• Announcements

    • Mopar1973Man

      Quadzilla Tunes   06/12/2017

      QUADZILLA TUNE REPOSITORY - There is now a Quadzilla tune download area. When you submit a tune file to the download area it will automatically create a forum topic that allows discussion of your tune. So export your tune and upload it to the site. Then we all can help out in building better tunes. Check it out gang...
    • Mopar1973Man

      911 Support Group   06/22/2017

      Hey Gang, I've got the 911 support group database back up and running once again. It's listed in the 911 support category. It will allow members to list their contact information and location so other have a listed of members to call upon in the time of need. So if you wish to support other member please stop by and add your listing into the database. https://mopar1973man.com/cummins/911-support.html/contacts/
martinique78

Re-gearing for the Cummins

7 posts in this topic

Posted (edited)

So i have been driving my Fummins Excursion for a few weeks now with no real issues.  However on the freeway i'm turning some pretty high RPM's at 70-80.  Like around 2700 rpm.  At first I thought I wasn't getting lockup but I installed the lockout switch and an LED to show when the PCM was commanding lockup.  all was working properly even without using the switch.  So my next though was to check the door tag for the axel ratio...4.30!!!!!!  holy crap that explains it.  Now I know why from a dead stop that thing feels like it could rip the rear end right out from under it. 

 

What would be a good ratio to switch to?  I have the 2001 24V and the 47RE trans. I'm currently running 315/75/16 tires but I plan to lift the truck and run 36's on it in the future.  Is it even worth changing the gears if i'm gonna be turning larger tires soon or is that ratio still too big for even that setup?

Edited by Mopar1973Man
Edited the title

Share this post


Link to post
Share on other sites

Here ya go

 

 

 

Share this post


Link to post
Share on other sites

You could just change over to the 36's before any regear an see how it does.

 

 Like to see that rig. Did you put the engine in yourself?

Share this post


Link to post
Share on other sites
1 minute ago, JAG1 said:

You could just change over to the 36's before any regear an see how it does.

 

 Like to see that rig. Did you put the engine in yourself?

That's what I was thinking too, it doesn't really bother me that the RPM's are that high.  I just know I could get better fuel mileage if I brought the gearing down.

 

Yeah I did it all myself.  Destroked mounts, switched the input shaft on my Ford transfer case to the dodge input shaft and mated up perfectly to the 47RE.  No change in drive shaft length. Used the V10 radiator and the intercooler from a 7.3. Once I sold off the rest of the parts from the donor truck and my old V10 setup i actually made money on the conversion. Only took me a week and a half to do the swap.  However about of month of prep and lining up the parts I needed. Best decision i've made for that truck.  I was only getting 9.5 mpg with the V10 and now i'm close to 19 mpg if I keep my foot out of it but it's hard to do when it runs and sounds so good.

2 people like this

Share this post


Link to post
Share on other sites

Just remember larger wheels and tires will mean less braking performance and shorter brake life span. This will increase wear in the steering and suspension parts on the front axle. That being said I'm a bigger fan of re-gearing the axle than installing larger wheels and tires. 

 

Just consider I've got 301k miles now and only 1 set of ball joints, 1 track bar. Still got factory tie rod ends, steering box and power steering pump. I've only done 1 brake pad change back at 185k so I'm good till about 360k miles yet. Smaller and lighter wheels mean less wear on steering parts and better MPG's being I'm still holding 27.2 MPG as a high mark.

Share this post


Link to post
Share on other sites

Nice excerpt about the conversion. How did you know about swapping input shafts? That's pretty cool, I must say.

Share this post


Link to post
Share on other sites
11 hours ago, JAG1 said:

Nice excerpt about the conversion. How did you know about swapping input shafts? That's pretty cool, I must say.

Thanks! Lots of reading and knowing that the 2003 and newer dodges came with the same transfer case NP271/273.  NP271 being the manual shift and the NP273 being the electric shift.  Only thing different was the input spline count on the transfer case.

1 person likes this

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now