[rianbechtold]

Ok guys, so I've been doing some free-lance mechanics work and I have a vehicle I'm pondering working on. I'm a little new on the diagnosis side so I was wondering if anyone could help out.

It is a 1999 GMC Sierra 1500 4wd. It has no trouble codes showing when scanned. It developed a problem in which it makes a clunking, metallic pinging sound. I checked the all fluids and they were in good condition. It does this in idle when reved and when driving. I Listened around and it is not coming from the engine. It sounds as if it is coming from the driver's side near the bellhousing. Thats when I noticed the catalytic converter is right there also. I have heard this sound come from bad cats before. I held a screwdriver to it and to my ear and couldn't really tell, then held it to the transmission and couldn't tell from that either.

I concluded it was most likely coming from the cat. I explained that it does it even when the truck is in neutral or park and it is more dependent upon rpm's then it is speed of the vehicle.

Well, today a professional mechanic looked at it and says it is undoubtedly the transmission. I haven't found out what he says it is yet but I was wondering if anyone had any ideas?

 

[Chevello]

I once stopped a guy about to buy a new transmission by convincing him to pull the converter cover first. It had a rattle about like that and even the guys at the dodge dealer where he worked (in the body shop) agreed it was a bad trans. When he took the cover off two bolts fell out. New flex plate bolts and he was good.

Did you try banging on the cat with a rubber mallet to see if it does it when the vehicle is off?

Rubber mallet is my favorite rattle diagnostic tool.

K

 

[rianbechtold]

That is the only other thing I could think of is the flexplate.

And I didn't talk to the other mechanic, the information is being relayed to me, which makes it extremely frustrating when someone says you are wrong and you haven't heard their explanation!

I didn't think of hitting it with a rubber mallet! I'll make sure to remeber that:thumbsup:

 

[LevonH]

Check the trans mount as well. They loosen up on occasion especially when 4 wheeled a lot.