Clanking Question

OK, I have a TH 400 trans, 406 chevy engine, 73 Nova rear all in a 37 Chevy. When I accelerate or decel from either first to second, or second to first there is a clank (like a double clanking) sound. It sounds like it is coming from the transmission or front u-joint area, but the car is short so is hard really to tell. Obviously I can run beside the car and listen from the outside. I have had the car on stands (actually still is) and I cannot find any thing. U-joints seem tight, I pulles the diff cover and all looked good in there. it only does it going from 1st to 2nd on the upshift or from 2nd to first on the downshift. Does not matter how hard or how easy the accel is.

Any ideas? Is there somethign in the trans that could be the issue, but that would allow the car to drive perfect other than that clank.

Brett

How's the transmission mount? The 1-2/2-1 shift is the harshest - could it be bouncing a bit on the mount? Just a thought.

Mount is fine, bolts are tight. I agree the 1-2 is the hard shift, but not coming back down from 2-1 is it? I for th elife of me cannot figure out wha tit is.
I can't make myself believe there is something broken in the tranny that owuld only clank between 1-2 or 2-1 yet be perfect otherwise.

Could it be something other than the transmission. Is this a new build or something that just started. Are the motor mounts tight could it be an exhaust pipe close to something and the torque from 1 to 2 and 2 to 1 has it klunking? Do you still have the ears on the transmission? I will try to find a picture and post. Does it klunk harder if you get on it? Is your cross member tight to the frame? I don't know what it is just trying to come up with something.

I'd go with your first thought, U-joints.

You know I guess U-joints are cheap enough to change and see. As far as new build/old build, it is old, well about 7 years. No problems to date. everything else looks good as far as everything else mentioned on here. At least no one so far has said hey tha tis a broken tranny and it will cost a hundred million dollars to repair....LOL

I appreciate the help, I will certainly post what I find when I find it.

I hope it is that good of news. Good positive thinking!

My money is a pinion bearing going south.

put it up on jack stands in nuetral and turn the drive shaft back and forth quickly by hand and see what you hear

Sometimes a cracked flex plate will make a metallic clank when the trans shifts. Usually they make other noises too, but not always.

Hoss429, I did that. Did not hear anything. However it is not easy to turn. I have a friend tha tis a pretty good mechanic, he is goign to come over and see what he can hear. Believe me, it is not listening hard to hear something. It is pretty loud, but it is the exact same noise everytime, very consistant. It is two clanks everytime and does not do it on acceleration like a u-joint would normally make. Only does it from 1-2 and 2-1.

take the pan off the trans and you will find a pile of chips/metalic sludge below the 1-2 planetary----in a few days you will be leaving a traffic lite and the noise will be worst(louder) but the car will continue---til the next stop, then it won't move at all

For proof----you can do a couple of things--lock the trans in 1st and accel then decel---will be quiet----lock in second----might not move at all but if it does, it will be quiet

But---you are cruuising around looking for a ride on a flatbed---parts to fix it about $80 plus oil and gaskets

You might want to check to be sure all of your flex plate bolts are tight and for a crack like R Pope suggested.

I would start with U joints buddy.

Quote:

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Originally Posted by jerry clayton

take the pan off the trans and you will find a pile of chips/metalic sludge below the 1-2 planetary----in a few days you will be leaving a traffic lite and the noise will be worst(louder) but the car will continue---til the next stop, then it won't move at all

For proof----you can do a couple of things--lock the trans in 1st and accel then decel---will be quiet----lock in second----might not move at all but if it does, it will be quiet

But---you are cruuising around looking for a ride on a flatbed---parts to fix it about $80 plus oil and gaskets

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I'd listen to Jerry and drop the pan, or try his proof tests first close to home. If he's right, you are on borrowed time for a flatbed ride home....

Thanks guys for giving me some other things to look at. As soon as the weather clears I will take it out and do as suggested. In the mean time I will go ahead and drop the pan. At least it will get a fluid change. If nothing found will change u-joints. maybe by then the weather will be clear again.

Well I think I figured it out. I have about 1/2" of play in the rearend. Meaning I can turn the pinion shaft about 1/2" in either direction without turning the wheels. I suspect that is the noise I am hearing. So I guess it is time for a rearend rebuild. I was so fixated on the U-joints that I didn't notice the rearend slop. Now to find someone that can do the rebuild without a bend over. Guess I will also get rid of the 2.73 while I am in there.

Quote:

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Originally Posted by MrChips

Well I think I figured it out. I have about 1/2" of play in the rearend. Meaning I can turn the pinion shaft about 1/2" in either direction without turning the wheels. I suspect that is the noise I am hearing. So I guess it is time for a rearend rebuild. I was so fixated on the U-joints that I didn't notice the rearend slop. Now to find someone that can do the rebuild without a bend over. Guess I will also get rid of the 2.73 while I am in there.

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Not sure about your area, but around here the local 4x4 shops are the place to go for rear gear work. They're into them all the time, know the ropes with the different units and often are cheaper than the other guys. Might be worth a few calls, or if you have a local Jeep/Offroad Club ask them who the good local guys are. They'll fix you up with a locker, too :LOL:

I have got a 1982 chevrolet work truck that does that.In my case it is backlash in rear axle.Been doing it for years.I can put tranny in neutral,with engine off of course, and rock driveshaft back and forth a lot.:(