Strange noise has me stumped.
 

Hey everyone, this issue is on my 72 c10 lwb with leaf spring suspension. Brakes are brand new(last weekend) all the way around. Yukon gear posi with richmond 3.08 ring and pinion and timken bearings all installed last year. Th350 rebuilt last year with shift kit and stock torque converter. Factory steel wheels 5 lug. Swaybars front and back. Caltracs traction bars. Timken center support bearing (last year). Spicer life series non greasable u joints. Slip yoke greased recently. Kyb gasajust shocks 2 years old

Hopefully that helps with the questions regarding what I'm running. Now to the issue. When I'm driving down the road, doesnt matter how fast, time of day, loaded/unloaded, turning or not, if I hit successive bumps in the road I get a loud metal on metal grinding sound. But only if I keep accelerating. If I let off the gas it goes away. I dont even have to hit the brakes because ad soon as I let off the gas pedal the sound stops and does not return unless I hit a bump in the road a certain way. At first I thought it was wheel bearings or brakes. Well I've replaced the front wheel bearings and have them properly adjusted. Then I thought it was a brake pad backing plate loose and dragging on the rotor. I replaced/overhauled the rear drum brakes and the front disc brakes. Now it stops great and have no squealing or chatter. I tightened up my exhaust connections and now the truck sounds and brakes awesome. One time as I was experiencing the noise I kept my foot into the pedal only enough to maintain the noise and I shifted into neutral, the noise did not change and was still there. I let off the gas the noise went away. Shifted back into drive and noise did not come back. There are certain parts of the road around town that I know will cause the noise on my truck. If I coast through these areas the noise does not happen. If I am accelerating through these same areas i get the noise. Let off the gas, noise goes away. Lastnight late at night driving home and the only vehicle on the rural road. I heard this noise, so I leaned over to the passengerside with the window down and the noise was less noticeable. So I put my head down towards the floor didnt hear anything. Stuck my head out of the drivers side window, could hear the noise louder. It sounded like it is coming from the rear of the truck. Possibly the rear drivers side drum brake. Or something in the rearend. I just had the rear drums apart last weekend. I replaced the shoes (installed them correctly) installed brand new spring kit. Greased the backing plate where the shoes ride. Wheel cylinders are raybestos and were replaced a couple of years ago. The drums showed no scoring. The drums and brake assembly are dry. I dont feel like its dragging. Truck stops just fine and in a straight line. No skidding. Brake fluid level is where it's supposed to be. Master cylinder is about 3 years old. No broken springs or debris inside drums when I pulled them. Didnt appear out of round. No dragging when I adjusted them. Self adjusters are new and parking brake is adjusted and works perfectly fine. I'm stumped!!

Re: Strange noise has me stumped.
 

This is probably totally off base but it popped into my mind so I'll mention it. I know you said it sounds like the noise is coming from the rear of the truck. But sound can travel and be tricky to locate. so bear with me.

It only happens under acceleration. Motor mounts will normally keep the engine in position, but a bad / broken / loose motor mount can allow the engine to rotate upwards on one side. Not sure what noises might be caused, but one possibility is the fan contacting the shroud. Should be easy to see evidence of that on the shroud.

That's all I have....

Re: Strange noise has me stumped.
 

If it is a motor mount, the engine torquing up can cause the exhaust to ground somewhere. Take a look for dents or shiny spots on your exhaust system, too, especially where components are close to the frame.

Re: Strange noise has me stumped.
 

Metal on metal, only on acceleration, you had your transmission out last year... pinion angle/something to do with driveshaft? just an idea. Hope you figure it out.

Re: Strange noise has me stumped.
 

Check the center driveshaft bearing support

Re: Strange noise has me stumped.
 

Since were looking for some thing strange check the torque converter cover.

Re: Strange noise has me stumped.
 

^^^^^^^^^^^^I'll second this^^^^^^^^^^^^^^^^

Easy quick check with a pry bar

Re: Strange noise has me stumped.
 

