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Old 12-19-2005, 09:44 PM
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Turbo 400 help, Need to know what I did wrong

Hello , I have a fairly new reverse manual valve body Turbo 400 with T brake. It is in a pro street car that is mostly driven on the street. Last week while driveing it lost second gear, it would stay in low in first and second gear postion and then shift to third when you moved the shifter to the high postion. I was told that it was probably the intermedent sprag so first I pulled the pan and it looked pretty good the fluid was nice and red and not burned. Next I pulled the transmission and had a friend that has some experience with turbo 400's dismantle the transsmission ,the clutches all looked like new(even still had writeing on them) when we got to the sprag we found it would spin both ways with ease and it had scared the drum where it rides. It has the 34 element sprag, I guess I will have to replace the drum and sprag. What do you think made the sprag fail? We can not find any other signs of trouble. what can I do to keep from haveing this problem again? Any help would be greatly appricated Thanks

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Old 12-20-2005, 08:45 PM
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Second gear in T400 brakes or reverse manual valve bodies rely on the sprag to hold the drum stopped. This can only happen under load (throttle on). If you decelerate or lift off the gas, the drum the sprag is on begins to freewheel (rotate backwards). The freewheel speed is dependent on drivetrain speed and load conditions. When you jump back on the gas, the drum loads the sprag and comes to a complete stop, instantly, under the full load the engine is delivering. You have done the same damage as a neutral drop. It may not fail immediately, but it will fail.
These transmissions and valve bodies are designed and intended to be used on the drag strip under full load shifting, not street driven under on & off throttle driving. If you must drive this setup on the street, keep it in third when you are cruising and DO NOT downshift until you come to a stop. These issues are due the the fact that there are a great many hydraulic circuits and controls we delete when manufacturing these valve bodies. Remember, intended for use on the race track.
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Old 12-24-2005, 05:35 AM
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Does this go for all reverse valve body t-braked 400's? this is the third 400 I have used like this and I have never had any problems before . The first trans was an ATI and the second was a TCI both with reverse valve bodys and trans brakes they never gave any problems. I am not sure what brand this trans is ( it came in a car I bought) but if there is a way to make it more durable I would like to Know.
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Old 12-24-2005, 07:25 AM
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The last TCI brake that I did said do not use the reverse position on shifter to back up , use neutral and press t-brake button.
Said damage would result, but didn't specify what type.
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Old 12-24-2005, 08:05 AM
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The brand or manufacturer of the valve body does not matter. The mechanical function of the transmission itself is what is causing your problem. There is nothing set in the trans or valve body that will cause one trans to fail before another. Sometimes car weight and torque converter prep can influence this phenomenon. The real answer is don't drive reverse pattern/transbrakes on the street. If you do, keep them in third when you are in & out of the gas....
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Old 12-24-2005, 09:49 AM
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So if I start out in 1st shift to 2nd and then drive , leave the car in drive until I completly stop the car the trans will hold up better?
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Old 12-24-2005, 10:06 AM
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Yes. When the trans is in third, there is nothing freewheeling internally. If/when you decelerate in third, you will feel engine braking also..
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Old 12-24-2005, 11:32 AM
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Thanks, the car makes enough torque do make that possible. It is not a dailey driver but I like to go to car shows and cruise it around some.
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Old 12-28-2005, 08:39 AM
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I have one more question. If I am in stop and go slow trafic(like at a rod run or cruise in) can I leave the transmission in low without damageing the sprag?
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