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The old 53 is being primed to be my shop truck. I need something that I do not care if I get a little dirty. I want to toss an engine in the back or go to the salvage yard and not worry about anything. This truck has one last flaw I need to correct. It still has the Stock Gear Ratio of 4.11:1. Living in Rural Kansas we spend a significant amount of time on the road so I would really like to toss the idea of having a maximum speed of 50 mph. There are TONS of articles on what to do about this, but the one that is the least invasive and makes the most sense is often overlooked. Rather than install open driveline, different transmission, custom driveshaft, leaf springs or an adapter, etc, how about lets just change the Rear End Gear Ratio from 4.11:1 to 3.55:1. This is not a simple operation by any means, but any competent shadetree mechanic will be able to do it with my new How-To Article on the subject. It has not been released yet, but it's almost finished so stay tuned. What makes this procedure so special is that it's the first of its kind to offer a method that will not require you to remove (or mess with) the connection at the transmission at all. You work strictly in the back to accomplish the swap.
What exactly do you get when you do this Gear Swap? Let's talk about the engineering behind this...
Differential Gear Ratio determines the number of times the drive shaft (or pinion) will rotate for each turn of the wheels (or ring gear). So if you have a 4.11:1 gear ratio the drive shaft turns 4.11 times for every turn of the wheel.
Gear ratio is calculated by dividing the number of teeth on the ring gear by the number of teeth on the pinion gear. The higher the number, the lower the ratio: a 4.11 gear has a lower ratio than a 3.55 gear. With a lower gear ratio the drive shaft (and thus the engine) turns more for each revolution of the wheel, delivering more power and torque to the wheel for any given speed. Lower ratios are generally desirable when going off-road. Higher ratios are better for freeway driving since they run at lower RPM’s and offer better fuel economy.
The gear ratio calculator I used put the stats as follows:
4.11:1 Gear Ratio at 60 mph will require you to push the engine to 2950 RPM.
3.55:1 Gear Ratio at 60 mph will require you to push the engine to 2500 RPM.
(Calculated with 28 inch diameter tires (16 inch stock rims)
You can see the pics for the new How-To Article Here. I will announce its completion hopefully in next week's Tip of the Week. Special THANKS to my friend Joe over at Mother Trucker. He is the guy who supplies these 3.55:1 Gear Sets for the Torque Tube systems for $350 (a hundred less than the vendors) and has lots of them in stock and ready for shipment. I got mine in 4 days! This is not just cheaper but will prevent you from getting hit with the usual Backorder Ponzi Scheme known to happen from another vendor.
Since I am not in a hurry to get anywhere, this mod will allow for faster speeds, but also better fuel economy. Most stock AD Owners say that was the single most significant modification they ever did. While this modification will probably not satisfy those who want to drive on the freeway as a daily driver, sometime in the future we will discuss how to do a proper bolt-in driveline swap to take this idea further.
By the way, I am in need of help in completing this document in one area... I need a reliable vendor for the Shim Pack. These Shims are round and are placed on the shaft (see pictures) so I am not sure where to reliably find them. Once this How-To goes live, all "Installation Pack" part numbers will be available for us to choose JUST the bearings, seals, sleeves, gaskets we need rather than getting gouged for things we do not need. Seeya Next Week!
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