Digging for info - front drum explosion on 727s

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71Demon528 said:
Low band apply valve body
Bolt in sprag
Billet front drum

Problem solved.

I’ve considered the glide dozens of times. And I have as close to a bulletproof 727 in my car. However, if you have a 727, simply buy the billet front drum, low band apply valve body, and bolt in sprag. Those 3 pieces will cost less than converting to a powerglide.
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The sticky thread in this sub forum has a video by Cope that covers exactly this. Low band apply in 1st gives an extra holding measure so the sprag isn't the only part working to engage 1st gear. Bolt-in sprag is a good safety measure but alone won't save the trans. Billet front drum is what will save you from an explosion from over revving internals at the end of the day.

Cope also makes the point that TH400s also explode, not sure if Powerglides work in a similar way but 400s explode at the big end instead of at the starting line. IMO if my transmission is going to explode I'd rather have it happen when the car is first accelerating than when it's going 120+ mph...

Regardless of all this talk about explosions I have no reservations building up the BB 727 I have with these 3 upgrades to go behind a 600-700hp 440 in a street/strip car.
 
MopaR&D said:
The sticky thread in this sub forum has a video by Cope that covers exactly this. Low band apply in 1st gives an extra holding measure so the sprag isn't the only part working to engage 1st gear. Bolt-in sprag is a good safety measure but alone won't save the trans. Billet front drum is what will save you from an explosion from over revving internals at the end of the day.

Cope also makes the point that TH400s also explode, not sure if Powerglides work in a similar way but 400s explode at the big end instead of at the starting line. IMO if my transmission is going to explode I'd rather have it happen when the car is first accelerating than when it's going 120+ mph...

Regardless of all this talk about explosions I have no reservations building up the BB 727 I have with these 3 upgrades to go behind a 600-700hp 440 in a street/strip car.
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Yep! Tons of info out there on how various transmissions can explode, especially in a racing environment. And I agree a street strip car with these 3 upgrades will be more than fine.
 
Great discussion going on. Here is what I got so far.

- Any 727 can grenade the front drum
- A drag car should start the burnout in 2nd (manual valve body)
- No dry hops (I'm not on board with this, it is just like a launch and confirms that you can do a 100% launch)
- Launch a car in 1st (Low/Reverse band applied)
- Don't lift and get back into the throttle while in 1st (this would be hard to overcome, this is an instinct for a gearhead)
- Use a valvebody that applies the Low/Reverse band in 1st
- Wrap that rascal

So if the sprag is the problem and isn't being used in 1st, can the transmission be run without the sprag when running a manual valve body?

The only danger comes into affect is when the Low/Reverse band doesn't get applied when in first.
 
a70duster said:
Great discussion going on. Here is what I got so far.

- Any 727 can grenade the front drum
- A drag car should start the burnout in 2nd (manual valve body)
- No dry hops (I'm not on board with this, it is just like a launch and confirms that you can do a 100% launch)
- Launch a car in 1st (Low/Reverse band applied)
- Don't lift and get back into the throttle while in 1st (this would be hard to overcome, this is an instinct for a gearhead)
- Use a valvebody that applies the Low/Reverse band in 1st
- Wrap that rascal

So if the sprag is the problem and isn't being used in 1st, can the transmission be run without the sprag when running a manual valve body?

The only danger comes into affect is when the Low/Reverse band doesn't get applied when in first.
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The sprag is an overrunning clutch which is the holding device that locks the low reverse drum from spinning counter clockwise when in first gear. In second and third gear, the low reverse drum spins freely clockwise and the sprag is “overrunning” at that point. With low band apply valve body, in first gear, you are applying the low reverse band to also hold the low reverse drum in addition to the sprag holding the low reverse drum. Yes you need a sprag to run the transmission. A 6 bolt 16 roller sprag is stronger than the stock 12 roller sprags which do not bolt in, and is also stronger than a 4 bolt 12 roller sprag. The extra 4 rollers give more locking power while in first gear and the bolt in outer cam helps support the load the sprag sees as well.

Yes the stock front drum is what explodes if the sprag were to fail. I have heard of others seeing aftermarket drums exploding, however, I, myself have not witnessed or heard of a aftermarket billet front drum exploding

Personally I do 2nd-3rd gear burnouts. I am in second gear for only the hit of the throttle then immediately into 3rd gear. I do no dry hops and still manage to hook my car up all the time. 1.18-1.21 60’. A dry hop is just placing extra load on your entire car. But if you feel it is necessary, have at it, although I would steer clear.
 
What is the difference between a dry hop and a launch beside the dry hop only lasting a fraction of a second? Both are equally hard on the drivetrain.

I'm talking foot braking the car, not a tranny brake.
 
a70duster said:
What is the difference between a dry hop and a launch beside the dry hop only lasting a fraction of a second? Both are equally hard on the drivetrain.

I'm talking foot braking the car, not a tranny brake.
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Difference is, on a launch you are not abruptly stopping the revolutions of the internals and continuing onto 2nd and then 3rd gear.

