need help please

[72kool]

im in need of some opinions on what to look for. while driving down the road i feel a bad knocking/thumping in the driver floor board next to the dimmer switch. it feels like something is banging on the floor board and only stops if im on the brakes.there is nothing actual hitting the floor thoe and nothing looks out of place or loose.ive checked the brakes and shocks (new) and wheel bearings and ball joints. any ideas? ive run out and dont know where to go from here. thanks in advanced

[SS Tim]

Dude we all need "help" thats why we hang out here! :-)

Anyway is you problem variable in any way? Does it change with road speed independent of braking action? Have you tried cross rotating the front tires to move the problem?

[72kool]

Very true.we all do haha. I have not tried rotating tires yet.didnt feel like tire issue but worth trying. It does not have any variance.doesnt matter speed or anything

[Boog]

If the upper shock mounting stud is loose it can sound like a hammer knocking under the floor. Also loose or broken engine or tranny mounts. Loose trans crossmember bolts for a few things to check.

[hamjet]

Don't know if you have disc brakes or not but if disc calibers don't have the rubber bushing in place or if the bushings are worn on the bolts that hold it to the spindles it will act and sound the same way..

[hugger6933]

I am gonna lean toward the caliper bolt missing and when the brakes are applied, the caliper is slapping around on the rotor making all kinds of noise. Jim

[davepl]

More detail in the titles and descriptions helps, folks. If you'd even mentioned the year then we'd know if it was disc or not, for example. And we all need help, otherwise we wouldn't have picked fixing 45 year old trucks as our hobby.

The problem is that braking loads the suspension in a number of different ways, so it can stop a lot of shakes and so on. My brother had an issue with the passenger front ball joint such that by the top of the quarter it was shaking violently (at 130mph!) but as soon as he was on the brakes it "held" in such a way it smoothed out.

When you say you checked the ball joints, how'd you check them? Prybar? How much slop is too much slop?

[69chevytrucker]

check for broken ring on coil spring

[michael bustamante]

Check for broken exhaust mount. Maybe the cab mount bushing rattling around also?

[72kool]

Sorry i forgot the details.ok so its a 1972 c20 350/350 with disc front brakes.the coil is not broken ive checked that and also the shocks are new and have all new mounting bolts for them.the exhuast is solid i checked that becuase it broke and is now straight piped so i madesure it was intact when i did that.the ball joint i havntused a pry bar yet but had someone shake it down while loaded and watched for movement( had loosewheelbearings and repacked them) anythingelse that would help info wise?

[GSFMECH]

I had a similar problem with a 71 once. It had a knocking clunking sound in the floor near the dimmer as you described. I tried everything, searched for months for it. What I eventually found just forward of the cab mount the brace that runs forward has two sections that are spot welded together from the factory and evidently it was not welded good and had come completely loose. It was really hard to see. The cab flexing caused the two pieces to clunk. I put a couple of tack welds on it and this cured my problem. I know it sounds crazy but that was what it was.

[72kool]

Never would of thought of that.i will deffinatly check on that!

[Sillyoldman]

Originally Posted by GSFMECH

I had a similar problem with a 71 once. It had a knocking clunking sound in the floor near the dimmer as you described. I tried everything, searched for months for it. What I eventually found just forward of the cab mount the brace that runs forward has two sections that are spot welded together from the factory and evidently it was not welded good and had come completely loose. It was really hard to see. The cab flexing caused the two pieces to clunk. I put a couple of tack welds on it and this cured my problem. I know it sounds crazy but that was what it was.

Good info. My odd noise was actually a loose fender tip bolt.

[72kool]

well i checked on the seperated support and it was in fact no longer welded so i welded it back together but unfortantly it didnt solve the problem. I finally did get to test the lower ball joints properly and found that they are completely shot...i think we found the issue. now just need to find the time and money to fix it. sad timing on it thoe because we just had our huge cruise night this weekend and had to leave her home. oh well,glad we found the problem

[72kool]

Arg!! I had to wait awhile to work on the truck more, but recently replaced the ball joints and sway bar bushings while under there. Unfortunatly no improvement! Im getting to my wits end on this now.im going to do all new front brakes here soon but they do not look bad at all.everything is to spec on them just want newer parts there. Any more ideas guys?

When i turn a corner it starts to bang like zomething hitting the floorboard. When i hit the brakes it stops until i turn another corner..the coils look good, repacked and cheked torque on wheel bearings.new shocks.new ball joints..i dont know what else it might be

[72kool]

Any ideas guys?? I really want to get this figured out. Hoping to make this my dd but cant until i know that it is reliable

[Stocker]

It's a long shot, but you said the noise goes away when you are on the brakes. Maybe a missing brake pedal return spring allowing the pedal to flop around and make a thumping sound?

[davischevy]

I bought a 72 Cheyenne brand new. I had a noise in the left front corner. One of the sleeves in the lower A-arm bushing was cast in the rubber off center.

I am the second owner of a 69 Chevelle SS396. When I was loading it on the trailer I noticed one of the A-arm bolts had been hitting the frame. It had the same poblem. On the cover of the warranty book, is a hand written note (noise in left front corner).

[hamjet]

I still stand with my post #5...

[markedgar5]

You have been trying to figure this out since July?
I wish I lived closer to you. Cuz now it's buggin me what it could be. There has to be a mechanic in the area that can give it a check. Likely a free inspection anyway.
The disappearance of the sound when braking? Does that happen if you were to only use the emergency brake. Or just the pedal. If it stops when u use the e-brake that may help to omit the possibility of the issue in the front brakes. Pm me and maybe we can try to get this figured out. I can make a few calls as well.

[AirSpeed]

I feel for you! I've had two sounds buggin the crap out of me for years! One is when I back up I hear a clicking noise in my drivers side hub (4X4) and a loud clunck when I make slow right turns. Replaced all the tie Rod ends, everything else is solid. Bugs the crap out of me! So much that I mounted a camera aimed at different areas to see if I could see what was making the noise, no luck. Good luck, hope you figure it out!

[72kool]

Haha thats the sad part. I am a mechanic for a living and come from a family of em. Although i will say i havnt had much time to actualy work on it since july. Its the fact that it doesnt seem anything obvious that is annoying. Im going to replace the brakes in front fully and inspect every part closely and see what happens.whats puzzling is the symptom is a banging/thumping.if somethings is moving and hitting another part, logic says it will leave a mark of presence. I have not found one anywhere

[72kool]

Something i have wondered about is could it be the steering gearbox? It has a really good leak in it but its always kept filled and has been then way for years.could it possibly jave worn something out inside? But my problem with that theory is that i dont see how the brakes being applied would stop it

[davischevy]

Originally Posted by hamjet

i still stand with my post #5...

x2

[72kool]

calipers are on their way right now. should have them here within a few hours. going to replace the calipers and pads and guide pins and clean everything else. i drove it to work today (7 miles from home) and she was hitting pretty good. the more i felt it, the more i believe it is in the caliper. i guess well see