Transmission failure or something else?
 

The car in question is my 1980 300sd with a 722.120 transmission. When I bought the car three years ago I noticed right away I had a jump shift condition. The car would go from 2nd straight to 4th. This was most noticable at 3000 or above rpms. I changed fluid using redline synthetic fluid, put in a new modulator in and set it at 41 psi. I also tweaked a few of the other vacuum adjustments. The condition continued but I decided just to live with it. There hasn't been a problem until friday when going to work. As I turned a corner, it refused to go from 4th gear into third. When I slowed down for another corner I heard a big clunk and then grinding. As I nursed the car toward a local parking lot the downshifts were horrible and the grinding continued. I pulled into the parking lot and checked the fluid which seemed ok. The grinding noise continued even with the car in park. I called a tow truck and had it towed to a independent mercedes shop. They told me they didn't think it was the transmission but a failed differential or carrier bearing. They were going pull the differential cover off at cost of $123.00 to see if that was the problem. That was the last I heard from them until monday. What do you guys think?

Well to check the differential you could remove the cover yourself for a lot less than 123 USD...

...but as you say that the grinding noise continued even in park I would say that it has something to do with a part that was moving - assuming that when you select park the vehicle is stationary (!) - the only parts that are still moving are engine and transmission related.

from what i've read the 4 bolt transmissions (like the .120) are very sturdy and probably wouldnt break down into grinding gears like what? the loud clunk could have very well come from the rear end and may be a completely separate issue from your stacked shifts (which my 722.120 does as well..very annoying)

If you have a clunking problem during shifting I reckon you'll end up with this problem

http://www.peachparts.com/shopforum/diesel-discussion/297960-722-118-transmission-problems-stripped-out-splines.html

in the end.

Having seen the growth of this problem in my transmission (722.118 vacuum only) I started this thread to try and find a solution. I didn't really get one in the end but here it is

http://www.peachparts.com/shopforum/diesel-discussion/299729-advice-reqd-shaft-spline-wear-measurements-possible-fix-722-118-transmission.html

I've more recently taken another 722.118 transmission to bits and found that this type of spline wear isn't limited to just the front planet gear set. You can see the same type of shimmy wear on the second planet gear too.

I urge you to solve this problem ASAP. Clunks are bad news for a 722.1 (well bad news for any transmission). If you want to see what's involved in a rebuild I've put loads of pictures in this thread

http://www.peachparts.com/shopforum/diesel-discussion/304903-722-118-automatic-transmission-rebuild-monster-diy.html

My advice is not to think that this is something you should learn to live with.

Got word from the shop today that is was definetely the diff. They took off the cover and found metal bits inside. I just happen to have a 2.88 diff from a 1985 300d. Anybody know if this would work in a 116 chassis?

Don't believe the shop. If the noise continues when the transmission is in Park, it can't be the differential. Someone doesn't know what they are doing or is trying to rip you off for unnecessary repairs. The early 300SD 116 transmission were known for stripping the ears on the front transmission pump. If that is the source of your noise, it would account for why the noise can be heard while in Park.

I think metal debris in a differential is quite common. Don't worry about that just yet unless there are great big chunks missing on the cogs.

You could change the differential to the 2.88 but it will mess up your speedo reading and alter the transmission shift points slightly... I think your car originally had a 3.07

...but if what you say about the noise happening in park is correct then you're not going to have a solution to your problem. Please confirm this.

what about neutral mate?

I can not comprehend how the clunking could
come in existence as everything is physically disconnected (considering the diff.)????


cheers

.

I'm inclined to agree with Army and Kerry. Grinding while in park is not going to be the differential as the gears in it are not turning.

I believe this is what Im also up against in an 83 300cd ,its clunking behavior was similiar .It drove on the hwy fine that day ,homewards bound I was stopping at a Parts store ,missed a gear while parking by accident (from forward to reverse at very low speed). After this nothing. Now Ive checked the linkage ,ok ,the pump seems to work fine since the cooler line was gushing fluid when opened up for pressure at line..Now its a question if this can be replaced while the trannies on the car?

Have you got a 722.1 in your '83 CD or is it a 722.3?

This thread (mostly) has 722.1 based information.

In any case - in almost every case - if you can measure transmission hydraulic pressures you have the best idea of what is going on / going wrong. If you don't / can't / won't measure hydraulic pressure =>

If you have a 722.3 I'd check the governor for damage before removing the transmission - but you are clutching at straws a bit here. You are better off making the effort of making some measurements.

If you have a 722.1 you probably need to remove the transmission if you have no forward or reverse motion. In this case I'd expect sheared splines - but really all I can do for you is guess! Again you are better off making some measurements.

noise with lever in park, engine started points to the main pump or the convertor itself, it may have grendaded itself internally.

Since Ive got the idea of the torque converter as a possible ,what would be a sure way of difining it at fault Z. Ill check the pressure Army ,it pumped out 2 qrts from the time I started it til shut down at the motor ,15-20 secs at most .I dont mean to hyjack but since this threads got the originators problem nixed I feel its more of a borrowed bus .

Why do you think that?

Apparently the only way to know for sure is to cut it open!

http://www.peachparts.com/shopforum/diesel-discussion/321655-torque-converter-ripoff.html

My input was because I have seen a first hand failure of a mitsu automatic, that failed from the convertor, At first it was a slightly clanging noise, which got worse then the car refused to move.

Transmission showed pressure at the oil cooler, When the mechanic opened it up, removed the convertor and stuck a spare input shaft into the snout, the one way clutch actually had sheared off, there were remains of a needle bearing too.