T-19 gear ratios and shift points

PossumTruck

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(I have no tach, so MPH is really my gauge) What exactly are the shift points for a 6.9L with a t-19? Specifically, I'm working through losing a power bad in the 3-4 shift. At one point, I was doing research and was told about 35 mph was the high end for 3rd gear. I knew that wasn't right because I could run it to 45 when I wanted (and the engine sounded loud), but it drove better that way. Rear axle is a Sterling with a 3.55.

My issue has been that the 3-4 is basically that I lose power as soon as I shift to 4 - and in a way that seemed odd/pathetic.

I could strain on the road to keep 55 on a steep hill, unloaded. Unburnt fuel cloud and all.

Today I took 3rd gear over 50 mph a few times, sure made the 3-4 better, but my reading/research has told me that is way too fast.

Any insights? Truck is a Cab & chassis, not sure if that has an effect on the ratios or if my research was bunk.
 
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u2slow

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Whatever anyone says, needs to be qualified with an axle ratio (assuming a certain tire size.)

Sounds like you're geared 'tall'. 3.54 and 4.10 are the most common ford ratios.

Have you turned up the fuel? That helps the power. Good idea to get a pyrometer though.
 

ROCK HARVEY

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You can play around with this gear ratio RPM calculator from spicer to see what your speed is at various RPMs: https://spicerparts.com/calculators/transmission-ratio-rpm-calculator

3rd gear in a T-19 is 1.41:1, so assuming 4:10 gears and 33” tires, you would only be doing 2050RPM at 35mph. 45mph would be 2650, and 50 would be 2950RPM. Of course if your tires/axle are different so will your RPM
 

ROCK HARVEY

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With 3.53 gears, you’re only at 1780RPM in 3rd doing 35mph. If you shift into 4th at that point, you’re entering 4th gear at only 1260RPM. You can definitely stay in 3rd longer.

That being said, I shift into 4th around that RPM all the time and don’t feel like I’m lacking power. I wonder if your timing is slightly off or your injectors/pump are wearing out.
 

PossumTruck

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holy cow I was way off. For in town and regular driving, short shifting is never an issue, but there are some long/steep grades in my normal driving that always annoyed me. I was just never certain as to where I should be cautious with the rpms. My ear-tach was being quite the nanny. 55 MPH is just under 3K rpms, so I assume safe if redline is 3500-3800.
 

franklin2

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It has a governor, so don't worry about over revving the engine going up hill. You do need to watch it going downhill though.
 

FrozenMerc

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See the chart below. I created this in Excel to understand where my truck is at. I have a T19 with an Advance Adaptors Ranger Gear Splitter (27% Overdrive, dotted lines), and a 4.11 Rear axle, spinning 31" tall tires. Really, the 2-3 shift is the biggest gap. About a 1200 rpm drop in my truck with a 4.11 rear. I typically shift between 2500 and 2800 rpms (Black Line), unless I am puttering around town. This means shifting at 15, 25, and 45, (unless I have a trailer on, then I like to split 2 and 3 as well). With the over drive, there is one more shift between 55 and 60.

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Here is the same chart for a 3.55 rear end and the Overdrive removed. Shift points are now 18, 30, and 52.

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u2slow

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Honestly, i think you'll like a tach more than trying to shift by the speedo.
 

PossumTruck

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Frozen Merc: That is incredible. thanks!
U2slow: Working on it. The ~$200 they are asking on ebay is just off-putting to me. I have a sensor to screw in and I think I have the circuit board to enable a Tach if all I could get is a tach (no cluster).
 

PossumTruck

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I wonder if your timing is slightly off or your injectors/pump are wearing out.
Injectors are newish, pump is from before I got the beast in 2019, so unknown there. All things are possible culprits, but knowing how hard I can run it will certainly help.
 

PossumTruck

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Update for internet/history/completeness/purposes. I put into action the 18-30-52 shift points and it worked beautifully. Thank you.
 
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