sound diagnosis help

[Lee]

yes, i need help diagnosing a sound via text :gay: :confused:

ok here goes:

when i am going anywhere from about 60-65 and just holding the pedal such that i am maintaining that speed, i get a pronounced vibration (almost like one would with our awd systems at 50 but harder). when i let off the pedal, the vibration disappears. now if i do this in a tunnel where road noise is amplified back to me, i hear a gnashing metal-on-metal sound.

the truck otherwise runs well, i do have a really bad alignment issue and am in need of new rotors (have em, need to go in), and i have a weight knocked off my rear dshaft which i need to get fixed, but besides that the truck is good.

it doesnt make this vibe/noise combo at any other speed.

thanks for any theories... please dont say transmission or t-case, i will fly to where ever you are and beat you up for making me think its something potentially expen$ive :chair: :rofl:

[20005spd]

i read this and am trying to think. off the top of my head i wonder if its a u joint, but prolly not. the correct way to do this type of diag when there is nothing visibly wrong is to figure out the frequency of the vibration. then find out what would give that frequency using speeds etc. i have all the formulas in my note books from school. it basically narrows you down to an area, then the rest is up to you.

i didnt really help you much with this post but if nobody else can help i can dig out my book find the formulas and we could get to work. in order to find the vibration frequency. you need a tool(i forget the name) its made by briggs and straton. its for finding out rpm on their motors. you put it on your truck, drive it on a lift till the vibration happens. then do calculations

[Seanz0rz]

well i would go get all those things fixed first, see if one of them isnt causing the problems you are having.

after that, if its still there, come back!

[Lee]

i highly doubt my alignment and rotors are causing this :laugh:

its possible the rear dshaft missing a weight is, i was thinking maybe ujoint, bit it is odd that it happens only at 60-65mph..

[20005spd]

ya thats what steered me away from the u joint. how long has the d shaft been missing that weight?

edit: now that i think of it, if your missing a weight on your d shaft it hasta be the cause of your vibration.

[Lee]

yeah it likely is. its been missing for a few weeks now...

[MTL_4runner]

I'd get the driveshaft rebalanced and then see how you do because there are harmonics involved which may confuse the situation further if that isn't fixed first. I don't think it's that expensive either.

[Lee]

i think its a little under $100

[Lee]

bump, turned out a majority of this was a bad ujoint. a... VERY VERY VERY bad ujoint :laugh:

replaced it, replaced my rotors, made new trailing arms out of DOM, and my truck is aligned.

all is right in the world. :)