ChevyShelly, make sure you get a slip-yoke for your TH400 tranny as the ones from a TH350 will not fit.
Myron, I have more than enough knowledge to get me in trouble
I would say that after you torque the yoke nut, if you can pull the rear cover and look at the gear teeth contact patch(people who do this use a lead paint to do this)and it is within acceptable limits it should be fine.(you can look things up at the local library if you do not have books).
If things are not set up correctly, the gears can destroy themselves in a short time or it could go for a while and get worse with time(couple of weeks or a month or so).
There are critical measurements/settings such as pinion depth(set by using shims and the crush sleve on some rear-ends),then there is the bearing pre-load set by the torque on the pinion nut. Then there is the back-lash which is set either by shims (on some) or adjusters on either side of the two carrier bearing caps (which look like main-bearing caps in an engine).Then the carrier bearing caps need to be torqued to proper settings. After all that, the gear teeth contact area needs to be checked again to make sure it is in its proper spot so it will give you a long trouble free life
Read up on it a bit so you will have a getter understanding. It is not really hard to do,one just needs the proper tools and a lot of patience.
