| ne vibrations can be tricky to diagnose, because | | | | you can end up with a car where the transmission |
| you can't get under the car and see what is going | | | | touches the car body and the driveshaft angles |
| on while it is driving down the road at 60 MPH. If | | | | are unacceptable. This of course isn't always the |
| you have read my first article on the three types | | | | case, but if you run into a vibration problem on a |
| of driveline vibration, you have a pretty good | | | | heavily modified car you need to take this |
| way of narrowing down the list of possibilities | | | | possibility into account. |
| based on if the vibration is engine speed related, | | | | If it is a recent restoration that was vibration-free |
| vehicle speed related, or engine load related. Here | | | | before, then first look at anything that was |
| are some other considerations to keep in mind | | | | changed, and the relationship all those components |
| when diagnosing a classic car vibration. | | | | have with other systems on the car. If you just |
| The first thing to consider is the overall current | | | | swapped a Ford 9" rear end into your Chevy, the |
| situation. If this is a new build that has never been | | | | rear end itself may be fine, but you could have |
| run before, then everything is suspect. You may | | | | altered the driveshaft angles. An angle that was |
| have total faith in your engine builder, but could | | | | barely acceptable before might be slightly beyond |
| one of his tools be out of calibration? Is the | | | | the limit now, creating a vibration. |
| engine supposed to be externally balanced, and | | | | Sometimes you have to "think outside the box". I |
| you ordered the correct flywheel but actually | | | | once corrected a "vibration" in a two year old, |
| received one for an internally balanced engine? | | | | 25,000 mile Buick Lesabre that had a vibration |
| Are your driveshaft angles out of spec? Could | | | | complaint since day one. It had been to three |
| you possibly have a defective pinion or axle | | | | different dealerships, where they had rebalanced |
| bearing, a bent axle, a warped wheel, or a tire out | | | | and replaced the tires and wheels several times, |
| of balance? Is your exhaust touching the body or | | | | had multiple wheel alignments, and even had the |
| another component at any point? Are all the | | | | shocks and struts replaced. I noticed on a test |
| suspension bolts, body to frame bolts, and | | | | drive that the vibration was only in the steering |
| steering linkage nuts/bolts tight? | | | | wheel. I could not feel it in the seats, the |
| If this is a modified car, there are so many more | | | | armrests or the dash, or see it in the mirrors. I |
| things to think about. If you have 1968 Camaro | | | | took it back to the shop and ran over some |
| (my favorite year!) with a Total Cost Involved | | | | speed bumps at about 10 MPH to see what |
| front end, a late model LS3 engine with | | | | happened, and the steering wheel moved about |
| home-made engine mount towers, a Keisler | | | | three inches up and down! I was a service writer |
| transmission, a Currie 9" rear end, and a Detroit | | | | at the time, and all of the technicians refused to |
| Speed rear spring and shock package, there are a | | | | believe that the steering column could be loose |
| number of different opportunities for | | | | from the factory, so none of them would work |
| incompatibility, not to mention the fact that the | | | | on it. I dug into the dash and found that two of |
| car is almost 40 years old and the production | | | | the four bolts that secure the steering column to |
| tolerances back then were considerably "looser" | | | | the dash were about three turns shy of being |
| than they are now. Aftermarket companies | | | | even finger tight! It had come that way from the |
| usually design their parts to fit a completely stock | | | | factory, and none of the previous technicians had |
| car, and their parts will usually fit an otherwise | | | | taken the time to pay attention to what was |
| unmodified car very well. When you start to | | | | actually happening with the car. I tightened the |
| combine aftermarket parts from different | | | | loose bolts, and I had a customer for life! |
| manufacturers, you sometimes run into problems. | | | | Sometimes you have to open your mind a little, |
| The aftermarket front end may be designed to | | | | and throw all assumptions out the window. |
| improve cornering ability which changes some | | | | The bottom line is to take your time and consider |
| geometry that the aftermarket transmission | | | | all the possibilities. Assess the overall situation, |
| system also changes due to tunnel interference | | | | drive the car, and think about what is happening. |
| with the transmission, and then the rear end | | | | Don't make any assumptions, and realize that |
| company also takes a few liberties with their | | | | aftermarket parts from different reputable |
| design to make the rear end fit several different | | | | companies aren't always designed to work with |
| cars, and the rear suspension company modifies | | | | each other. Have an open mind, and with patience |
| the geometry for maximum traction when drag | | | | any vibration problem can be diagnosed and |
| racing. Each part by itself works perfectly with an | | | | corrected. |
| otherwise stock car, but when all are combined | | | | |