'71 K20 Growling/Grinding noise

[flyingtim01]

Hey Guys,

Saturday morning I got into the truck to go pick up a new dishwasher. Halfway there, before I even got on the highway, I started to feel this growling/grinding noise from under the truck as soon as I hit 35-40 mph. Got on the highway, and it feels like it mostly went away around 60-65. Got back off the highway, and slowed to 35-40, and it came back. Loaded the truck (after it sat for about 30 minutes) and it didn't immediately come back. Did 40 mph or so for a while and it was quiet, then I hit a bump and it came back. Got back home and parked it and got to work on the dishwasher.

Sunday morning, I went and picked up a cord of wood with it. As soon as I got onto a main road, the growling came back. Loaded it with a full cord of wood, and got it back out onto the main road, and the noise was gone, or at least severely diminished. (No insulation/carpeting left in the cab, it's pretty loud even when it's quiet)

Just to run down the list of obvious things: U joints are all greased (all of them), axles have plenty of oil, as do the tranny (SM465) and transfer case (NP205). It doesn't feel like a vibration from a tire. After I parked the truck on Saturday, I went around feeling the hubs. The only one that was warmer than I thought normal was the right rear (full floating eaton) so I'll have to take a look at that. Isn't that bearing oiled directly down the tube from the pumpkin?

Anyway, the grinding/growling seemed to be coming much more from under my feet, so I was thinking a front wheel bearing, though nothing was hot in the front, and I've never known a bad wheel bearing to get better the faster you went.

It is odd that the noise almost completely went away when fully loaded with a cord of wood though, so this afternoon I'm going to crawl underneath and see if anything is contacting the driveshaft or something along those lines. I wonder what would be different when the suspension flexes (it seemed like going over a bump triggered it to start with, and then when loaded down it goes away) so I guess I'll have to eyeball everything. Any suggestions?

[Stocker]

Originally Posted by flyingtim01

The only one that was warmer than I thought normal was the right rear (full floating eaton) so I'll have to take a look at that. Isn't that bearing oiled directly down the tube from the pumpkin?

Yes, it is.... and that's the only real answer I can give you about anything right now.

I wonder if you might have a u-joint going bad -- they can, even if regularly greased. An internal passage can be blocked resulting in dry bearings. Look for any sign of red powder (rust) around each bearing cap. Moving them by hand isn't necessarily a good test, either. If possible, put it up on a hoist and have someone run it up to 35 or so on the speedo and look for vibration at each u-joint.

Other possibilities are bad bearings in the tranny or t-case.... not sure how you could easily isolate those though.

Quite a mystery you have for now....

[flyingtim01]

Thanks Stocker,

Just a little background on the truck. Its a rack body, and was initially a power company truck when new. There's a Braden PTO winch and massive bumper, the apparently used it to pull line with. After that, it was purchased to tow a horse trailer and haul firewood. The guy I bought it from was the third owner and last registered it in 2000, and did just about nothing with it. From what I can gather, the truck basically sat in his yard and when he needed to pull something (like one of his other projects) that's when the truck would get started and moved 50' and parked there for another large amount of time. So when I got it, it needed a lot of work. It hadn't been on the road for at least 10-15 years. I replaced the pads, rotors and shoes, put on a new MC and booster, replaced the parking brake cables, swapped out the cast iron intake and two barrel for a Qjet and an Edelbrock Performer, gave it new tires, did a once over on the electrical system, replaced some brake lines, changed the fluids, and greased everything, including the wheel bearings. I also swapped out the old Spicer hubs for a set of Warn hubs.

It seems to be doing really well, that is until this weekend. I was thinking that I should be replacing the U joints anyway, just because I don't know how old they are, and they're relatively cheap. I suppose that could be it, since I've been driving it, on and off I can feel a slight wum-wum-wum kinda vibration around 35 mph, though I've always written it off as unbalanced tires. I'll do a visual check of the U joints, but I think I'm going to plan to replace them, at least the two in the rear, ASAP.

[Stocker]

Originally Posted by flyingtim01

on and off I can feel a slight wum-wum-wum kinda vibration around 35 mph, though I've always written it off as unbalanced tires.

I've always thought of tire unbalance as more of a shake (or low-frequency vibration) and bad u-joints as more like a high-frequency vibration...... possibly what you are describing.

