We've broken an O/P shaft, at the time the car was making around 880hp and weighed 3950ish (w/d). We had just put a new set of slicks on. We upgraded both the i/p and o/p shafts while it was apart. We got round the speedo issue going to a Dakota Dig dash with a GPS speedo.

Yikes! Killed the sprag, too!

About gear ratios, doesn’t the Pro-Flight guys (A1?) make many different gear sets for a 727

Thats the 2nd shaft I've ever actualy seen that broke. The other was years ago in Dan Dye's blown alcohol modified street Cuda.
Doug

Monte Smith broke one years ago, running a load of nitrous and over 1,000 hp. That kind of a combo would provide the shock and or torque load strong enough to kill stock shafts. So depending on your combo, like mine, under 1,000 hp should live a while.

Thanks Tig, that is helpful and definitely indicates at 900 hp and 4000 pounds the stock shafts are questionable.

I think the other option would be to add a gear vendors, since it moves the speedo gear to after the 727 output shaft, but then it's adding even more weight to the car.

Yours, Chip's, Tony, Al and Doug's experiences are promising. I should be around the 950 hp mark (but unfortunately at 4300 pounds...) in my car once the 540 is done, and am worried about the longetivity of any 727. Figure it needs the parts Doug has listed in it for sure and I'll also move to a LBA valve body, and debating the billet input and output shafts as well. Bummer with the billet output shaft though, it doesn't have the speedo gear provision and I'd hate to lose the speedo on a mostly street car.

Stock TH400 can handle some power if they are properly prepped but they do have there weaknesses with stock componentry like anything else. Where one may consider them better is that they have a stack-shift strategy where on every shift a new clutch pack is engage without having to disengage or have a timed shift. That makes the shift quality superior over a TF727/904 that always have a timed shift and no matter what, you have to deal with some degree of overlap. This is of course no correlation to overall strength.

Just to note some of the mechanical differences. The TF727 has bigger clutches and can run under significantly lower pressures than a TH400. The stock TH400 intermediate sprag or roller clutch(depending on model year and how it was equipped) is a failure point, even with the better 32 element sprag. The TH400 intermediate band is useless in all performance applications and is often removed defeating any compression braking in 2nd. TH400 and TH727 low reveres band are probably about the same capacity based on surface area,

AG.

I don't buy that they are faster because of the shift sequence, 727 just apply the 2nd gear band to go from 1st to 2nd and it is just a matter of how fast (hard) you want it to shift (unless your running low band apply), good 727s can shift 2nd to 3rd in a matter of milliseconds so even if a TH400 did it slightly faster your not going to be able to tell the difference from that one single shift on a time slip.

AS said its more the availability of aftermarket parts. There are many parts out there to make a 727 live at that power level. With a TH400 there are just more options, kinda like a BBC vs a BBM. Both capable of making power one just has many more options. The one thing you cannot get for a 727 is an SFI case, to me that s a big deal. FWIW my 64 Savoy has a 727 built by Joels on Joy, it makes north of 1000hp. From what I've been told torque is the larger issue with a TF than raw HP. The Vette has an A1 built 727 and it makes a tick over 1100hp. They are both very nice pieces but are not a budget friendly one.