Andy,I am waiting for Tom to call me back.I am not sure if the 6 pinion fir without machining anything as it mat be a tad wider.

Tom just called. It is a drop in,,mine was machined for the torrington bearing.

Well I’m assuming you’re running a big block since you’re 727 shopping.... if you wanted to go fast you’d put the dump truck trans aside and do a 904. For what you’re doing put the steel drum in it and be done.

If i'm not mistaken, Andy is running a 470 in his Duster. A 904 would be difficult.

I have this if you are interested in an aluminum drum.

https://board.moparts.org/ubbthread...m-front-drum-piston-new.html#Post2807039

I looked over my stash of transmission cores and I have a '76 440 HP core as well as a '78 truck core. Both have the 4 pinion planet assembly as well as the wider front drum bushing. So I could swap my valve body and torque converter over to one of those cores then add a steel front drum, a bolt in sprag and some misc parts. That would probably work for what I'm doing with this trans.

From my understanding the bolt in sprag came about to be a case saver for when the sprag had slipped in the case. I have one in my transmission and when it's apart again I'll replace it with a super sprag.

wasn't the super sprag a ford C6 part originally ?
i remember reading something about that many years ago, or maybe it was something else.
it did have something to do with the C6 transmission.

I've race 727 for many years, I've had one sprague failure related to a driveline failure in 1st gear, it smashed all the springs and didn't hurt the case,rollers or other thing(CRS) the rollers and springs ride in
One of the local Mopar racers had a tranny built with a super spraque that failed after very little use

I had not paid attention to the splines before since I had never opened up a late model 727 but it turns out that two of my cores are from '78. So as I was taking things apart and comparing them I had a chance to look at the different pressure angles. The parts will fit together wrong so a person has to be careful if you're working with a mixed bag of parts.

I'm slowly developing a plan of attack. Since I have the parts on hand I think I'll build a second trans for the Duster using the best of the spare parts plus a mixture of aftermarket stuff. I'm going to go with a steel drum, an ultimate sprag, a 4.2 lever, a late model 5 gear steel front pinion, and then sprinkle in a few lightweight parts. I have a nice output shaft from the '78 truck trans as well as a really nice pump and front hub with the wide bushing.

Don't forget the front band apply strut, either buy a HD one or reinforce the factory.

A billet rear servo is a nice upgrade too.

I'm no transmission builder, so I'll just relay what my trans guy has told me and what's been done to my 727. It's held up to 1100+ hp in a nearly 2 ton car and doing fine.

5 pinion steel planetary...b/c the stock aluminum ones will strip the splines right out.
Bolt in super sprag.
A&A billet steel front drum.
Heavy duty front band strut...the stock ones bend.
TA pro tree transbrake and a deep cast aluminum pan.
As far as I know, everything else is pretty much stock. I know the input and output shafts are factory pieces.

The output shafts are not "weak". But they do fail. I had one break at a lot less power and no transbrake.
I did break a ring and pinion at some point in the years prior, that may have started the "crack".

I expect to break it in the near future, lol.

That looks like a classic fatigue failure since it started on an edge and is square across the face. A torsional failure would have more of a spiral shape. So you're probably correct, the shock of the reared end failure probably started a crack and then it just spread over time.

I have 5 or 6 core transmissions to pick parts from so I'm going thru them and grabbing the best parts from each. Most of them have good internals but a couple of them have toasted rear drums. Not sure why, but the rear bands are shot and the drums show signs of being overheated. So I'll probably toss those parts unless they are worth something as cores.

Check the valve body to case bolt threads. The bolt nearest the low reverse apply case passage can strip, cross leak and partially apply the band. I always check that location carefully.

I have had one of the aluminum drums with the steel sleeve for 15 years, and it looks like new every time I pull apart the trans, to check it out. As a matter of fact, my 2nd gear band has never failed, but on inspection, it sometimes looked dark with the stock drum, but since using the sleeved drum, I can still read the part number on the lining after 400 runs. I assume the stainless steel sleeve has a slightly different Coefficient of friction, and it works just right on the overlap of the shift.

That is a good tip. I've been chasing all the threads but I hadn't thought of paying special attention to that location. I've been pulling cores apart all day. Once you start doing a bunch of them they go pretty quick. I did notice that one of my cases had multiple threaded holes stripped out of it so someone really treated it rough. A couple of the other cores appear to be all original. It doesn't look like they have ever been apart. All the original little clips and brackets are still there and no sign of abuse anywhere.

I ended up putting A&A input/ output shafts in mine. They get a twist in them through the lube holes right before they break. If your lube holes not round, but look more oval, you are just a few hits away from losing it.