350SD Transmission Problem - PeachParts Mercedes-Benz Forum

A Man · #1 12-14-2011, 08:27 PM

I'm new to MB ownership and the forum but not to mechanics. I've searched this forum and the internet as a whole, but I cannot find any mentions of the problem that I am experiencing as described below...

I have a 1991 Mercedes 350SD that I just purchased. The car did not move when placed in either drive or reverse, although you could feel it engage in Drive. Supposedly the brakes were dragging but I was unable to verify this prior to purchase. After purchase, while attempting to move it, I had the transmission dipstick removed and happen to notice a wisp of white smoke coming from the tube whenever I applied throttle. I checked the fluid level; it was low so I filled it to the appropriate level. I decided to go ahead and check the brakes but upon raising the rear wheels, they both turn freely with no rubbing sounds or any friction. The car now will move forward with throttle, even shifting up at least once and accelerates quite ferociously. It does have a second or so where it revs up, or flares, between shifting. It seems to roll freely when coasting in Drive and will roll downhill in neutral.

Reverse is a different story altogether. It doesn't move without revving up but it doesn't feel as if it slipping. The engine torques in its mounts, as if there is a load applied to the driveline, and if the throttle is applied rapidly, the right rear wheel breaks free. Steady throttle will produce steady rearward motion and shifting to neutral will allow the car to roll, but shifting back into Reverse will bring the car to a halt unless more throttle is applied.

Ideas?

ChiefRider · #2 12-14-2011, 09:19 PM

Look up transmission flares. Sounds to me like it's time for a rebuild.

Stretch · #3 12-15-2011, 03:21 AM

Welcome to the forum.

'Cos of the low oil I expect the worst. But before we start wringing our hands and start talking about rebuilds and swaps I would consider doing the basics.

Change the transmission oil

Change the filter

Warning - if the transmission is shot - then you are wasting a filter and an oil change.

Make sure you drain the torque converter as well as the transmission.

Look carefully at the fluid that comes out.

Does it have bits of paper like crud (very very small bits) in it?

Does it have metal in it?

Does it smell like it is burnt?

When you come to refilling the transmission measure the amount of oil you put in it.

showme · #4 12-19-2011, 08:51 PM

There's also the "magic reverse adjustment bolt"! I couldn't back up for months, and feared a rebuild. Then someone on the forum told me about that bolt that adjusts the reverse band. A ten minute fix, and it worked. It's since loosened up again one time over the years, but it only took me five minutes the second time. Try the easiest and cheapest way first.

compu_85 · #5 12-19-2011, 10:06 PM

Quote:

Originally Posted by showme

There's also the "magic reverse adjustment bolt"! I couldn't back up for months, and feared a rebuild. Then someone on the forum told me about that bolt that adjusts the reverse band. A ten minute fix, and it worked. It's since loosened up again one time over the years, but it only took me five minutes the second time. Try the easiest and cheapest way first.

Care to share more info? I didn't think there were any adjustments for reverse on the 722.3.

-J

showme · #6 12-19-2011, 10:52 PM

Sorry, I didn't notice the year on that. Just one more reason I like the 617's, though.

A Man · #7 12-20-2011, 08:42 PM

Ok, so there is NO adjustment for the reverse, correct?

I have since driven the car for about ten miles, whereupon the transmission was slipping and shifting very erratically. Now I don't know for certain that the transmission fluid was low, as I previously thought, because after the car was last started, the level was a half inch below the ADD mark and after driving it was a half inch above the FULL mark, with less than one quart of Trans-X having been added. While driving, transmission fluid was spraying out somewhere and smoking on the exhaust. Reverse slipped bad and then slammed into gear. At one point the car would not move in forward nor reverse, no matter how much throttle or shift lever's position. Additonally, the car wanted to pull when started in park and you could feel the pressure/tension release from the car once it was shut off.

I dropped the pan and I have metal shards and pieces of wire clips or springs in the bottom. Fluid was dark, dark brown... never have seen any this bad lol. Does anyone know the principles of hydraulic operation in this model of transmission? ie which clutches, bands, etc are engaged, applied, etc as the gears/speeds are selected/achieved. Does anyone have any ideas as to what would cause the above described problems?

I've rebuild many manual transmissions, transfer cases, and differentials but have not attempted an automatic transmission. Always a first time for everything. =D I'll gladly entertain options for a good used 722.361 as well. Does anyone have any leads on a good or rebuildable used one?

compu_85 · #8 12-20-2011, 10:01 PM

Quote:

Originally Posted by showme

Sorry, I didn't notice the year on that. Just one more reason I like the 617's, though.

Most 617 powered cars also have a 722.3.

-J

Stretch · #9 12-21-2011, 03:15 AM

Quote:

Originally Posted by A Man

Ok, so there is NO adjustment for the reverse, correct?

I have since driven the car for about ten miles, whereupon the transmission was slipping and shifting very erratically. Now I don't know for certain that the transmission fluid was low, as I previously thought, because after the car was last started, the level was a half inch below the ADD mark and after driving it was a half inch above the FULL mark, with less than one quart of Trans-X having been added. While driving, transmission fluid was spraying out somewhere and smoking on the exhaust. Reverse slipped bad and then slammed into gear. At one point the car would not move in forward nor reverse, no matter how much throttle or shift lever's position. Additonally, the car wanted to pull when started in park and you could feel the pressure/tension release from the car once it was shut off.

I dropped the pan and I have metal shards and pieces of wire clips or springs in the bottom. Fluid was dark, dark brown... never have seen any this bad lol. Does anyone know the principles of hydraulic operation in this model of transmission? ie which clutches, bands, etc are engaged, applied, etc as the gears/speeds are selected/achieved. Does anyone have any ideas as to what would cause the above described problems?

I've rebuild many manual transmissions, transfer cases, and differentials but have not attempted an automatic transmission. Always a first time for everything. =D I'll gladly entertain options for a good used 722.361 as well. Does anyone have any leads on a good or rebuildable used one?

If you are going to rebuild you need to get hold of a 722.3 / 722.4 ATSG manual - or a paper copy of the FSM. Sometimes you'll find copies of the ATSG manual on the internet => use google. I don't think the CD version of the English translation of the FSM has a transmission section. That is certainly the case for W123s - not sure about yours though...

Before you look into rebuilding however have a look at the cost of parts. Again the internet is your friend. Fastlane might be able to help.

Clutch packs are quite cheap so long as you only have to replace the linings - but as you've got metal shavings and clips in the oil pan - well the thrust plates are more expensive.

Brake bands are seriously expensive.

Gears / cogs / shafts => well you might as well buy a new car or another transmission(s) to get the parts you want...

Here's a PDF showing the bits you might need

http://www.ganzeboom.net/images1/ganzeboom/parts/Mercedes/722.3,%20722.4.pdf

To get an idea of the work involved have a look at this thread. It is for a DIFFERENT transmission than yours but it gives you an idea of setting up clearances / shims etc etc etc

722.118 Automatic transmission rebuild (Monster DIY)

There is also this thread running at the moment that shows some parts in the rear end of the 722.3

Help - stuck on road 722.3 no 3rd/4th gear

A Man · #10 05-08-2012, 02:20 PM

Hello All! Thanks for all of the advice and information. A forum member had a used transmission that was supposed to be rebuilt tho no records were ever found. I changed the fluid and filter, which showed no abnormal signs of wear. Hopefully she'll go another few hundred thousand miles before I have any problems.

ChiefRider · #11 05-08-2012, 04:25 PM

Good luck with it!