Good luck, if you throw new u-joints in, I hope that fixes it. Keep us posted!

Your truck sounds like a real workhorse. I retired from telecom construction and some of our rigs got a pretty good workout at times.... same with the power company trucks!

Incidentally, my truck also has a Q-jet (OEM) on an Edelbrock 2101 Performer that I got when my stock cast iron intake cracked. Pretty good setup for all-around use IMO.

[flyingtim01]

Didn't get a chance to do the visual last night, but it's on the list. And I am going to do the U joints just because, so I'll report back on both those fronts.

The truck is definitely a work horse. I'm pretty sure the original 307 has been replaced by a 350 from a '75 truck. I haven't managed to get at the casting number yet, but the stamped number on the passenger side of the block at the front of the head seems to bear that out. The cab is shot...but it's also a replacement, it's a '72 cab. Other than that, it doesn't look like it was beat on too much by the PO's.

The PTO and winch is somewhat of a mystery to me, though. I wonder if it was dealer installed, or if the power company installed it? The Braden LU2 winch came on a lot of Dodge trucks of this era, so I'm wondering if the power company had a wrecked Dodge with that setup on it, and swapped it over to this truck. It doesn't look homegrown at all, with the correct frame extensions and massive bumper. I don't think I'll ever know for sure, but I doubt the dealer would have installed it this way. All the Chevy PTO winches seemed to have a cable installed in the dash, this one has a lever that sticks up through a hole in the floor.

[flyingtim01]

So the visual inspection turned up nothing. Nothing seems to be rubbing, no exhaust issues, no driveline issues.

Thinking over the symptoms (aggravated by bumps, worse/louder when truck is empty, much quieter when fully loaded) leads me to believe that it's one or both of the U joints. With the truck loaded to the gills and the suspension compressed, the driveline is a bit straighter, and it stands to reason that the U joint wouldn't be at such a severe angle as when the truck is empty.

Ordered up a couple Spicer 1350's and a couple U bolt kits. Funny, when you look it up on the Spicer website, they say the truck should have two 1310's. Other research I did around says that some trucks have a 1350 in the rear and a 1310 up at the transfer case. I measured mine and both are 1350's.

Hopefully get them changed out this week, and I'll report back!

[bilfman]

I would think it is the u joints from the info so far. Also being a 4x4 you might want to see if your front shaft is turning eventhough hub and t case are not engaged, this could indicate a tcase or diffy internal problem.

[flyingtim01]

I took the driveshaft out last night, and when I was under there, noticed that the tops of the mufflers are contacting the bottom of the bed supports. It's a Heartthrob kit that's about a year old, and everything is tight, but I wonder if I'm getting a slight exhaust vibration transmitting through the frame. Something else to check!

[Stocker]

Originally Posted by flyingtim01

the tops of the mufflers are contacting the bottom of the bed supports.... I wonder if I'm getting a slight exhaust vibration transmitting through the frame.

Interesting.... you might have just found the problem! If there's metal-to-metal contact, I'd bet there's gonna be noise.

[flyingtim01]

I hope I have, one way or the other. Don't mind changing out the u joints, they were always an unknown quantity to me and was always afraid of losing one on the highway and pole-vaulting over the driveshaft...

I've been meaning to get under there and adjust the exhaust a bit, one tail pipe exits just a bit lower than the other, and it's always bothered me, just not enough to crawl under and move it...I guess now is the time!

[flyingtim01]

Little update, thought nothing conclusive.

Saturday morning I changed the U joints in the rear driveshaft. Took it out for a spin, and I had the exact same condition as I did previously. Made it to the dump and back with no issue, however.

Sunday morning I woke up and realized that of all the work I've done to this truck, I've never changed the transmission and transfer case fluid. I checked Sunday, and both of them did indeed have fluid in them (the speedo cable leaks from where it contacted the exhaust pipe once upon a time) but I wanted to see what it looked like. Drained the t-case, and the fluid looked pretty normal, if a bit low. Drained the transmission, and it was rather milky. Don't know if that was just condensation or if water had actually gotten into the tranny, but it was time for it to go, anyway. A quick visual inspection through the shifter tower didn't turn up and pitting or any other signs of water, so maybe just condensation. Filled them both up with fresh gear oil, and took it back out on the road. It was much quieter, though the pessimist in me may have felt a shade of the same growling. I didn't adjust the exhaust at all, next on the list are the wheel bearings. On the highway this morning I could hear this squalling noise right at 60mph. It was hard to say if it was a wheel bearing or just wind noise, but I know that one rear bearing is at least out of adjustment, and at worst it's shot, so I might as well do all four corners.

