Our 1911 seems to have a little too much wear compared to our other T's. When you come to a stop, it will rock front to back a couple of times. Is there a way to determine how much is too much wear? I was tinking of jacking up the rear end, having someone step on the foot brake, and moving a back wheel to test how much wear is in drive line. Am I on the right track with this and how many inches of play are acceptable?
Not exactly. Jack up the left rear wheel, pull it back and forth (toward the center of the car and away from the center of the car). If it moves in and out, you probably have worn out babbitt thrust bearings on the ring and pinion and too much ring & pinion end play.
I'm sure others with more knowledge than I have will post here and give you some more pointers.
And, if the axle moves in and out indicating worn thrust washers, it's best not to drive the car until it's fixed. I can post a picture if you want to see why.
There are several factors that can lead to the condition you describe. The thrust washer issue, above, is certianly a possibility and should be inspected for. Also, wear in your universal joint, ring & pinion wear and even loose rivets where the transmission output shaft attaches to the driving plate can also be culprits. Also, look for excessive fore & aft play in the torque tube ball & socket. Loose wheels and worn keys/keyways can do it too. Most likely, it's not just one thing, but the additive affects of many. Some of the above are just a nuisance, some are potentially dangerous.
Worn or disintegrated thrust washers are evidenced by in and out play, although if the ring gear moves away from the pinion, the driver's side thrust washer may be the blame. What you describe is common in most all Ts, some more than others. As Jerry says its a combination of slop in the drivetrain from the ujoint on back, not the least of which is the play between the differential spider gears and the axel gears.
If, as you say, it is more noticeable than your other cars, I'd consider opening it up to make sure everything is good. It really depends on a couple things. How much rocking is going on and whether you get in and out play at the axels. If the latter, you have either a thrust washer problem or an axel gear is loose on the axel. Just going by what my Ts do, if the wheel rocks 12" at the circumference, I'd investigate.
One more thing comes to mind. By jacking one wheel off the ground while the other is resting on the ground will double the effect considering much of the play you are experiencing is from the spider/axel gear lash. A 12" rock might be expected if you were to jack up one wheel.
Update, I just checked two cars I own that are on jack stands and the rock is less than 2" on one and about 4" on the other. By that standard 12" rock would be way too much.