60 mph at 2600 rpm

[Soaringcook]

I have a 2000 international 3800 with a dt466e and an allison mt643

I cant figure qhy the rpm are so high at 60mph. I have 4.10 differential.

I was told it should be at 2200 rpm when going 60mph

It seems to shift all gears. I feel a tug when going from 1st to 2nd and one from 2nd to 3rd and finallt one more when 3 to 4th. The only odd thing is that i feel a bump when slowing down fast from 45 mph to a stop sign. Like a little push at the end before it stops completely. Please any help apreciated.

[EastCoastCB]

what size tires does it have?

[Soaringcook]

Tires arw 11r225

[s2mikon]

Mine was 2000 @ 60 mph with 4.1 gears and llr22.5 tires. Have you checked for speedometer and tachometer accuracy? Also are you sure that the torque converter clutch is locking up?

[Soaringcook]

Not sure if i would even know if the torque converter was locking up. Not sure what to look for.

[Soaringcook]

I doubleckecked the tachometer and speedometer with a nexiq reader and servicemaxx

[s2mikon]

The shift into 4 gear will be a large drop in rpm compared to the other shifts. 4th gear is only lock up. About 40% change.

[s2mikon]

Is this a front engine or rear engine.

[s2mikon]

Torque converter pistons on these can sometimes crack and leave you without lock up.

[s2mikon]

Your transmission is new enough to have modulated lock-up in other gears.

[Soaringcook]

Front dog nose

[Soaringcook]

So how many drops in rpm should i notice if i go from stop to 55 mph?

Its an allison mt643 qith 4 gears

[s2mikon]

Mine drops from about 2500 in 3rd to about 1700 in 4th.

[Soaringcook]

Does anyone know how to chexk the modulator and kickdown cable?

[s2mikon]

If the modulator cable fails it will short shift. In other words it will not rev up to the limit on each shift. The governor overrides the modulator and makes it shift sooner, and the modulator delays the shift point depending on the throttle position.

[EastCoastCB]

I know with my old 466/643 The lockup in 4th almost felt like a 5th gear with additional boost. Just throwing that out there fwiw.
If you're not seeing/feeling any trans slippage my only guesses would be its not getting into 4th or it no longer has a 4.10 ratio.

[Soaringcook]

I just found out i have 4.81 gears, not 4.11

So what should my rpm be at 60 mph?

[s2mikon]

2300?? I think.

[s2mikon]

Here you go. Save this website. https://wellertruck.com/road-speed-calculator

[Soaringcook]

Ok so 2350 it is, so why am i runint 2650 at 60mph?
Im getting so frustrated with this bus