I have a weird rattly noise coming from under my car. It only makes the noise around 2k rpm in 4th gear only. It sounds like a loose exhaust bolt or something.

Is there a way to put the car on jackstands and run it to test for the noise so I can locate it better? I tried running it before like this when I replaced the cv axles, but the angle was too severe and the cv axles made noise. The car needed more weight on the rear suspension.

Just checking to see if anyone else has a method that works. Thanks!

Well clearly it is safer to have the Car on jack stands and not running.

However on the vehicles you have in your profile; 1981 300d, 1985 300d turbo if you block both front and rear of the front Wheels you can raise the rear wheels and put the Jack Stands under the rear Subfame Bushings.

You can do the same with the front wheels on ramps but with the ramps it is not so easy to block the front wheels. It also means the jack stands need to be extended higher. The advantage is you have more room to get under they Car.

Anytime you are under a car it is a good idea to have a mind set that you may need to get out from under there fast.

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84 300D, 82 Volvo 244Gl Diesel

What car?

As as guess, with a W123 car, put the jackstands under the shock mounts of the rear LCA's, then you'll have a nearly as driven angle on the axles.

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CC: NSA

All things are burning, know this and be released.

82 Benz 240 D, Kuan Yin
12 Ford Escape 4wd

You're four times

It's hard to

more likely to

concentrate on

have an accident

two things

when you're on

at the same time.

a cell phone.

www.kiva.org It's not like there's anything wrong with feeling good, is there?

I've done it with my solid axle 240. It vibrated enough that I wouldn't have gotten under it. I might have been over 2000, though, I forget. Maybe if I'd had the wheels balanced first.
Give it a try from the driver's seat and see how it feels.

If you try this... in addition to the stands, have SOLID secure points with 4 straps 2" webbing type, securing the vehicle front and rear to hold the car from moving AT ALL...


IT SOUNDS LIKE YOU WANT TO SUPPORT THE AXLES WITH THE STANDS... to keep the parts loaded like on a road, will be difficult...

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

If the 123 is similar to a 126, there is a metal shield that covers the drive shaft and is bolted to the body. That shield would "rattle" like thin metal. Most other things would clunk. The exhaust is the other suspect. Make sure the down tube is clear and that all 4 rubber exhaust hangers in the rear are intact.

I've added exhaust hangers to the traveling in-trunk parts list because one didn't last long and dropped to the ground. Bailing wire is also in the kit - now.

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85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.

"I have a weird rattly noise coming from under my car. It only makes the noise around 2k rpm in 4th gear only. It sounds like a loose exhaust bolt or something."


This sound may or may not be apparent while raised on jack stands with the car running. It may be quieter. Jackstands are not designed for running the car on them!

Find a proper lift if you want to run the car while you are under it!


You can do plenty checking for loose parts/fasteners without risking dropping the car- if you come out unscathed, you still may wind up creating a whole new repair job.

Leave the engine off, get under there with a good light source, a prybar if you need it, and a mirror to check it over. Don't forget safety glasses, especially around old exhaust components.

My car does not have definitive reinforced flat pads for locating the jackstands as it is. There is always a small angle involved. Starting the car will add vibration, and this can cause a jackstand to slip.

Just my .02, I would rather have a my car with a rattle than a big crush on me!

Cheers,

snapped_bolt

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'81 240D For now, a good place to borrow new parts
'80 300TD Probably will be put back into service!
'79 240D BACK IN SERVICE SINCE 09/16; limited use, oil leak. Guide pin r/sealed/replaced. Still a leak. Front crank seal....

[QUOTE=Blazemaster;3730600]I have a weird rattly noise coming from under my car. It only makes the noise around 2k rpm in 4th gear only. It sounds like a loose exhaust bolt or something.


You might take a look at the muffler heat shield, or the possibility of one of the mufflers interior baffles having come loose, and making noise due to harmonic vibrations at certain rpms.

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96 E300d

I'm so paranoid of getting under cars, I have jack stands for my jack stands. Seriously I double up so if one fails another catches the car. lol

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1983 W123 300TD US spec Turbo engine, with Euro bumpers and manual climate control, and manual transmission.

I don't know what's available to you but if you can get some chassis dyno time that's a great place to run the car while you poke around to see where the noise is coming from. I've used something as crude as a broom handle to reach under and poke a heat shield to determine if that's the culprit. Running a car under load reveals a lot of stuff you just can't find any other way shy of running down the road next to the car (I'm not that fast!). Locally I can get a few minutes pretty cheaply - as little as $60/hr. and he will sell me a part of an hour. You can grab your peak wheel HP while you're at it.......

Dan

NO, take it to a garage and pay them to put it on the rack and tell you what's rattling.

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84 300SD
85 380SE
83 528e
95 318ic

With the wheels on, it is fairly safe to crawl under as you only get squashed so much if it falls. But, you will be spinning the wheels and drive-shaft, so be sure to set a "keep-out" zone. I would stay to the side and hold a large mirror under to view. When I do need to crawl under a car with wheels off, I jack up the vehicle and lower the frame rails only a square lattice of 4"x4"'s (cut fence posts). That looks more comforting than metal jack stands. With drivetrain running, I would tack the 4x4's together with nails so they can't wiggle.

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans

Your rattling happens at 2k rpm in 4th gear that's what 45 mph. Mighty scary crawling under a raised car with wheels spinning that fast I wouldn't do it. Maybe you can find some cheap remote ears and move them around to identify what's the problem.

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92 e300d2.5t
01 e320
05 cdi
85 chev c10

Thanks for the replies. I didn't really mean to climb under the car when it's running and in gear, more looking from the side/mirror idea to see if there's anything obvious.

I should have stated this is an 85 w123 turbo that I just converted to manual, and deleted the rear muffler with a custom exhaust. I work as a machinist/welder so it's not just a hack job, everything seemed solid. The car seems to drive and sound great other than this weird noise around 2k rpm in 4th gear. The noise could be a resonance thing, it's coming from the rear of the car. I'll do some investigating and report back.

Mount a go pro camera and review the footage after a test drive? You can always move the camera and do it until you found the source.