Transmission failure or something else? - PeachParts Mercedes-Benz Forum

KJenkins · #1 09-09-2012, 12:09 AM

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?

Stretch · #2 09-09-2012, 02:51 AM

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.

sleepstar · #3 09-09-2012, 05:12 AM

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)

Stretch · #4 09-09-2012, 11:52 AM

Quote:

Originally Posted by sleepstar

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.

KJenkins · #5 09-10-2012, 08:43 PM

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?

Stretch · #6 09-11-2012, 03:06 AM

Quote:

Originally Posted by KJenkins

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?

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.

cho · #7 09-11-2012, 03:50 AM

Quote:

Originally Posted by KJenkins

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?

what about neutral mate?

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

cheers

.

Codifex Maximus · #8 09-11-2012, 04:24 AM

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.

kerry · #9 09-10-2012, 08:48 PM

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.