What makes a TH400 stronger than a 727?

Everyone says to "upgrade" to a TH400 or PG once you get over 1000 HP. Other than the obvious things like the availability of aftermarket SFI cases like the Reid, what makes the GM units better?

Excellent ?....i was just thing the same I would like to think that a 727 will live with 1000 HP but I'm no expert.
Maybe some of the trans gruels will chime in, I'll keep an eye on this thread.

Did a search and found this old thread here it should give you an ideal
https://board.moparts.org/ubbthreads/ubbthreads.php/topics/578024/2.html

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.

no expert but, my opinion is your question has the answer in it. lack of aftermarket support and parts. my closest friend has a 727 in a 1500hp procharged duster and works great. no issue for 3 years. the lack of gear ratios is a draw back also. if we could get billet shafts and sfi cases etc. i think the 727 would be the better trans. my 2 cents

I have no comment really on the strength aspect, just always heard they'll handle more power reliably.
The biggest thing I see is gear ratios. Once you make 1,000+ HP (especially on a small tire), you need a lot less starting line ratio. Not many options w/ a 727.

The aftermarket makes it stronger and a better option. The SFI Case is a HUGE bonus.

And the converters are better. There is more room in the chevy style bellhousing for a larger/thicker converter. High hp applications can utilize that.

In my experience up to about 900 hp has been good.The aluminum drum won't come apart. Parts I think are a must at higher power level? A good front drum, steel front planet, good quality valve body, 518 deep pan with a long enough extention to get the filter at the bottom, reinforced band strut, 3.8 or 4.2 lever, solid rod front servo or shimmed solid late servo, lube hole for the sprag. Just took mine down for service as there was a few pieces of low roller clutch spring in the pan at about 250 runs. It does not use no low band apply. It shakes the tires once in awhile, so regular maintenance. New inner race, spring set, and a filter. Ready to go back in service. The band has been in the trans for over 700 passes, the clutches for over 250. In fact the old front clutch frictions and steels were moved to the rear clutch last time around. No metal on the filter either. If you need less 1st gear ratio or a aftermarket case at a higher power level? Then it's time for a 400.
Doug

In stock form I would say a TF727 and a Turbo 400 are about equal - however the aftermarket support for a T400 is a lot more robust than you can get for a TF727 - If You go with an SFI T400 case and all the good billet parts for a T400 a TF727 can not compete at the high HP levels.

Its not a matter of whats stronger, its a matter of whats better supported by the aftermarket. TH400 is like the 9" rear, there are tons of stuff availible , from case to gear sets. When i switched to a t400 the converter was literally 400.00 cheaper. Seriously i priced the same converter for a t400 and a 727,
Best move i ever made becasue there is so many parts availible and the technology of so many people using a t400 now trickles down

I know I know its hard for people to accept but who cares whats stronger, i care about what WORKS the best

Brad Watt (A93demon) still runs a 727 in his demon. He has been in the 4's at 3200? lbs so i would say he making over 1000. He does leave in second gear so that solves the gear issue ,
727 is just as strong as a th400 , but the aftermarket for the th400 is way better, thats really all it is

Totally agree! I tire of the "KEeP iT aLl MopAr" crowd when most of their engine is filled with aftermarket parts anyway!

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.

I know 3 mopar racers that switched to TH400's and improved et. I don't know if this was due to a better converter or if the TH400 is more efficient? The best improvement in one of those cars was almost 2 tenths, motor and rear was untouched, all mid to low 9 sec cars.
Anyone else had the same result ?

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.

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.






Very surprise how was the fit

Since the subject is "stronger", another thing not often mentioned is the case. The TH400 has a "wrap around" case where the 727 is wide open at the bottom...this makes the 727 case more susceptible to flexing under torque and this can affect the internal component's alignment.

how much, if any, does using a deep cast pan on a 727 affect the lower strength of the case ?

Well everythitn gin this car is tight.,Its a shorty version. FWIW we had a TH210(TH400) in the car before the Proflite. It is much quicker with the Proflite hands down not even close. My guess is if someone picked up with a 400 in a non power adder deal they did not have a good work 727 with the right parts for the combo.....

We also ran Dizusters turbo car (3575) with a brake and radials. Pretty much the same set up. Both cars have stock 65 output shafts, And 71-76 input shafts. Neither car ever hurt one. Dizusters snaped a pinion shaft and a Dyno -Tech drive shaft yoke. I've cracked 3 Dana pinions. Both cars have the shafts they were built with.
Doug

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.

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

Hope this isn’t too far off topic but a lot of guys run 904s in high horsepower cars, are parts more available for them than 727s? I know they can be run behind a big block but I think the adapters to do that are pricey but if money is no object is it a viable option?

Yikes! Killed the sprag, too!

It did !! You can see the weak point on the shaft was the oil feed.
I also heard you can run 904 internals in a 727 case and that they are maintenance intensive, the reason to do it is likely to be it takes less H/P to run. A lot of the stock eliminator / super stock folk run them I'm told. A and A also do different ratios for the 727 but only 4 or 5, I was looking at a 2.28 1st gear set but it was cheaper to change the ratio in the rear (Dana 60). Try as I may, I could not find a 3.73 Ratio for a Dana in a pro gear and ended up using a street gear but that's another story.

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.

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

Yes Pro-Trans has many different ratios for 727s and 904s.

Unfortunately their website is way out of date (shows them still in CA) and has no information.

Current contact information on Facebook, I guess you would have to call or email them for a list.

