Help with Underdrive

[Big-D]

Can someone offer advice on whether to purchase a US Gear Under-drive or change ring and pinion?



My truck is a '99 auto transmission with all upgrades from DTT. The rear end is 3. 54 and too high a ratio for towing in 4th gear at 65mph. Third gear runs my rpm's up too high for good mileage, but the transmission likes the higher rpm's. I have seen many the post of newer trucks using the 3. 73 gears without complaints and wondering if a change is worthwhile or the under-drive is a better choice by splitting 3rd and 4th gears.



Appreciate all comments and recommendations. Thanks in advance.

Dave

 

[Shooter]

I had a GV on my 00 auto/354s. I only used the GV for towing out west where the speed limit is 75. To high for 3rd and DC od was 2000 rpm, to low tho pull the grades and not recommended by any one even DTT. The GV and 3rd ( direct was ) 2250 @ 75. REAL SWEET.

 

[Turbo Horseman]

What are the cost and maintenance/durability comparisons?

 

[rweis]

I have pondered this same question. Have read every thread I could on 3. 73, 4. 10.



Right now I have a 8k 5er and 3. 54 and it pulls good at 65. In about 4 years I am going to a 12k+ 5er and at that time will go to 4. 10.



The points I am unsure about the Underdrive are total weight (30k I think), but 80% (safety factor) of 30k = 24k



The shifting of the US Gear harsh. GV not an option with e brake.



Heat build up of the US gear assembly (have to have exactely the correct amount of fluid, not over, not under, seems unforgiving in this area).



If you change the ring & pinion then you know you have a engineered solution and not an add on. It should be > 100k and you probably will change axle and carrier bearings as well, ie a complete job.



Cost is probably about the same when it gets all said and done.



Not convenced yet, but leaning that way.



Bob Weis

 

[Snow man]

Dave,you can drop a tire size,and pick up a 125RPM or so. If you have 245 tires,go to 245. If you go with 4. 10 you will love htem towing,but empty they can get annoying at hi speeds.