42RLE Overdrive Questions

Grandpastyx

Grandpastyx

Member
Supporting Member
Joined
May 25, 2018
Messages
32
Location
Australia
I have a two part question I have the 42RLE with 3.73 gears and 31in tires and I was wondering if it would hurt if I always drive with the overdrive off? and if so is there a way to rewire the switch so that the overdrive switch default is off so that I don’t have to switch the overdrive off every time I start my Jeep?
cheers Peter
 
Grandpastyx said:
I have a two part question I have the 42RLE with 3.73 gears and 31in tires and I was wondering if it would hurt if I always drive with the overdrive off? and if so is there a way to rewire the switch so that the overdrive switch default is off so that I don’t have to switch the overdrive off every time I start my Jeep?
cheers Peter
Click to expand...

No harm in driving with your OD off. Only downside is you’re losing a gear. The only way to get that gear back is go down in tire size or regear your axles. If you are willing to cover the cost of regearing then shooting for around 2200-2600 rpm range is most ideal. You can achieve this by regearing and keep all your gears, improve your acceleration, and possible your MPG depending on the weight of your rig! I’m at 5.38 gears...which to those who don’t know the 42RLE is extremely deep. On my 35”s I’m turning 2400 rpm at 60 mph....and that’s perfect.
 
Last edited:
No, that shouldn’t hurt the Jeep at most speeds. At 70 MPH you’d be turning roughly 2800 RPM, which is acceptable. The stock TJ Rubicon with NSG370 turns 2700 RPM in 6th gear at that speed. As to wiring it there are probably ways to do it but I’m not familiar with them.

An alternative would be a regear to something deeper like 4.56 or 4.88 or even higher.
 
  • Like
Reactions: BuildBreakRepeat
BuildBreakRepeat said:
No harm in driving with your OD off. Only downside is you’re losing a gear. The only way to get that gear back is go down in tire size or regear your axles. If you are willing to cover the cost of regearing then shooting for around 2200-2600 rpm range is most ideal. You can achieve this by regearing and keep all your gears, improve your acceleration, and possible your MPG depending on the weight of your rig! I’m at 5.38 gears...which to those who don’t know the 42RLE is extremely deep. On my 35”s I’m turning 2400 rpm at 60 mph....and that’s perfect.
Click to expand...
I’m even wondering if I should just keep my 4.10s when I go to 35s. 2700 RPM feels high to me. 4.10s would put me closer to 2400 RPM which to me feels ideal.
Otherwise I plan on no higher ratios than 4.56.
 
I have the NSG370 which has the .84 OD. The 42RLE has a .69 OD. So that’d be about equivalent to a 5.00 (nonexistent) gear ratio on the 42RLE. A 4.56 gear ratio would be about equivalent to a 5.55 gear ratio on a 42RLE.
On paper the 4.56 is a better option.
I do a lot of freeway driving and I don’t mind downshifting to 5th or even 4th when needed
 
Steel City 06 said:
I have the NSG370 which has the .84 OD. The 42RLE has a .69 OD. So that’d be about equivalent to a 5.00 (nonexistent) gear ratio on the 42RLE. A 4.56 gear ratio would be about equivalent to a 5.55 gear ratio on a 42RLE.
On paper the 4.56 is a better option.
I do a lot of freeway driving and I don’t mind downshifting to 5th or even 4th when needed
Click to expand...

I’ve always subscribed the notion that you want the lowest rpm that will maintain your speed with whatever load in whatever environment you plan on driving. For me the only time I even get to OD is on the freeway to the beach or mountains, and since I like 60/65 mph max (no tickets for this guy been there done that) my Jeep can maintain its speed of 65 mph with 5.38 gears, 42rle .69 OD, and 35” tires while in the final gear. Going up the mountain pass? Sure drop one or two to get speed, but my Jeep was never able to maintain 65 mph with 4.10 gears...I sat at 1100 rpm and lugged the shit out of it just to keep speed! You have the manual and out OD is obviously different, just giving you my train of thought. Why not consider 4.88 when you go to 35s?
 
  • Like
Reactions: Steel City 06
BuildBreakRepeat said:
I’ve always subscribed the notion that you want the lowest rpm that will maintain your speed with whatever load in whatever environment you plan on driving. For me the only time I even get to OD is on the freeway to the beach or mountains, and since I like 60/65 mph max (no tickets for this guy been there done that) my Jeep can maintain its speed of 65 mph with 5.38 gears, 42rle .69 OD, and 35” tires while in the final gear. Going up the mountain pass? Sure drop one or two to get speed, but my Jeep was never able to maintain 65 mph with 4.10 gears...I sat at 1100 rpm and lugged the shit out of it just to keep speed! You have the manual and out OD is obviously different, just giving you my train of thought. Why not consider 4.88 when you go to 35s?
Click to expand...
4.88s in an NSG370 would be the equivalent of 5.89s on a 42RLE. 5.38s on a 42RLE are between a 4.10 and a 4.56 on an NSG370 (4.41).

