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My 1970 250C makes a klunking noise on acceleration.
It's coming from the rear of the car & continues up to about 40 m.p.h.
Once I get up to cruising/highway speed (above 40) the noise goes away & the car rides smoothly.
I suspect the center driveshaft support bearing.

Does anyone have any other ideas?

Also, is it dangerous to drive it like this?

Thanks!

It could be the bearing or the flex disks. It could also be the links for the sway bar. They use a plastic bearing and it falls out after a while.

Any of these can be dangerous. The drive shaft can come loose or a link can get caught up in moving parts.

I had Mike at Walt's Radiator check my flex disks on my 450SEL during an oil change because I had a thumping noise on acceleration. He knew exactly what I was talking about, told me the front was shot and needed replacing soon. I ordered one from Phil and Walt's put it in for $85. My mystery noise is gone.

Michael

Thanks so much.

If all this winds up costing me is $85 I'll be glad to pay it!

The car is far from perfect but, after only a month of ownership, I do love it!

Hello,

My first guess is the rubber in center driveshaft support has gone bad. This condition will cause a knocking/thumping sound under acelleration. The sound originates from between the front seats under the car.

Normally the driveshaft is removed, the rubber carrier and bearing are changed. All the flex discs should be checked at this time. Some models have two driveshaft supports and a three piece driveshaft! You'll have twice the cost in parts if this is the case since you should replace both. Always mark the drive shaft parts so they assemble exactly to prevent any balance and vibration problems.

Hi,

That sounds like what's happening; it's coming from between the front seats (possibly just slightly behind them?) & definitely from the underneath of the car.

It's a rotating kind of a sound; with rythmic, repetitious "klunks" that increase and decrease with acceleration and deceleration.

Sometimes, when turning hard from a stop (as in pulling out of my driveway into traffic), it even makes a loud "POP" or two before the klunking begins.

I haven't had a chance to jack the car up & really get a good look at it yet but tomorrow I will.

Thanks for the info!

- Wil

That's what mine sounded like, although a bit more of a muted thud than a metallic clunk.

The pop sound may be coming from a rear CV joint and not the drive shaft. You might want to check out the CV joints while you are under there.

Michael

Thanks, I'll do that.

I got under the car today & the center support bearing itself seems okay but the rubber around it is DEFINITELY toast.

I don't have the ability to do the work myself so I'll be dropping it off at the mechanic on Tuesday. Any idea what this should cost?

I looked at the CV boots last week & they (along with everything else on this 38 year old car) are dried out. I think that might be something I can do myself, though.

Also, just out of curiousity, how much play should there be at the U joint itself? With the rubber around the center support bearing shot, I can move both the front & rear driveshafts ALOT but they move together.

Thanks again!

- Wil

Hello,

I have been able to just remove the front driveshaft and replace the support and bearing saving a lot of time. I use a air chisel with a blunt end to drive the old assembly off the shaft while in the car after the front driveshaft is removed and the lock ring is removed. Remember to mark the driveshaft halves so they go back on exactly. I use the correct size metal or plastic tube to drive the new parts back onto the shaft. I am able to do the job in about 45 minutes. Most mechanics will remove the entire drive shaft quite a bit more work figure at least 2 hours. Also the drive shaft will have to be compressed. There is a telescoping section locked by a large nut 46mm and 42mm. You will have to loosen these to start.

The CV boots require an expensive MB tool to crimp the metal cans after the new rubber is installed. Find someone who is supplying split boots for this model. I heard they are available. You can also get re-built half shafts. Still expensive. It requires a bit of work to remove the half shafts. Lower diff, remove rear cover, remove lock rings, unfasten bolt at rear brake disc and remove the half shaft. The split boot still seems like a good idea!

Hi Joe,

It's good to have an idea of what may be involved.

Thanks for the info, it's greatly appreciated!

- Wil

Whilst I will normally bow down to Joes extensive knowledge ( especially regarding W113's) the situation regarding CV joints on the W107 (etc etc ) is one where split joint rubbers are NOT available and will not work on a high speed spinning axle. BUT there is an answer because dismantling those joints can only be described as bastard of a job which requires special tools .
You can get both axles rebooted (?:D) by anyone who has a Astoria Flex boot gun. It takes around 20-30 minutes to do each side and the boots cost under $20 each.
http://www.thetoolwarehouse.net/shop/ARA-FB5000PK.html

Using as Asotia gun there is no need to remove the axles,just undo the 13 mm bolt in the center of each rear hub and push the 1/2 shaft free. replace the boots and refit the axles and your done.

BEAUTIFUL!

Thank you so much!

- Wil