Cracked Flywheel (W126)
 

My tech just told me that my 1983 300SD (227000 miles) has a cracked flywheel (not the ring gear). The engine had started making this high pitched whiney-squelly noise and we thought it was the turbo charger but he said he looked into a window near the transmission bell housing and could see the crack. The noise is worse at idle and quiets as you accelerate. (he said the torgue quiets it down) Car has been starting fine and drives except for this occasional whine.

He said he has a used fly wheel for $150 ($350 new) and it will be an 8 hour labor job about, $700 total!!!

Do you think the diagnosis is correct? Is the 8 hour labor too long? Can I buy a used fly wheel and Do it myself? Special tools, transmission jack, balance? I did not know the car had a fly wheel just a ring gear?

I want to get out cheap so I can sell.

Thanks for the help.

There's no getting around the labor since the transmission has to come off to replace anything between the engine and transmission.

I got my 81 SD (sold) after the transmission locked up and shredded the flexible 3-arm part of the flywheel/flex plate. I can probably do it in less than 8 hours but I can see where that's the standard book time for the job.

You can do it yourself with basic tools. You can lower and raise the transmission with a floor jack. You don't have to lift the car very high if you're not pulling the transmission out from under the car.

The flywheel/flex plate on this car has 3 peices and I don't know all their technical names. The ring gear has the teeth that the starter engages. It's just an annulus (sp?) that fits over the main flywheel. There's also a flexible plate that has 3 arms that the torque converter bolts to.

I think you have to replace the flywheel to crank bolts when you remove the flywheel. At the very least use Loktite.

Sixto
91 300SE
87 300SDL
83 300SD

It is a pretty straight forward job for a competent diy'er. 8 hours soulds about right. Replace the front tranny seal while the tranny is out.

Thanks for the replys!

Should I replace the ring gear also? ($65.00), Bearings, flex arm?

Good tip on replacing the flywheel bolts.

I may do it myself with the floor jack, can this be done with the car on jack stands? Can I get the leverage I will need to loosen the transmission and flywheel?

Looking at the service CD it talks about; angle of rotation tool, detent tool, neckdown tool, balancing the flywheel, angle of rotation torque 90-100 degrees, heating or using oven to attach ring gear to flywheel using special heat chalk.

Do I really need to do all of this as I doubt my tech would do any of this.

No need to replace the ring gear if the replacement looks as good as your old one. You really don't want to mess with the ring gear. Consider that the starter spins a cold engine through the interference fit between the ring gear and the starter. It's going to take more than a nautical vocabulary to get a ring gear off an another one on.

If you don't tackle the ring gear, the only special tool you might need is a degree of rotation measuring tool. I've never seen one but you can probably get one at any auto parts store since many cars have degree of rotation specs for final torquing.

I painted a line on my socket, painted a mark at 90-degrees near each bolt (relative to the line on the socket, of course) then eyeballed it. The key is to turn in 90-degrees in one step.

I don't know what bearings you can replace.

Is the flex arm that 3-arm plate that the torque converter bolts to? It should be easy to tell if the old one has any damage. I think it was a $30-40 part new.

If your transmission has never been off the car, the bolts won't be too tight. MB has very light torque specs compared to other cars. You should be able to loosen the bell housing bolts with little more than a combo wrench and a good grip.

The flywheel bolts are a different story. I used an electric impact wrench to get them off. You can rent one for $10-15 a day.

Jack stands will get the front end high enough.

You might balance the flywheel when you attach a new ring gear. If you use an old flywheel with ring gear, it should still be balanced.

When you pull the transmission, the manual says to mark the flywheel and torque converter so you can put them back together in the same orientation. When you replace the torque converter, it doesn't say to get the flywheel and new torque converter balanced. The advise to mark parts going back together is probably there to minimize the chance of introducing imbalance, but I think chances are you won't introduce any if you don't get them back the same way or if you replace one part or the other.

Sixto
91 300SE
87 300SDL
83 300SD