mechanics in here - what's my next step to find an intermittent drivetrain noise on F-150

[P49Y-CY]

my 2004 f-150 (fx4) was running fine until i installed a new cowl and wiper blades and now all of a sudden it's making a loud banging sound when i drive it. (no i don't think the two are related lol) although i did use compressed air and a water hose to clean out leaves and such in the inner fender area

it's like a loud clanking sound that seems to only appear when i give it a little gas. the noise does not match vehicle speed or engine rpm, it is comes and goes randomly. but usually when i give it gas. if i just idle around in drive or drive very slowly, it does not make the sound.

otherwise the truck seems to drive just fine. no codes or anything. but i'm afraid to drive it because when i do hear it, it sounds like something could explode violently. i cannot tell exactly where the sound is coming from, but it sounds like it's generally the middle of the truck

so far i've ruled out:

- engine sounds fine at all rpm in park and neutral.
- in drive with the rear wheels off the ground, it sounds like something could be loose only if i give it a lot of gas
- brakes and suspension all sound/look good
- no leaks anywhere
- front iwe's working fine (locked w/no vacuum, unlocked with vacuum)

could something inside the transmission be loose? (torque convertor?) flywheel to tc bolts are all tight. but the trans would not be working fine if it was the tc, right? maybe transfer case related?

or just drive it until something blows up lol

thanks

 

[TORQUERULES]

When you have it up in the air and you have it in drive, listen with a scope on the bellhousing. It could be the converter flexplate. I have seen some crack/separate where they bolt to the back of the crankshaft. They will clank like that. Or heck, the converter could be loose. Easy to check.

Be very careful. It is super dangerous running one on the stands like you are.

 

[mc01svt]

i would bet money its the sound of the driveshaft binding and then suddenly releasing in the slip yoke. Super crew f150s are notorious for this. Theres not really a permanent fix just have to use lube it up every once in a while.

in my truck it used to sound like someone whacking the under carriage with a mallet on acceleration

 

[svtfocus2cobra]

Have you checked the motor/trans mounts? Have someine help you brake torque it and check for excessive movement.

 

[P49Y-CY]

When you have it up in the air and you have it in drive, listen with a scope on the bellhousing. It could be the converter flexplate. I have seen some crack/separate where they bolt to the back of the crankshaft. They will clank like that. Or heck, the converter could be loose. Easy to check.

Be very careful. It is super dangerous running one on the stands like you are.

great advice thank you very much. it sure does sound like it could be a cracked flywheel and only gets out of shape under load

i would bet money its the sound of the driveshaft binding and then suddenly releasing in the slip yoke. Super crew f150s are notorious for this. Theres not really a permanent fix just have to use lube it up every once in a while.

in my truck it used to sound like someone whacking the under carriage with a mallet on acceleration

i just got the truck last year and i did a pinion seal and at the same time i put in a new driveshaft (with actual u-joints) so i doubt that is it, but thank you for the idea, and i will double chekc that

Have you checked the motor/trans mounts? Have someine help you brake torque it and check for excessive movement.

i do have a feeling that one of the engine mounts is bad because i could always tell there was movement leaving from a stop light, esp sort of uphill. so i bet that isn't helping and i will see what could be making the noise from that if it is totally gone

thanks very much all!!

 

[Crimson2v]

Is this a new body style or heritage 04? Anyway to get video of this noise?

 

[BlckBox04]

so you were working on the truck and everything was fine and dandy before hand, you didn't do any large mechanical work and now all of a sudden a loud bang? Might sound crazy but is it possible you dropped a tool down somewhere you can't see?

