Results on 3.73 to 4.56 gears

[BSilveira]

I finally broke in my new 4. 56 gears. I had 3. 73s before. The first 5 break in runs were 10 miles each. Then I made 2 runs about 40 miles each. Today I drove 250 mile with a few cool down breaks in between. After I let is cool down for 2 hours, I opened her up a few times and did a few starts.



It pulled a lot hard at those speeds. Starts were an improvement. The 37" tires were on the edge of spinning. I was kinda hoping to roast them at take off. The launch shot the RPMs to 3,200 and the transmission couldn't keep up. What causes this? When it shifted to 2nd, it pulled real good going at an incline. Getting on the freeway at an incline made the front end feel real light.



What rpms should these trucks be running going 65mph in 4th? I was around 1800 going up a slight hill.

Sorry for the long post.

 

[Bodie]

I think 1800 @ 65 would be great. The whole need for a lower gear in a diesel thing is kind of controversal to me... . Considering you only have 3k rpm to play with 4. 56 would be to low for me, but I do alot of highway driving, if I cruised around town and wanted more light to light power, the lower gears would be a good choice. I say 2000 @ 70 is perfect, when unloaded.

 

[CBrahs]

I too was considering making a gear change but have to think about what kind of weight I will be pulling to justify that kind of gear. I think at most I will change over to 4:10's but I was also thinking of going to 40 inch tires. I like the fact I am at 1850 RPM @ 78 MPH and still get 18 MPG. Am selling my 5er since the truck is too tall and not big enough to pull it (42 footer).



What are your RPM's on the freeway? If I did my math right, I would need to go to a 4:34 gear to match what it was with stock tires. 4:56's might be too much with only 3k of RPM range.

 

[Summit]

Silveira, did you adjust your computer for larger tires? if so and your shifts seem to hang too long than you might need to adjust the kickdown cable.



your transmission will thank you for the 4. 56's with 37's.

yeah, it seems too low at high speeds but it sure is good for racing/towing.