My '81 300SD (250k miles) started yesterday making a new noise. Taking a left turn I got a clunking from directly under the shift knob. Not a rattle or anything, just a clunk clunk clunk clunk until I eased out of the turn. I have been able to duplicate it once and I'm sure it's almost directly under the shifter. Could this be my tranny mounts, or something more sinister? Am I in trouble?

I would get under there and look at the front and rear flex disc, the center d'shaft support brg and the tranny mount. I would put it as a pretty high priority too.

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Jim

I was under the car a few days ago, and did look at the flex discs. They seemed ok. I replaced the front exhaust section, but I don't think that could be causing the clunking, it's quite secure. I guess I'll lift it up this afternoon and start checking things. Can the transmission mounts be replaced without dropping the transmission?

Good idea is to paint mark position of old tranny mount for exact allignment.

The same people who pull trannies for fixing tranny mounts probably like to remove the entire engine just to replace engine mounts.

Ok, just got out from underneath the car. The flex discs appear to have been replaced by the PO. The front engine mounts also appear to be new. The rubber part of the rear engine/transmission mount is soft like jello and provides no support, the metal part is just resting on the crossmember. Could not get to the center drive shaft support bearing just yet. Am I missing something, or is the transmission just supported by the rear engine mount? I can move the exhaust enough to sort of replicate the clunking noise I heard, and even though I hope that is the culprit, I'm never that lucky. Back to work....

AFAIK, the engine/transmission is mounted as a unit using a three point suspension--one on each side of the engine, and the third is the tranny mount. Mount should not be soft like Jello.

Seems weird that somebody replaced engine mounts and flex-bushings without doing the tranny mount and center support bearing too. Maybe the previous tranny mount was misalligned causing it to fall apart early.

There's also a small discrepancy which calls for one side of the tranny mount to face forward, something to do with the metal collar inside it. Installing these things backwards is a common problem. And hell yes, you want to scissors jack the tranny to proper height for alligning the mount for an exactly level driveshaft coupling.

Poorman's method of alligning the tranny mount is to install it loose and them roll the car forward and back a bit or spin the rear wheels back and forth if they are off the ground, so the driveshaft can decide for itself how it wants the tranny to be alligned.

And I'd probably be leaving the center support bearing alone as it generally just causes vibration inside the driveshaft tunnel detectable from inside the car instead of clunking on corners when it goes bad.

Hey Diesel Dog. Yeah, I'm sure the font engine mounts are new, and I'm sure the transmission mount is not... I also wonder sometimes why people do what they do. The PO replaced the entire brake system, all lines, calipers, discs, etc. to the tune of $1,000. But they didn't touch the broken air cleaner bracket. Car stopped on a dime, but was quite the rattletrap when I got it.

I can put up with a little rattling but if it don't stop then I am going to have some issues.

Anyway, did the noise start AFTER you messed with the exhaust system? I suspect something is going on with that to cause the noise. Personally, I would change the rear tranny mount just because it needs it anyway.

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Jim

Change the tranny mount, it can't be mushy if you want to avoid driveline vibrations. It can also move around enough to cause the exhaust to bang.

Make sure the exhaust hanger at the rear of the transmission is installed correctly and is tightened, else the pipe will be able to thump on the floorpan. The rubber mounts on the tranny often turn to mush if you have oil leaks. This may be what happened to the tranny mount, too!

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

Well of course I have oil leaks! Since there is no exhaust mount in place at the rear of the transmission, and the exhaust pipe appears to be mere millimeters from the driveline shield I will hope this is the cause. Time to find the proper mount. I will also replace the transmission mount, since it's mush.
I'll report back when I get the parts...

I get a similar sound but it comes from somewhere from the front end end when I take corners really hard. I never noticed it coming from under my shifter but I usually don't drive with my hand on the shifter while hitting the corners hard.

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DJ


84 300D Turbodiesel 190K with 4 speed manual sold in 03/2012