Manual Valve Body, Over-run Clutch, Explode!!!

[Mopar_Mudder]

Trying to further my knownedge on 727 (brain overload), so I can build one for my mud racing truck. I have been searching and reading all of the post on this message board that have to do with the 727.

I want a manual valve body, but a common thing I have read in everypost has to do with a band that is not applied in 1st gear and getting on and off the gas can cause the tranny to fail quickly in 1st.

Well in the land of off road and mud it is very common to have to get in and out of the trottle many times as you try to control 500hp out of control and keep it going in somewhat of a straight line. Not to mension trail riding where you may spen all day in low gear going up and down hills.

So is their a way to fix this problem, or a manual valve body that doesn't have this problem? Also I read that some vavle bodies raise pressures which steels more HP, I don't want that, need all I can get.


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Mopar_Mudder
http://mopar.rockcrawler.com

[BugEyedValiant]

Call Joe Chrisman at Tranzact Engineering. He is a good guy that has been VERY helpful to me. Tell him Brent Lidgard sent you. 317-846-4933

[451Mopar]

I think both front and rear bands are applied in low gear (I will have to check), but I know the rear band takes a beating from doing burn-outs and it is common for this band to break in 4x4's (the B&M transpack modifies the rear band servo, but I don't know if this fixes the problem, but so far I have not broken the rear band.)
I think the part exploding that you refer to is the over-running clutch in the rear of the transmission case, I think this can spin twice as fast as engine RPM in first gear?
Most of the performance transmission shops sell a "bolt-in" rear sprag for about $100 that is supposed to be stronger than the stock pressed in sprag.

[Mopar_Mudder]

I was surfing the net last night and ran across this, sounds good but know nothing about it.

Has anyone heard of the Means One-Way Clutch?

Here is a link to the page: http://www.meansindustries.com/oneway.html

Sounds like it is a replaycment for the sprag and over run clutch deal.

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Mopar_Mudder
http://mopar.rockcrawler.com

[Jack Z]

Mopar Mudder:

Some aftermarket performance valve bodies apply the reverse (rear) band in first gear and some don't. I don't know anything about mud bog racing but it sounds like you probably need one that does. I would think that any of the good Mopar oriented racing transmission parts companies (Pro-Trans, A&A, Turbo Action, Dynamic, etc.) would have or could easily build what you need. I'm no expert, but it's my understanding from people that are that to modify a valve body to apply the reverse band (or not) in first gear is a relatively minor change as is adjusting the system hydraulic pressure.

And to clarify your and other peoples understanding of what the problem and potential related failure is in not applying the reverse band in first gear, I can describe a drag racing oriented scenario. To start off, if you are not aware, the sprag or "overrunning clutch" is a device in the rear of the main case on a Torqueflite transmission (and about all others as well I think) that allows rotation in only one direction. When a car is leaving the starting line, the transmission sprag is very highly loaded in the direction it doesn't normally turn in. If a driveshaft or ring gear or other driveline part breaks (or maybe the mud bog driver gets full on and full off the throttle several times) or something else happens that causes the instantaneous unloading of the sprag, it immediately springs (slams) back in the other direction and usually flattens the springs and/or dislodges the rollers which obviously makes the sprag fail. After that is when the really bad stuff can happen!

When the sprag fails, the high gear drum in the front of the transmission can immediately spin up to about three times the engine speed. And if the engine is still at full throttle and the transmission has the standard cast iron high gear drum in it, this extreme rotational speed can cause that drum to explode which is what usually happened when you see pictures of or hear about blown out floor boards, injured feet, etc.

The most logical way to prevent that type of situation is to try to keep the sprag from failing and applying the reverse band in first gear is probably the easiest way to try to do that. The reason for that is (if you go back to my example above) the reverse band would keep the sprag from slamming back and flattening the springs, etc. when the driveline failure occurred. Even if the band is applied the sprag can still fail however, so another thing that is highly recommended for racing type applications is to use an aluminum high gear drum in place of the iron drum. This will not prevent a sprag failure or the high rotational speed of the drum that is associated with it, but the aluminum drum can withstand this high rotational speed without exploding. An aluminum drum also has the advantage of being lighter, which obviously helps to decrease the rotational weight in the transmission.

Also, relative to your and other peoples comments about a heavier duty or bolt-in sprag, I don't think a heavier duty sprag of the same design is the answer because that's not really where the problem is and as for a bolt-in sprag, I can tell you for sure that that is not the solution, because the part that bolts in isn't what breaks. I had two bolt-in sprags fail in my race car as I described above before I had the valve body modified.

