Quote:
Originally Posted by 74baja
Thanks, Cody. Some good info there. The only thing I am confused about is the shift firmness/quickness. Isn't some of that accomplished through tuning by increasing line pressure anyway? If so, how much would a valve body do anyway? From what I have heard, the quicker the shift, the easier it is on the tranny, because it reduces the amount of time internal clutches are engaged. Is this not true? Oh, and I forgot to mention my mods (not that it effects the tranny specifically) I have 4" exhaust, 6637 air filter, EGT, boost and tranny temp gauges, and 285/75 tires... I that that's everything significant).
Thanks,
Jack
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Jack,
Yes, most aftermarket tuning WILL increase shift firmness significantly with a stock valve body. This helps reduce clutch "burn time" while pushing significant amounts of additional power through the transmission. This can be a good thing because as miles get put on vehicles, piston seal bores wear, clutch material and steels begin to glaze, etc. Increasing the holding pressure and shortening shift time help with these problems by giving a good feel.
The main difference between setting up the tuning for increased shift firmness versus using an aftermarket valve body is that with the VB upgrade, the fluid simply flows faster and easier through the orifices. With tuning, the fluid is usually forced through under higher pressure. When thinking about that aspect, it makes sense to go with the valve body upgrade. On the other hand, it's $300 that could be better spent because the increase in shift pressure to firm up the shifts is only momentary DURING the shift.
However, there are other things to consider as well like torque reduction during shifts. A lot of tuners command 100% torque during a shift. The factory runs between about 85-93% of torque during loaded shifts. Just doing this makes the shift feel more firm. I don't do it because I hate firm shifts when hauling a trailer. Don't get me wrong, there is a HUGE difference in a soft, long-burning shift and a "good" shift....the latter is what should happen under all driving conditions. A short "burn time" with a noticeable yet pleasant shift. I usually run 70-80% torque during a shift with the lower output under heavy load shifts.
There are mechanical components ("hard parts") inside the transmission that wear. Typically these are splined shafts and hubs. They also include friction element drive teeth. Under operation, there are many instances where a splined shaft or hub needs to reverse directions almost instantaneously. The more miles that are on the transmission, the greater the free play or "lash" between the spline teeth. At this point, reversing the direction becomes like more of a hammer and wear (to the point of stripping out or breaking) becomes more likely at an increasing rate. Clutch friction teeth suffer the same fate.
Wear is a fact of life, but purposely trying to force something to occur faster than designed is more likely to break it. If you play nice and don't try to abuse your truck, a program with firmer/quicker shifts WILL help extend transmission life. Racing stoplight to stoplight and performing multiple 1-2 upshifts under full load WILL kill your transmission in a hurry though, stock or not.