"Chicken-Fried Steak" > wrote in message
...
> Got a problem with my 1999 Mazda B2500 (Ford Ranger under the hood), and
> before I take it to my "plug it into the computer, no error codes,
> nothing's wrong with it" mechanic, I wanted to run it by some people that
> know a little more about vehicles. Here's the basics of my truck & the
> problem
>
> 1999 Mazda B2500
> 4-cylinder engine
> 5-speed manual transmission
> 130,000 miles +/-, original everything (including clutch)
> 2-wheel / rear wheel drive
>
> Problem: vehicle makes a metallic chattering sound (like someone with
> steel dentures chattering their teeth in the cold, best way I can describe
> it, or maybe like a dime rattling around in an empty beer can)
> intermittently. Sound seems to be coming from under the floor boards,
> close to the back end of the vehicle. Sound is worst when there is a load
> on the engine, especially in higher gears & when going up hill, or if I
> let the clutch out too slow when up shifting to a higher gear. Sound only
> happened once when there was no load on the engine. Engine sounds are
> normal, engine idles within normal parameters (500-750rpms), accelerates
> well both on flats and up hill. No idiot lights have come up on my panels
> (and this truck is like a nervous child, if it thinks even the slightest
> thing MAY be wrong, my dash lights up like a Christmas tree). Sound
> happens more often at lower RPMs (just before I down shift) or when
> accelerating suddenly.
>
> I had chalked it up to an old vehicle with a loose panel or something else
> that's pointless to worry about, until today when a friend (and former
> mechanic) said it may be something in the driveshaft and/or rear
> differential. At first I thought the worst this could be was that my
> 130,000 mile clutch is finally giving out on me, even though it feels ok.
> When he mentioned this, I had nightmare images of a bearing seizing up and
> my transmission blowing out as a result.
>
> Obviously to diagnose a problem, it helps to be IN the vehicle, but
> anybody want to shed some light on the above? Feel free to ask for more
> info. I'm just trying to get some feedback & suggestions before I take
> Chicken Little's advice about the sky (and my driveshaft) falling.
>
> C.

From your description of the noise it sounds like you may have a bad
u-joint. Put the trans in neutral, apply the parking brake and crawl under
the truck to inspect the u-joints. Check for slop in the u-joints but also
check for rust were the u-joint cross goes into the bearing caps. If you
find either condition replace the u-joints. I am thinking you will find they
are rusty and that is causing your noise.