I hope this helps.

p.s.: The starting line situation that I illustrated above is also the reason why you should never start a burnout in first gear with a Mopar and probably other brands as well. This is because right before the tires break loose, the sprag is highly loaded and when they do break loose (as you want them to when doing a burnout), the sprag slams back like I described and the trouble starts. If you start in second gear, the sprag is not loaded and this won't occur.

[Mopar_Mudder]

That is a great reply and answers many questions. Sounds like I for shure have to do something to stop this kind of failure. In a mud race situation you start off the line and the tires break loose instantly, you want this to gain as much wheel speed as possible before you hit the deep part of the mud. So it is basically a burn out in 4 wheel drive. Now I can get the gearing down enough to allow me to start in 2nd gear but it wouldn't be my first choice.

Are their any adverse effect to down shifting from 2nd to 1st? Say if you start running out of power and need to grab a gear. Would this have the same problem with the sprag?

What is the purpose behind not appyling the reverse band in first gear? I assume it is eating up some HP, not applying get more power to the rear tires.

I have talked to a bunch of Mopar Tranny guys, when you mension 4x4 truck and 6000+ pounds they don't seem to know what to say or where to go with it.

Thanks again for spending the time to type up the reply.

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Mopar_Mudder
http://mopar.rockcrawler.com

[BugEyedValiant]

The reason that the rear band is not engaged on the Turbo Action valve bodies is because it makes for engine braking in first gear. It makes for nice driving in the pits because you coast instead of eating the dash when you let off of the gas.

[340king]

I kinda disagree with you Bug eye, sorry. I think the main reason for the lack of band apply is for faster shifts. I know that in our Duster, the convertor is so loose that it won't really engine brake much under 3,500 rpm, at least from what I have seen. We had a stock valve body with a shift kit in it for a while. Then we went to a reverse pattern manual valve body. Now we have a trans brake and it does not apply the band either. You would think that with the loading that the brake puts on the trans, it would have the band applied.

[BugEyedValiant]

I too have a transbrake in my car, but it does have the engine braking. Mine is from Tranzact, and when I questioned Joe Chrisman about it having the braking, he said it was because the low band was applied in first. I am not 100% sure on this so dont hold me to it though. I will try to remember to ask Joe the next time I speak with him, and then I will post a new response to this, either confirming the above, or showing my stupidity.

[Leigh]

I think the coasting valve bodies are set that way to avoid the timing of the release of the low reverse band and the apply of the kickdown band. TA tranzbrake v/bodies release the band after the brake has been released. This winter I'll trace the circuits and see how they do it.
You NEVER go from 2nd to low with a manual unit, it will die an ugly death.
Not trying to sound like a wise ass, I would never use a brake without low band apply. (becomes transbreak)
Mudder, build up a Tansgo valve body and use manual low. Your problems should be solved.
JackZ, that was a very accurate description of the functioning of a Chrysler auto trans.

[Tim_K]

Ok, let's see if I can get a good answer to this question.
In both my cars, my '71 Valiant /6 daily driver, and my '79 Aspen R/T 360-4, when I go to the dragstrip and do my burnouts (just to dry off the tires, not to see how much smoke I can make), I put the shifter in manual low, use the gas and brake to get started, then let off the brake and let the car roll forward, spinning tires in manual low until the tires dry off and traction makes them stop spinning. Is this ok with stock valve bodies? I've cranked up the line pressure in both, but they are otherwise stock. Haven't had any problem in years of doing this, but I'd like to know if it could become a problem. The shifter stays in manual low throughout the whole burnout. I used to do it in drive (shifter position, trans was in low), but I'd rather have the rear band applied for this.

[Morris Brown]

Chysler had basically two valve bodies in these transmissions. In first gear only the forward clutches apply. You can put the shift lever in manual low and the reverse band applies. Making it easier on the over running clutch. The valve body for the 426 hemi when putting the shift lever in drive applied the reverse band without having to put it in manual low to apply that band. Look in your mopar magazine under advertisments for transmissions, they have valve bodies you can purchase to do this also. And yes you are correct. 500 horsepower on the over running clutch without the reverse band applied is way too much. You would need a scatter shield without it.

[Billydelrio]

Jack Z, I am copying yor comments into my notes. I now have a good reason to explain to my wife why I "need that aluminum part"
Thanks, Billy