The Stovebolt Site Forums The Shop Area General Truck Talk help - lost for what is next!

Springs were re-arched a few years back. At the time the shackles were good. I have taken the springs and given them a good shake (well the best I can) and all are tight.
I am still wondering if it is not the lack of rubber pads under the bed blocks as I have mentioned. The bed bolts are tight. I am tied up for the next few days but come Monday I am going to see if I can pick up some 1/4" rubber to make some pads.

I just looked under mine.There is two rubber pads,one on each side.They are at the very most rear of the bed to frame.I noticed that my two outer wood planks are very close to the frame where it arches.Could your wood be popping against the frame ?
I've got a 2003 silverado that has similar noises,the dealership says it's normal.I think they have too much lash in the rearends.

Rubber pads are standard on the 49 but when I put my bed wood in I forgot (or didn't know) about them. The wood blocks are in good condition and bolted down tight. On the rear the bed is bolted to a steel "block" instead of wood. I do not have rubber pads in that place and now I am narrowing this problem down to possibly this. I have the impression that as long as the bed is tight it should not thump but maybe the metal on metal in the rear is doing it.
Tell you if I ever find the answer to this there will be one heck of a party and you are all invited!

Maybe the rubber is gone from the rear cab mounts? If you get a big friend to jump up and down in the box while you're under it you might be able to pin it down. Good luck and don't give up.

Curt B.

When I worked at the stealership I would ride in trunk, on the hood or anywhere needed while someone drove the vehicle to reproduce the noise. We also had some neat "ears" that attached to the vehicle, you could hear the noise thru headphones-you moved them around to find where the noise was loudest. they worked really well to listen to truckers on the freeway w/their linear amps. I feel the rubber pads are a good place to start. brian

Good point Brian. I have someone willing to ride in the bed which I will do next week. The truck has not been looked at for a few days as I decided to go to a fly-in at Arlington WA instead. Jumped in the old Nanchang and had a good day there.

Sounds like most everything probable has been covered but I didn't notice anyone mentioning the racket when guts of the muffler come loose.

I chased a rattle of this sort for some time....it would wedge itself tight for a while and then when I hit a good big bump, would rattle like the devil until it re-wedged itself.

Guess it wouldn't take much to give the old muffler-tailpipe a good solid rap and see. You've just about covered all the serious stuff...maybe you're looking too deep for the problem. Good luck with your search!!

Thanks again. The exhaust system was the first thing I checked. Still think bed pads as it is more of a 'sheet metal' sound than a rattle. I am now concentrating my search to the front of the truck as sound can carry.

I know you have already done over these things, but my dads 73 chevy had the same kind problems. Turned out to be a combination of a loose bumper bracket, worn out shock mount, and tailgate. The shock mount bolt that goes into the frame was worn out and loose, I welded it and that reduced most of the noise.

I didnt see this mentioned anywhere, but have you checked your drum brakes to make sure everything is in its place? Other than that...Im have no idea without being there to help.
- Shane

Shane, wish you were here to help. I've gone thru all of those things and I can believe it might be a combination of things. Just spent another hour under there and everything I have touched, pushed, pulled and probed is tight. I am going to re-think spring shackles (front) but the rears have been looked at.

Have you tried jumping up & down in the back of your truck bed to reproduce the sound? You will want to start with a mild up & down motion action to a more aggressive jumping. Good Luck!

I know u all think this is silly but i new an old cobber who had the same complaint about his old holden after everyone had a guess it turned out to be a loose number plate (rego) ect...

Not the plate and yes I have jumped up and down in the bed and on the running boards. Thanks for trying.

only one thing left to do now olblu.Next time you visit plattsburgh you can tie me under your truck,i know some back roads

Have you tried a careful inspection with flashlight and mirror of everything under the truck? If two pieces are banging together like that you should see something flattening, making metal (bits of metal coming off), or pieces getting bent or smushed. Look above the axle and diff. How about the whole bed? How about jacking the truck by the bumper and dropping it quickly with a shop jack while you listen behind the truck. Or have someone drive it slowly over a curb or traffic bump while you stand by it.

arnswine. this is why this thing is becoming a frustration. I have spent hours on my back under the truck with a light, wrenches, pry bar and a soft hammer and checked everything. Even things like brake lines and tail light wiring. Everything is tight, nothing seems to be rubbing, no chaffing and nothing visibly broken. The only thing I have not really looked at are the shackle bolts. If they are worn there could be metal-to-metal noises there. I am not giving up. Today I'll be at it again.

Bit the bullet today and took it to a shop where the guy has been repairing cars for decades. He has a bunch of old classics himself.
Test drove it and figured the spring bolts were worn as are the bushings. Not all but there is play in them. He also discovered the rear leaf springs were wearing out against each other making a groove in the next (longer) spring. This groove is about one-third through the leaf. Also discovered a hairline crack in the frame where the body mount shackles are attached (both sides). Now I have to find bolts and bushings but my local jobber cannot give me a part number. Wants me to measure them. I am curious about that spring wear too as it seems to perfect a groove to be worn.

Sounds like you may want to take the bed off and test drive. This will let you know if you need the mounts at least! good luck!!! Jim

truckernix - you may have nailed it with your post about the springs. My springs are worn and there is a notch from the smaller spring riding against the longer. I never saw it until the springs were spread a bit today. Looks like springs are on the want list.

I can imahgine you must be going nuts! Did you locate that rubber bumper on top of the frame underneath the rear of the cab which the park brake rod could be smacking? It should be located right where the rod passes over the left side of the frame as it passes toward the rear cross shaft.

I did find the rubber you mentioned. It is good. I paid a visit to our only truck spring shop this morning and was pleasantly surprised that the person I spoke with had a clue. If you are following this post you will know what I mean. He figures that as I am not carrying a load I could get by with having the buttons installed at the end of each leaf. He did not see the truck but I gave him a good idea of the wear. When I mentioned the elusive clunk/thump the first thing he said was spring bolts/bushings. So maybe we have found something here.

Keep us up to date - inquiring minds want to know!

Hey, Oldlu
If the springs don't cure the problem, check your fuel tank straps. Maybe the tank is banging against the cab back on the larger bumps.

Good point highflyer but they are tight. I installed the tank with good insulation around the straps as well.
It is really strange. I put some thin plastic strips between the leaves today to see if there is a difference. No. The thumping sounds so much like oil canning that it makes me wonder if it is the spring bolts. It could be telegraphing from the springs into the bed. I guess the best thing I can do now is to change the bolts and see what happens.
Golly gee, from a 737 to an A320. Bet your typing has improved! Needle, ball and airspeed is all I need. That plus a duck (IFR) and a cat (artificial horizon) and I'm all set!

I mentioned at the outset of this post my concern about not having the rubber pads under the bed blocks. I went to a lot of effort this weekend to raise the bed using a floor jack and installing the rubber pads. It took some work lining up the bolt holes. However the biggest problem was getting the holes in the fenders to line up with the rear of the running boards. Although it was raised only 1/4" it would not work without forcing. Anyway I took her for a ride to my favorite test track and on the first bump came that terrible thump! At least I found out that the noise is not coming from the lack of pads.
My final bit of work will be the spring bolts and shackles. The noise is getting worse and I am getting desperate! I'll post what happens after I do that repair.

oldblu49,
You had a post a while back about changing your knee action shocks with "modern" shock absorbers. Did you ever do that upgrade? If the shock absorber "bottoms out", it would make a noise similar to what you are describing. Just for giggles, exactly when did you notice this noise? Maybe if you back-tracked in time, a clue might show itself. Keep us informed!