Would you really consider going to 5.89s?

I currently turn 2700 in 6th at 70 on 31s. 35s and 4.88s would take it even higher than that. 2500 RPM at 70 would be preferable. Even 2300 would be tolerable.

5th gear is 1:1 so there’s not much difference between 5th and 6th, so I’d be fine running in 5th for an extended period driving up/down hills
 
Last edited:
  • Like
Reactions: BuildBreakRepeat
Grandpastyx said:
I have a two part question I have the 42RLE with 3.73 gears and 31in tires and I was wondering if it would hurt if I always drive with the overdrive off? and if so is there a way to rewire the switch so that the overdrive switch default is off so that I don’t have to switch the overdrive off every time I start my Jeep?
cheers Peter
Click to expand...
Man that sucks. I’ve got the 42RLE with 4.10 on 32’s and my finger is always on the O/D off switch . Can’t rewrire it. Only a regear
 
  • Like
Reactions: Steel City 06
I have the 42RLE, 4.56, 33s. Mostly freeway driving when not on the trail. Cruise at 70 to 75 mph. Around 2300 rpm. It's great. I only touch the OD button on steep grades.
Would be fine with 35's as well. And that was my initial plan. But at about 2,500 miles a year, I'll be dead and buried before these 33s wear out.
Lots of folks on here like to high rev with 4.88 or numerically higher gears. I'm just not a personal fan of that. My 4.0 seems happy and isn't screaming down the hiway with 4.56s.
 
Last edited:
  • Like
Reactions: Steel City 06
Look at it this way; the Rubicon comes with 4.10 and a 31" tall tire from the factory on both the auto and manual trans. How would a 35" tall tire be appropriate with the same combo?

4.88/NSG370/35's is around 150 rpm faster than the stock combo. Running 4.10 with 35's effectively changes the gear ratio to 3.50. 35's on the auto reducing the 4.10's to 3.30.
 
I'm a little late chiming in here but...

I never drive in OD around town in any of my vehicles, I only used it on the highway.

On my '99 ram, there was a way to mod the OD mode. You just need to find out if the switch is momentary in the jeep. What I did was wire relay switch contacts (the N.O. ones) across the OD switch contacts, in parallel with them. Then, you would power the relay off of the starter circuit. While you are cranking it, it energizes the relay, as though you are holding down the OD switch. After you start, the OD switch will still work as normal.
You can test to see if this would work by actually holding down your OD switch while you start the jeep but, only while you crank it. As you move from "start" to "run" release the switch. What happens?
 
OldButStillJeeping said:
I have the 42RLE, 4.56, 33s. Mostly freeway driving when not on the trail. Cruise at 70 to 75 mph. Around 2300 rpm. It's great. I only touch the OD button on steep grades.
Would be fine with 35's as well. And that was my initial plan. But at about 2,500 miles a year, I'll be dead and buried before these 33s wear out.
Lots of folks on here like to high rev with 4.88 or numerically higher gears. I'm just not a personal fan of that. My 4.0 seems happy and isn't screaming down the hiway with 4.56s.
Click to expand...
In the past, I've looked into a re-gear, and don't plan on running larger than 32 in. tires. The advice that came back generally settled on 4.88, but a lot of folks said that in lieu of 'if you ever go to 33s'. It sounds like you are happy with 4.56 with your 42RLE and 33s, so I can't see why they wouldn't work with my 32s...mine is on the edge of perfectly fine, but almost not, with 4.10. Did you re-gear after you got your TJ, or was it that way when you bought it?
 
It gad 3.73 when I bought it 12 years ago. I put in 4.56 a couple years ago.
My wifes yj has 3 speed auto, 4.10s, 35s. Cruises at 3000 rpm at about 60 mph. Blew a rod, complete with a hole in the block when she was on freeway going 65 mph. That was several years ago.
So. I try to keeps rpms down on our 4.0s.
 
OldButStillJeeping said:
It gad 3.73 when I bought it 12 years ago. I put in 4.56 a couple years ago.
My wifes yj has 3 speed auto, 4.10s, 35s. Cruises at 3000 rpm at about 60 mph. Blew a rod, complete with a hole in the block when she was on freeway going 65 mph. That was several years ago.
So. I try to keeps rpms down on our 4.0s.
Click to expand...
The rod didn't blow through the block due to the 3k rpms at cruising speed, that's a perfectly normal/fine rpm for the engine. We need to stop fearing rpms like that. I ran 3k rpms for years after converting my previous TJ from its OE 5-speed manual to the 3-speed 32RH with my 35" tires and 4.88 gearing.
 
  • Like
Reactions: strumble8
OldButStillJeeping said:
But I prefer a lower rev.
Click to expand...
So do I, I would have liked to have regeared to 4.56 after converting to the 32RH to bring the rpms down to 2700-2750 at 70 mph. My only point was to say that your 3k cruising rpms were not the reason the engine threw a rod. The engine does perfectly fine at those rpms which are only 57% of its max rpms. :)
 
Top Bottom
Back