904 vs 727 sprag

Why is the 904 considered safer the the 727 as far as exploding the sprag? Lighter weight parts? Sprag is close to same size but drums are quite a difference. I want to put the 904 stuff in a 727 case and want to get input on whitch low drum to use (a little work on each to make work) . Rest is easy so far. Thanks

The stock 727 sprag is not fastened to the case very securely. The 904s are fastened with some heavy duty rivets from the factory. You can find aftermarket bolt-in 904 sprags but the 727 bolt-in are more common.

Lightweight parts mainly. The mass of the 727 drum coupled with how it's made is the problem , the 904 drum is a lot smaller. also the 904 sprag is pinned to the case, but it can still fail, it's just doesn't have the explosion risk of the front drum near as much ... I had to say that instead of it doesn't ...

you can put 904 parts in a 727 , it's already being done but it's pricey as I think there are some specialized parts .

The clutches and bands are smaller though so you'll have that issue to deal with.

Probably cheaper to put a 'glide in it ?

I was going to drill out the rivets and install bolts but that would work better, I'll pm you. There is a lip that holds the sprag that I need to machine off, it hits the back of drum, no big deal. Also have to make new anchor for band now, all doable.

I'm building a 69 cuda with a 383 to run in NHRA stock class, 904 guts should free up some hp and still pass tech. Most of the basic measurements are right on between the two trans but certain parts will have to be adapted.

Call ProTrans, they do it all the time.

I'm not that rich

You say that and you are building a car to run in NHRA STOCK ???

I looked at the protrans sight and the 727/904 starts at 1695 plus the valve body , that is a lot cheaper than I was expecting , it would probably be enough to handle the 383

The biggest hurdle is the combo at the front pump/reaction shaft support/input shaft. To gain any benefit you need to run the 904 drums and shells. It also requires a a new band anchor location due to the small drum diameter
Doug

I like doing it myself and have the only one but some have to buy everything then hope they got the latest greatest parts, you don't have to brake the bank to run fast or run under the index. I have zero cost in car so far other than labor and I'm not chasing a record.

Going through that now, I'll be doing some welding and machining this week to see how the cleances work out.