Learning Curves
I, for one, have never been a fan of noise-hunting, but it's always an adventure. Some guys live for it. Noises can telegraph from one end of the vehicle to another and can sound like unrelated noises. Belts and pulleys are notorious for making strange and confusing noises.
Back in the 1970s, I was working as a mechanic at an independent shop in Alabama, and a high mileage 1972 Ford pickup came in sounding like the engine was about to knock its brains out. I was shocked when the old guy who owned the shop removed the belt (which had numerous chunks missing) and made the engine run quiet. A new belt was all that Ford needed to stop the knocking.
More recently, a brand new aftermarket belt on a 1999 Chevy had a really slick and shiny traction surface with cross cuts that were catching the air and making a whining noise that caused the owner to replace some bearings. A normal belt with a fuzzy traction surface eliminated the noise.
Last week, a student from the welding department had us look at a 2003 Nissan Maxima with badly rattling lifters; the oil wasn't touching the dipstick.
But the truck that's the focus of this month's article is a 2000 Silverado four-wheel drive. The ticking noise was kind of faint to begin with, almost a non-issue.
Nowadays, I like to click a mouse before I click my ratchet, and in so doing, I found Service Bulletin No. 01-06-01-028 (March 2003) that spoke of carbon-caked pistons causing a noise on startup. But that bulletin didn't recommend any kind of repair, because GM engineers didn't see the noise as a big deal. Not surprisingly, a good carbon cleaning has been chronicled as a confirmed fix by aftermarket information sources.
There was another TSB that spoke of heat shield concerns, but this noise wasn't an exhaust rattle. It was tied directly to the speed of the engine and appeared only during a certain temperature window somewhere between bone cold and blistering hot. At either of the temperature extremes, the noise was less pronounced or wasn't audible at all.
There were a few reports I found of oil pump O-ring failures that would allow the oil pump to suck air and cause lifter noise, but the dash oil pressure reading looked decent and there were no other noises. So the owner (who also happens to be my immediate supervisor) decided to listen carefully for a few weeks to see if it got worse. It did.
Quick and Easy — NOT
There are some pricey electronic toys out there that can help pinpoint noises, but my initial grab in a situation like this is a plain old $13 stethoscope, and this time it didn't disappoint me. As I traveled around under the vehicle with it up on the lift and the engine running, I found that the ticking was really loud in the bell housing area. I told my supervisor he had a cracked flex plate, which isn't so terribly uncommon. We worked for weeks on a noisy 1999 Alero 4 banger that had a rattling balance shaft, a sticking timing chain tensioner and a badly cracked flywheel. There were noises coming from everywhere on that bomb. Last summer we fixed a 1999 Ford Ranger that had broken the center completely out of the flywheel and ruined the torque converter.
My parts supplier couldn't say for sure which flywheel flex plate the Chevy 6.0 was spinning back there (there are several possibilities), so I called the dealer with the last eight of the VIN and ordered a $130 replacement part before we even started on the job.
What to Remove?
The guy I put on this job is only 18, but I have to say he's the most seasoned technician for a guy his age that I've seen in years. David's hands are big and scarred, and he doesn't grab hold of too many things that don't move. Furthermore, he doesn't ask for help, he doesn't leave bolts loose and he doesn't quit. When he starts a job, he's going to win, one way or another. And in most cases, he does his work quickly and picks up a torque wrench where it makes sense to use one. He's one of those guys like some of the ones you might know who oozes engine oil instead of blood when he nicks a finger. So I put him on the flywheel job, totally confident that he could make it happen rapidly. As he worked his way into the job, he did have one question:
"Should I pull the transfer case?" he asked.
I was swamped, and my answer was an offhand reply: "Not unless you have to... It's faster just to yank it out with the transmission, but make sure you securely strap the tranny to the jack."
Well, I guess I could have paid more attention to what he was doing under there, but I was from pillar to post helping the other students with their projects and worksheets. The next thing I knew, he had the torsion bars and their bushing bracket out on the floor. Would this be a problem? I hoped not.
With the flywheel in his hands, David showed me a dandy crack that had formed around the crankshaft bolt holes – we had verified the source of the ticking, and it felt good to be right.
The new flywheel was installed, and the bolts were carefully torqued to GM's 74 foot-pounds spec.