On a dry hop, it is very similar to a doing a burnout (think high revving internals) and then all of a sudden the wheels are spinning as fast. Kinda like the tires spinning then hooking while in 1st gear.
 
Torque converter.
Your torque converter also has a sprag inside of it, just like the one in your transmission. A one way locking device. The converters sprag is part of the stator which is the device in between the turbine and impeller inside the converter. The stator is what helps multiply the torque and couple the fluid. When the car sees load during initial acceleration, the sprag inside the converter is “locked” into place, multiplying the torque. As the car continues to accelerate and torque multiplication is no longer needed, the stator begins to free wheel when engine speed increases, coupling the fluid. For the same reason you see broken torque converters when guys have poor burnout procedures, the same applies for a dry hop. When the tires are loaded and unloaded at a rapid rate, the converters sprag goes from free wheeling to locking in place at a very uncontrollable rate. The more you load and unload that converter sprag, the weaker it gets until it breaks. Then the car slows down big time, and you have a junk converter as well as a transmission full of metal. even if you have a mechanical diode in your converter or spragless insert opposed to a conventional sprag, you’re still weakening parts inside what is arguably one of the cars most important pieces in drag racing. And that is just one piece of the car that is taking abuse.

Again if you feel it’s necessary, have at it, I’m just explaining one of the many reasons I do not do it is all.
 
-Boosted- said:
Difference is, on a launch you are not abruptly stopping the revolutions of the internals and continuing onto 2nd and then 3rd gear.

On a dry hop, it is very similar to a doing a burnout (think high revving internals) and then all of a sudden the wheels are spinning as fast. Kinda like the tires spinning then hooking while in 1st gear.
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Then our definition of a dry hop is different. After the burnout box about halfway to the staging lights I'll quickly power brake to launch RPMs and launch. The tires 99% of the time stick so there is no wheel spin. If there is tire spin, it is brief and the wheels aren't even rotating at 10 mph. I also don't get back into the throttle. I know to not launch at 100%.

Plus the dry hop is maybe 80% - 90% of a full launch.
 
71Demon528 said:
Torque converter.
Your torque converter also has a sprag inside of it, just like the one in your transmission. A one way locking device. The converters sprag is part of the stator which is the device in between the turbine and impeller inside the converter. The stator is what helps multiply the torque and couple the fluid. When the car sees load during initial acceleration, the sprag inside the converter is “locked” into place, multiplying the torque. As the car continues to accelerate and torque multiplication is no longer needed, the stator begins to free wheel when engine speed increases, coupling the fluid. For the same reason you see broken torque converters when guys have poor burnout procedures, the same applies for a dry hop. When the tires are loaded and unloaded at a rapid rate, the converters sprag goes from free wheeling to locking in place at a very uncontrollable rate. The more you load and unload that converter sprag, the weaker it gets until it breaks. Then the car slows down big time, and you have a junk converter as well as a transmission full of metal. even if you have a mechanical diode in your converter or spragless insert opposed to a conventional sprag, you’re still weakening parts inside what is arguably one of the cars most important pieces in drag racing. And that is just one piece of the car that is taking abuse.

Again if you feel it’s necessary, have at it, I’m just explaining one of the many reasons I do not do it is all.
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I don't agree with your explanation of the torque converter sprag lockup with regards to a dry hop. The car is brought up to launch RPMs. The stator is put into lockup mode after some throttle and stays locked up after the launch. Then the car coasts about 10 feet with no throttle applied.

I'd agree that if you're ON-OFF-ON the throttle that would be bad for any sprag BUT that throttle action doesn't happen in a dry hop.
 
a70duster said:
Then our definition of a dry hop is different. After the burnout box about halfway to the staging lights I'll quickly power brake to launch RPMs and launch. The tires 99% of the time stick so there is no wheel spin. If there is tire spin, it is brief and the wheels aren't even rotating at 10 mph. I also don't get back into the throttle. I know to not launch at 100%.

Plus the dry hop is maybe 80% - 90% of a full launch.
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I know how to dry hop....lol

My explanation may not have been clear. Obviously a dry hop is different than a burnout however you are still spinning the internals in 1st gear (unless you are dry hopping in 2nd which I doubt) and then you're not. With the horror stories about explosions and such, I built my 727 stout enough to hopefully never explode and sever my foot. Doesn't mean it can't fail and I would prefer that not happen either, therefore I will do 2nd gear burnouts shifting to 3rd and rolling out. Do a good burnout (getting the tires to the right temps) and dry hops are not needed.
 
You don’t have to agree. I am just simply saying it’s one extra step I do not do for many reasons. I merely picked the converter as an example. You may not associate a converter sprag failure with a dry hop, but a poor burnout combined with a dry hop can very well kill a converter. I’ve spent hours upon hours talking on the phone with different converter manufacturers,
one in particular, Paul forte from turbo action. He explained to me doing a dry hop after a burnout is the same thing as pushing the trans brake button and flooring it, then taking your foot off the pedal without launching the car. Those two actions load the sprag in the converter but never unload the sprag by free wheeling the stator as you accelerate down the track. So it’s putting more force on the sprag, making it more prone to failure.

