727 deference between D and 1 from a stop

[toolmanmike]

Why it happens:

It all starts when the over-running clutch (aka the sprag) in the rear of the transmission case is damaged. The roller bearings will commonly "roll-over" the posts or fingers on the spring retainer. This action will cause the transmission's geartrain to over-rev the engine rpm multiplied by the first gear ratio, commonly 12,000 rpm or more. The stock OEM powered forged high gear/front clutch drum retainer will explode at approximately 9,000 rpm. The sprag can be damaged by one or more of the following:

1) Driveline failure such as:
-Broken ring and pinion
-Broken u-joint or u-joint straps
-Broken driveshaft
-Broken axle shaft
-If you have a driveline failure, remove the transmission and carefully inspect the case and tail shaft area for cracks. Disasemble the transmission and check the sprag in the back of the transmission case. If it is not damaged, it is recommended to replace the springs and rollers to be on the safe side.

2) Using a reverse manual or trans brake valve-body that does not apply the low/reverse band in first gear.
-Ask the manufacturer of your valve body if it has the low bandy apply feature. This is very important, and I blame the majority of transmission explosions on valve bodies that are not applying the low/reverse band in first. If your car "free wheels" in first (early turbo action valve bodies), it is not applying the low/reverse band.

3) Misuse/abuse on the street or strip in first gear.
-Remember you can only damage the sprag in 1st gear. Start your burnout in 2nd, and shift to 3rd. When on the street, repetitively getting in and out of the throttle while in 1st gear can damage the sprag.



Transmission/sprag/drum explosion only happens in 1s gear. You either start in first to start your burnout and shift into second without over revving, or you start out in second with a manual valve body

 

[66 Sat]

Absolutely wrong! Kim

From the reading I had done I thought that was correct. The burnouts I used to do at the track were always done like this, start in manual first and then shift to second before the tires grabbed.
Why is this wrong?

 

[toolmanmike]

Transmission/sprag/drum explosion only happens in 1s gear. You either start in first to start your burnout and shift into second without over revving, or you start out in second with a manual valve body

 

[RemCharger]

Yes, if you do a high rpm burnout in drive and back off the gas without allowing the trans to self shift to second, you can take the sprag out and do some damage if not destroy the transmission.

This is because the drum( and therefore the sprag ) are only mechanically locked while in low position.

Transmission/sprag/drum explosion only happens in 1s gear.

Again, in the D position, yes the sprag is vulnerable in 1st gear.

You either start in first to start your burnout and shift into second without over revving, or you start out in second with a manual valve body

well put

 

[oldkimmer]

Ok, I was at work with not very good internet. So he goes once again. This is with an auto shift valve body aka factory. There is nothing wrong with doing a first gear burnout as the band has the drum locked in first gear along with the sprag/over running clutch. When u shift to 2nd and have the power to keep the tires spinning to complete your burn out without the tires grabbing hard u are good. The problem is when u shift to 2nd and don’t have the power to keep the tires spinning the tires grab and the tranny shifts back to first and all that is holding 1st gear is the sprag/over running clutch. Then without the rear band applied u get the Big Bang/boom with flying shrapnel. Kim

 

[oldkimmer]

You know, at least when I try to correct some one I prove the point. looks like you need to study up Kim.

3) Misuse/abuse on the street or strip in first gear.
-Remember you can only damage the sprag in 1st gear. Start your burnout in 2nd, and shift to 3rd. When on the street, repetitively getting in and out of the throttle while in 1st gear can damage the sprag.

Mike, see post 45 and see what i explained . Kim

 

[dvw]

You know, at least when I try to correct some one I prove the point. looks like you need to study up Kim.

3) Misuse/abuse on the street or strip in first gear.
-Remember you can only damage the sprag in 1st gear. Start your burnout in 2nd, and shift to 3rd. When on the street, repetitively getting in and out of the throttle while in 1st gear can damage the sprag.