The transmission was reinstalled, and now it was time to put the torsion bars back in. These 5-foot long bars are the standard design, with a hex on each end, one fitting into a wrench-shaped hole in the lower control arm and the other fitted to the trim height adjustment arms. The adjustment arms had to be loaded, and the trim adjustment hardware had to be installed. It was tough to get those doggone things back in there, but let's be serious, we're working with springs here, and everybody knows springs can be a pain in the fanny, right?
One point of fact is that an American made C clamp style ball joint separator can move mountains when driven by a good impact wrench, and so the torsion bars went back in place and the adjustment screws were driven to their previous thread positions.
When we lowered the truck, the suspension was pretty stiff, but it was the end of the day, and because the truck was drivable, I took it for a road test. I wasn't used to driving the truck, but it didn't feel quite right, and I told the owner of the truck that I thought we might have to revisit the adjustment and configuration of those torsion bars. He figured it might be all right; he'd evaluate it on his drive home.
"It's a heavy duty truck," he told me. "It rides kind of rough on a bumpy interstate. I think it'll be OK."
Whoops!
The next morning the truck was sitting in front of the shop and I had a voice message from the owner on my office phone. I was right. The suspension was "way too hard."
Well, I wasn't too terribly surprised.
Back on the lift with it, we unloaded the adjusters with the ball joint separator again and removed the torsion bars. I noticed they both had part number stickers wrapped around them and that the part numbers were different. A look at the GM shop manual mentioned left and right and how they were different, a possibility David and I had considered, but he was sure he had put them back in the same way they came out.
Wrong! A call to the GM dealer with the part numbers from the stickers verified the foul-up. Furthermore, the end of each torsion bar is stamped either L or R along with rotation arrows to prevent that kind of nonsense from happening. David had put the torsion bars backwards and transposed. This time they went back in a lot easier and the truck felt a whole lot different on the road.
Concluding Thoughts
Actually, there were a lot of other jobs under way, and because they contributed to the learning curve, they bear mentioning as well.
The 1995 Grand Am mentioned briefly in last month's Motor Age Garage (the one with the locked A/C pulley bearing) got a used A/C compressor this week (its old compressor was leaking badly) and a replacement tire and wheel for the left rear, because the existing wheel was wobbling to the point that it would chatter the teeth of anybody sitting in the seats at road speed.
After replacing the A/C compressor, the student panicked when she discovered that her automatic transmission would take off in high gear when she started out in drive. But I showed her how it could be shifted manually; it had been working fine when she pulled the Grand Am into the shop for the A/C work. I felt sure the problem wasn't as serious as it seemed, but she was dreadfully confused when I told her to take her trusty test light and check the fuses. She had to put her diagnosis off until she got home, and when she told her dad that I had said to check the fuses for the trans concern, he thought I had bats in my belfry until she replaced a fuse that was blown and it fixed her problem.
The supposed warped wheel she replaced turned out to be a warped hub, a fact that was painfully obvious when she installed the replacement wheel and it wobbled just as bad. Changing the hub was nasty, because all four bolts were so rust-caked that they looked like they had been submerged along with the Titanic.
On another front, a seemingly quick and simple A/C repair on a 1994 Chevy pickup turned nasty, because the fittings were leaking and their cores weren't replaceable. Furthermore, the fittings are part of the line, so an $80 line had to be ordered. When the A/C suction/discharge manifold line assembly came in, we removed the brush guard and the grille only to find the line's fitting had galled itself to the condenser, and so that part had to be ordered as well. We had a '96 Chevy pickup in the shop for cracked head replacement at the same time the '94 was in there and by some nasty turn of confusion, we found that the A/C line the parts guy had ordered was for a '96 instead of a '94. It may have been my fault, but the line had to be reordered.
The jobs that turn into problems are the ones that teach volumes. I can lecture in the classroom all semester long about situations like the ones we encountered here, but the kind of battles we won this week and the ones we'll fight next week will bring a level of experience and integrity to my students that they simply can't develop any other way. These jobs shorten the learning curve like nothing else.
A ticking time bomb?
Richard McCuistianis an ASE-certified Master Auto Technician and was a professional mechanic for more than 25 years. He is an auto mechanics instructor at LBW Community College/MacArthur Campus in Opp, Ala. E-mail him at [email protected]
