Dodge Cummins Diesel Forum banner

1 - 20 of 54 Posts

·
Registered
Joined
·
718 Posts
Discussion Starter #1
Just curious if this is something I should plan for or if it would even be worth to consider - I get really good mileage on my short bed crew cab SRW, and do about 80% highway driving unloaded (weekend trips to family beach house mostly, 175 miles one way)

Since I upsized the tires by 1" my only complaint was that around town, if Tow/Haul was not on, it would lug and search for a higher gear decently frequently - I'm on 285/65/20 so listed size is 34.5", the real height was exactly 1" taller than stock - Yes I have corrected Tire size in AlfaOBD to get speedometer to match so it helped slightly -

I know gears are worth it for who has done them - but I dont have a trailer or tow frequently at all, so 4.10's are out of the question - I only considered 3.73 just to be able to not have to run in Tow/Haul mode, and maybe have the truck have a bit better performance around town (not hunting for higher gear so easily) -

Any insight? I usually go at 70-75 on the highway and I notice I'm right around 1500rpm or so now? Maybe I'd be adding 100rpm on highway cruising? I imagine I'd lose a bit of mileage vs. my current gears too.

Obviously its a $2k investment - I could put that towards redoing the interior in leather and a headlight projector retrofit, for the cost of gears.
 

·
Registered
Joined
·
1,797 Posts
You can go to grimmjeeper and plug in your info and see what the change would do. Here is an example of mine. Left is 3.42 with stock tires, right is 3.73 with stock tires. Bottom picture is 3.42 and 3.73 with my current 35's. (285/75-18)
I'm in the same boat, don't need 4.10's but not sure going to a 3.73 would be worth the investment and trouble?
In my case going to 3.73 would put me abut ~60 rpm higher then a completely stock truck @75mph. Right now I am about ~140 rpm Lower so it would be a 200 rpm jump total.

910836


910837
 
  • Like
Reactions: G. Mcpherson

·
Registered
Joined
·
5,840 Posts
it depends on how easy it is for you to drop 2k. if it's a drop in the bucket then go for it, bang for the buck, probably not
 
  • Like
Reactions: Andy2500

·
Registered
Joined
·
14,458 Posts
Sure wouldn't be worth it to me.

I'd change tire size back to stock before I'd drop that kind of coin on such a small ratio change just to boost around town driving.

Why not lock out 6th gear around town? Maybe even 5th...

You can run 4th gear up to about 60 pretty easily.
 

·
Registered
Joined
·
177 Posts
It's my understanding that the OD on the 68RFE is the weak link and doesn't like to be lugged when loaded. I would think that 3.42's shouldn't hunt gears if empty (?). When towing, lock out 6th and use tow mode. That's what I would do, but here to learn.
 

·
Registered
Joined
·
2,157 Posts
Sure wouldn't be worth it to me.

I'd change tire size back to stock before I'd drop that kind of coin on such a small ratio change just to boost around town driving.

Why not lock out 6th gear around town? Maybe even 5th...

You can run 4th gear up to about 60 pretty easily.
I used to keep 6th locked out most of the time. Different story now. Tuned and don't like the trans tune right now. Another story.

There are better options than dropping several grand on gears that are more likely than not going to sing like a UPS truck. Switch to a newer Ford, switch to a gasser so you can get the 8-Speed ZF trans or wait until the HD Diesel gets the ZF 8-Speed and trade it.

No way I'm gonna drop that kind of cash on something that will NEVER return me a dime and most likely hurt the value of the truck.

You go to sell or trade the truck and you're gonna tell people it was driven to Church once a week by your aged Grandma?? With steep gears and over-sized tires? And even if it's mostly true, people aren't gonna believe you.

So you put big bucks in it and lose even more on sell or trade?

And, OBTW. Every truck I've bought in the last twenty years was gonna be my last one.

Right
 

·
Registered
Joined
·
2,094 Posts
I used to keep 6th locked out most of the time. Different story now. Tuned and don't like the trans tune right now. Another story.

There are better options than dropping several grand on gears that are more likely than not going to sing like a UPS truck. Switch to a newer Ford, switch to a gasser so you can get the 8-Speed ZF trans or wait until the HD Diesel gets the ZF 8-Speed and trade it.

No way I'm gonna drop that kind of cash on something that will NEVER return me a dime and most likely hurt the value of the truck.

You go to sell or trade the truck and you're gonna tell people it was driven to Church once a week by your aged Grandma?? With steep gears and over-sized tires? And even if it's mostly true, people aren't gonna believe you.

So you put big bucks in it and lose even more on sell or trade?

And, OBTW. Every truck I've bought in the last twenty years was gonna be my last one.

Right
3.73 wont be steep esp with 35” rubber. Most people buying a used truck don’t ask ratio either or care. It’ll probably “feel” better with 3.73. I’m considering doing it on stock rubber. But truck gets such good mileage empty right now.
 

·
Registered
Joined
·
14,458 Posts
It's my understanding that the OD on the 68RFE is the weak link and doesn't like to be lugged when loaded. I would think that 3.42's shouldn't hunt gears if empty (?). When towing, lock out 6th and use tow mode. That's what I would do, but here to learn.
Don't tell my 68 that.

Been towing in OD for 538K miles, you know both 5th and 6th are OD ratios.

And I rarely use tow/haul anymore.
 

·
Registered
Joined
·
737 Posts
I have 3;73’s and 35’s on my 11’. At 1500rpm’s I’m 70mph, at 75mph I’m at 16-1700rpms. I can roll into the throttle and it not down **** to pass if I’ve got a lot of room before oncoming traffic.
 

