Hey guys. I have a 1994 Chevy Blazer (Full Size) with the 350 TBI, and I'm hearing some odd noises coming from under the engine compartment area, possibly under the truck. Here's the deal. It has had the glorious valve ticking for awhile now, as it is a bit old (200K miles now), but this noise is new, and bear with me as I do my best to describe it. I hear a metallic scratching noise, kinda like a cross between dropping some finishing nails into a coffee can and the sparking noise that comes off of a welder (sorry, that's the best description I can do). I wouldn't call it a faint noise, but it wouldn't be loud enough to catch on tape, or I'd try. It is pretty inconsistent, but it only seems to happen when a drive gear is engaged. Speed and acceleration rates don't seem to matter, but I haven't tested this enough to be certain. It seems to have zero affect on driveability, as the truck still runs smooth (for its age).

My question is, what can I check before I take this thing in and get raped by a repair shop? I looked up the symptoms and it sounded like it could be the drive shaft, if that makes sense. If you need any more information, please ask and I will do my best to provide you the info. Anyway, thanks for any advice/help you can give me.

 

Have you made sure that there isn't any loose heat shields anywhere on the engine and that the exhaust system isn't contacting the frame or drive train components?

I'll typically go along the underside of a vehicle with a small ball peen hammer and hit a few places on the exhaust system/chassis to see if I can recreate the sound. For exhaust systems, a random orbital sander can be used (without sand paper on it) to put some vibration into various components as well.

*Moving to Full Size Tech*

 

I will go under it tonight or tomorrow night and see if I can find anything loose on it. I drove my Z28 to work today, as I've been babying the truck now that I hear its new noise. It has a new catback system on it, but I get the feeling that the manifolds/Y-pipe/catalytic converter may be factory original, or at best replaced only once. I've also noticed quite a few "little things" coming loose on the truck, so the heat shield is another possibility.

Thanks for the info. I'll report back with my findings.

JC

 

Worn needle bearings in the u-joints can make some odd "pinging, metalic" noises also.

 

Ok, I got under the truck tonight, and nothing was loose on it. Since I didn't think of it at the time, I'll check the rear differential gear and the trans fluid levels, just to be sure, but after driving it around the parking lot tonight, I'm sure it is coming from the rear somewhere, which makes me think drive shaft or rear diff.

Is that something I can change myself, or should I take it in?
If this is accurate, how dangerous is it to drive the truck in that condition?

Thanks again for the help/advice guys.

JC

EDIT - Nevermind. I ran a search, and it sounds like this may be what it is. This kind of repair is a bit out of my league as well. I'll check the fluids tonight when I get home from work, and if they are good, then I'll call the shop and take it in. I'll keep you all posted on this.

 

Update - 6/27/08

I just talked to my brother, who previously owned this truck. I told him the u-joints were bad in the truck, and his response was "again?". So I'm going to call him tonight (we chatted online) and find out what all is required to change these things and how involved it really is. If anything, I may be slightly more mechanically inclined than he is, so if he did this repair, then I can handle it. He said that he used the Brute Force u-joints last time. I think I'll go with the Duralast Gold ones this time. From the looks of the parts at AutoZone.com, it looks like I just pull some clips off, drop the drive shaft, install the new u-joints, and clip them into place (I'm sure there is more to it, but that is the general idea). Anyone done this repair before? How involved is this? I just hope I'm not setting myself up for an America's Funniest Home Videos moment by attempting this.

Thanks again.

JC

 

The best way to check for bad needle bearings in the u-joints is to pull the cups off. Unfortunately that's almost as much work as replacing them.
Before you pull the driveshaft out, use a paint pen or a marker of some sort and make some alignment marks on the rear diff yolk and the driveshaft, also the front yolk and the driveshaft so that when you put the shaft back in it's aligned the same way. If the shaft goes back in and the yolk has turned 180 degrees, you may experience a vibration on accelleration.
This is called keeping the driveline in "phase".
There are a couple of ways of replacing the u-joints. One way is with a hammer and punch, the other is with a press.
I personaly use a ball joint press.
The thing to watch for is that the cross of the u-joint is put in place, then the cups (that contain the needle bearings) are installed. If a needle bearing drops out of place while installing the cups they will probably become damaged and the cups won't fully seat.
It's a fairly easy job if you've done it before. If not, read a manual and ask any questions that you might have.

 

Well, I've been quite lazy lately, and haven't gotten a chance to rip into this thing. I plan on buying the u-joints tonight so that I can rip into it on Friday (July 4). I'll read through the manual (Haynes repair manual from AutoZone) tonight or tomorrow, and try to fire off any questions that may come up. Thanks for your help thus far, Chevy Lover. I have a tendancy of overthinking even the easiest of tasks, but I'd rather be 100% sure before proceeding than to rip into this uninformed and have to pay for a tow bill as well as the repair costs.

I'll update this with any questions that may come up. Thanks again.

JC

 

Completed.

I finally got around to fixing this (weather cooperated and everything), and I must say, it ended up being a bit harder than I imagined. The worst part was getting the old u-joints out. I ended up beating them out with a hammer (hitting a socket, so I didn't bend the drive shaft anywhere), but even that took awhile. After finally getting them all out, I noticed one of the bearing caps was completely dry inside, and when I turned it upside down, the needle bearings fell right out, along with some black powder. I'm assuming something went wrong in this one, which was causing my noise. The rest of the bearing caps looked to be in decent condition. Reassembly was much easier. After taking a test drive and hearing nothing (besides the valvetrain ticking, but that's another issue), I got that satisfying feeling of a job well done - all that effort and struggle was worth it. Thanks again for all the tips.

JC

 

Congrats on the successful repair! Glad you found the info you needed!!