Help! Clanking sound under acceleration, getting very loud!

11psi5.0

Registered User
Car: 1989 SC 5 speed, 150k miles, bone stock

About two months ago, my car started making a noise under acceleration in any gear. There would be a thump-thump-thump coming from under the car, from the transmission or driveshaft area. The thumping would increase in speed in relation to the car's speed, not the engine RPM. It would get louder under WOT or 3/4 throttle, but go away when coasting in gear, clutch in or out.

The past couple of days, the thump-thump-thumping has increased to a very loud metallic clanking sound. Again, it's loud when accelerating in gear, and it goes away completely when coasting in gear, clutch in or out, or in neutral. It's very loud and can be heard from outside the car as it drives by.

Any ideas? I was thinking maybe a U-joint on its way out? How can I check that? What else might be causing it? I have to go to work in a little bit, but when I get home I might be able to get the car up on ramps and inspect underneath it

Thanks for any help :)
 
update: OK, I took a look under the car real fast. When I try to turn the driveshaft, it does turn a small amount.. probably like less than 1/4 inch. And it makes a clank sound that could very well be the sound I'm hearing when driving... does this sound like the u joint is shot? Are you supposed to be able to move the drive shaft a very small amount? Please help!!
 
I think I am having the very same problem as you. The sound is really weird and hard to discribe on the computer. Mine does the very same thing as yours does, only while accelerating and in any gear, but goes away when coasting. I was going to post about it before, but couldn't think of how to discribe it. I looked over the underside of my car (but not the driveshaft) for loose heat shileds or anything that might be making the noise. Everything was intact, so I figured that is might have something to do with the driveshaft angle in relation to the tranny. So I replaced the trans mount and trans kmemeber bushings. It seemed to help, but the sound started to come back. If I accelerate slowly I cant hear it, but if I start getting into it, thats when it starts to appear. It anoys me so much.

Mine is a 5spd too. Maybe its time for new universals, or better yet maybe a new light weight driveshaft. Hey, might as well take advantage of the situation.

Let me know what you cme up with.

Shane
 
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11psi5.0 said:
update: OK, I took a look under the car real fast. When I try to turn the driveshaft, it does turn a small amount.. probably like less than 1/4 inch. And it makes a clank sound that could very well be the sound I'm hearing when driving... does this sound like the u joint is shot? Are you supposed to be able to move the drive shaft a very small amount? Please help!!

I think you found your problem. You should not feel the driveshaft move even the smallest amount when you try to turn it by hand and handbrake on. The fact that you can hear it also points to the u-joints (one or both). However, the cv joints can also clunk if worn out. John
 
i had the problem that i think you guys are describing. except mine was reverse i believe.... it was a while ago so im tryint to remember for ya but im pretty sure under acceleration it would be ok but when i coasted there was a loud thumping noise...i dont remember a clanking but definately a thumping lol...loud too...it ended up being the half shaft in the rear went bad......isomething for you to keep[ in mind
 
Maybe its time for a nice aluminum driveshaft and some raxles.

Is there a company that makes an aluminum driveshaft for a 5spd SC?

Shane
 
Y'all check your cats, if you have them. When the inside breaks apart, it can rattle like that. Bump the cats and see if you can hear a rattle. I just had that problem on mine. They are really high flow cats now. :D

David
 
NCredSC said:
Y'all check your cats, if you have them. When the inside breaks apart, it can rattle like that. Bump the cats and see if you can hear a rattle. I just had that problem on mine. They are really high flow cats now. :D

David

I cant remember if I did that or not, but I think I did. If so they didn't make any noise.

Shane
 
Hmm, its definetly not my cats making the noise. This is more of a heavy-duty thudding/clanking, and I can feel it a little through the shifter if I keep my hand on it. It's REALLY thumping/clanking

I'm kind of a car noob in some ways.. what's the CV joint on our cars, and where is it located? Also, if a half shaft in the rear end is shot, how can I diagnose it myself?

edit: and if it is one or both U-joints on the driveshaft, what's the install like? Do-able by a wrenching newbie?
 
CV stands for Constant Volacity(sp). CV joints are on the halfshafts. There is one per halfshaft. There is a metal shaft sticking in the rear dif. and at the end of that there is the CV joint then the longer shaft that goes to the wheel assembly. The CV joints allow the rear halfshafts the flex with the rear suspenssion.

Now I am not sure it that is what is wrong with our cars or not. I would think that if you can feel it in the shifter that it would more likely be the drive shaft not the CV joints. I would figure most of the vibration be contained in the back of the car and you would feel it back there, and it would be a constant thing. I will have to take a look at my drive shaft tomarrow and see if it moves at all.

11psi5.0, I would maybe replace your trans mount and trans kmember bushings and see if that helps. It could fix your problem or at least make it so that the U joints last alittle bit longer.

Shane
 
I agree. I think if a halfshaft was bad, you'd feel it more in a rear wheel vibration and a u joint might be felt in the shifter.


David
 
Actually there are two CV joints on each halfshaft.
I would check the balancing weights on the driveshaft. They may have rusted and fallen off.
 
i had a noise like that a while ago. it turned out to be the rear diff. the pin that hold the spider gears in place snapped. i drove it for two weeks like that untill i lit the tires up and broke it completely. when i took the cover off there was broken parts everywhere. even the case broke. now i have an auburn posi. not sure if you guys have the same problem, it would only make noise under acceleration.
good luck
joe
 
i know you would think tha but when mine went bad i actually thought it was coming from the front at first but my dad drove it and thought it was from the rear...figures the mechanic is always right.....anyway it definately wasnt a constant thing and it was a loud thump...and i caught the problem early on so your can be worse......and plus think about it...the half shaft is only 2 solid metal pieves away from the shifter so y wouldnt you feel it??? im not sayin its def it but i think your ruling it out without good reason
 
Well if its a driveshaft or even a halfshaft then it sounds like my car is going to be in some trouble as I have an autocross race this weekend and then an open track event the fallowing weekend.

So when I jack it up this weekend what should I look for on the driveshaft and the halfshafts?

Shane
 
UPDATE

I had my neibor whick is a mechanic look at my car today. I let him drive it and listen to the noice it makes. From what he said is that I have play in my tranny. So now the plan for me is that I am going to leave it alone for the rest of the season and then when winter rolls around I'll take the tranny out and have it rebuilt along with lots of other things.

Hope you figure your problem out 11psi5.0

Shane
 
quick35th said:
UPDATE

I had my neibor whick is a mechanic look at my car today. I let him drive it and listen to the noice it makes. From what he said is that I have play in my tranny. So now the plan for me is that I am going to leave it alone for the rest of the season and then when winter rolls around I'll take the tranny out and have it rebuilt along with lots of other things.

Hope you figure your problem out 11psi5.0

Shane

Shane,

Guess what? I took my car to a shop over the weekend.. they also said it was my tranny, which probably needs a rebuild. :(
 
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