[flyingtim01]

It came back yesterday evening, on the way home from work. The truck isn't a daily driver, but I needed to pick up some pallets, so yesterday it was the commuter.

Same circumstances as before. It seems quiet and smooth, then you hit a bump at about 35mph and all of a sudden there is the grinding feeling from under the floorboards. I noticed that once it starts, and you slow to a stop, it doesn't come back right away once you start moving again. It really does seem to be triggered by a bump. While you're slowing down, the tone of it changes, almost like a baseball card in your spokes. Making me think it's something to do with the tires or wheels. Would a wheel bearing make such a pronounced grinding noise/feel? I did verify that it was in 2 hi, both hubs are newer Warn hubs are are unlocked, so nothing in the front drivetrain should even be moving, let alone making noise.

Am I missing something here? What else could be making a noise like that, while the truck is moving? Would a throwout bearing make a noise like that if it were on it's way out? The truck has always chattered in reverse unless the clutch is either all the way in or out, trying to feather it in between will give you whiplash. Could that have something to do with it?

At my wit's end here. Thought I had it nailed down and here we go again...

[Stocker]

Originally Posted by flyingtim01

I didn't adjust the exhaust at all

Might be a long shot, but if the mufflers are still contacting the bed supports, why not take care of that next? If nothing else, you'll eliminate that as a source of the noise.


Edit: Another long shot here... any possibility that the PTO is engaged? Doubtful, b/c it should be making more noise than what you are describing.

[flyingtim01]

Well, two things. I feel like the noise is more associated with speed than RPMs, and I feel like if it was the exhaust, I'd feel it change with a change in RPMs, which I'm not. But I agree, I know it's something that I have to do anyway (like changing the U joints and tranny and t-case oil) so I'm not losing anything by just doing it.

I thought about the PTO as well. I used the winch about month ago to pull some stumps, and it seems like the noise started at some point after that. The winch doesn't engage and disengage very well just by using the handle, I have to get under the front bumper and use my pry bar and liberal usage of penetrating oil to get the engagement collar to move. So while I usually keep it disengaged (in case someone were to kick the PTO into gear while doing 40) I had forgotten to crawl back under and disengage it, which I also did this weekend, and it didn't seem to make an difference. I did verify that the PTO driveshaft isn't moving at all while the truck is running, but I didn't check to make sure that the PTO itself wasn't partially in gear like you suggested. The PTO handle is pretty vague as to where neutral is, so that will be something I check tonight. It would make sense that hitting a bump at speed may jostle the linkage a bit, just enough to move the PTO enough into gear that there may be some gear to gear contact, which would explain why I seem to feel it most under my feet. Hmm. I'll have to check into that one. Thanks for the hint, Stocker!

[Hoods69BadBowTie]

Originally Posted by Stocker

Might be a long shot, but if the mufflers are still contacting the bed supports, why not take care of that next? If nothing else, you'll eliminate that as a source of the noise.


Edit: Another long shot here... any possibility that the PTO is engaged? Doubtful, b/c it should be making more noise than what you are describing.

I am glad your gonna do the mufflers I would get that out of the way to eliminate it from being the issue. I was also wandering if some how the PTO was not completely disengaged? That's the only other thing that came to mind since you did u-joints already. Have you pulled your rear diff cover recently and looked at gears and put new fluid in it?

[flyingtim01]

I don't know what counts as recently, but about a year ago I pulled the cover and changed the oil in the rear. Couldn't hurt to check the level while I'm under there, though. Although I don't see it leaking anywhere...

[flyingtim01]

Just a small update. Don't yell at me, but with all the storm prep I was going through here in Southern CT, I haven't had a chance yet to adjust the exhaust.

However, I have driven the truck twice since I took Stocker's suggestion and played around with the PTO a bit, and the noise/feeling hasn't returned. I suspect that it has something to do with the PTO, which I'll need to look at further.

