What are the differences in 24 spline input shafts? I have some the are not in hubs and not if they can be used from say 67 to 73 hubs .I thought I read somewhere the lubrication circuits could be different.

'67-'73 input shafts are interchangeable. HD shafts will have groove or yellow paint or both.

Thank you John

How appropriate, I am pulling apart a neglected 68 transmission, but internal parts seem to be a mismatch of years. The pump looked like an original 68 style with reaction support having 24series casting number.

But the input shaft / rear clutch when disassembled had metal in the pilot hole that the output shaft connects too. Even to the point of the oiling hole solidly plugged. After closer examination the oiling hole on the shaft side is not in the typical bearing surface, it is closer to hub and partially under it. I will try to post picture later. Is this a 74 up shaft? Why not compatible. There was a metal thrust washer on the output shaft, but looking at the nose of the output shaft, it looks like it was hit with a ball peen hammer. What could be wrong that the input and output shaft are slapping each other and galling the metal which plugged the lubrication hole? Any thoughts. The clutches and bands are in like new condition. Someone but a combo together and it didn't work?

The oil hole partially hidden by the hub is '74-later. If there is a thrust washer between the input and output shafts, it's not common for the output pilot shaft to peen over...this usually occurs when the fiber washer breaks and allows the pilot to travel too deep into the input. Does your front clutch piston retainer take the 3-tab thrust washer like in the pic below? If so, two thrust washers were used, one thicker one with three tabs and a thinner steel one.

No three tab thrust washer as shown. Maybe the converter failed on this. There was metal chip also in output shaft, the shaft was partially seized on the rear sprag support, and the rear drum as well. additionally the gear that is clutched in the rear sprag was driven rear into the support and grooved the case.
Here are pictures. There was no fiber thrust washer for output shaft pilot, just the metal one. The fiber washers for the clutches were larger. While this was a 68 case and pump. The clutch have cast 76 pistons. So I am assuming the drums are 76ish too. Can that be determined, does it matter?

More pictures.

After more research looks like the pump reaction shaft is 74 later despite early casting number.

The casting number didn't change over the years, the machining is what makes the difference. Easiest way to spot the '74-later support is the absence of the front clutch lube hole. (see pic)

BTW, the rear clutch piston is wrong for the Belleville, the later Belleville needs a thicker piston with the casting number 3743623.

What is the hole on the input shaft with the red arrow for?

Ok, need to check it. I did think it had a 37... casting number. Appreciate all your help and expertise on this. I just finished going through Tom Hands book, but it does not get into all the details of the different parts and what is compatible and what is not.

So what can cause the output shaft to move aft and damage the case at the sprag? This trans had some failure that induced a lot of metal and blocked oil ports in both shafts. The rear reverse drum galled the output shaft support and the shaft scored the inside. The sprag inner clutch ring was being driven into the case and scored it pretty bad. What is the output shaft thrust component? You have the cast iron pump and a thrust washer for forward thrust, but it seems like nothing prevents aft thrust from being taken by the case itself. Is that correct?

The hole in the input is the new (for '74) source of front clutch lube. It replaces the hole in the support.

The output shaft is held in place by the ball bearing in the tail but the shaft moving aft isn't the cause of the sprag race galling the case, the race and drum are free to float for/aft. I believe this damage is caused by lack of lube. BTW, there is a kit to repair that case damage.

https://www.sonnax.com/parts/1828-case-repair-bearing

The input shaft is free to float for/aft within the confines of its thrust washers between the clutch drums; the only way for the output pilot shaft to bottom in the input shaft bore is if the thrust washer(s) between the input and output shafts are missing.

Thanks! Does that mean you can't use the pre-74 input shaft with a 74-up support? The reason I ask is that when I built my pre-74 727, I replaced the the stator support with a later one in order to run an aftermarket drum. Does that combo not work? The trans hasn't run yet.

So that rear clutch piston is correct casting number 623. Lot of wear on these parts, loss of oil has done some damage.

You can if you drill the hole in the support; I use a long #40 bit. I've seen these parts mismatched and it doesn't seem to cause any harm; the factory is a little conservative when it comes to parts interchange.