The Mystery that is the 68RFE

Try having it go to 4th unlocked passing in the interstate.
 
4x4dually said:
So someone 'splain dis to me. I come from a long line of manual drivers and this is my first diesel auto so bear with me.

I'm sick to death of this downshift to 5th when I stomp it on the highway and wrap it to 3200 rpm bull crap. If a lock up switch were to be installed and turned on, that would keep it locked into 6th correct? How does that work exactly....I'm an auto dummy. I shouldn't need to downshift when running 1800 in 6th when I want to pass. It just wastes time and wraps the hell out of it.
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I'm trying to comprehend this in a way where your desired result is actually desirable. If you "stomp it" at 1600 RPM in sixth you're going to wipe out both sides of the highway with smoke when throttle input doesn't match the boost input at such a low RPM.

Somewhat related, re-applying cruise control causes this to happen. Dropping gears and seemingly 100% throttle to get to the previously saved speed. That, is a bit outrageous in my mind.
 
USARMY12V said:
I'm trying to comprehend this in a way where your desired result is actually desirable. If you "stomp it" at 1600 RPM in sixth you're going to wipe out both sides of the highway with smoke when throttle input doesn't match the boost input at such a low RPM.

Somewhat related, re-applying cruise control causes this to happen. Dropping gears and seemingly 100% throttle to get to the previously saved speed. That, is a bit outrageous in my mind.
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6.7's spool so effortlessly you don't get the plume of smoke with good tuning.
 
Yes...my truck wouldn't smoke out a lane of highway unless you dump a gallon of used motor oil in the filter.

I see Lavon reading...please educate me, Sir. I don't want to rip her guts out, I just don't want it to downshift when I slowly push down on the pedal. I'm not stomping it to the floor....I just want it to GO not spin up and not move.
 
I believe the downshift is to save the under/overdrive unit.
 
AHall said:
I believe the downshift is to save the under/overdrive unit.
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This is exactly what I've heard as well. Even with the oversized OD you can get aftermarket, most tuning still does this to avoid eating those clutches up.
 
I realize this....but if a person keeps their foot pressure decent and pays attention...is the lockup switch capable of keeping it from downshifting? Isn't that how it works on a dyno or no?
 
Lock up switch I'm referring to is for the converter. A good tuner should be able to adjust the kick down strategy to satisfy your driving habits.
CompD Mobile Device
 
rjp said:
Lock up switch I'm referring to is for the converter. A good tuner should be able to adjust the kick down strategy to satisfy your driving habits.
CompD Mobile Device
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I'm running the H&S OD tune. I guess I need to see what all I can do with that. Someone told me that if you lock up the torque converter...it won't shift down. I'm just trying to find out if that is true or not as I have no clue.
 
4x4dually said:
I'm running the H&S OD tune. I guess I need to see what all I can do with that. Someone told me that if you lock up the torque converter...it won't shift down. I'm just trying to find out if that is true or not as I have no clue.
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Mine will shift up and down just fine with the converter manually locked. The adjustments you're looking for will need to come from MCC,OD alone is only capable of so much.
CompD Mobile Device
 
I see. Back to knowing nothing about a slush box. LOL I'm gonna have to buy Lavon lunch sometime and pick his brain...what's left of it. :hehe:
 
rjp said:
Just a fyi; I run straight OD tuning with all settings maxed except line pressure. I've been running this way for years now and the results have been very positive. Last I checked, Suncoast was basically using the same tuning for the Mega units as I am, just in the form of MCC. My tuning never changes and I run mine on the 3200 pulse setting all the time. This may be why my trans seems to hold up so well...

I am also running a manual lockup Valve body.


As of current, Intermediate and output shafts are still stock, It's apparent they are solid enough to hold 1000+ HP as I have yet to break one.
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So are you saying that you somehow tuned out the adaptation feature of the transmission?
 
AHall said:
I believe the downshift is to save the under/overdrive unit.
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Automatics shift into whatever gear is best suited for the input/load conditions unless you manually tell it otherwise. You romp down on any vehicle, it's going to drop gears for mechanical efficiency. If you kept a truck locked in 6th and floor it, it's not going to accelerate nearly as fast as if you dropped gears to create a mechanical advantage. Try accelerating in a manual from 50-70 in sixth then do the same thing in say fourth or fifth.

Even on old 47RE, the TPS is connected to a wire that in stock form commands line pressure at the valve body and can cause a kick down if input requires a gear change.
 
I understand the concept. Difficult to explain. With a downshift the truck falls on its face and has a major delay. When locked in 6th under partial throttle the truck hits boost nearly instantly and sucks you to the seat. Really utilizing that low end 6.7 torque. We are discussing part throttle acceleration, not full throttle sweeps also.
 
4x4dually said:
I realize this....but if a person keeps their foot pressure decent and pays attention...is the lockup switch capable of keeping it from downshifting? Isn't that how it works on a dyno or no?
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From what I've discovered, throttle position dictates nearly everything a 68RFE does in positive and negative regards. The 3-4-3 downshift clunk a lot of people experience happens on my truck when I'm going about ~40mph then have to get off the throttle when I had just been accelerating under normal conditions. It seems to also happen under certain scenarios around the same speed when slowing down with the exhaust brake. At roughly 55mph when sixth is first hit, if you give it any more than probably 30% throttle quickly it down shifts, if you slowly apply power it seems like it will stay in sixth but take significantly longer (but is more fuel efficient and easier on the trans) to slowly accelerate. If you give it to much, it drops down into 4th and rises like 1000rpm as you have experienced.
 
AHall said:
I understand the concept. Difficult to explain. With a downshift the truck falls on its face and has a major delay. When locked in 6th under partial throttle the truck hits boost nearly instantly and sucks you to the seat. Really utilizing that low end 6.7 torque. We are discussing part throttle acceleration, not full throttle sweeps also.
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It seems to me in general that third and fourth are finicky gears in this transmission. If you accelerate from first or second onwards fourth does work fine, if you get in it anytime thereafter it's like it lets the engine race for a second unlocked before locking the converter in fourth. Perhaps this is to dampen the shock of an instant load? That's all I can figure. Shock load is arguably the biggest threat to these transmissions whether it be tearing up the converter, input or OD
 
Also, I don't know this because I've never inspected mine to see as of yet, but turbine housing soot buildup could also factor into this weird boost response.
 
Mine shifts great most of the time. Every now and then a clunky shift. I was hoping that Hardway could change the 6th to 4th tps input from something like 20% to 50% and I would be happy. I need to follow up with them to see if Ryan has any ideas to refine the tune.
 
CorneliusRox said:
So are you saying that you somehow tuned out the adaptation feature of the transmission?
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No Sir, just stating that I never adjust my tune. Its always WFO so its always seeing the same throttle to torque input.
 
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