Slant Six Forum :: When a 904 blows up after burnout

You rarely if ever see a 904 explode. I have seen a bunch of 727's, T-400's and Powerglides go, but never a 904.

As said before, the overrunning clutch in the back of the case on a T-Flite rolls the sprag, which in turn lets the front drum overspeed and explode. The 904 front drum is a lot smaller than a 727 drum, and that seems to keep them from exploding.

The 904 has the sprag riveted in the case to start with, while a 727 sprag just sits in splines.

A good sprag is just the start. IF you want one explosion proof you need a low band apply valve body and a billet front drum.

If you are using a stock valve body make sure to put it in manual low to start a burnout. That applies the low band and keeps a lot of bad things from happening.

Author:	Bren67Cuda904 [ Thu Jul 15, 2010 12:54 pm ]
Post subject:	When a 904 blows up after burnout
Mine has NOT blown up. I hear that it can if the tires catch traction in 1st gear the next time down the track. What part of the trans is exploding and where do the parts exit the trans housing? Is there a balistic blanket avaiable to cover this area to help keep the parts from coming into the car and killing me? If so, any ideas on costs and types. Homemade options??

Author:	hellion_locdogg [ Thu Jul 15, 2010 2:48 pm ]
Post subject:
It is the sprag clutch at the back of the main housing, they have better bolt in sprags. From what I understand it only really happens at very high rpm, like if a driveline breaks. I've also heard that a slant will not make enough hp to even worry about. The key is to not do 1st gear burnouts, stay in selected 2nd. I will post a thread from FABO if I can find it. ,Cliff

Author:	hellion_locdogg [ Thu Jul 15, 2010 2:50 pm ]
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http://www.forabodiesonly.com/mopar/sho ... loding+904 Trans blanket- http://www.jegs.com/p/Deist-Safety/Deis ... 2/10002/-1 ,Cliff

Author:	slantzilla [ Thu Jul 15, 2010 3:01 pm ]
Post subject:
You rarely if ever see a 904 explode. I have seen a bunch of 727's, T-400's and Powerglides go, but never a 904. As said before, the overrunning clutch in the back of the case on a T-Flite rolls the sprag, which in turn lets the front drum overspeed and explode. The 904 front drum is a lot smaller than a 727 drum, and that seems to keep them from exploding. The 904 has the sprag riveted in the case to start with, while a 727 sprag just sits in splines. A good sprag is just the start. IF you want one explosion proof you need a low band apply valve body and a billet front drum. If you are using a stock valve body make sure to put it in manual low to start a burnout. That applies the low band and keeps a lot of bad things from happening.

Author:	Shaker223 [ Thu Jul 15, 2010 3:45 pm ]
Post subject:
Quote: You rarely if ever see a 904 explode. I have seen a bunch of 727's, T-400's and Powerglides go, but never a 904. As said before, the overrunning clutch in the back of the case on a T-Flite rolls the sprag, which in turn lets the front drum overspeed and explode. The 904 front drum is a lot smaller than a 727 drum, and that seems to keep them from exploding. The 904 has the sprag riveted in the case to start with, while a 727 sprag just sits in splines. A good sprag is just the start. IF you want one explosion proof you need a low band apply valve body and a billet front drum. If you are using a stock valve body make sure to put it in manual low to start a burnout. That applies the low band and keeps a lot of bad things from happening. Ditto and sound advice!! Could not have said it better.

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Author:	Bren67Cuda904 [ Fri Jul 16, 2010 12:20 pm ]
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I have a "basically" stock valve body. Just to clarify. Your saying to start burn out in 1st gear and then move shifter up to "drive" or just keep shifter in first? While where on the topic of proper burnouts. When the guy motions me to the burnout box, (which is 90 degrees from the staging lanes) I just drive forward and turn sharp to the right and pull through the water. I stop with my rear tires just past the water puddle. Wait for track guy to give the nod and heat them up good. I don't have a line lock yet, so I am holding the break pretty hard. Once I see smoke I release the brake and burn forward until it catches or I am about to go pass the staging light beams. I have had a few people say I should pull around the water box and back into it, pull forward and then do the burnout. My thoughts were, at my hp range (14.6), that picking up a little water on the front tires should be no big deal. With manual steering its a pain to maneuver around them and still get line up straight. Your thoughts.

Author:	slantzilla [ Fri Jul 16, 2010 2:23 pm ]
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I drive through the water all the time. Most places don't have that much water down to start with, so it really isn't an issue anymore. Start the burnout in manual low, and as soon as the RPM's start climbing shift into 2nd.

Author:	Dolmetsch [ Mon Aug 02, 2010 1:51 pm ]
Post subject:
The overspeed drum info is right. When you let off from a low gear burnout with a manual valve body the drum overspeeds. Some will explode. Solution. Dont do your burnourts in low gear. Period. It is ok to start it there but up shift immediately to second and high f you have enough wheaties. If you do that you will never have any trouble. The problem only exists in a low (ist )gear burnout. It DOES NOT is NOT a problem anywhere else. (2nd or high. ) It has been like that from Day one. No 1st gear burnouts.

Author:	slantzilla [ Wed Aug 04, 2010 4:22 pm ]
Post subject:
Quote: The overspeed drum info is right. When you let off from a low gear burnout with a manual valve body the drum overspeeds. Some will explode. That is only partly correct. The front drum will never overspeed unless you destroy the sprag. You can destroy the sprag by doing a burnout in low and getting traction on the 1-2 shift. You can also kill a sprag with a driveline/diff failure. Also, with a manual valve body with no low band apply you will kill the sprag if you get off the power and get back on in low gear. That is why a Cheetah says right on the box "NOT INTENDED FOR STREET USE". Bottom line is that you should never start a burnout in low gear anyway.

Author:	727specialist [ Thu Aug 05, 2010 9:49 am ]
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Quote: Bottom line is that you should never start a burnout in low gear anyway. This is what you need to know. To sum it up No 1/2 shift in the water box. A drive line failure--Such as broken drive shaft/ rear gear failure- broken axle etc. Can damage the overrunning clutch. Start out in second gear in the water box. You wont damage the overrunning clutch. Also-- For the 727 there is the super sprag. It is a better design and doesn't fail as easy as the stock overrunning clutch Hi Slanty...Cool forum

Author:	slantzilla [ Thu Aug 05, 2010 2:10 pm ]
Post subject:
Hi Keith, welcome to the board.

Author:	Dart270 [ Fri Aug 06, 2010 4:28 am ]
Post subject:
Thanks for the expert info, folks. I will start my burnouts in 2nd. One more question: Does a stock valve body, or a B&M Manual Pak modified valve body have low band apply?? Thanks, Lou

Author:	emsvitil [ Fri Aug 06, 2010 4:36 am ]
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If you select 2nd gear, then floor it for the burn out... Doesn't the tranny downshift to 1st

Author:	slantzilla [ Fri Aug 06, 2010 2:14 pm ]
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A stock valve body will apply the band in manual low only, not in drive. I would believe a B&M modified stock valve body would do the same thing. Yes, selecting 2 will start the burnout in low gear.

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Author:	Dart270 [ Fri Aug 06, 2010 2:32 pm ]
Post subject:
Cool. Lou