3700 SP Overdrive?

[jwchameleoncorp]

Vehicle is a 2007 M1083 with CAT C7 and Allison 3700 SP. I already have 307 gears installed but would like to reduce RPMs even more on the highway. Is it possible to add an overdrive to the transmission?

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[Reworked LMTV]

I don't think so. This is definitely a Alison question. Might be much less hassle and cheaper to go with a set of larger tires.

 

[jwchameleoncorp]

Thanks for the reply. Yep, looking at 1400's. From what I've researched that's the largest size possible without lifting the truck or cutting wheel wells to avoid tire rub or limitations.

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[coachgeo]

Presented this question to an Allison Guru who ownes an Allison rebuild and parts supply company with experience in these transmissions. Answer is basically no.

sure one could custom make a gear...... but still would be no go cause the changes would set off a firestorm in the software and put you into limp mode. Now a whole rewrite of software would be required...... and that is all proprietary software and would light of legality firestorm

 

[jwchameleoncorp]

Presented this question to an Allison Guru who ownes an Allison rebuild and parts supply company with experience in these transmissions. Answer is basically no.

sure one could custom make a gear...... but still would be no go cause the changes would set off a firestorm in the software and put you into limp mode. Now a whole rewrite of software would be required...... and that is all proprietary software and would light of legality firestorm

Thanks! That's what I needed to know.

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[Ronmar]

The top 2 gears in the Alison core are already overdriven, but the fixed gear reduction in the transfer case cancels that out... you really want to do this in the axle/wheel area anyway to lower driveshaft RPM...

 

[jwchameleoncorp]

The top 2 gears in the Alison core are already overdriven, but the fixed gear reduction in the transfer case cancels that out... you really want to do this in the axle/wheel area anyway to lower driveshaft RPM...

Thanks for the reply. I have the high speed 307's in the axles. Looking at 1400s for tires. Any other suggestions to get those RPM's down?

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[Ronmar]

Thanks for the reply. I have the high speed 307's in the axles. Looking at 1400s for tires. Any other suggestions to get those RPM's down?

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Figure out a way to get a different ratio other than 2:1 out of the gear sets on the ends of the axles...

 

[Reworked LMTV]

Honestly, these truck don't handle that well at higher speeds. Roll overs are known to be deadly with these vehicles. Saw one article recently. I know it is not what you want to hear, but driving slower isn't always a bad thing : )

 

[jwchameleoncorp]

Honestly, these truck don't handle that well at higher speeds. Roll overs are known to be deadly with these vehicles. Saw one article recently. I know it is not what you want to hear, but driving slower isn't always a bad thing : )

Totally agree, but high speeds isn't my motivation. It's low RPMs to reduce wear and tear on the engine at reasonable speed. I don't plan to exceed 65mph ever.

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