im thinking about changing from 4:10s to 3:55s and im running 2200 at 72 in 6th now, and i think it will be around 1700 with the 3:55 is this correct or close?
what rpm do you guys run in 5th because i dont think i can pull my camper at 1700. i do run 100 highway miles a day ,no trailer and it would be great to run 1700 instead of 2100- 2200.

 

Why not try Gearvendors for overdrive unit. [url]
Two or four wheel drive units.
http://www.gearvendors.com/

 

to expensive and you have to cut the drive shafts. i can get a set of gears.

 

what about a set of 373's?

can 373's be put on a 2nd gen?

 

Where in Indiana are you? I have 3.55s in my truck and have been thinking of going to 4.10s...swap???

 

315's, 6 speed and 3:55's is a nice combo, I ran it for a couple of years and it was great.

In town it pulls you down a bit but highway was perfect. Actually after my 285's are cooked off, I'm going back to 315's.

Jeff

 

you could get a set of 3:73s but not out of a 3rd gen. im looking to run in 5th towing and 6th to get mpg out of it.

 

Just sent you a PM

Dave

 

in 5th gear running over 65mph empty I'm hitting close to 2250-2300
6th gear is 1750ish at 68-70ish on the gps. 70-75mph is 1800ish.

 

i think that would be about right. doesn't a 6 spd with 4:10s and stock tires run 2400 @ 70 mph? i had one but it was a few years ago. thanks for the info.

 

We you able to open and use the spread sheet?

Dave

 

I have 3.55's in mine.In 6th loaded or empty it turns 2000,at 70 mph.

 

umm, weather it loaded or empty it going to run the same rpm. i see you have a 2wd so im assuming a way shorter tire than a 35 so 2000 is probably about right.

 

I am running an automatic tranny with 3.55 right now and 315 tires. Its hard on the truck! I pulled a trailer with about 6500 lbs for 700 miles at 55-65mph twice in the last 3 months and my tranny got HOT! it finally went out 3 weeks ago. If you plan on doing an towing or dragging I would do some research because I am hearing nothing good about the 3.55. Some friends of mine told me the 3.55 seriously underdogs the tranny and makes it work a lot harder than it need to.

Its all opinion and speculation but has been proven in my situation to be right.

 

The rear ratio you currently have, could be part of the problem, but the tire size is most of the problem in my opinion. At 1700 rpm with the 315's should be around 71 mph. With the stock tires again 66mph. (rpm's vs mph are estimates)

The point I'm making is your effective rear end ratio has been changed with the larger tires. Your ratio is somewhere around 330:1 and not 3.55:1. To much load on the tranny in OD.

3.73's at 1700 rpm would be 68 mph and 4.10's 57 mph with the 315's.

If your going to tow with the 315 tires you should change the rear or put the stock tires back on or tow in 3rd gear. (2200rpm at 65 mph) If you decieded to go with a 4.10 ratio, be prepared to buy another carrier for the rear as the 355 won't work. Gears and Carrier about 850-1100 dollars.

I'm pretty sure if you do tow in 3rd gear, the converter will not lock up.
The good thing is Cummins says, when towing you should maintain a speed
that is 2100 rpm or more.

Dave