79 F150 4X4, 400 C6 NP205, D44 front, 9", 3.50 gears, at this point we'll say heavily customized.

It is making a noise, a sickening noise. The noise happens on acceleration, no other time. I can be idling or going 80 and if I'm at least very close to steady speed, the noise goes away. The harder I accelerate, the louder the noise, but it is not RPM dependant, crusing on the hiway at 3000 and I'm just fine. The noise is part loud shuffling sound, imagine shuffling cinderblocks like a deck of cards, and part loud metalic rattling, think throwing a chain under a rototiller. I THINK there is vibration from the drivetrain associated with the noise, I can feel a very fast, sharp vibration at the same time as the noise on the T case handle. Strangest of all, the presence of the noise doesn't seem to affect performance. Power, throttle response, RPM capability, heat, and shifting do not seem at all affected. Lastly, after a few hundred miles of driving, I drained the fluid, filtered it through a cotton T shirt, and there is NOTHING in there. No clutch material, no metal, nothing but smooth scarlet DexIII/Merc fluid.

Last winter, I crushed the wavy edged conicle spring plate in my stock C6, which meant no pressure on the forward clutch, which meant no forward gears, so I pulled the trans out, overhauled it with all new seals, clutch packs, band, shift kit, the whole deal. Shortly after the engine went, so this fall, I put in a new 408, all the bells and whistles, lots of power and runs great.

Since I did the overhaul to the trans, there has been the noise. I thought at first it was the trans, but it was working GREAT after the overhaul, rock hard shifting, no slips, and when just a few months later the engine tore itself in half, I figured the noise had been bad bearings, but to my utter amaaaazement, I put in a neeeew engine this fall, different block, no parts from the old one used, and as soon as I get on the road, the noise is back!

My thoughts turn to the T case (which has new 80/90 oil in it, and is functioning as it should), but can aaaanyone shed some light on this really nervewracking problem?

Thanks, AleX

 

Is eeeeverybody on here as stumped as me?

 

maybe 1 of the differentials are trying to go out? and dumb question....did you make sure the gear ratios of the differentials were the same? i know from another guys mistake there, that makes a God-awful racket and will kill t-cases and transmissions and doesnt show itself immediately every time...

 

Well, you know it could be the rear end, unfortunately the single major system left on this truck that I can say I've never dealt with is the rear end, so I don't know, but I guess it's possible.

I don't get the sense that that's where the noise is coming from though, more an engine/trans type thing, but I could be wrong.

As far as the gears being different though, I'm not positive, but the problem happens in 2wd. I guess I'll try a long 4X4 road run tomorrow and see if it makes any difference, but this issue is not mismatched gears.

I may also try popping the T case into neutral as the noise is happening. I would think that this would make it stop, whether it is a T case issue, or an acceleration load issue, but I dunno.

Thanks for the suggestion though, anybody else?

 

A longshot but is it possible you have broken a motor mount and its torquing over and the fan is hitting something? I'm guessing not as you would probably have noticed this under the hood but thats just a guess.

 

Well now that's an interesting idea. When I had the engine out one mount was pretty loose, but when I looked at it closer, it was just that the nut to hold it tight was rusted on, not at all tight, and it must have always been like that, so I left it. The engine miiight be lifting a tiny bit, and the fan cooould be hitting? I haven't ever noticed any wear marks though, anywhere, and I'm driving with no hood recently.

I doubt it's that honestly, but the general concept is something I'll check tomorrow.

 

it sounds like you chucked a ring gear most likely in the rear 9".

 

Really? I mean it drives very well? I would think with something like that gone bad, I'd just be chunkalunking all over the place, maybe not moving at all?

 

Just because it moves doesn't mean it couldn't have broken a couple teeth. What mainly makes me think that is the fact that you said it happens only under power. If not a ring gear it could be maybe you are running a cheaper locker it the back like maybe one of the lock-rite lockers that replace the spider gears in the diff. If one of those crapped out it could still make power to one side while the other is eating itself. My guess it's something in your diff. I have seen race trucks blow ring gears and still finish the race though.

 

I had a truck that made a similar racket while accelerating and it turned out to be the axle bearing.

 

Well there's no locker in there, factory or otherwise, at least to my knowledge. From all I could tell the chassis was pretty virgin when I bought it, and I know the rear end wasn't locking even when this noise wasn't present.

Missing a few teeth does sound possible though, and I just redid all the bearings seals ball joints on the front end, but I've never touched the rear, so I guess it could be one of the bearings back there too.

Really though thats just not what my gut tells me, the sound seems pretty clear from the area of the truck right under or ahead of the cab, and since this is the second engine, and the trans seems absolutely clean, I'm thinking T case. I'm going to pull off the 4wd shifter boot and have a better listen, and I'll pay special attention to anything coming from the rear end on this test.

 

You could be right. Is your t-case chain or gear? Does it shift into 4wd? If its chain driven you could have tossed a chain too. Gear driven are stronger but I've broken those before too. Remember sound can travel though. I had jeep once that I swore had a broken body mount. Ended up being a suspension bushing that was never fully pressed in.

 

Dunno chain or gear, but yes it shifts into 4wd just fine, and pulls, both 4H and 4L, and neutral of course.

Going out right now for a test drive. Going to make sure the noise happens even from a dead cold start, going to do some long runs in 4wd, high and low, going to drop the T case into neutral while the noise is hapenning, and later I might even disconnect the rear drive shaft, hang it up, and drive with the front wheels.

Will report back, I just REALLY want this thing gone, I've put in way too much work and money to still be unsure whether I'll make the next mile.

 

Id drain the oil out of both diffs and the Tcase and see if you find metal. Might even take a magnet and fish around in the bottom of the Tcase. I would probably even pull the 3rd member out of the rearend. any problems there would be apparent if you did. Im assuming its a D44 front end so you should be able to just pull the cover and look things over.

 

Could be rearend but the noise only at acceleration I would put $ on it being a driveshaft either out of balance or slip yoke not in phase. I recently found this problem on another truck with same issue. Give me some specs on shaft whether it's a cv or single cardan one. Make sure the ujoint from slip yoke and top joint are in line( in phase) as it could a spline or 2 out and need to be put back on right...