JTDR with 373 Conversion to 488: Requires Entire Front Axle Changeout

[tampahoosier]

It was asked once but the OP didn’t answer… why in the heck would you go 4.88s with the Diesel??

I plan to regear my diesel as well when I jump from 35s to 37s but my research has shown 4.10 or MAYBE 4.56. Going 4.88 is extreme. That’s what people are doing on 37s with the gasser.

I have see plenty of people say you don’t need to re-gear with the diesel because of all that torque. I plan to regear because I bought the diesel for all the torque. I don’t intend to lose all of that fantastic torque by leaving gears at 3.73s! I want to rock my diesel with 37s like it’s rolling on stock sport tires. Not like it’s a gasser on stock 33s.

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[redrider]

For the same reason dealerships don't typically replace just gears for warranty, full axle replacements are significantly less labor and have a substantially lower return rate. They probably don't want to do gears because there is a ton more liability that goes with it.

I suggest finding a reputable, local off road shop and having them do it because everyone here is right - the JTR has identical axle housings and carriers regardless of engine.

I wonder if it is more likely they do not have a qualified and experienced mechanic who knows how to properly set up a ring and pinion. The process is very easy but time consuming. Faster to swap the whole assembly. (I have 3 shaft drive Guzzi bikes and I roll my own)

 

[ShadowsPapa]

I wonder if it is more likely they do not have a qualified and experienced mechanic who knows how to properly set up a ring and pinion. The process is very easy but time consuming. Faster to swap the whole assembly. (I have 3 shaft drive Guzzi bikes and I roll my own)

Shaft drive bikes are cool and so smooth. I had a Yamaha Maxim 750 shaft drive for a few years.

Otherwise, on topic - odd to find a certified mechanic who doesn't know how to set up a ring and pinion. That's part of the college I had, part of my training. Maybe they never stuck with it or something, but if you are trained/certified/college educated in automotive, that's part of the program, or was when I got my papers.

Who knows, these days, though. Some seem to barely understand some other basics.

 

[FitfulGoat]

@MOPAR Boy just as a reminder… anyone with a gladiator rubicon is going to have post 2018 axles…. These came out in 2020 so the comments on pre 2018 are pointless.

 

[ShadowsPapa]

@MOPAR Boy just as a reminder… anyone with a gladiator rubicon is going to have post 2018 axles…. These came out in 2020 so the comments on pre 2018 are pointless.

Please don't take this wrong - and maybe you mean 2020 model year, but these were used in 2019 - early 2019 even, and were new with the JT/Gladiator I believe - correct me if wrong please!
Anyway, they were new for 2020 model year, and used in 2019 for all Gladiators. They are the same Dana number (44), but are Advantek - although that also covers a lot of territory these days!

I THINK I have all of that correct - anyone jump in if not because solid correct info can make a difference here.

 

[LostWoods]

I wonder if it is more likely they do not have a qualified and experienced mechanic who knows how to properly set up a ring and pinion. The process is very easy but time consuming. Faster to swap the whole assembly. (I have 3 shaft drive Guzzi bikes and I roll my own)

I know even 20 years ago, we had the differential guy who did 95% of all R&P work. He was also an old-school guy 20+ years in industry. I did a fair few there just out of interest and many more at my next gig but do not recall many others doing the work, they normally handed it off to him.

The reality is that it's all about risk aversion and it's why a lot of OEMs have moved toward assemblies instead of individual parts. Independents exist for people wanting powertrain rebuilds but for a dealership, it's easier just to R&R with a reman unit built at the factory to factory spec.

The factory setting up an axle leaves less to interpretation which is both good and bad... that driveline guy knew which side of the spec to be on for lash as he had done hundreds of 9.25" and Dana setups and it was perfect nearly every time. Someone newer probably wouldn't and any mistake in a setup means you're blowing half a day redoing any callbacks. Even worse, dealership warranty is nationwide so if someone screws up a job near your home that blows up halfway across the country, that shop is going to have to fix your work. It's just too much a headache.

 

[JAVIERGONZO]

Why don't you just go with a 60 in the rear? Just curious. Keep cost down?

 

[FitfulGoat]

Please don't take this wrong - and maybe you mean 2020 model year, but these were used in 2019 - early 2019 even, and were new with the JT/Gladiator I believe - correct me if wrong please!
Anyway, they were new for 2020 model year, and used in 2019 for all Gladiators. They are the same Dana number (44), but are Advantek - although that also covers a lot of territory these days!

I THINK I have all of that correct - anyone jump in if not because solid correct info can make a difference here.

Yes, obviously 2020 “model year” the point is still the same. No gladiator will have a 18MY axle assembly.

 

[MNDZLJT]

Yes ive done that exact swap. yes it can be done. Bottom line 4.88s are to much gear for 37s in a diesel.......i run 4.10s with 40s and the jeep does really well

 

[InvertedLogic]

This thread hurts my brain

 

[WXman]

Isn't 4.88 a bit extreme with the diesel?

Kevin

Echoing what other folks have said here--my diesel cranks with 35s and 3.73s. Unless you're running 42s (which would require a stronger axle in general), I don't really see the benefit of 4.88s.

This thread hurts my brain

What hurts my brain is trying to figure out why somebody with a turbo-diesel would install 4.88 gears.

There's a reason why traditionally checking off the box for the diesel engine gets you a numerically lower gear ratio, even on HD 1-ton trucks.

If a guy is going to run 54" Michelin industrial tires on an extreme build, OK I get it. But with 35 or 37 inch street tires? Get outta' here... lol. That's just silly. 4.10 ratio on 37s would be equal to stock on 33s....but we need to remember that the stock ratio is already overkill.

 

[ShadowsPapa]

What hurts my brain is trying to figure out why somebody with a turbo-diesel would install 4.88 gears.

There's a reason why traditionally checking off the box for the diesel engine gets you a numerically lower gear ratio, even on HD 1-ton trucks.

If a guy is going to run 54" Michelin industrial tires on an extreme build, OK I get it. But with 35 or 37 inch street tires? Get outta' here... lol. That's just silly. 4.10 ratio on 37s would be equal to stock on 33s....but we need to remember that the stock ratio is already overkill.

Due to the superior low-end grunt? And the ability to cruise at low RPM and still get up and go when pressed?

This thread hurts my brain

 

[Chance575]

Saw 4.56 and 4.88 are coming as options to the wrangler next year, maybe his dealership will just wait for those axles to drop

 

[Digger 5]

Not nit picking here but the carrier does not change size. it moves the mounting flange of the ring gear either closer or farther away from the center line of the pinon. In this case, if a carrier would be needed it would move the ring gear away from the center line of the pinon as the ring gear would be thicker. If memory serves me correct.
But with the added information I added to my last post from West Coast differential it does not need a change.

Sorry but this is incorrect. A lower gear, such as a 4.88, would move the ring gear flange closer to the pinion center line. The smaller pinion head (yet thicker ring gear) of the lower (higher numerically) requires the move of the ring gear flange.
In the case of the JL/JT, I'm not aware of any carrier break being used on the m210/m220. I haven't worked on a 3.73 set yet but I doubt it would change.

 

[JTPatriot]

Sorry but this is incorrect. A lower gear, such as a 4.88, would move the ring gear flange closer to the pinion center line. The smaller pinion head (yet thicker ring gear) of the lower (higher numerically) requires the move of the ring gear flange.
In the case of the JL/JT, I'm not aware of any carrier break being used on the m210/m220. I haven't worked on a 3.73 set yet but I doubt it would change.

Thanks Digger 5 I should have confirmed that before I posted. Memory did not serve me well this time. I have corrected my original post as to not give misleading info.

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