Look for marks on the drive shaft from things like exhaust pipes, mufflers, parking brake cables, etc. Also remove the torque converter cover and drive it. I had one do much the same and that cover was slightly bent and scraped the flex plate on acceleration but stopped on decel. And sound travels.

Re: Strange noise has me stumped.
 

That has the earmarks of a worn thrust bearing, though another cause can be the flex plate bending just enough from transmission pressure on the converter.

Re: Strange noise has me stumped.
 

Yes it does but in my case I had just r&r'd the trans and that cover got bent a bit.

Re: Strange noise has me stumped.
 

I am guessing its the Caltracs contact point rubbing on the top of the leaf spring when you hit the bump. Hit the leaf spring contact area with some grease and see if it goes away, or shorten the bottom bar. It is supposed to contact the topside of the leaf spring when you accelerate hard.

Re: Strange noise has me stumped.
 

I have prothane polyurethane engine mounts and energy suspension polyurethane trans mount. Those are only about 3 years old and in good shape. I dont run a mechanical fan anymore so no shroud for contact. I run dual electric fans that are mounted in their own shroud.
I had my driveshaft out last year for the trans rebuild. So I took the time to paint the drive shaft satin black just so I could see better for any type of contact. Nothing so far. The center support bearing was replaced at the same time and I special ordered the correct Timken brand support bearing.
I hadn't thought of the torque converter cover yet. It is an after market chrome one. I've already had it come loose on me before and lost a couple of the original screws. I'll take it out today and drive it around.
Yes it sounds like it's coming from the rear but inside the cab it's almost like it happens directly under me. I cant feel it in the seat or steering wheel or floorboard or anywhere for that matter. But it is definitely a sound caused by road conditions. I think the best I can compare it to is if someone hasn't done the brakes in a really long time. Like past the point of saving the rotor and the wear tab indicator has been gone for months. Sad to say people let their brake system go into such disrepair. But I've seen it with my own two eyes and worked on a few over the years.
Wen it happens it doesnt slow do the truck or lug the engine down. If I keep my foot into it the truck accelerates but so does the sound. It's not at engine rpms. It's at vehicle speed. It stays a constant volume though but will be at a faster rate if I'm going faster. It seems to be happening more frequently and even little variations in road conditions seems to make the noise happen. I figure it will show itself sooner or later. I just hope it's not something serious. Or expensive...lol.
As to the caltracs, I was running them with a piece of heater hose over the contact bars and had them adjusted just until they touched the heater hose. But after a few days the heater hose would be cut through and disappear. So I started running them where the contact bars would just touch then back them off a half turn and lock em in. But I was getting a really bouncy ride because of the extra travel. So last weekend I adjusted them until they just touched the leaf springs and locked them in. Basically zero preload. Ride stiffened up but made no difference in the noise I'm experiencing. Thank you guys for the suggestions and help. I will keep this post updated as I try and figure it out or something changes.

Re: Strange noise has me stumped.
 

I had this issue. A torque converter bolt sheared off and was sitting in the cover. When I would go over a bump it would throw the bolt causing it to rattle around. After a while it would settle back into a spot where it wasn't hitting anything

Re: Strange noise has me stumped.
 

Well I got under the truck yesterday to do some investigating. Nothing obvious was found. Well except for my oil leak. The back half of oil pan studs were loose. Tightened those up. Pulled torque converter cover off. It was tight to the trans though. No signs of rubbing. Torque converter bolts are still there and tight. No loose bell housing bolts. No loose crank flange bolts. Tires were low on air. Pumped them all to 35 psi. Passenger side rear lugnuts needed a little more torque on them. Torqued all four tires to 105 ft. Lbs. Just to make sure they were all the same and tight. Drove the truck and thought the sound went away. NOPE. Actually I could hear it better and louder without the cover. It literally sounds like it is coming from directly beneath me. Which would be transmission. So I started thinking about what another member said regarding pinion angle. I have 2 piece driveshaft and leaf spring suspension. The center support crossmember has 2 mounting locations from the factory. I've searched high and low for info on which of the 2 locations is correct for my setup. I have the "horseshoe" style center support bearing. Not the more common pedestal type that are cheap and flimsy. The difference between the 2 mounting locations is about 2 inches higher or lower. Which in degrees of operation can make a difference. I dont have a magnetic angle finder available and money is kinda tight. So I think I will try and switch to the upper mounting location. It's currently in the lower position. And I cant go by the witness marks because everything has been painted under there. And years ago before I knew anything about my truck I never thought to mark the original position before disassembly. I've had the truck since 2004 when I was 18. Wrecked it back then and I ignored it for 8 years. Learned a lot since then. And am happy I never got rid of the truck no matter how many people told me I should. If the mounting position change doesnt fix the issue, I'm gonna take it back to the tranny shop and have them take a look inside. It's still covered under warranty. Never had the noise before the rebuild. I am positive of that. But I also had the rearend rebuilt around the same time. Trans shop is closer though. So I will start there. I'll report back after driving it for a day or 2 with the driveshaft mounted in a different position. I'm sure I will eventually figure this situation out.

