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Discussion Starter · #1 ·
Only occurs when trans is cool, but doesn't always happen. Engine starts normally, and gear shift to D is normal. What is not normal is that there is nothing there...as if you had steoped on a clutch and were revving the engine. After a few seconds, it returns to normal function. Any thoughts?
 

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If it feel like it's "oozing" into gear, then you most likely (99% chance) have converter drainback, where part of the fluid in the torque converter is draining back into the trans when the engine is shut off. Then when you start the engine, the converter is half full of air (instead of oil). Since air does not transmit torque very well, you basically get no torque (from the engine, into the trans) when you first shift it into gear. Then as the converter refills, the torque level slowly rises, until finally it's back to normal. That gives you an "ooze into gear" feeling - you are actually feeling the trans input torque slowly building. Once you move the truck, everything's fine, so it works great from then on (until you park it again and it drains down).

Also, when that slug of air that's in the converter gets pushed out through the oil cooler, it then comes back to the trans and goes through the pump. This can give you a momentary dip in line pressure, which can cause a P0868 (Line Pressure Low) fault, and in some cases can drag the torque converter clutch (TCC), which (if you're in gear) can make the truck want to take off (where you have to mash the brake to hold it) or stall the engine. Fortunately, those issues are far less common than the slow engagement / “oozes into gear” problems.

The most common cause of drainback is changing the fluid and filters, and using an aftermarket spin-on (cooler return) filter. The spin-on filter has an internal diaphragm to prevent converter drainback, but on some aftermarket filters, the diaphragm doesn't work well enough, giving you converter drainback and a slow engagement after the truck's been sitting overnight or for several hours. So the fix would likely be a new spin-on filter. Use a Mopar filter (05179267AC) and you should be OK.

By the way, this is NOT something that will harm your transmission (or converter). As I noted, the problem is too little torque (not too much), and the trans is NOT slipping - it's all in the converter. So you don't have to get it fixed right away if it's not convenient - you can wait until your next fluid change if you want. Drainback is annoying but it will not harm anything. If you let the truck idle (in Park or Neutral) for a short period after you start it, the converter will refill and you'll be fine.
 

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Discussion Starter · #6 ·
Wow!!!

Now THAT's what I call a RESPONSE!!! And that is exactly what I am experiencing. I had it serviced a LONG time ago, but I don't remember if it was doing it before the service, or if it started afterwards. Either way, I'll look into it.

The Sonnax wire is also intriguing, and I am interested. Could that also be used with the stage 2 valve body upgrade on Airram? Would that still be streetable?
 

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Personally, I don't recommend the Sonnax (or any other) LP booster for the RFE transmission. These "boosters" artificially adjust the Line Pressure Sensor voltage, so that the PCM thinks the LP is perhaps 20 psi lower than it actually is. In theory, this then causes the PCM to crank the line pressure UP by 20 psi (to bring the sensor reading up to the Desired Line Pressure [DLP]).

In actuality, you do get some benefit, but not as much as you might expect. There are a couple of reasons for this:

1. The DLP value is based on input torque level. Under light cruise conditions, DLP is adjusted down (for fuel economy) to a level that is just high enough to avoid clutch slippage. For example, DLP may be 120 psi at heavy throttle, but then adjust back to, say, 50 psi at light throttle. If you install a "booster," the Actual Line Pressure (ALP) may be 70 psi when the LP sensor reading is 50 psi. Now, the PCM will gradually learn the minimum DLP down, since now it could run at "30 psi" (sensor reading) without slipping the clutches. If it were to learn the minimum DLP down to 30 psi, then you'd be right back where you started (50 psi actual line pressure). Now in actuality, we have a certain minimum LP that the PCM can't learn past, so it wouldn't really go all the way down to 30 psi, and you would have SOME benefit, but not as much as you expect.

2. Similarly, the clutch-to-clutch handoffs during shifts are affected by the line pressure level. The PCM adjusts the duty cycles and timing of the applying and releasing clutches to achieve smooth shifts. When you first install a "booster," your LP will be (actually) higher than the PCM thinks it is, so you will immediately notice "firmer" shifts and think, "Wow! That LP booster really makes a difference!" Unfortunately, the PCM will also notice the firmer shifts, so it will gradually adjust the shift adaptives to get you back to "smooth" shifts. Once again, you will eventually wind up back where you started.

So because the PCM will "learn," it will adjust to the faked-out LP sensor readings, and you will not get the full benefit you expect. You will get some benefit, but I'm not sure it will be enough to justify the cost of the "booster."

I am not sure what's in the aftermarket valve body you mention, but generally there should not be any problem with using a "booster" along with any VB. The shift controls are really in the PCM (electronically), not in the VB.
 

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Discussion Starter · #9 ·
Ok, then, let's get to the root of it. If you were to hop-up your engine from the 235 hp I'm supposed to have to something more substantial, will the stock tranny keep up, unmodified? Seriously, if I didn't have to alter anything, I would like that better.
 

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Ok, then, let's get to the root of it. If you were to hop-up your engine from the 235 hp I'm supposed to have to something more substantial, will the stock tranny keep up, unmodified? Seriously, if I didn't have to alter anything, I would like that better.
From a geartrain standpoint, it depends on how far you go with your mods. Geartrain life will go down with any increase in torque - the more you increase the torque, the more the life will be shortened. And the decrease in life is not necessarily linear with torque. In the case of pinion gear needle bearings, for example, life decreases based on torque to the 10/3 power. So doubling the torque will give you 1/10th the life.

You will probably not get to the point where your trans will instantly self-destruct when you mash the pedal. Also, remember that you don't drive at wide-open-throttle all the time, so you only really see max torque values for brief periods. Still, there will be a decrease in geartrain life. How much is difficult to quantify.

A bigger concern would be the clutch packs. They have a fixed torque capacity (based on line pressure), so if you exceed that, they will slip and fail very rapidly. You will slip your clutches long before you break gear teeth or other hard parts. Frankly, I would avoid making any performance mods with a stock trans. I'm not sure just what's offered in the aftermarket, but it should be possible to use the UD and OD clutch packs from a 68RFE (diesel) transmission (in your 545RFE / 65RFE trans). That would give you significantly more torque capacity. You do have to change some of the hard parts (the UD/OD reaction plate, and OD/Rev pressure plate) in order to use the 68RFE clutch packs. So I would recommend that, if you're doing performance mods. I'm not sure how this would affect the trans controls. You would definitely need to re-learn (quicklearn) the clutch volumes, and then take it easy for a few hundred miles while the shift adaptives adjust. I believe the adaptives would compensate for the added clutch capacity, but I am not a controls expert, so I'm not positive.
 
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