

:)

I asked you to join because he's a noob[1] and I'm afraid that I "set the tone" that we can't help because of too little information (besides the fact that none of us have heard it), and I really don't mean to do that....

Just noticed something, it doesn't make the noise with the transmission disengaged - which eliminates the brakes as a possibility...

[1]And he writes well, none of this im-id-iv-u-textese crap...

Good points! So, there's hope for him. ;)

Anyway, my experience is that no one lubes the splines and that causes serious wear that allows the shaft to "bend". That means you have a vibration, which is right under you so it comes through the seat.

My first thought was a tailshaft bushing.
Though I have a slip yoke in the transfer case and not a slip joint in the driveshaft like Gary suggested.

The symptoms all fit.
Trailing throttle, disengaging the clutch takes the bind off the driveline and the shaft stops shuddering.

Sorry guys. There is no hope for me I'm sure. I'm not a "him". :-)

I have talked to a local mechanic, and his first response was throw out bearing, which it's not. I have replaced the entire clutch assembly before, and I know what that sounds like.

I pulled the transmission and took it somewhere before she went down and got bearings replaced. I've talked to him since it seemed transmission related or transmission activated. He suggested engine mounts. I have given them a visual, but I intend to get the engine pressure off them Monday and get a good look.

I don't remember the driveshaft like that, unless I'm not visualizing what you are saying. It's been a while since I've played with the driveshaft after all - 4 years. I remember just solid driveshaft after the slip yoke but I will crawl under Monday and check that, along with the universals. Family coming over and all this weekend so Monday will be my day.

Thank you for any and all help. I am a noob but I've had to work on my own stuff since I started driving. I bought this truck because 1) She was all I could afford after my divorce. (He got it all) 2) She has a carburetor therefore I can work on her and 3) She's a Ford and absolutely the prettiest hunk of junk I've ever owned. Sorry if I don't give specs on my truck, but I'm learning a lot of this as I go. By the time I'm done, she'll be fully restored and I'll be able to tell you every piece on her.