Probably jump in
I only have twd and for the fwd application, all I read indicates that the getrag is a few teeth shy of a real tiger. More in the range of a gummy bear.
But, I have had extraordinary service on mine. So I tend to think that if you pet it, it will go a bit longer. If there are noises that are developing, you may have real trouble coming. Drain the oil and open the side covers. The condition of the oil and then inspection of the gears should give you some indication of what to expect in the near term. The gears should be mirror bright. If you have scuffed one, (usually third or od) that could account for the heat. You can see the teeth of the input shaft and easily see the third gear teeth on the mainshaft and countershaft. OD is way in the back and harder to tell much about.
Bearings that have lost preload will allow the gears to run out of proper mesh and will cause heat as well. To check for preload, or loss of preload, use a soft bar and try to move the countershaft (layshaft) forward and back, engine stopped of course. There should be NO noticeably movement.
Of the trannys I have gone into, the ones that had complete failure did so because of the front countershaft bearing or the pocket bearing between the input and main shaft. If there is movement on the countershaft, you don't have long to drive that transmission. And best to not drive it at all. Bearings are not all that expensive and replacement is doable by any fairly good mechanic. The various parts are too heavy to take down without a transmission jack. EZGZ has a good writeup on the process.
You mention loss of oil. You may have already run the transmission low long enough that you have scuffed the gears to the point that there isn't much chance to continue to run it. They get to a point that they will just boil the oil right back out. Hope not however.
Now you mention that you can't keep a finger on the transmission. Well I can't on mine either but it carried me to Vancouver Island and back (to Georgia 6400 miles total) and it has some slight noise as well but it also has 425k miles.
I have a 4500 that was run low (not by me) and I can tell you that they won't hold up to that either.
Check yours out and do the bearings if you have slack. Carolina Cummins just did his and could give you some input as well. If you don't use the fwd to hard, you should be able to go a good while more. Save your money and go to the 4500 as soon as you can but don't run the getrag to destruction. It is worth a good deal more complete and running than busted. Good luck with whatever you find.
Andy Mikonis is the founder of the Getrag preservation society and should have some helpful comments as well. I would venture to say that anyone who is running their personal rebuild is a member in good standing.
BillMaine is running a 4500 that he and his sons installed in their home shop. He is fwd as well and is at last report very pleased.
Last, and I think I stand alone on this, I run 85aw and have since about 125k miles. So I have 300k miles on 85aw. It does not shift as original till it warms up but I can adjust for that. It has ordinary brass syncro rings and I understand that the syncro rings in the 4500 will deteriorate if you don't use syntorque 50 dollar a gallon lube. Mylar,kevlar or something of the sort.
So I will stick with the Getrag and 85aw. That is not a recomendation just a comment.
1stgen4evr
James
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