With a stock valve body in the manual 1st selection the low band is holding the low/rev drum. The low roller clutch's
(not in reality a sprag) only function is to hold the low/rev drum. Since the drum is already being held by the band, the low roller isn't doing anything. So there is no danger of hurting the low roller in manual 1st.
Doug

 

[toolmanmike]

Mike, see post 45 and see what i explained . Kim

This looks like what I said.

 

[68 Sport Satellite]

Ok, I was at work with not very good internet. So he goes once again. This is with an auto shift valve body aka factory. There is nothing wrong with doing a first gear burnout as the band has the drum locked in first gear along with the sprag/over running clutch. When u shift to 2nd and have the power to keep the tires spinning to complete your burn out without the tires grabbing hard u are good. The problem is when u shift to 2nd and don’t have the power to keep the tires spinning the tires grab and the tranny shifts back to first and all that is holding 1st gear is the sprag/over running clutch. Then without the rear band applied u get the Big Bang/boom with flying shrapnel. Kim

one more scenario - what if I leave the shift selector in Drive and from a stop I stab the throttle and do a hard very short burner but lift off the throttle before it shifts to 2nd? Is there danger of the Big Boom? When I had my trans rebuilt I should have had them install a billet drum. This is not something I want to need to remember and worry about if things catch traction when not intended....

 

[toolmanmike]

one more scenario - what if I leave the shift selector in Drive and from a stop I stab the throttle and do a hard very short burner but lift off the throttle before it shifts to 2nd? Is there danger of the Big Boom? When I had my trans rebuilt I should have had them install a billet drum. This is not something I want to need to remember and worry about if things catch traction when not intended....

It's probably best to just do a burnout in manual low and call it good. Because you are all stock, you can't start in second and shift to 3rd. That takes horsepower and is unnecessary unless you have a race car.

 

[OneWheelPeel]

one more scenario - what if I leave the shift selector in Drive and from a stop I stab the throttle and do a hard very short burner but lift off the throttle before it shifts to 2nd? Is there danger of the Big Boom? When I had my trans rebuilt I should have had them install a billet drum. This is not something I want to need to remember and worry about if things catch traction when not intended....

It's probably best to just do a burnout in manual low and call it good. Because you are all stock, you can't start in second and shift to 3rd. That takes horsepower and is unnecessary unless you have a race car.

So I describe my town as a cross between Mayberry and Hazard County, but with taquerias. That means dirt roads or paved roads with dirt blown on them, could taking off aggressively while in D on these roads where traction is unpredictable blow something out? I get wheelspin all the time in my Ranchero and sometimes in my Crown Vic in those conditions, so I can only assume when I drive the Coronet more it will happen there too.

 

[RemCharger]

one more scenario - what if I leave the shift selector in Drive and from a stop I stab the throttle and do a hard very short burner but lift off the throttle before it shifts to 2nd? Is there danger of the Big Boom? When I had my trans rebuilt I should have had them install a billet drum. This is not something I want to need to remember and worry about if things catch traction when not intended....

This is the scenario we are talking about that goes boom.
Get in the habit of shifting manually when your on the gas

 

[Photon440]

So I describe my town as a cross between Mayberry and Hazard County, but with taquerias. That means dirt roads or paved roads with dirt blown on them, could taking off aggressively while in D on these roads where traction is unpredictable blow something out? I get wheelspin all the time in my Ranchero and sometimes in my Crown Vic in those conditions, so I can only assume when I drive the Coronet more it will happen there too.

Are you taking off with full throttle on a gravel road? If so, why?

 

[toolmanmike]

So I describe my town as a cross between Mayberry and Hazard County, but with taquerias. That means dirt roads or paved roads with dirt blown on them, could taking off aggressively while in D on these roads where traction is unpredictable blow something out? I get wheelspin all the time in my Ranchero and sometimes in my Crown Vic in those conditions, so I can only assume when I drive the Coronet more it will happen there too.

It could if you were spinning in first (not manual low) and hit clean pavement. especially at high rpm.

 

[OneWheelPeel]

Are you taking off with full throttle on a gravel road? If so, why?

You ask that like its a bad thing Its happened with spirited input but nowhere near full throttle.