And if you have a 727 without the proper upgrades we talked about, now your putting that 727 at risk as well.

But again, if you feel a dry hop is necessary and haven’t had any issues with it, then have at it. Just simply explaining my thought process is all.
 
a70duster said:
I don't agree with your explanation of the torque converter sprag lockup with regards to a dry hop. The car is brought up to launch RPMs. The stator is put into lockup mode after some throttle and stays locked up after the launch. Then the car coasts about 10 feet with no throttle applied.

I'd agree that if you're ON-OFF-ON the throttle that would be bad for any sprag BUT that throttle action doesn't happen in a dry hop.
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My understanding is if the "dry hop" happens to be not-so-dry & You hit it, if the tires spin unloaded for a split second then hook, the stator sprag goes from freewheeling to locked in the juice wheel...like neutral dropping it..it may not explode, but could be damaged & just seize, and the converter is junk.
Also, depending on the condition of the surface (& I'm no Pro Drag Racer here), some have told Me the dry-hop messes up the surface of the slick. They state the best traction is rolling out & backing of before they can "bite", and the first "bite" is the best, a dry-hop wastes it. You Pro's here can chime in & correct Me (or argue, :p) if You have a different experience/opinion.
 
Killer6 said:
My understanding is if the "dry hop" happens to be not-so-dry & You hit it, if the tires spin unloaded for a split second then hook, the stator sprag goes from freewheeling to locked in the juice wheel...like neutral dropping it..it may not explode, but could be damaged & just seize, and the converter is junk.
Also, depending on the condition of the surface (& I'm no Pro Drag Racer here), some have told Me the dry-hop messes up the surface of the slick. They state the best traction is rolling out & backing of before they can "bite", and the first "bite" is the best, a dry-hop wastes it. You Pro's here can chime in & correct Me (or argue, :p) if You have a different experience/opinion.
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Hoosier has told me not to do dry hops. They say the heat created by the burnout activates a chemical in the rubber and brings it to the surface. This chemical reacts to the glue on the track and increases traction. The dry hop removes the chemical from the surface of the tire and defeats the purpose of the burnout.
Dry hops were standard back in the 60's and 70's when tire technology was not good and it was a way for the driver to confirm that the burnout was effective.
 
mopowers said:
Is there a way to modify a stock valve body for LBA?
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If You are trying to prevent low band apply in manual low, You can weld a hole in the transfer plate up & toss the low/reverse check ball, I've done that...with 4:11's I wasn't concerned with coast-braking in 1st with the trans so....I just wanted a clean manual 1-2 shift w/o burning My kickdown band again. With a stk. 904, & a Slanty making ~190hp, it worked well.
 
Aluminum, aluminum with a steel band around it, and a new STEEL drum
Super-Cuda said:
Here's some info that may help.

Gallery: Bulletproofing a 727 Torqueflite With TCI Auto - Mopar Connection Magazine | A comprehensive daily resource for Mopar enthusiast news, features and the latest Mopar tech
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is being manufactured by T.C.S. Check out their website. Lots of HD mopar transmission parts being made by them. Ask about their dealers in the U.S. WWW.TCSPRODUCTS.COM
Keep in mind, your old cast iron drum has how many miles on it???
 
transman said:
Aluminum, aluminum with a steel band around it, and a new STEEL drum

is being manufactured by T.C.S. Check out their website. Lots of HD mopar transmission parts being made by them. Ask about their dealers in the U.S. WWW.TCSPRODUCTS.COM
Keep in mind, your old cast iron drum has how many miles on it???
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It's not the miles on the drum, it's the overspeeding that causes the drum to come apart.
 
What would cause a 727 to explode in 3rd gear at 7800 rpm? I built a 13 to 1 340 had 727 built with a manual valve body 3500 stall converter. I was building it for drag racing but my rear gear was a 3.21 so I was building a 8.75 with 3:91 gears but before I got it swapped I decided to do a top speed run with the high gears and at about 7800 the transmission exploded. Just wondering if anyone has ever experienced that before?
 
Do you know which part failed, or exploded as you say?

I absolutely would not shift a 727 with stock drums to almost 8k rpm.
 
Yes I’m lucky I didn’t wreck. Luckily is sheared off the rear driveshaft fasteners so the rear of the shaft fell down instead of the front. The transmission case broke into 3 pieces. It broke the tail shaft housing right in front of the rear mounting pad, the bell housing was in a 1000 pieces and the torque converter was wedged between the frame and floor. The center part of the case was most intact but it was sitting with the pan against the floor as well. The tail shaft was snapped off, the main shaft was snapped and the front pump was destroyed. Inside all the drums, bands and planets seemed to be ok except for the sprag. I’m not sure what really happened but it could have been something else because when the torque converter came loose it chewed the 4 lower transmission bolt holes off the block so I pulled the engine apart to see if I could reuse the rotating assembly in a new block I found that the crank was broken. I just don’t know if the crank broke the transmission or the transmission broke the crank.
 
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