1979n 300D automatic popcorn machine *Tranny problem**
 

Hey gang,

I have been driving my 300D that i have fixed up thanks to a few on this board. Its been about 2 weeks now and i was just cruising down the highway at 60 and all of the sudden this horrible noise starts up. It sounds like someone dropped a nut inside the transmission bell-housing or something. It kinda like a continual pop of a popcorn machine. It lessens when you slow down. I check a few things then limped it home at 15-20 mph. At that speed there is no noise.

Now i a a decent mechanic, but have not come across this issue before, especially on a foreign car. The transmission still shifts in and out of gear fine, and the engine seems to run the same....so i am a bit miffed as to what happened. Seems like something should be showing signs of being broken other than a noise at speeds above 20 MPH. I feel the tranny tunnel and it seems like its coming from the tranny area, but ???

So has anyone encountered this oddity before ? Your help is much appreciated as i done quite know where to start looking.

Check the condition of your flex disc - it's the rubber bit that connects the transmission to the driveshaft. If shot, it could be whipping the tunnel as you go along, and that's dangerously close to massive failure (which can cause the car to be a total loss, and you too). If that's not it, you may need to drop the trans pan if you're sure it's the trans.

x2 on the flex disc. It could also be the plate that joins the torque converter to the flywheel. These have been known to crack and make noise. Pull the cover at the bottom of the bell housing and take a look at the condition of the bolts and the plate.

Check the central bearing of the driveshaft too.

anytime i've had a noise like that caused by something internal in the trans it lasted maybe a few blocks before going no further.

well looking under it today i saw that the carrier bearing assembly thingy is torn loose and the rubber sheath boot it torn where it covers the splines and hitting the body (fresh looking rubbing marks). So i think the bearing failed and its the noise of it bouncing around combined with the sheath smacking the body. The rubber (1" thick) connector "joint" seems solid.

So my plan is to poof some primer in there and cover the rubbing marks. Go for a drive until the noise returns. Then check for the rubbing (to confirm its fresh rubbing). Price out a carrier bearing assembly or just bearing, etc and most likely replace that.

I will post up my finding. Thanks for the tips on where to start looking.

Fleckster

did i get the right bearing?
 

So i ordered a bearing #106CC in the BCA brand and got this tiny thing. I think i need the whole assembley as the rubber surrounding was all torn out. Anyone have a part number?

You mean one like this?

PeachParts FastLane Mercedes Parts Store

Yup ordered that and the dust boot as well.

Got the parts lightning fast. Got the drive line and bearing assembly out. I just disconnected it at the read and then undid the carrier. Its out but i hope the splined section is not "Phased" as it doesn't seem to have a key or special spline pattern to realign it. I am inspecting it and the u-joint has "detentes" in it as it bends. I really don't think that joint flexes much, but i am not about to pull it out and not replace it if it needs it.

Is the "detentes" special to MB or? On standard u-joints it would be a sign of bridling or wear. Also i see the u-joints are swagged in there. I don't see an issue getting it out, but do you just re-swage the new one in or is there a newer design with some sort of clip. Well off to search the forum and web for info. If anyone wants to shorten up the process please chime in. Thanks

John

Oh i found all the info, crazy how special these MB rigs are compared to american rigs. Lots of good info on this forum

well i pressed the new bearing and carrier mount on, said screw the u-joint its not that bad, and it runs down the road with no noticable vibration i can tell. Hope it stays that way, but in another 50,000 i can see doing the u-joints. Thanks guys, and thats peachparts for the mounts

Fleckster