chirp/tap under acceleration: what would you check first?

[cscmc1]

I just installed a hood pad in my 1009, and wonder whether the "new" noise I'm hearing is really new at all, or just newly audible with the hood pad installed...

Anyway, I now hear a faint chirp/tap (or even light knock) under acceleration; it varies with engine rpm, and is only audible when accelerating in gear. When I rev the engine in park, I don't hear it. There's a little bit of play in the pass side alternator belt with the engine running, but the belt feels appropriately tight. I'll buy some belt dressing and try using it sparingly to see if the noise goes away, but beyond that I' not sure what to look at.

Any ideas would be very much appreciated; thanks!

 

[Barrman]

Pull your torque converter cover and put a wrench on each and every torque converter bolt through the flywheel. The flex plate actually does flex under load and a loose bolt will tap the cone of the starter. At least that is what I have found.

Yes, the belts you are checking should be done. So should the motor mounts. I just wanted to mention a common noise many of us have had that takes a lot of searching to find. Check the metal vacuum line running between the top of the transmission to the modulator for body contact too.

 

[cscmc1]

Excellent suggestion, Barrman -- thank you! I am hoping/praying it's nothing significant (like rod knock, etc...), but am always extremely proactive with new/suspect sounds. I just want to be on top of this before it becomes a major issue; I will check those bolts out pronto.

THANKS AGAIN!!!

 

[cscmc1]

Also, dumb question -- are the TC bolts easily accessible from the inspection cover? I've never fiddled with a trubo 400 trans, believe it or not. Always been a German car (or Ford) guy 'til now, and usually drive manuals. Thank you!

 

[Barrman]

Yes, you can get a wrench on them. You will also need to turn the flywheel over to get to them all. Plus, figure out a way to hold the flywheel when tightening the bolts.

 

[cscmc1]

Yes, you can get a wrench on them. You will also need to turn the flywheel over to get to them all. Plus, figure out a way to hold the flywheel when tightening the bolts.

This I can handle -- thank you, sir!

 

[Matt1031]

Check the simplest possible cause first - U-Joints. Hood insulation cuts down on engine noise, so there's a possibility you're hearing driveline noises that were previously drowned out by engine noise. A rear driveshaft U-joint on it's way out will often produce the noises you describe. If one or both are bad enough that you can hear chirping and clunking you'll be able to tell for sure with a quick visual inspection.

To Check:
If you have access to a lift use it. If not, apply parking brake, chock wheels, and put T-case in neutral to take any torsional load off driveshaft/s. Rotate driveshaft back and forth by hand lock-to-lock (shaft should only be able to rotate as much as backlash in ring and pinion/ diff side gears allows) also try to push up and down (driveshaft shouldn't budge at all up and down or side to side). Look, listen, and feel while rotating - it helps if your finger is touching both yokes of the joint in question to be able to feel any play. Any noticeably felt freeplay in needle bearings and/or powder rust stains around U-joint cap seals (evidence they were run dry/not greased) = replace 'em. While you're down there looking at stuff, check front driveshaft and grease the front ball joints and steering linkage.

 

[cscmc1]

Thank you, Matt -- I did crawl under and eyeball the u-joints as a first check, and didn't notice anything suspicious. I greased the rear shaft u-joints just-in-case, which didn't help the chirp/knock. I'll do as you suggest and check them closer, though. They were clearly old(er), and as cheap as they are, they could probably stand to be replaced. I have a slow leak at the rear of the t-case anyway, so I suppose I could swap that seal out while I'm in there, too.

Thanks again for the suggestions, folks. I guess there is mild relief in the fact that my truck runs so darned well and that this is more of a tap or high-pitched knock and chirp than a lower knock. I'm guessing less internal engine and more "something simple." That's what I'm hoping for anyway!

 

[cscmc1]

Well, got under and checked the flex plate bolts -- all were nice & tight. Belt dressing didn't eliminate the noise either, but I didn't get as far as checking the u-joints real well. They felt good when I greased them a couple of days ago, but I'll give them a closer look this weekend.

This one's bugging me! I have to listen for it, and lean forward and toward the window a bit to hear it clearly, so maybe I'm making more of this than I should. I mean, it's a MV, not a Mercedes diesel, right? I'll keep an eye on things, though.

Thanks again, folks!