722.120 Trans Losing Reverse - PeachParts Mercedes-Benz Forum

TdTno499 · #1 10-22-2007, 05:21 PM

Reverse has been taking a long time to get moving for a while now. Better when warmed up. Fine for parallel parking, but no longer when it's uphill! Anybody with experience on this transmission that can tell me if this is fatal?
I've heard that an internal pressure leak could be causing a band to not engage fully, possibly curable w/out dropping the unit. Also heard that in the later boxes, this was due to deterioration of the reverse clutches, and is fatal. If clutches are the problem, I'll see abundant clutch material in the pan when I drop it.
Near Philadelphia if anybody has one of these, known to be good. (used in 116-bodied 300SDs)

PETE

rrgrassi · #2 10-22-2007, 05:24 PM

Sometimes it can be fixed by adjusting the B-2 band, I have been told. I have the 722.3xx tranny.

rs899 · #3 10-23-2007, 01:31 PM

Reverse has an adjustment on the 722.1xx. It is a locknut type stud on the passenger side of the case in front above the pan. I would see if the whole thing backed out (like it did on the 77 240D I bought for cheap "without" reverse), or can be adjusted in a half turn at a time.

TdTno499 · #4 10-24-2007, 11:59 PM

Thanks, Admiral, that's the kind of answer I was hoping to hear!
Is this a band adjustment? When you say "in front", does this mean "facing forward?

PETE

rs899 · #5 10-25-2007, 07:29 AM

not sure what you mean by "facing forward"?

passenger side of the case, above the pan.

As you are looking at that side of the case, the bolt is toward the right, closer to the "thick" end of the tranny. I believe it may be a four-sided stud with a six sided locknut , but I don't recall the details.

TdTno499 · #6 10-26-2007, 05:43 PM

Still anxious to check this out...if it ever stops raining here.
Haven't heard that I can test the working pressure externally on this or what the spec is for that yet.

PETE

pimpernell · #7 10-27-2007, 09:59 AM

Had the same thing happen to my prior 240D in Florida, my reverse went south. Took it to an independent mechanic, who put it up on a lift, and said that the adjustment nut had backed out for the reverse gear. Made a minor adjustment, locked it down, and presto, reverse was back in action. This guy had the "nerve" to charge me $26.00 for his time and labor. Needless to say, this did not sit well with me, and I did pay him what I considered a "fair" price above what he was asking for. Good luck with your car....

rs899 · #8 10-27-2007, 12:32 PM

...so you would have been happier if the mechanic had told you it needed a rebuild.

Jeez $26 and honesty......I mean his time, expertise and tools (rack) are worth something....

TdTno499 · #9 10-31-2007, 10:15 AM

Not having a lift, I used the jack method last night to have a look for this adjuster, and didn't see a likely candidate. Above the pan on the passenger side is what looks like a pressure check valve of some sort. It comes out of the case at about a 45 degree angle, has a large, perhaps 27mm-headed bolt capping the end, and an electrical connection on the side.
I am assuming this is not what I'm looking for. Does anybody know what this is?
Plan on getting the car down to my garage in the next couple of days to get it safely jacked up a bit higher to have a better look.
Any more clues are appreciated!

PETE

sedecrem · #10 10-31-2007, 01:13 PM

TdTno499

I think the item you are looking at is the kickdown solenoid. Just above it is the band adjusting stud. You can actually see it from the engine bay looking down on the right(pasenger) side of the transmission. At least that is where it is on my '82 240D. There is a threaded stud with a 17mm locknut. On mine it looked like the tip of the stud sheared off. However, just by tightening in the lock nut a couple of turns with a socket I got reverse to work where before there was no engagement at all.

The guy I bought it from sold the car because a Mercedes mechanic told him it would be $2800 to rebuild the transmission without even looking at the car. Also the brakes were trashed. It needs front rotors and calipers. However the body is very straight with no rust and the interior is about 90%-95%. Has 210k miles on it and the engine seems to run well. Only real negative about the car is that someone threw a cheap paint job on it that is fading/peeling off in places. But I only paid $1,000 for it so I figure I can afford a decent paint job.

rs899 · #11 10-31-2007, 03:32 PM

you won't be able to see it from topside on a W116 300SD with all the clutter.
In fact, you may have to feel for it rather than look for it. I would guess it is about an inch or two back from where the bellhousing meets the gearbox portion and below the centerline of the gearbox section (that would put it in the middle of the front band at the bottom of the "omega" shape of that band).

that would make it 85 and 86 on this picture- if it helps any:

http://www.jie.com/Mercedes/4_bolt_pan.htm

TdTno499 · #12 10-31-2007, 07:22 PM

The diagram is great. The adjuster was hidden well above the solenoid, and behind the wire, the exhaust, and 27 years of grime. And YES, that S.O.B. was loose! Managed to turn it "finger-tight" with the screwdriver I was using to clean off the schmutz, then struggled for about an hour to try to get a wrench on it. I managed to get a stubby 19 to span two flats, but interference prevents any turning. This will need to be addressed when I can get it on a lift. That solenoid may have to be removed for access.
Bottom line is; she SNAPPED into reverse when I went to pull out! Wish I would have explored this a long time ago when it was just starting to fade a little...
Now, the question is, what is the proper adjustment? the center bolt has a "nipple" of sorts in the center, rather than a screwdriver slot, so it doesn't look like an adjustable bolt. I wonder what the official procedure calls for. Any tranny guys out there that have the book on this unit?
Thank You Admiral, Pimpernel, and sedecrem, I had a feeling that this was not a fatal condition, but info on transmissions is hard to come by.
By the way, I didn't want to muddy the water before, but this box came installed on my '80 TD Turbo, not a 300SD. They weren't building Turbos for US market yet, so mine got the SD powerplant and driveline. It's an early model (no. 499), and even the motor is #575. Gray Mkt. w/ Euro bumpers. They changed the lights and speedo cluster back then when the original owner brought it back.

PETE

rs899 · #13 11-01-2007, 06:52 AM

Glad to be of service.

I have the almost useless ATSG 722.1xx rebuild manual at home and I will try to remember to look up what it says about adjustment. I know what you mean about the lack of information about transmissions. Most people have no concept of how they work, and no interest in rebuilding them. A virtual bonanza for the repair shops

Sounds like you have an interesting ride.....

Rick

TdTno499 · #14 11-01-2007, 11:59 PM

Would have been happy to pay the $26 that Pimpernel's wrench wanted to charge, but I don't know any transmission guys that I trust that much to even ask.
If it's not much trouble, could you see if there is an adjustment for the other band while you're looking. As long as I'm doing tranny care, I should check it. Reverse is working well, and maybe I'm just not used to it any more, but it seems "fast" at idle...hard to explain. I'll have to live with it a bit, don't drive around in reverse much around here.
Might even do the pan gasket and filter anyway, since I've been sitting on the parts for some time now. See about that.

PETE

rs899 · #15 11-02-2007, 10:18 AM

Sorry- there are no other band adjustments. The others are adjusted via replaceable little studs of varying lengths from inside the case. I did a quick look at the book this morning before work and I didn't find the adjustment in there. I think it says something about it, but I will need to study it a bit more.

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