·
Registered
Joined
·
659 Posts
Sure wouldn't be worth it to me.

I'd change tire size back to stock before I'd drop that kind of coin on such a small ratio change just to boost around town driving.

Why not lock out 6th gear around town? Maybe even 5th...

You can run 4th gear up to about 60 pretty easily.
Exactly. With 342's, lockout is necessary, especially with grade.
 

·
Registered
Joined
·
2,175 Posts
When I'm towing my 18' tandem or 32' triple axle trailer across country, I'd say about 85% of the time I'm in 6th. Just no reason not to be if it's not lugging. If you'r concerned about it, just drop it down to 5th. Can't imagine the gearing change would be worth the expense in your case/example.
 

·
Registered
Joined
·
946 Posts
The truck would definitely feel better but you hardly work the truck hard enough to make it worth the investment. Craig
 

·
Cummins Freak
Joined
·
3,309 Posts
I went with 4.10’s and is the best gearing behind the Cummins!! IMO still get 18-20 mpg going 70 mph on the highway running 295’s.


Sent from my iPhone using Tapatalk
 

·
Registered
Joined
·
213 Posts
I'm running 4.10's with 37's up from 3.73's and its barely 100 rpm delta at 70. I tow heavy at times and wish 4.33 was an option for the 11.5 rear. You can run 4.10's and be very happy, its not like running a 4.10 in your 69 Camaro with a 350 turbo trans. 2k is an investment for most folks, but a trans is more.
 

·
Registered
Joined
·
718 Posts
Discussion Starter #17
Thanks for the input guys - I definitely can understand both sides -

I think it will be one of those "If I do everything else and want to throw 2k at it" things, 4.10 is out of the question because I don't tow and I want to keep max fuel economy (I can push 22mpg highway at 70 right now) -

As I told another friend from the forum last night, my wife's face for the price tag of gears, when she can't really see or hear anything different, definitely puts it behind doing a proper headlight retrofit and having the seats redone in leather, if I was to compare a total cost of one vs. the other. Maybe tuning and exhaust hardware will be less black market in the future as well.
 

·
Registered
Joined
·
14,458 Posts
Okay.......

Why?
I feel like it has better power when not in tow haul.

Lock out 6th when towing at less than 70 and I'm good to go.
 

·
P2609 Fanatic
Joined
·
1,971 Posts
@Ricky_Bobby you started a great thread here...

"3.42 to 3.73 - Worth it?"

I've asked myself that question many times with my own SRW 3500. In my case its more of a motivation problem (too lazy) than anything else. I've done ring & pinion swaps before and you defiantly need to be motivated and deal with the down-time too.

What I have learned. . .
Once you see what's involved it becomes obvious that letting anyone else do it beside "you" is a gamble.
Personally, I cringe at the thought of some gear shop using my truck as a training platform for their latest hiree.

The AAM's in the newer trucks are (IMHO) more involved than the Dana's were. Not that I've ever done anything but Dana's, but I did want to swap the 3.42's to 3.73's in my own 3500 and it was more than I wanted to tear into on a bran-new $70,000 truck.

Closing thoughts. . .
Swapping from 3.42's to 3.73's is an excellent idea! (y)
Considering how anemic these trucks are, and the fact that FCA arrived at that 3.42 ratio via a computer simulation tweaked to meet EPA fleet requirements and NOT what works in the real world, I would say a gear swap should be high on your bucket list.

All in all its not really a matter of the money, its a matter of getting motivated and just doing it yourself, correctly.
Or paying twice as much and letting the new kid at the local gear shop take a crack at it.

Good luck & keep us posted if you move forward on this.
-Ej-
 

·
Registered
Joined
·
718 Posts
Discussion Starter #20
EJ - an absolutely excellent reply - I do agree wholeheartedly that yes it would be worth it, if I wanted to spend the funds to do it correctly - I do agree you need to find an absolutely more than competent shop to do it - I don't know if mechanically I have the skill/tool set to DIY it myself, I do agree with you that "if you want it done right you need to do it yourself" - but on a job like this I think its worth every penny if you find or have a competent mechanic - I would never trust the job to a new guy or a new shop without a ton of driveline experience


@Ricky_Bobby you started a great thread here...

"3.42 to 3.73 - Worth it?"

I've asked myself that question many times with my own SRW 3500. In my case its more of a motivation problem (too lazy) than anything else. I've done ring & pinion swaps before and you defiantly need to be motivated and deal with the down-time too.

What I have learned. . .
Once you see what's involved it becomes obvious that letting anyone else do it beside "you" is a gamble.
Personally, I cringe at the thought of some gear shop using my truck as a training platform for their latest hiree.

The AAM's in the newer trucks are (IMHO) more involved than the Dana's were. Not that I've ever done anything but Dana's, but I did want to swap the 3.42's to 3.73's in my own 3500 and it was more than I wanted to tear into on a bran-new $70,000 truck.

Closing thoughts. . .
Swapping from 3.42's to 3.73's is an excellent idea! (y)
Considering how anemic these trucks are, and the fact that FCA arrived at that 3.42 ratio via a computer simulation tweaked to meet EPA fleet requirements and NOT what works in the real world, I would say a gear swap should be high on your bucket list.

All in all its not really a matter of the money, its a matter of getting motivated and just doing it yourself, correctly.
Or paying twice as much and letting the new kid at the local gear shop take a crack at it.

Good luck & keep us posted if you move forward on this.
-Ej-
 
1 - 20 of 54 Posts
Top