722.1 transmission jerks forward in park

[KAdams4458]

Okay... So my 300D is trying to kill me.

A long time ago while working on the car, I turned my back on it for a moment and heard a single soft bang while it was in park with the motor running. At the same time, I thought I saw the car move forward. I finally caught it doing it a few times, and attributed it to worn shifter bushings possibly not putting the car all the way in to park. The shifter bushings have since been replaced, and I thought all was well.

While tinkering under the hood the other day with the car in park and the engine running, I raised the idle a bit, and was presented with another bang sound, and the car jumped forward and bashed me in the shin! Argh! I thought I had solved that problem!

Now, with the parking brake set and the car in park, I can increase throttle and repeat the bang and forward jerk reliably. It never happens at the same RPM or at the same time, but it can be recreated fairly easily. I've spent a great deal of time searching the corners of the Internet for this symptom, and cannot find another documented instance.

I have confirmed that the transmission is completely entering park, and that there are no linkage problems. What is going on here? Has anyone heard of this?

[rs899]

so...after it bangs the car stops dead, right, after a few inches?

[KAdams4458]

Originally Posted by rs899

so...after it bangs the car stops dead, right, after a few inches?

It moves forward a few inches if it happens at idle, which is rare. If the engine is idling high via the control on the dash, the car will jump about half a foot forward, and then jerks to a stop violently as the parking pawl in the transmission catches. Of course, the engine speed drops a little while it is in motion.

The thing is, it will do this repeatedly. I can leave it in park and just blip the throttle a little and it will repeat the bang-scoot-stop routine over and over. The higher the throttle, the more often it will bang and jerk forward.

[rs899]

I'm not sure what is going on here. Once the parking pawl is engaged (the first time) it should not move forward any more.

Have you ever inspected the internal portions of the linkage- the linkage to valve body area under the oil pan?

[KAdams4458]

Originally Posted by rs899

I'm not sure what is going on here. Once the parking pawl is engaged (the first time) it should not move forward any more.

Have you ever inspected the internal portions of the linkage- the linkage to valve body area under the oil pan?

I've had the pan off for a filter change and did look over everything that was visible. Everything was pretty clean in there at the time, and I didn't see anything that seemed out of place. I don't have the technical specs for the 722.1 transmission, and books seem to be non-existent at this point, so I can't get technical with this thing.

[babymog]

Since reverse is next to park, not drive, I wouldn't think that this is a linkage problem but an internal problem.

[KAdams4458]

Originally Posted by babymog

Since reverse is next to park, not drive, I wouldn't think that this is a linkage problem but an internal problem.

That would seem to make sense, as it isn't jerking backwards.

Something is broken, huh?

And of course no one seems to have the technical literature for 722.1 transmissions. I have rebuilt more complex transmissions, but there's nothing I can do for this thing without the specs!

[rs899]

Yeah, sounds to me like a band maybe dragging or ...?

I have a 722.1xx ATSG manual home (it's really a pathetic manual). I'll see if it says anything.

I think you will have to rip it apart to fix this. Anything wrong with neutral ?

[KAdams4458]

Originally Posted by rs899

Yeah, sounds to me like a band maybe dragging or ...?

I have a 722.1xx ATSG manual home (it's really a pathetic manual). I'll see if it says anything.

I think you will have to rip it apart to fix this. Anything wrong with neutral ?

Neutral is great. In fact, the entire transmission is otherwise great. The shift points are too early due to linkage issues, but it shifts firm and slip/flare free between all gears.

Ah, the rare and NLA ATSG manual! I've actually rebuilt several transmissions using those, and I have to agree that they seem pretty pathetic. Mostly, it's because they're written for professionals, so they seem to leave out a lot of basic information and pictures. There's a little bit of a steep learning curve with those, but I have muddled my way through them well enough in the past, and every one of the transmissions I put together has performed perfectly.

I don't suppose you'd ever want to part with that manual, would you? I'd kill for one of my own right now.

[rs899]

Kill? Hmmm...lemme think. PM sent...

[KAdams4458]

Originally Posted by rs899

Kill? Hmmm...lemme think. PM sent...

Okay, maybe kill is too strong of a word.