It could if you were spinning in first (not manual low) and hit clean pavement. especially at high rpm.

Ok thanks, will bear that in mind. I wonder if they were manually shifting the automatic mopars in all the shows and movies where they drove like maniacs. I've rented to and driven some of my cars in locally produced B movies(Troma, the Toxic Avenger people) and taking off aggressively may come up if I do it again.

 

[BSB67]

How about when you are driving 30 mph in D, and you simply drop the hammer and the transmission automatically down shifts to 1st (no low band apply) and the car jumps violently.

If the 727 was even slightly as vulnerable as being made out to be, there would be none left. We beat the daylights out of these things every day for years.

 

[68 Sport Satellite]

Not sure what they mean by Manual Low. My column shift gear selector is P-R-N-D-2-1. I have modest HP/Torque, but more than stock (At rear wheels is 391 hp / 523 ft-lb torque). My trans has a shift kit and aftermarket later valve body that kicks down to 1st at 3/4 throttle.

 

[dvw]

What is being missed here? In D either down shifting 1st, or in 1st. If traction goes away, or the rear gear breaks, or the drive shaft brakes what happens? Does the low roller come into play? No, the trans upshifts to 2nd gear. To many worry worts. I ask, who here has blown up a drum? Who has even witnessed a exploding drum in person? Not many I'd bet. With a stock style valve body the chance of hurting the low roller and exploding a drum is next to nothing. I've run no low band apply on the street and track for ever. So have most guys I know. 1000s of passes. Have I hurt a drum? Never, have I seen them explode? Yes. The only one that blew up that I was personnaly involed with? I told the owner it was hurt on the previous pass. He disagreed. Came apart on the next pass.
Doug

 

[68 Sport Satellite]

What is being missed here? In D either down shifting 1st, or in 1st. If traction goes away, or the rear gear breaks, or the drive shaft brakes what happens? Does the low roller come into play? No, the trans upshifts to 2nd gear. To many worry worts. I ask, who here has blown up a drum? Who has even witnessed a exploding drum in person? Not many I'd bet. With a stock style valve body the chance of hurting the low roller and exploding a drum is next to nothing. I've run no low band apply on the street and track for ever. So have most guys I know. 1000s of passes. Have I hurt a drum? Never, have I seen them explode? Yes. The only one that blew up that I was personnaly involed with? I told the owner it was hurt on the previous pass. He disagreed. Came apart on the next pass.
Doug

can you share with us less experienced folks what was the sign you observed that made you think it was hurt on the previous pass? Did you hear a sound, observe wheel hop? Is it something an onlooker could tell, but possibly the driver would not be aware of? Thanks in advance.

 

[dvw]

can you share with us less experienced folks what was the sign you observed that made you think it was hurt on the previous pass? Did you hear a sound, observe wheel hop? Is it something an onlooker could tell, but possibly the driver would not be aware of? Thanks in advance.

This was a real A990 Hemi 65 Coronet owned by a friend. With another friend driving. I had raced it as well. It was actually 4 passes. Pass #1 it wheelied pretty good And Dave got out of it. Steve told him he was a *ussy. Dave looked at him. "Are you questioning my manhood"?. Pass #2 it went up and up and Dave never lifted. Dragged the back bumper and lifted the rear tires off the ground. (Yes, I straightened the front rails and squared it all up at a later date.) Pass #3 It left flat as a pancake. I watched the video, zero tire spin. Told Steve it was hurt. He said "No way". Pass #4 I was walking towards the starting line when Dave came out of the Burnout box. This was back in the day at Memphis with ESPN with Brett Kepner being filmed for TV. Dave left and the car went about 2 feet. The trans had a sheild but the bottom half wasn't bolted on. It came apart so violently the it knocked a 1"chunk of asphalt out of the track. The chunk was propelled forward and stuck in the radiator. All the clutches and steels were just hanging on the trans shafts loose. There were no drums. The Vavle body was hanging by a piece of case attached to the AN line. I salvaged the valve body. It's still in use.
Doug