545RFE not shifting into overdrive

[LennynSquiggy]

I have a 2008 Ram 1500 5.7L Hemi with a 5 speed transmission.



My truck doesn't seem to want to shift into 5th gear at highway speeds. I had diagnostics done on the transmission and the shop said it was doing exactly what it's being told to do. They did not recommend servicing it at this time.

Fluid is full and red with no burning or dirt.

PCM has been reset (battery disconnected overnight)

TPS/Accelerator pedal calibrated

There are no fault codes or dash lights.



Today I took it on the interstate and at 70mph I switched to Tow/Haul mode, the transmission downshifted and the rpms went from 2100 to 3200. Then I switched to O/D Off and the rpms didn't change and no transmission shift. In Tow/Haul mode 5th gear is disabled. O/D Off mode 4th and 5th gears are disabled so I should have seen another downshift but didn't. When I switched back to normal mode the transmission upshifted once but I believe it should have been twice since two gears had been disabled. (Maybe when it upshifts in that situation it bypasses 4th and goes straight to 5th?)



Normally at about 70 mph the transmission will shift into overdrive and the rpms will drop from about 2100 to 1100/1200 and go up 2 or 3 hundred at 75mph..



I noticed the problem when during a 120 mile round trip on the interstate saw me burn 13 gallons of gas. Normally during that round trip I burn half that.



If the transmission is doing exactly what it's being told to do then what part/sensor isn't giving it the instruction to shift into overdrive? And how do I test it's functionality?

 

[Burla]

OD pistons always go out first on the RFE. You can just take VB off and see if the ring rubber is toast are still good. Yeah you will want to service trans since it is open, could be cross leak if pistons are good, which means new VB pr gasket.

Product Overview: ATS 68RFE Valve Body and ATS Co-Pilot

Clint Cannon, President of ATS, describes the inherent weaknesses of the 68RFE (545RFE, too) valve body. This is a comprehensive overview of the numerous pro...

youtu.be

 

[Fast69Mopar]

I have a 2008 Ram 1500 5.7L Hemi with a 5 speed transmission.



My truck doesn't seem to want to shift into 5th gear at highway speeds. I had diagnostics done on the transmission and the shop said it was doing exactly what it's being told to do. They did not recommend servicing it at this time.

Fluid is full and red with no burning or dirt.

PCM has been reset (battery disconnected overnight)

TPS/Accelerator pedal calibrated

There are no fault codes or dash lights.



Today I took it on the interstate and at 70mph I switched to Tow/Haul mode, the transmission downshifted and the rpms went from 2100 to 3200. Then I switched to O/D Off and the rpms didn't change and no transmission shift. In Tow/Haul mode 5th gear is disabled. O/D Off mode 4th and 5th gears are disabled so I should have seen another downshift but didn't. When I switched back to normal mode the transmission upshifted once but I believe it should have been twice since two gears had been disabled. (Maybe when it upshifts in that situation it bypasses 4th and goes straight to 5th?)



Normally at about 70 mph the transmission will shift into overdrive and the rpms will drop from about 2100 to 1100/1200 and go up 2 or 3 hundred at 75mph..



I noticed the problem when during a 120 mile round trip on the interstate saw me burn 13 gallons of gas. Normally during that round trip I burn half that.



If the transmission is doing exactly what it's being told to do then what part/sensor isn't giving it the instruction to shift into overdrive? And how do I test it's functionality?

At 70mph, even with a 3.92 rear gear, you will cruise at about 1900rpm. With a 3.55 rear gear, you will cruise at about 1750rpm.

If yours is dropping from 2100rpm to 1100/1200rpm something is wrong.

You should look at the shift schedule chart to see which clutches are applied for each gear.

You will see that 4th gear utilizes the O/D Clutch and the 4C Clutch. 5th gear utilizes the O/D Clutch and the 2C Clutch. When you have your scan tool connected, look at the data stream in the TCM and monitor each clutch application so you can verify that each gear is being commanded and the transmission is responding in the appropriate manner.

4th gear ratio in the 545RFE is 0.75:1 and the 5th gear ratio is 0.67:1 The RPM drop between 4th and 5th gear is very small and almost impossible to feel while cruising and upshifting.

 

[LennynSquiggy]

I'll check that, thanks.

What could be wrong that made the rpm drop like mine did?

 

[LennynSquiggy]

I think the PCM is still in the relearning process because today I was running 1900 rpm at 70mph. I've noticed that its much harder to feel each shift than it was before the reset. According to my scanner it looks like the transmission is shifting properly and utilizing the correct clutches.

So it looks like this was much ado about nothing.