what the he11 is this sound??

[ocbaud]

its a loud thumping/wood pecker sound that happens sometimes, mostly during coming to a stop. its under the truck and sounds like its coming from behind the cab. its a really fast thumping sound too. the driveshaft and ujoints look good and its not hitting on anything. everybolt on the rear end/susp. is nice and tight, the exhaust hanger IS a little loose, but it wouldnt be clattering around that much or as fast as it is. i checked the drums and all the hardware is in place and looks good.

if i had to describe it better, i would say it sounds like a rod knocking. but it only does it for maybe 1 second at the MOST and only when decellerating but not always. it started 2 nights ago.

the only thing that has changed on my truck is that i am using my friends valve covers with no baffles and i lashed my valves because some of them were loose(havent been adjusted since we started up the engine for break in).

i'm positive its not engine related, because the engine still has tons of power. taking it up to 6000rpm's it doesnt sound anything but great. at speeds of 100+ it doesnt make any weird noises either. just when coming to a stop.

i checked the caliper bolts and they are all tight too.

[76cheyenne]

Does it sould like it is comming from you tranny. Get under it and listen. I have the same noise and it is my flex plate.

[ocbaud]

yes, it does sound like it COULD be coming from my tranny. but i cant get under and listen to the sound unless i was under the truck while i was driving it and coming to a stop

i checked my flexplate and it looks fine, damn well better too for it being a SFI approved tci flexplate.

my flexplate on my 305 engine cracked in a couple places and made a similer sound, although, it made it at low speeds accelorating, starting the truck, and reverse really bad.

i guess i should also mention that when i had my 305, my tranny was rebuilt. it should shift nice and very fast and firm/hard. i even through my dads head into the back window one time. but since i've gotten my new engine, it seems like the shifts have been getting softer and softer. it still shifts fast, but you can barely feel it shifting. i knew one day i would have to replace my tranny, because i know its not built to hold 400+ hp. i just wish i knew if it was the tranny or something else making the noise.

[swervin ervin]

Hard to say without hearing it in person. Could be anything.

On the same note, I know a lot of you will remember my popping sound coming from the frontend I couldn't find a while back. Well, after my upper control arm bolt breaking and me replacing it, the popping sound I had is gone. Guess that was the popping sound, a loose bolt or something.

One thing is for sure, if you have a strange noise, you will find it when whatever it is causing the noise breaks.

[stan79chevy]

maybe a back pressure issue or something. do you have a pcv valve in the new valve covers?

stan

[phantom dually]

I had a tranny make the same noise you are describing. I replaced u joints, checked the pinion angle, had the muffler moved down a way from the frame etc etc. It was the tranny!!

[hotrodhomi]

do you still have Cats? If you do the wafer inside might be broken up and it might be bouceing around. This happened to me once. you could only hear it at slow speeds or when stopped. I found it by banging on the exhaust with my hand and I heard the rattle. Just a thought.

[SanitysBane]

as soon some said, it could be anything at all on the whole truck, he had a sounds like that on our 88 van, it was the muffler hitting the frame.

[ocbaud]

no cats.

the exhaust shield was really close to the driveshaft thought and i bent that way, didnt help.

yes, i do have a pcv valve and a breather on the covers, but like i said, his valve covers i'm borrowing dont have baffles.

if i had to guess on something mechanical, i would guess on the tranny. if i listen really carefully, sometimes when i just barely tap the gas i can hear a little bit of clattering coming from under the truck, around where the other sound is coming from. not far enough up to be the engine, but far enough that it could be the tranny.

and i should mention also, that driving around tonight, it seemed to be doing it more often.

[ocbaud]

http://www.bowtieoverdrives.com/cata...m.php?ITEMID=8




thats the tranny i'ma gonna get if mine is going out.

[1FaastC10]

TH400, if a TH350 wont hold up to the power, a 700R4 surely wont.

[ocbaud]

Originally Posted by 1FaastC10

TH400, if a TH350 wont hold up to the power, a 700R4 surely wont.

They will handle a steady diet of around 450/500 horsepower and 400/450 lb./feet of torque.

[pissonNOS]

if u have a 2 piece drive shaft check ur steady bearing cause mine made a noise like that and the rubber came out of the holder so i just pushed it back in and were good to go

[ocbaud]

1 piece drive shaft

[stan79chevy]

the bolts holding the tourqe convertor to the flywheel could be loose and it can rattle you would hear it during deceleration.

stan

[ocbaud]

Originally Posted by stan79chevy

the bolts holding the tourqe convertor to the flywheel could be loose and it can rattle you would hear it during deceleration.

stan

checked those yesterday, all tight, along with the bellhousing bolts.

[ocbaud]

i just jacked the truck up and looked all underneath it. nothing at all i could find was broken or loose or rattling when i shook/hit it.

[ocbaud]

update:

when coming to a stop in 2nd gear, i can hear some clattering, but it is very minimal. when coming to a stop in 2nd gear and shifting into drive(3rd) when i'm almost to a complete stop, it will start making the knocking sound again....

[86 Red_Bowtie]

Sound like a F up tranny to me. Jack the truck up and support it on jack stands and stick your head underneath it and have someone give it gas and hit the brakes and see if you can tell where the knocking is coming from.

[ocbaud]

Originally Posted by 86 Red_Bowtie

Sound like a F up tranny to me. Jack the truck up and support it on jack stands and stick your head underneath it and have someone give it gas and hit the brakes and see if you can tell where the knocking is coming from.

it wont do it unless i'm moving

[swervin ervin]

Put it in gear while the back is up on jackstands. Don't forget that the wheels are spinning, so don't shove it back in park until you bring it to a full stop.

[ocbaud]

Originally Posted by swervin ervin

Put it in gear while the back is up on jackstands. Don't forget that the wheels are spinning, so don't shove it back in park until you bring it to a full stop.

will do today soon

[ocbaud]

okay, i put it up on jack stand. here is what i'm seeing:

with it on jack stands and in park, without the engine running, i can spin both back tires with out the driveshaft turning, if i spin one tire forward, the other tires spins backwards.

with it on jackstands and in drive, both rear tires spin, and every once in a while(20-30 seconds or so) the clattering happens again. i put my hand on the rear diff. cover and felt what seemed like something hitting it whenever the clatter happened.

so, i guess its my rearend going out?

about 2 years ago i replaced the diff. fluid and put a chrome cover on. nothing has leaked out of it though.

[76cheyenne]

Ya just don't pull a Ferris Bueller at let it fall off the jackstands.
*edit* I saw you just posted. Ya I would take the diff. cover off and see what is going on.

[ocbaud]

if i take the cover off, that means i gotta buy new fluid and refill it.

i dont wanna work on it anymore today....