700R4 Conversion -vs- Ring and Pinion Conversion 3.73

[Thomas_G]

Has anyone exchanged the gears instead of the replacing the transmission for more highway speed?

I noticed the cost of transmission exchange vs ring and pinion (3.73 or 4.10) and wanted to know if anyone has had good results in gear ratio exchange over the 700r4 swap. The parts are hard to come by for the transmission swap and seems like quick and easy to do the gears?

 

[tim292stro]

I'm assuming you have a Non-M1009 to be asking this question... You leave a lot of potential variables open.

Go to www.grimmjeeper.com/gears and pop in your specs.

The TH400 is a 1:1 3rd gear, so if you keep the standard 31" tires (can actually be 29" or less diameter), your top speed will still be crippled. Just popping in a few numbers, it looks like 65MPH with 3.73's would put your engine at 2770RPM - wicked high. It's only an improvement of -300RPM over the 4.10 factory gears about 3000RPM for 65MPH.

The M1009 has a 3.08:1 which puts 65MPH at about 2300RPM. IIRC redline for the 6.2 is 2500RPM...

 

[patracy]

M1008, M1010, M1028, and M1031's had 4.56 gears Tim, not 4.10. Governed high idle (AKA redline) is 3400rpm.

 

[tim292stro]

ACK! Error, error, burn everything

Yeah, woops

 

[Chaski]

No, I have not done it.

I went the opposite way... 4.88 gears with a 700r4 and 37" tires.

Changing gears in the 14 bolt is easy, a shade tree mechanic one day job. However swapping gears in a Dana 60 is a lot more involved. You should really use a case spreader, and it involves a lot of trial and error to get bearing preload and pattern correct. You also need a direct read inch pound torque wrench and a clamshell bearing puller. That being said I did mine myself. You can swap in 4.10 ir 3.73's but you will not be able to use your carriers. Because of the 4.56 gears your carriers place the ring gear closer to the pinion. I don't think a "thin" gear set is manufactured to install on a 4.56 & up carrier. This would mean you would have to find a 4.10& down carrier for both axles. Of course this makes the swap an even bigger pain, because it takes more work to correctly set up the bearing preload and pattern when using a carrier that was not originally installed...

Honestly I think the 700r4 is easier. If you want to rebuild it yourself you can, the specialty tools are pretty easily home made, or bought online. Plus the 700r4 gets you a lower first gear and overdrive. The only difficult part to track down is the TV cable bracket. Expect to do some fiddling if you do the 700r4 swap. You may need to tune the governor and fidget with other things to make it 100%.

 

[Csm Davis]

700r4 will be much easier

 

[Recovry4x4]

Aside from the pure mechanicals of it, the 3.73 gearset will hurt performance. The anemic 6.2 needs that gearing to do any heavy work. Not only will the 700R4 better reduce RPMs at highway speed, it will also increase power at the wheels during takeoff thanks to the 3.06 first gear.

 

[Jozseph]

[SNIP}..... I went the opposite way... 4.88 gears with a 700r4 and 37" tires. {SNIP]

Chaski,

What was the reason to go 4.88 gearing?

Joseph

 

[Skinny]

The TH400 is a great pretty much bulletproof transmission that works in many HD applications. Having said that, it is quite a turd performance wise for any normal day to day driving. It lacks gearing on the low end, no OD, and no lockup converter...very inefficient. Unless you are loaded at max GVW all the time, running some serious HP through it, or never drive above 45mph, you will win by getting rid of that transmission.

I love mine because it works flawlessly but EVERY time I hit 45mph, I keep waiting for it to shift and realize "oh yeah, that's all she has"

 

[Chaski]

Chaski,

What was the reason to go 4.88 gearing?

Joseph

I have a confession... I own a 1982 GMC K2500 diesel with a home built 700r4 and D60/Corp14 with a detroit. Kinda a M1008 clone.. It used to have 4.10 gears, I installed 4.88 gears so that my final ratio would be identical to what it was with 4.10's and stock tires. Since both of my axles had 4.10 & down carriers I couldn't install used 4.56 gears. Since I needed "thick" cut gears and had to buy new ones I went with 4.88 just because the math worked out. If I would have had 4.56 gears I would have left them alone.