Re-gear 14B FF from 4.10 to....?

[someotherguy]

1993 C3500 dually, 7.4, NV4500, 4.10 14B FF, 225/75/16 tires about 29.3" tall.

On the roads in Mexico folks are driving around 80MPH which has the truck turning 2800ish (2745 RPM according to gear calcs) for extended periods.

Every 14B FF I've seen in these trucks is a 4.10 so if I wanted to change gears I'd be spending some bucks to do so, instead of just hunting boneyards looking for a unicorn.

3.73 would only drop about 250 RPM - from 2745 to 2498

3.42 would drop 455 RPM - from 2745 to 2290... which seems more worthwhile for cruising speed..

...but I wonder how it would impact the overall driveability of the truck? This being the early version of the NV4500, it's geared L-6.34, 1-3.44, 2-1.71, 3-1, OD-.73

*DISCLAIMER* since major project creep has already taken its toll on what I've intended to spend on the truck, the likelihood I will actually DO this is very, very low - just "getting it on the list" is unlikely, nevermind the $1K+ it could cost just in parts. But it's an interesting thought exercise, for me, anyway.

Richard

 

[bluex]

I want to do this with mine as well. 3.42s if not a 3.21. I did the calculations an tried pulling the gears in it now as low as I could to simulate it (say 25 mph in 4th) an it was no race car type acceleration but it pulled out of it fine.

I have had 3 different places tell me not to do less than 3.73. I don't understand why either. It's not that much of a change to justify the expense imo. I want 3.42 max if I'm going to do it.

At most I'm going to tow something a handful of times a year. My trailer is just under 3k an even if I put a 5k car on it I'm only at 8k total. I understand where they are coming from but I think I'll be fine for how I use it, especially after I get it tuned with the 411 swap.

 

[Caman96]

Looking car-part.com, it looks like it was definitely a factory option as they are listed.

Car-Part.com - Used Auto Parts Market

www.car-part.com

 

[someotherguy]

Looking car-part.com, it looks like it was definitely a factory option as they are listed.

Car-Part.com - Used Auto Parts Market

www.car-part.com

I don't doubt they exist, but finding one that was ordered that way seems like a unicorn. Never, ever seen one in person. Heck I've never seen one in person. After checking car-part, I see a total of 8 listed (actual GU6 indicated) around the country - 2 of those are the same truck, 4 of those say "CHECK ID" and 1 of those says "round housing" ... so I suspect they may not be very accurate listings.

...especially the one with the 3500HD pictured, as those only came 4.63 and 5.13, and are Dana 80's (or Rockwell in the very first trucks.) No way the SPID label in that truck reads GU6 unless it has a glovebox insert from a different truck.

Richard

 

[Caman96]

I don't doubt they exist, but finding one that was ordered that way seems like a unicorn. Never, ever seen one in person.

Richard

I was surprised at how many I found on car-part.com in my area.

 

[Komet]

You can do 3.42s as long as you can bring the torque down low. I'd assume the 7.4 would excel in that area so I think you'd be good to go.

 

[1998_K1500_Sub]

...but I wonder how it would impact the overall driveability of the truck?

For simplicity sake, I often equate a one-step gear change (e.g., 4.10 to 3.73, ~10%) to a similar change in weight of the vehicle (e.g., ~10%).

In your case, to get a "feel" for a 4.10 to 3.42 change (~83% decrease in axle torque), trying loading the vehicle to increase it's total weight accordingly, e.g., by 1/.83 = 1.20x. Load it down, take it out and drive it. See how it feels accelerating.

This isn't a perfect simulation, but it's easy to do.

 

[someotherguy]

I was surprised at how many I found on car-part.com in my area.

I was editing my post after looking, but my wife just popped in the door so my edit came after your last reply. Look at the distances, and the results - nationwide, there's only a couple that seem like they could possibly be legit, accurate listings.

Richard

 

[someotherguy]

For simplicity sake, I often equate a one-step gear change (e.g., 4.10 to 3.73, ~10%) to a similar change in weight of the vehicle (e.g., ~10%).

In your case, to get a "feel" for a 4.10 to 3.42 change (~83% decrease in axle torque), trying loading the vehicle to increase it's total weight accordingly, e.g., by 1/.83 = 1.20x. Load it down, take it out and drive it. See how it feels accelerating.

This isn't a perfect simulation, but it's easy to do.

That sounds reasonable. I was coming at it from an RPM drop vs. labor/expense viewpoint. I don't see spending a grand on parts (gears and install kit) and my sweat and blood, to drop only 250 RPM.

The truck is just a toy, so I never expect to pull anything heavy with it. If that was my intention for it, I would have taken a somewhat different approach to how I've been modifying it. Of course, if I geared it so low numerically that it seriously impacted the acceleration, it would be less fun as a toy, so that's a factor, too.

Richard

 

[Caman96]

I was editing my post after looking, but my wife just popped in the door so my edit came after your last reply. Look at the distances, and the results - nationwide, there's only a couple that seem like they could possibly be legit, accurate listings.

Richard

I wasn’t trying to find one for you, just examples of their existence. You could call and ask what transmission it came with to answer your question. There’s one very close to me with 88k on it, that would be nice if you did find something like that though.