Big power & 727… input or output shaft the weak link?

I’ve got a 727 with all the normal heavy duty must haves, billet front drum, super sprag, steel front planet, billet servos and heavy struts and pump gears. I’ve got the trans out for a converter check and refresh, and just considering my remaining options for making it even stronger. Who has had a failure with an input shaft/hub, or an output shaft? Both look to be approaching $1000, so trying to decide if one or the other is more of a weak link. Also considering a rear roller kit.

Car is 3600 lbs with driver, leaving off a transbrake, running low 10’s, 60’s high 1.3x, and hopefully a little faster in the future.

Thanks all!

I only know one person who had an issue and it was the stock input hub that failed not the shaft. It was a 3,000 lb car that ran 8.80s-8.90s @ 150+. It was trans brake as well. But other than that, I have never heard of anyone having one fail. I know plenty who have ran high 8s-low 9s with heavy cars running stock input and output shaft. To include DVW.

I know if you were to do one or the other I’d say do the input and the hub. But I personally would do the roller components first. Just my own opinion.

I had an output shaft break, but not an input shaft.

3200 lb car & driver, 1.2x sixty foot, footbrake only

Dang Jim! That’s crazy.

I know mine has hardened input and output shaft and steel input hub. But for what he’s doing I wonder if it will be ok running 10s.

I know Rick Allison gives a general recommendation of 800hp and above 3,000lbs, he recommends the aftermarket shafts.

I’d run em! Personally I’ll think you’ll be fine.

My input and output shafts have 850+ passes. Though all are footbrake. I've broken 3 Dana pinion gears. Dizusters turbo car also ran stock shafts. Its broken rear axle pinion shafts, aftermarket steel drive shafts. But never either trans shaft, Both were over 850 hp. His weighed 3750, mine 3350. Both are 65 push button. Both have stripped stock front planet carriers. Both run stock pump gears.
Doug

I broke the "ears" off one set of stock 727 pump gears also. It happened during the Mopar weekend about 2008, during time trials.
With the help of a couple racers, we pulled the trans, took it apart, found some new pump gears at a vendor; and I made the first round of eliminations.

At its current power level, I think it’s ok, but being it’s turbo’d, it’s really easy to pickup another 100 horse. I did already break a set of stock pump gears, and I plan to do a drag and drive this year, so considering all upgrade options since it’s already out. I think my combo is potentially pretty hard on hard parts leaving on a bunch of boost with the transbrake, and stiff/short radials.

Rollerized rear support is a no brainer.

Dizusters ran 22lbs boost, trans brake, radials. 1.38/9.55@142 3750lbs full exhaust with the same M/T radials it ran on tthe street.
Doug

Interesting on the pump gears….. I lost a set in my old dump truck trans.

What kind of power were you making?

if you have it apart, look at the oil holes in both the input and output. when they’re getting ready to let loose, the oil holes will be oval instead of round. also check the input splines. if they aren’t straight, you’re at the limits of stock shafts.

Broke an O/P shaft, 9.60 / 9.70 1/4, mid 1.30's 60, car w/d was 3900lb, motor around 880hp at the time, footbrake only. We upgraded the I/P and O/P shaft while it was apart.
We have a 655 waiting for parts, to go in. We will run it behind that but before we fit N20 we are going to a TH400 derived box.

What does this remind me of?
"When should I stop "improving" my 8-3/4 and get a 9"?"

Rossler T400

Mid 9 sec small block. 3k weight. Leave 4500-5k off the brake. I’m now at low 9’s with an incredibly stock component 904…… but I used simple mopar math for that swap 904>727. 86 passes and ok so far. Good thing I don’t race much I guess.

As most probably know, there is a factory HP input shaft identified by a radial groove and (sometimes) a yellow paint daub, it's made of a better alloy steel. I believe the majority of input failures aren't the shaft itself but the hub at the rear clutch piston retainer.

[ [/quote]
I broke the "ears" off one set of stock 727 pump gears also. It happened during the Mopar weekend about 2008, during time trials.
With the help of a couple racers, we pulled the trans, took it apart, found some new pump gears at a vendor; and I made the first round of eliminations. [/quote]

I sheared the pump lugs/ears driving up the freeway , trans shop asked if I had any backfires . None , I think after 15 yrs use it was bad luck . But it filled the trans and cooler with metal . So I bought billet gears and a super sprag as upgrades . Footbrake low mid 10s . I do have a Griner vb .


Tex

A friend of mine was doing the burnout contest at carlisle one year and broke the output shaft at the end of the front planet splines. Car was stationary , 383 - 2bbl in a 69 Satellite wagon. What happened was the spiders in his single track 3.23 gear rear end seized on it's shaft shaft and in the split second it took for the spiders to break into pieces it shocked the driveline enough to break the output shaft. He was lucky because the rear sprag in the trans was also rolled, I don't know when that happened though as he didn't really beat on the car outside of that one burnout contest.

The Diesel trucks usually split the hub instead of breaking the shaft out of the hub.

They blow up too.

Spend it now or spend it later. Trans is out, it's hard to find 727 parts when everyone else is running .. insert GM trans here ....

My pumps gears broke on decel or engine shut off, after a usual pass. Fired the car back up at the ticket shack and it wouldn’t move.

I remember being under your Dart getting it out….lol
You helped me running a charger up to the lanes in later rounds

I broke a hub two years ago.
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And a band anchor last year.
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T400s fail too, just like every transmission can. Their biggest advantage is they have an aftermarket SFI certified case. So if they do have an internal failure, it will help contain the explosion. Being that the 727 we are discussing has a bolt in sprag and billet front drum, the main explosion risk is already addressed. He is simply asking about upgrading to hardened shafts. At his power level, and intended use, the stock shafts should be fine, but if he upgraded, he will never need to worry about it again.

Your hub broke due to the very common issue of hub to support interference.
Notice the shiny area just above the break.

Blast from the past. Eric on the back of my mini-bike, hauling a generator and charger to the staging lanes. From the date on this pic, it was 2005.
It looked so funny, someone took a picture and gave it to us later... LOL

Can you elaborate on this at all? Any specific cause, or just something to keep an eye out for? I imagine a thicker fiber washers would help push the hub back.

Edit - incorrect or broken #1 or 2 thrust, or mismatched parts.

Notice the earlier picture of a truly broken hub, it has a rough appearance. The second image is a smooth break, like it was machined in a lathe.

When first building the unit, place the empty support on the input assembly and see if there is interference.

I think I have a good 727 input shaft and hub in the archives. I’ll look. I certainly don’t need it.

Haha….I remember seeing that years ago. You guys bailed me out that night!

FWIW I still have the stock shafts in the 727 in my cuda. It's over 3800 lbs and ran mid 9s NA from 2006-2015 w/ no trouble. Been running 8s on nitrous ever since. I don't race it very often though.
From what others have experienced, it wouldn't surprise me if it snapped something the next time I ran it.

I do have a 727 input hub assy