Odd rattle at cruising speeds

[jlkuehl]

First off, my lil red warwagon is a 92 regular cab, 2.3L 5 speed 2wd with about 177000 miles on it. Now that it's nice and cold out, and I can't work on it, it has decided to contract an odd rattling sound at cruising speeds (65 -70 mph). If I decelerate or accelerate, the sound goes away until returning to a steady cruising speed. If push in on the clutch and run the revs to about 2000, there is no rattle, either. At an idle, clutch in or out, there is a slight tick, but not anything that would make me scream out "it's a rod knock!" or anything of the nature.

About a year ago, I put in a new flywheel, pressure plate, friction disc, and slave cylinder, along with all the required bearings (pilot and throwout). At that time, I gave the input shaft a quick feel for roughness and play, but didn't notice anything alarming, no unusual amount of endplay or bearing looseness. I also did the shift rail plug sealing and changed the fluid. There wasn't anything unusual in the old fluid, a little metal, but again, exactly what I would figure would be inside a transmission of it's age.

I thought it may be a crank bearing giving out, so I dumped a bottle of STP in the oil a few days ago, and it has made no change in sound (it's almost oil change time, so I figure it couldn't hurt).


Edit: I put this in the engine section because it sounds as though the rattle comes from the engine (louder if you lean forward than if you sit back)

Now I am puzzled! The rattle seems to be something driveline related, but I would think I could feel a rattle like this through the shifter while it is going on. If I grab the shifter at cruising speeds while it is rattling, it feels like any other manual transmission shifter while the vehicle is in gear, a little vibration, but pretty smooth and regular. Could it be a timing belt on it's last legs? I bought the truck at 150,000 on the clock, and I don't know if it has been replaced. Or could it be as simple as a U-joint? (I didn't replace them when I did the clutch.) If it is more sinister than that, is the trans or the engine worth rebuild?

 

[greenpus]

My gearshift knob rattles

 

[YZ250Rider23]

I had a similar noise not long ago. I figured out it was wind related. Underneath the truck I found the aluminum heat shield on the gas tank was partially loose, and was blowing around and slapping the drive shaft. Not guaranteeing that this is your issue, but it'd be something to look at.

 

[jlkuehl]

My gearshift knob rattles

Mine's a custom made doohickey held on by a nylon spacer and an o-ring, doubt that's it!

I had a similar noise not long ago. I figured out it was wind related. Underneath the truck I found the aluminum heat shield on the gas tank was partially loose, and was blowing around and slapping the drive shaft. Not guaranteeing that this is your issue, but it'd be something to look at.

That might not be the problem, but it's something I hadn't thought of. If the weather turns better soon, I'll get out and get under to check it. I did take the heat shield loose in a botched attempt at checking the fuel sending unit (over a year ago, though), maybe I didn't get all the bolts tight, or some loosened up. Rattles are hard to diagnose, and any thoughts are worth a try.

 

[Duane867]

Check out the intermediate pipe to cat connection on the exhaust.
A lot of times the intermediate to cat flange rusts through ( so does the hanger ) and creates a sag in the exhaust just enough to allow the cat to slap against the cross member at certain rpms and engine loads. This is usually followed by a pronounced audible exhaust leak though.

 

[jlkuehl]

This is another possibility, I noticed the exhaust flange at the manifold end of the pipe is rusted through, I can see light all the way through at times, but I don't really notice any unusual exhaust noise...It could be loose enough to rattle, but still solid enough to form a weak seal. As soon as the weather turns good, I have a lot to check out!

 

[super91(2.3)]

If the flange on the bottom of the manifold is loose or rusted thru, it will rattle only within certain rpms and sound like it is something coming loose inside the engine.

 

[jlkuehl]

It doesn't quite sound like a rod knock, or a valvetrain rattle. It's supposed to be over freezing on Sunday, so I may get out and give the potential causes a good once over.

 

[trommy]

It doesn't quite sound like a rod knock, or a valvetrain rattle. It's supposed to be over freezing on Sunday, so I may get out and give the potential causes a good once over.

Mine has been doing the same thing(92 custom/2.3/5spd).I kinda thought it was the valves rattelling.It's exactly as you described until today.I was about 8 mi from my destination when this seemed to increase in volume.When I got off the highway the oil was down to about the add mark and the oil (idiot)guage was completely down.(I had just added 3/4 Lt the other day)When I started it up,after about 30 sec,the oil guage came up to normal and fell down about 10 sec later and it sounds like a diesel(the former 'rattle' now magnified?).I did my shopping and when I started it up the needle came up to normal only to fall back down again.I drove home on the secondary hwy(25mi)
and it seemed normal except for the noise and maybe slightly less power?My buddy thinks it could be the knock sensor.So don't panic if yours does the same.Oh,there's no water in the oil nor any signs of leaks.I'll get back when I find out more.G'luck
(PS: I had an old mercury lynx wagon that had that same rattle.)

 

[jlkuehl]

I don't figure it's anything too terrible, I just find it to be annoying. The oil level is fine. Dad had an F150 with an inline 6 and 5 speed, and it had a similar rattle, and no one could find it either. I think the exhaust is a possibility, since today I went out and gave it a good shake where it bolts to the manifold...it didn't rattle, but a dime-sized piece of metal flaked away from the rest of it, and now there is an even bigger hole in the flange! I guess it'll be time to head to the local pick-n-pull and see if I can find a decent cat to replace this one falling apart.

I had thought of the knock sensor being bad, but haven't had a chance to do any looking into it.

 

[trommy]

Been doing a whole lot of searching and it sounds like the oil pickup screen is plugged up.This is a common problem with these engines.The engine has to be jacked up where it is possible to get at the screen to clean it.I just hope there is no permanent damage but have my doubts.If your oil pressure guage becomes eratic or drops completely then be prepared to face this scenerio.G'luck

 

[jlkuehl]

I suppose it could be a clogged oil pump screen, but I am still leaning more toward it being something external of the engine. I've put several thousand (literally...at about 400 miles a week, it doesn't take long) since the rattle started, and haven't noticed any change. It's more annoying than concerning. Either way, when the ol beast cashes it in, it cashes it in (but I'm not going to neglect it, either). I gave less than $1000 for it, and have put over almost 30,000 miles on it myself. I figure this spring it's almost due for a timing belt change, and I know a few of the idlers are getting loose, the exhaust is a butchery mess from the previous owner, and there are a few other minor problems to contend with. When I do the timing belt, a thermostat and a water pump will probably go in it, just as an added precaution. As long as I'm doing all this, it might be a good time to put in a pan gasket, and check out that pickup screen. I may even get a little froggy and see about a performance cam and put on one of the oh-so-debated electric fans! (ok, I'm dreaming about the cam and the electric fan.....I like my little world I live in, they know me there! )

 

[alwaysFlOoReD]

Another possibility is the heat shield/s over the cat/muffler.

Richard

 

[jlkuehl]

Another possibility is the heat shield/s over the cat/muffler.

Richard

Maybe on the muffler, but the ones on the cat have long since fell off. Yet another reason to rebuild that pesky hack job of an exhaust. Your post has led me to an interesting thought, though...Maybe it's the baffling inside the muffler rattling around, and the sound transmits through the exhaust piping? Maybe this coming weekend will give me a chance to look into it a bit, since the weather is starting to look nicer.

 

[kimcrwbr1]

From the symptoms do you have a carrier bearing try putting it in neutral and grab all the U joints and give them a wiggle same with the carrier if you have one.