 

[P49Y-CY]

Is this a new body style or heritage 04? Anyway to get video of this noise?

i wish i could but i suck at computers and dont even have a cell phone that can do that... guess i gotta get with the program lol

it's the new body style

so you were working on the truck and everything was fine and dandy before hand, you didn't do any large mechanical work and now all of a sudden a loud bang? Might sound crazy but is it possible you dropped a tool down somewhere you can't see?

that's what's so bizarre, i didn't do anything that would have affected the vehicle mechanically. it was running real good!

i bought a new cowl cover - they tend to go bad on these - so while i had it off i also removed the fender liners so i could really clean out the whole thing. after seeing on my other f150 how rodents chew the sound deadening insulation and make nests in the inner fenders where rainwater drains from the cowl, i wanted to clean all that out. so i used compressed air and a water hose to blow it all out. took it for a drive to dry it out and that was when i first noticed the noise, but assumed it had something to do with the fender liners not being on, cause it was just up and down my street. but when i got it all back together and took it out at higher speeds thst was when i could really hear it.

i'm thinking even if i dropped a tool it would only be stuck in the inner fender and not be touching any moving parts. but that would be a good possibility, and thanks for the suggestion

 

[Crimson2v]

Did it make this sound on jack stands or just driving down the street? Is it a popping sound? Grinding sound?

 

[P49Y-CY]

Did it make this sound on jack stands or just driving down the street? Is it a popping sound? Grinding sound?

it's more of a popping or clanging/banging noise.

it is very random and does not match the rotation of either the wheels or the motor

the only time i heard something even close while on jackstands was when i gas it a lot of gas quickly. but even then it was just like one little clang.

it only happens when driving down the street at higher than just an idle. if i idle it in drive and just cruise around the neighborhood streets with no load, it's silent.

so, it seems to start more if i apply a load, and then continues inconsistently until i stop or slow enough.

it's pretty loud, at least from the driver's seat.

 

[Corbic]

Sell it, buy a Chevy or Toyota.

 

[P49Y-CY]

tomorrow i am going to try applying load with the brakes on, in both forward and reverse, and see what happens. haven't tried that yet

edit: i forgot that i have the drivers seat apart to put on a replacement cushion so i won't be doing too much on it until i get that back together

 

[9397SVTs]

 

[Crimson2v]

It sounds like the IWEs are slipping in and out of 4wd, especially when vacuum drops on a heavy acceleration. Did you happen to do any damage to the vacuum lines while you had the fender liners out?

 

[mc01svt]

do a good search for f150 drive shaft clunk.. save yourself alot of time and trouble.

 

[kevinatfms]

Chassis ears are a god send. Buy a cheap set and start placing the probes as close to where you think the noise is. Drive, listen and pinpoint which probe/area is where its coming from. Readjust probes closer to sound. Drive again, listen and pinpoint.

 

[patc84]

^ that was gonna be my next rec.

 

[P49Y-CY]

It sounds like the IWEs are slipping in and out of 4wd, especially when vacuum drops on a heavy acceleration. Did you happen to do any damage to the vacuum lines while you had the fender liners out?

didn't think so but i will check them out. that def would be the most logical situation because that was the only area i was working on when the noise started. i did jack the front wheels off the ground to see whether they were engaging and disengaging and it looked okay but i will test again.

do a good search for f150 drive shaft clunk.. save yourself alot of time and trouble.

okay will do. the 04's came with non-serviceable u-joints so i bought a whole new driveshaft when i did the pinion seal. i still have the original driveshaft so i can put in there to test. what i looked at about that problem so far is that it's lube related so maybe i didn't prepare the slip joint well enough. thanks

edit: forgot to mention this is a one-piece driveshaft on a 133"wb supercab/short box

Chassis ears are a god send. Buy a cheap set and start placing the probes as close to where you think the noise is. Drive, listen and pinpoint which probe/area is where its coming from. Readjust probes closer to sound. Drive again, listen and pinpoint.

that is cool, thanks for the suggestion

 

[BlksvtCobra01]

I was going to guess u joints with no video or anything. Swap in your old driveshaft just to see Chris good luck.


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[93Cobra#2771]

Does the truck have a level on it? Sometimes, they can get clunky sounding. Especially if worn ball joints and such.