Hi guys. You said you're feeling this in the accelerator pedal? Could you mean in the entire body and seat? The accelerator pedal connects to a cable that will flex to absorb any engine rocking or roughness from misfires. To offer some ideas, if these are original wheels, Chrysler had a service bulletin about wheel vibration bad enough to cause the side mirrors to vibrate. The wheels were made by American Racing. We had to dismount the tire, then measure lateral run out on both lips where the bead seats, then radial run out at the same places. If it exceeded.045" run out in any direction, we were to replace the wheel under warranty.
You can check for this yourself with a dial indicator and mounting base that you can find at a Harbor Freight Tool store. Mark the location of any wheel weights on the outer lip, then remove them. Set the dial indicator up to run in that area, then slowly rotate the wheel while looking for the amount of lateral run out. If it's real low, look somewhere else or at the other wheels. If it's close to the maximum allowed, you may want to have the tires pulled off so the wheels can be measured more accurately for all four measurements.
If lateral run out is high, remove that wheel, then measure the run out on the outer edge of the brake rotor where the wheel contacts it. I don't remember the allowable spec for that, but it's not much. A few thousandths of an inch will translate into a lot more at the lip of the wheel. Look for rust or scale that got caught between the wheel and rotor when the wheel was off previously and is preventing the wheel from sitting squarely against the rotor. That can cause a vibration when that wheel and tire are true and perfectly balanced.
Likewise, if you have the rotor design that slides onto the wheel bearing's hub, debris can get stuck between those parts too. You see that as excessive run out with the dial indicator. This doesn't apply to "captive" rotors that require removal of the wheel bearing, then the rotor is bolted to the back of the hub. Those are more common with diesel engines and the larger trucks.
You can also get a weird shaking sensation when a front brake doesn't fully release. Stop on a slight incline, shift to neutral, release the brakes, then see if the truck creeps down hill on its own. If it doesn't, people always assume it's due to a sticking caliper, but that is a common Ford thing from the '80s and '90s. More often it's caused by the rubber flex hose, and on Chrysler products that happens most commonly when there's a metal bracket crimped around it in the middle. Rust forms and builds up inside that crimp and constricts the hose. You can push brake fluid through the constriction but the fluid can't release to flow back up to the reservoir. As the brake gets hotter and hotter, the brake applies harder. This is usually felt as a pulsation in the whole truck while driving, and when it's bad enough, you'll feel the brake pedal is higher and harder than normal when pressed. Those crimped brackets can be opened up a little with a large Channel-Lock pliers or flat blade screwdriver. There's no need to replace the entire hose for that problem. This problem gets worse the longer you drive, so it can appear to occur only after the engine warms up.
You can find the offending brake by feeling which wheel is hot after a short drive, then, while still on the incline and in neutral, place a block a little down hill of one tire, then open the hydraulic system at various places to see where the fluid is being trapped. It's easy to start at the soft metal line nuts at the master cylinder, but if the brake releases from there, we have serious issues to discuss. Most often the only way the brake will release is to crawl underneath and open the bleeder screw on the caliper. If that lets it release, that proves the caliper is okay. The rubber hose is the best suspect then.
Without rereading everything, if you have regular universal joints on the outer ends of the front axle, those can become tight and bind. When you switch to four-wheel-drive, then turn left or right while driving ahead slowly, the steering wheel will get forced back to center when the wheels rotate half a turn, or, if you hold onto the steering wheel really tightly, the truck will stop creeping ahead on its own. That symptom will go away when you shift out of four-wheel-drive, but the axle is still going to want to rotate freely with the wheel and wheel bearing. As the tight spot comes around, when you turn slightly either way, that binding will stop the shaft from turning freely, and it want to rotate back to where it is held in place by that refusal of the u-joint to swivel. That can set up a pulsing vibration, especially at a specific range of speeds. Once the tire is raised off the ground, this is easy to identify by rotating the wheel by hand. It will rotate fairly easily. Now turn the steering system to one side and try again. If the outer u-joint is binding, you won't be able to rotate the wheel, and if you force it, the steering wheel will get forced back to center no matter how hard you try to prevent that. Another clue is to look from behind the wheel at the bearing cups on the u-joint. With every one of these I've found, at least one of them had a reddish brown rust stain at the top of one cap, and sometimes two caps. When you pull that joint out, the roller bearings will fall out in little pieces and lots of powder, and no grease.
Most front axles on trucks use CV joints now. If you have those, another vibration in the steering wheel is caused by extremely subtle wear inside the inner CV joint housing, and is real hard to identify unless you have a really smart wizard like me to figure out what to look for. This problem mainly apples to front-wheel-drive cars because the symptom only occurs during periods of normal acceleration when the joint is under load, and it's much worse when turning, as in when accelerating out of a parking lot onto the street. I'll save that for another day as you aren't likely to be driving all day in four-wheel-drive, and that is the only time this elusive wear takes place.
Sunday, April 21st, 2019 AT 9:43 PM