Re: Strange noise has me stumped.
 

A couple of ideas.
1) Cracked flex plate.
2) loose bed bolts.
Sometimes it is extremely difficult to tell exactly where the sound is coming from.
Get someone to drive the truck in a circle around you. Should be able to do short acceleration bursts this way. Try it in both directions. I have had good luck with this procedure. It's a lot easier to pinpoint the sound source from outside the vehicle.
Good luck
Rick

Re: Strange noise has me stumped.
 

You can get an app for free to check your driveline angle using your smart phone. It is the Tremec tool box app.

Re: Strange noise has me stumped.
 

My neighbor just went through this with his Suburban. Chasing a rear noise that would only show up under certain types of acceleration. In the case of his, it was an outer pinion bearing race that was spinning. He used a bunch to raise metal in the bore and sleeve lock-tite and problem was solved.

This was REALLY difficult to chase down and diagnose.

Re: Strange noise has me stumped.
 

I changed the mounting location of my center support bearing to the upper location. The truck seems to like it better. The drive is smoother, I'm getting higher rpm gear changes. The sound still happens but it doesnt happen as easily as it used to. There were some sections of road that I knew would cause the sound. They looked pretty smooth as you are going down the road but they would get the suspension to move. Now the noise doesnt happen over some of those sections. But now that I have the torque convert cover removed, and i get the noise it is louder and it sounds like it is coming from directly beneath me. Yesterday i was next to a good sized center median with a high curb. And the noise happened. I swear the noienis directly beneath my feet and in the front end. But just the other night i swore it was behind me. I'm thinking it's something in the transmission. The flexplate is brand new when i did the transmission rebuild. It's a heavy duty pioneer flexplate. Not sfi rated but better than stock. I changed it because my old one was original and had some chipped teeth un more than a couple of spots. My starter doesnt drag and doesnt grind.
So far the best way i can describe the situation is, it seems the noise happens when the suspension is bounced. Almost as if something is bottomed out and something falls and gets stuck and is grinding metal on metal like if you drag a metal bar behind you while you ride a bike. But instead of the sound you get from it hitting the asphalt it sounds smoother like a grinding stone. As soon as I let up on the accelerator like even just slightly the sound immediately goes away. If I accelerate instead the noise does not get loud or faster. It stays consistant. Right now I am in the middle of a serious job of replacing the engine in a friends 2007 tahoe. The 5.3 had a collapsed lifter or wiped out cam. So I'm putting a reman motor in. I got it in last night. Now it's time to reconnect everything and put it back together. So this is my current priority for the next couple of days. But I will keep updating and checking back in if anything changes

Re: Strange noise has me stumped.
 

How much play do you have in the driveline yoke that slips on to the end of the transmission output shaft? Possibility could be the yoke bottoming out in the transmission tailshaft and has caused some internal damage to the transmission.

Gary

Re: Strange noise has me stumped.
 

That grinding that went away when you let off was what his spun pinion bearing race did. If you run out of other things to check...

Re: Strange noise has me stumped.
 