I also noticed that the transmission is a bit loud in neutral with the clutch out, so I'm thinking that the input bearing is on it's way out, if it's not already.

The clutch has also developed a clunk...so I'm wondering if it's out of adjustment or just ready to be replaced. I'm leaning towards just putting a clutch kit in it, freshening up the linkage, and while the tranny is out, putting in a new input bearing. From what I've read, I don't think the whole transmission needs to come apart to R&R the input bearing, so I might just try to kill three birds with one stone.

[86c20]

if that truck has alot of miles like one of mine i lean towards baerings in the trans. mine when light makes a loud grinding/ wineing sound load it down with about 5k no sound but when you let of the gas and the drive line slaks up. all new u jionts and a replace driveshaft also and still there seems to be comin with high mile 465 that are well used as mine is in a tow truck with some of the dumist drivers there are

[rjsdad]

My burb makes that same grinding noise when it hits certain bumps. Sounds like its coming from the front axle and I feel it right under my feet. It will go away either on it's own or if I stop the truck. I haven't inspected it yet but thought the axles needed to be repacked. I'm not very mechanical so I'm not sure.just wanted to let you know you weren't the only one going thru this
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[odog]

If you are dropping the trans to change the input bearing, you may look at the output shaft. You have to pull the adapter off of the trans side, but it is worth it while you have it out. Just a suggestion

[flyingtim01]

Glad I'm not the only one going through it!

I drove the truck two days in a row, unloaded, this weekend. I locked the hubs in, but left it in 2WD. No noise...at any speed, or over any bumps. Interesting. It won't cost me anything but time to inspect the front wheel bearings...I'm wondering if the driver's side bearing is loose/bad and is allowing the splines on the end of the axle shaft to contact the hub or something else in the spindle area, and now that the hub is locked it, the shaft is supported from the end and not making any noise.

Odog, thanks for the FYI. If it has to come out, I'll be inspecting everything. I suspect something might be out of whack in the adapter as well, when coasting there is a faint clunkclunkclunk sound coming from that general vicinity.

[flyingtim01]

So I just wanted to follow up here, I can't stand threads where the OP never posts up the solution to the problem!

I drove the truck all winter with the hubs locked in, and never experienced the same noise. I started to wonder if maybe I had a bad hub, so I got a stud kit and a rebuild kit for the hubs, and got after it this weekend.

Just as a small backstory, when I wanted to eliminate the old Spicers, I went looking for Warn replacements. I didn't want to spend the $250 on a brand new set of 9072's, so I found a used set off an old Dodge. I think Warn hubs were OE on those trucks for some years. Anyway, I gave them a quick once over 2 years ago when I got them, and slapped them on.

Fast forward to yesterday, with new gaskets, studs and screws in hand, I pulled them off to see if they were damaged/loose, kinda hoping that was the source of my noise in freewheel. What I noticed is that when I put the hubs on, only one side had a snap ring around the end of the axle. The side with no snap ring made no noise, the side with the snap ring is the one that made that grinding noise. So I took the snap ring off and pulled the hub. I went through them both and cleaned them up, didn't notice anything out of the ordinary. So when I went to put them back on, the kit came with new snap rings, so I thought I'd throw them on. It was then that I noticed those snap rings do just about nothing in there. The snap ring on the back side of the lockout keeps the internal hub from sliding outwards, and in addition, the snap ring was way loose in the groove on the shaft. As in, I didn't even need snap ring pliers to put it on and take it off. So I left them off. I don't remember when I took the old Spicers off, maybe it made more of a difference with them that it does with the Warn hubs.

Anyway, I'm thinking that because that snap ring was so loose, when the hubs were disengaged and freewheeling, that ring got loose and dislodged (like when I went over a bump) and then started grinding against the inside the hub. I didn't see any damage in there, but the snap ring was a little twisted.

So after it all went back together (looks great with the new studs) I took the truck out and hopped on it a little. Even after a couple trips up to 65mph and back, still no noise.

So I think I got it fixed. Thanks for everyones help!

[Stocker]

Thanks for the update.... and I'm glad the noise finally gone!

[oski6754]

Hey flyingtim01,

I'm having the SAME issue you described. Just want to check back with you to see if the snap ring was indeed the culprit?

Regards,
Miles