My tires are properly inflated yet i hear a distinct 'thump thump' when i drive down the road at any speed.

Is there a way to check if the belt is broken? there's still tread on they tire and i would hate to replace them unless i am sure.

Better question.... assuming one of the four tires has a broken belt, how do i isolate which tire it is?

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Jennifer
90 350sdl

First, isolate which wheel area.
Roll down all windows and drive slowly down a nice quiet residential street with lots of trees. That should make it easier.

If you hear a thump thump, it seems there might be something like a screw or a nail in the tire. Maybe the thumping item was against the pavement on the bottom of the tire when you checked?

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85' 300D No inspection, No registration fees, Cheap insurance
"If my calculations are correct, when this baby hits 88 miles per hour, you're going to see some serious %$&^."

Thumping can be a balance issue, or the tire could be out of round.

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1984 300TD

Figure out which wheel the noise is most likely coming from and jack that tire up and give it a spin. If the tire looks out of round have it replaced.
Tire stores always want to sell you a tire or four so if you have any questions about the tire have a mechanic look at it.

OK. Please explain out of round (other than the obvious). Why does it happen? Are you saying it would conspicuously look 'oblong'?

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Jennifer
90 350sdl

My parental units were having an issue with their car. It was right after a dealer service. I took the car for a ride and heard a thump that went up and down in speed with the speed of the car. Touching the brake had no affect on the noise. I parked the car and ran my hand slowly over each tire tread. I found a barely noticeable bump on one of the tires. He took them back to a dealer and they pro-rated the tire.

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'85 300SD (formerly california emissions)
'08 Chevy Tahoe
'93 Ducati 900 SS
'79 Kawasaki KZ 650
'86 Kawasaki KX 250
'88 Kawasaki KDX200
'71 Hodaka Ace 100
'72 Triumph T100R

Take it to a tire shop with a road force balancer, most MB dealers have this. If something is wrong with the tire like a broken belt a road force balancer will find it.

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1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200

Out of round condition is not something easily seen by naked eye.

If put on a spin balancer though it should be obvious.

Tom W

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Well then steal something more durable and it will last longer... oh... never mind.

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-Marty

1986 300E 220,000 miles+ transmission impossible
(Now waiting under a bridge in order to become one)

Reading your M103 duty cycle:
http://www.peachparts.com/shopforum/showpost.php?p=831799&postcount=13
http://www.peachparts.com/shopforum/showpost.php?p=831807&postcount=14

If you can feel it at relatively low speed then it should be well visible visually if you hand spin it. You might be surprised how obvious it is. I have seen some pretty bad ones! You should be able to tell if it is the front or back I would think. Is this a low profile tire? Those pretty much self-destruct at the first pothole.

Mike

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1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra

Sorry, lost track of this post. Like T Walgamuth said, you wouldn't see it with the naked eye.
As for why, usually it's a manufacturing problem.

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1984 300TD

If you feel a dramatic shake at low speeds it is more likely a belt shift or a bubble in the tread.

Tom W

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.