Through some wieght in the bed and retest. A couple hundred pounds should load the suspension and change the drive line angle some more. My big dodge has a slight vibration at speed that goes away when loaded and she becomes smooth as glass. Probably not your issue but I found a sound like a rattling heat shield today. The turbo style muffler case broke loose from the core. You could actually spin it by grabbing it. No visible rust on the case!

Re: Strange noise has me stumped.
 

It's funny you mention loading the suspension. Yesterday I helped a buddy move a baby grand piano. They weigh between 500-600 pounds. We had to move it about 12 miles. Various speeds. No hills or anything just flat road driving. I was paying attention to see if I could hear the noise. I did not hear it once. Even through some sections I thought for sure would make the noise happen. But it didnt. After we unloaded it, I went about my day eventually driving another 35 miles or so. The noise came back 1 or 2 times. But one time in particular I was going through a sweeping curve in the road. And I heard the noise but it was very different from any other time. It was a clicking noise this time. Like a baseball card in the spokes noise. It was while I was making a big sweeping left. My thought was it has to be torque converter bolts or the starter nose or pinion hitting the flexplate. I havent had a chance to get under there and look but I will today for sure. I have had trouble with a loose starter bolt in the past. Quite a bit of trouble actually because the outer starter mounting bolt hole is cracked in the block. I do have a starter brace on the starter. But also I've noticed it taking a little bit longer to kick over. It was just a flick of the key for it to turn over and run. No it sometimes take a second or a few longer to get it to turn on. I've also had 2 starters with weak bendixs and pinions. Both of those were reman starters. One of them took me 3 weeks to figure it out and had the pinion basically pinballing off the flexplate if I drove up any sort of incline or mad any fast accelerations. Let off the gas or hit the brakes the noise would go away. So now it's making me wonder if it's happening again. I'll keep you guys posted.

Re: Strange noise has me stumped.
 

Since loading the suspension seemed to help the situation you may try greasing the driveshaft and ujoints. Maybe they have some rust build up and loading the suspension helped. This is a long shot but I have heard ujoints squeak or make funny noises on equipment. My dad had a blazer that randomly would yank the steering wheel out of your hand and make a hard turn. After lots of head scratching and parts swapping it was a partially frozen u joint in the front axle that would grab and bind. Strange things do happen and grease is cheap.

Re: Strange noise has me stumped.
 

Well, I finally figured this damn noise out. Center support bearing. Driveshaft grease shield. Different center support bearing mounting location. 6 months of driving= driveshaft grease shield for the center support bearing would rub against the mount for the horseshoe style center support bearing on my truck when the suspension would travel a certain way. The bearing is perfectly fine. Timken brand. About a year old. The rubber support that the bearing sits in is not holding up too well though. It is intact, not cracked, not deteriorated. But it isnt doing a very good job of supporting the bearing. Also I left the original grease shield on the driveshaft when I replaced the bearing. It's a grease shield, what can go bad with that? Well, on the timken brand horseshoe style center support bearing, there are 3 metal tabs that retain the rubber cushion that the bearing rides in. All 3 tabs are located on the bottom half of the support. I'm guessing the pinion angle was off by just enough to allow contact on certain occasions. Which might explain why when I relocated the bearing to the upper location that the noise did not happen as often. Plus it had already made enough contact to establish a wear pattern. How I found this was I thought it might be a good idea to grease the slip yoke right behind the mount. It has been a while since I last did it. But when I was under there, I grabbed the driveshaft and just lifted it and pulled down on it. It seems to have quite a bit of travel. Remembering from previous mounts, and the bad trans fluid and oil leaks I used to have, these rubber mounts dont last long in these conditions. I now remember thinking" timken is good, maybe they outlast other brands in these type situations." Which may be true. I replaced it the same time I had the transmission overhauled along with new u joints. But here I am. The rubber is too soft and is not doing its job of suporting the bearing very well.
Anyways, here is a picture. My pry bar is just stuck in between the grease shield and mount and just hanging there on it's own. Not leveraging it at all.
From the back side there is no indication that anything is wrong at all. But from the front you can see the shiny metal tab and the grease shield now has a flare outwards to it. It didnt used to be like that, from what I can remember.

Re: Strange noise has me stumped.
 

See post number 5 ;)