Hello,

I have a 2001 7.3, CC, SRW, Automatic with OD.

Over the weekend I took my first long trip towing a Travel Trailer weighing in at about 6000 lbs. Also had 4 in the truck with a motorcycle in the bed.

I was in upstate NY from Poughkeepie to Tug Hill Plateau, then Ithaca on the way home (college tour). There were a lot of hills to climb.

I noticed that the transmission wanted to stay in OD until about 50 going up a hill, it would then drop down 2 gears when it could not hold OD.

I felt like it was trying to hold OD for too long, the rpms would go way down but it would hold in OD. I was expecting it to drop down only one gear. When it dropped down 2 gears the rpm's would go to about 2500 and felt like it should not have been in that gear. If I let up on the throttle a little bit it would jump up to the next gear and do fine.

Is this normal behavior for the transmission?

Thanks.

 

Sounds normal to me.
You need RPM when pulling a load on the hills.
.
There's another possibility.
Your truck is suffering from some cause of power loss and you are not aware of it.
Either a fuel restriction or a weak HPOP or something else that is not allowing the engine to develope full HP under a load.
What happens in that sort of scenario is either you or the cruise control call for more throttle than is normally necessary and the programming responds appropriately, ie downshift the transmission to raise engine RPM.

 

I understand that dropping a gear to raise the RPM's is needed, but why drop down two gears when dropping down one will solve the load problem?

The truck is new to me, but seems to have plenty of power, at least more power than my 6.9 85 F250 had. Does anyone on the list have a similar truck that drives the NY Thruway from Albany to Utica? Can you hold overdrive on those large hills pulling a heavy load? Or, route 81 from Rome to Binghamton?

 

Riddle me this......

Does the transmission only stay in the perceived 2nd gear for about 2 to 2.5 seconds?

If so, it's simply the torque converter clutch being commanded to release in 3rd gear on the 4-3 downshift and it's normal for most of the non-PMT1 programming of the time.

 

Once it drops down it will stay in the 2cd gear all the way up the hill unless I let up on the throttle a bit, then it goes into 3rd and holds third easily. I'm assuming this is a 4 speed transmission...?

To me it feels like it is holding in overdrive too long, its really loading up the engine at low rpms. then when it drops down it senses it should be in 2cd. But when it drops down it feels like its in the tail end of second if it should be there at all.

Maybe I'm just used to the C6 on my old 6.9 diesel. It never lugged the engine down to low rpms.

 

When you are approaching a hill, push the OD off button on the end of the shifter. You are hurting your transmission by trying to pull hills with the OD on.

 

What Cody is saying is that it's dropping down into 3rd gear. The subsequent "shifts" you feel is actually 1 torque converter lockup, and 1 upshift.

When the torque converter locks up, it drops the RPM's and feels like an upshift. At 50 MPH, it's dropping down into 3rd gear, not 2nd.

 

^^^^^ What he said.

If the transmission begins hunting for gears while in the hills, it's best to turn off OD and let it run in 3rd. The constant gear hunting when under load builds a lot of heat in the stock trans, reducing the life.

 

Ok, makes sense that the torque converter locking up makes it feel like a shift.

I've got it, no more OD on hills.

Thanks for the information.

 

I have manual transmission on my 7.3 and I pull 13k trailers on 6th gear on most of the freeway grades, so I can vote that the engine has good power for pulling. Maybe my engine is better than average, but still IMHO it might be the transmission program playing the games.
Converter lock usually makes rpm changing in 200 range, while gear change usually over 500 rpm. That should be easy to differ.
Than couple years ago I was towing Airstream trailer with SUV having on board computer. The SUV had enough torque to pull the hills on highest gear, but playing with shifting I noticed that I could actually improve mpg by dropping from OD in some situations.
Bottom line -don't grind the engine on high gear hoping it will save you some fuel, because it will not.

 

Actually, quite the opposite.

A gear shift with the converter unlocked (1-2 upshift or 2-3 upshift) will provide a smaller RPM change, depending on load, pedal position, and RPM's. Remember that the torque converter is unlocked, meaning it's going to slip while in gear. This is "fluid coupling". The engine is spinning somewhat independent of the transmission.

The actual point of when the converter locks typically causes a larger RPM drop than the 1-2/2-3 upshift, because the "fluid coupling" is gone. The converter is locked and the slippage is gone. There is also another large RPM drop at the 3-4 upshift. This is when both the converter is locked, and the upshift occurs.

Again though, RPM drops regarding shift points and/or converter lockup points vary depending on load, RPM, and pedal position.

 

Its definitely dropping into third and unlocking the t/c. The reason it doesn't lock back up until you let off is because there would be a very large drop in rpm and it would slip the t/c clutch too much at first.