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Old 01-05-2012, 09:17 AM
TransEngineer TransEngineer is offline
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Originally Posted by brad12kx View Post
Nope.....won't happen! The PCM doesn't know the pressure is different, as this unit is sending the PCM altered pressure information. If the PCM was able to react to this and alter the pressure down to where it was, then it would do the same without it, and that would cause the trans to burn up prematurely under normal driving conditions.



The opposite! Probably the best mod you can do for your truck at any price. The increase line pressure is not at all damaging, but rather to opposite. Hard shifts don't hurt transmissions, soft shifts do, as soft shifts cause heat and wear, which are pretty much the only things that kill a trans.

Why are factory shifts so soft then you ask????
The factory is too busy trying to make the trucks drive like a car, and nice soft virtually unnoticeable shifts is just one of those 'car' things that they did. Unfortunately, some of these 'car' things have a dark side, and those of use that drive hard and/or pull trailers are seeing lower transmission life then we should.

Do NOT hesitate. Spend the $50 and have the piece of mind knowing you just increased the life of your trans, and can finally 'feel' the shifts.
OK, let me try to explain things in a little more detail. Line pressure control (and shift control) on the RFE transmission is very complicated, but here is a simplified explanation:

Installing a line pressure "booster" will temporarily “firm up” the upshifts, since the actual LP is higher than the PCM thinks it is. But the PCM will see that the shifts are firmer than expected (what we call "overlapped," where the applying clutch gains capacity before the releasing clutch loses capacity). It will then gradually re-learn the CVIs and adaptives (to adjust to the higher-than-requested LP), and you’ll be right back where you started from, or close to it. There are limits on how far the clutch adaptives can learn, so if, for example, you learn one of the adaptives down to the low limit, that is as far as it will go. This may still leave you with a somewhat firmer shift than you originally had. But I suspect in many cases, you'll get back to "normal" shift quality before you reach the learning limits.

I believe the only real benefit from running a “booster” would be increased clutch capacity during heavy-throttle, in-gear operation, due to LP potentially being (actually) higher than the "max allowable" LP. But unless you're running performance mods, this is probably unnecessary, since the normal max LP is sufficient to hold the clutches at max input torque.

In normal operation, we use a learned line pressure gain factor that adjusts the ramp rate by which line pressure increases as torque increases. If the PCM detects slippage within the transmission, it learns this gain factor up to a higher value. Installing an LP "booster" will allow the LP gain factor to learn down, probably to zero, which would negate some or all of the “gain” from the booster. In vehicles that are already running at min LP gain (gain factor at or near 0), then there would be some increase in clutch capacity overall (with the “booster”). But since those vehicles weren’t experiencing clutch slippage at min LPs, this capacity gain would provide no real benefit (unless you consider decreased fuel economy a benefit).

If you've installed a line pressure "booster" and are happy with it, then I wish you all the best. Using a "booster" will not hurt anything (other than fuel economy), so enjoy!

But in my opinion, "boosters" are unnecessary, and likely ineffective in the long run, on a stock truck.
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