Befuddled mechanic and thumpy ride

Hello Car Talk Guys!

I have a 2004 Ford Explorer XLT that has about 70K miles on it. I had brakes and rotors put on my car about a month ago. I also had two new tires put on the front of the car. (the mechanic never mentioned the fact that I really should put four tires on instead of two). After I got the car back, I noticed this slight rubbing/grinding type of noise in what seemed like the front left tire. It was an intermittent sound/symptom and only got worse as the car warmed up. I took it back to the mechanic who said they ?couldn?t reproduce the symptom? so I had to go up to the mechanic and take them for a ride to show them the symptom. They still couldn?t? diagnose it. They checked the balance of the tires, the alignment, rechecked their brake job but had no luck figuring out the issue. They did state that they found something ?loose? in the brake parts but that they tightened it up. They didn?t say what they found.

I took it to another mechanic who looked at the TSB (technical service bulletins) on the vehicle. He thought that perhaps it was due to the fact that I had different PSI?s in the front and back tires; and/or since I had new tires on the front, and there was a slight difference in the tires in the back, that putting on two more new tires in the back would solve the issue. He stated that it seemed the TSB had something to do w/ the transfer case and the inconsistency in the tires and perhaps by doing this it would fix the issue. It didn?t.

So now I have four new tires on the car and still have the symptom. To clarify the symptom: when driving on the on the highway at speeds up to 65 mph, when I de-accelerate, or simply take my foot off the gas, (because I?m coming upon traffic and want to slow down), before applying the brakes, the car starts this thumping type of motion. It will stop once I slow down say below 35mph or so and/or apply the brakes to slow down. The sensation I get from the way the car feels when the thumping occurs is as if there is something that is rotating along with the wheel, or the motion of the car moving forward (maybe in the axle?); and then as soon as that rotation motion starts to slow down because I take my foot off the gas, this ?thing? ; that which is causing the thumping, doesn?t slow down immediately and because of its? own momentum, continues to move forward at the same speed it was going until it finally catches up (or slows down) with the rest of the car. Not being a car mechanic and knowing all of the parts, I have no clue what this part could be, but that?s the way it feels when it does this. It also makes for a very bumpy ride. It?s like riding over an old highway with those bumps every 20 feet. Thump thump thump!

I hope you have a clue as to what this might be. I suspect the first mechanic has left something un-intact or loose or something to that effect. But my fear is that short of having another mechanic dismantle the whole front end, I?ll end up spending another 1000.00 on it.

Also, the first mechanic in this situation had installed new rotors on the back tires last June, and in this last visit, said those rotors now needed to be turned? Do rotors really wear out that fast?

A good alignment shop is where you need to go.
You have four new tires on the truck? Are they exactly the same size? Is your truck four wheel drive, or all wheel drive?
Look at the tires. Is the tread straight all around the tires? If the tread is “squiggly”, the tire belt may be separated, and this would cause the tire to thump every revolution of the tire.

No. Modern rotors don’t have enough thickness to turn more than once. If they are warped, the lugnuts were probably unevenly torqued. No surprise since this guy let you out the door with loose brake parts.

It is impossible to say what’s wrong without seeing with my own eyes. All I can provide is conjecture.

But from your description, you have an axle problem. If you had a driveshaft problem, the frequency would be higher than the wheels. Axle noises run in phase with the rotation of the wheels. Again, it’s impossible to know from description alone. You need a reputable mechanic.

U joints!