4256 Gholson Road, Waco, TX, United States, Texas

(254) 749-5689

protrans@msn.com

Yes there are many rations available for the 727/904 as well as the Th400. We have three different sets for the Vette, two transmissions and one extra gear set. Never hurt one ever, just different rations for differing weather conditions really, also why we have a number of stators and rear gears as well.

Here is a link to the available gearsets for a TF. My 64 has a B-3 set 2.28/1.40/1.00
http://www.protransracing.com/images/PRO%20TRANS%20RATIO%20CHART.pdf

I've got a 904 that Keith Long at 727 specialist built for me. It's all roller ized., billet in and output shafts. 2.10 first gear. I really like it . And no problems so far. Best et 9.33 @ 141 mph. My car is two tenths quicker in the 1/4 over the 727 and almost one tenth quicker than with a power glide. But my car only makes 680 hp.

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.

The 655 motor we are going to install is well into 4 figures and peak tq was almost 970lb/ft n/a. We are going to run it n/a and hopefully get it into the 8's. Then the plan to put a dual fogger on it, so a 9" type rear and a TH400 derived 'box are to be installed before we press the button. I'd like to keep it all mopar but I can't see either the 727 or the Dana 60 living with it all

Anyone here ever weigh a gear vendors unit?



Also what makes a Turbo 400 more reliable than the 727 i think someone mention the bell housing being smaller than the 727.Are those shafts made of some sort of different material or what?

Nick...my 727 is still living, but I don't race my car very often. I killed a sprag a few years ago that took out the case. It let go mid wheelie in 1st gear, crunched the oil pan, but drove back in the trailer.
It still has stock shafts in it, but it wouldn't surprise me if it broke one on its next pass.
I have a 5 pinion steel planet, billet steel drum, non LBA Turbo Action transbrake, deep cast aluminum pan, etc. Nothing real fancy.
My car will go 8.60s, but my best 60' is a 1.30 (may not have tripped the beam w/ the front tire?).There's a fine line b/t wheel spin and wheel stand w/ my combo.


Scott Cheek still has a 727 in his blue '69 Dart. Wedge w/ one fogger. He's been 1.15 sixty foot I believe.

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. The engine can be spaced out for a bigger converter, there are some gear ratios available for the 727 so unless you really really need a ratio that is not available then the TH400 isn't really any faster. The only reason I see is if you absolutely need the SFI case and guys with typical 700 HP or less don't need it.

I slept at a holiday in once upon a time so I definitely know what I am talking about.

It's not all about the quickness of the shift, the 727's release/apply sequence requires some overlap to prevent RPM flareup...overlap produces more component wear than simply progressively applying clutches.

Not sure it's relevant to this conversation, but the Lenco 4sp trans uses some TH-400 internal parts

700 hp or less has no place in this conversation. You don't need anything other than a slightly beefed up 727 for that power level. Traction shouldn't be an issue no matter what tire or suspension you have for only 700 hp.

You are correct it's the torque that is the issue vs. the HP level. That said the diesel market is building 47/48RE's that handle over 2000 lb/ft of torque so it's doable , an SFI case would be nice though.

Thank you, someone finally gets it.

I built a number of them 20 some years ago for 500 - 650 HP trucks , that's over 1000 lb/ft , this was before they had hardened output shafts for the OD units which I twisted off doing a brake stand once in my own truck

That's helpful too, thanks Chip! I'm heavier but am definitely going to be making less power and torque than you.

Do you normally run your car at the track on slicks or the radials?

And one other question, is the LBA stronger for situations like those, or would the sprag have failed anyway even with a LBA valve body?

Yes LBA is the safest way to go to protect the sprag. Period. All the load is on that sprag in first gear. No matter if you have a bolt in 16 element or not, it can still fail. So if it fails, it’s only in first gear because the sprag is holding the low reverse drum from spinning counter clockwise then once you shift into second gear the sprag begins to overrun, hence the term overrunning clutch. So the L/R drum begins to spin clockwise freely in 2nd and 3rd gear with no load on the sprag. The low band apply protects the sprag so now the L/R band is helping dampen the load the sprag sees in 1st gear.

I’ve built 47/48 re’s for guys right at the 2000 horse level and pushing 3000 lb ft of torque !
Do they live long? Depends on the weight of the truck and gear ratio and of course your right foot!
The technology is definitely there for the flite to live and be reliable at most gasoline power levels we just need the Sfi case to make it all work out best
I’m surprised A&A or Cope hasn’t built a case ?

Nick...the sprag was probably damaged on one of the many passes when I was sorting out the suspension. I would rather have a LBA valve body in it honestly, but I'm using what I have.
I always run radials. I tried slicks several years ago and it didn't work well at all. Nothing works if you have too much SLR.

We failed the sprag on Dizusters car with LBA. But for sure it helps. I dont run LBA because the 1/2 shift isn't quite as quick. And not using a trans brake it lives pretty well. If I remeber correctly some trans brake valve bodies have a timed release of the low band. best of both worlds.
Doug

I’ve never noticed any difference in the 1-2 shift between A&A nonLBA and the A&A LBA. I only ever noticed a difference with quickness of the 1-2 shift when going from the turbo action valve body to theA&A both non LBA and LBA. How did you manage to kill a sprag with a LBA? That’s impressive lol.

Think of LBA as insurance, not prevention.

I certainly agree, anything can break especially in a race environment. The LBA is definitely insurance. I was just curious as to how it managed to take out a sprag with the LBA. I have never heard of one doing that so I was curious is all.