Hi Everyone,

I have intended to test this again before posting; but, the question came up again recently, and I thought I should just go ahead and bite the bullet.

Granted, this could be a case of operator error... so please be gentle. (I have also searched the forum without success.)

The question concerns the ability to start out in low gear while in 4-Hi. I have an automatic transmission in the '08 Rubicon. I originally recognized the problem when trying to mount Test Hill at the Silver Lake, Michigan sand dunes. Although one other person in our club had a JK (his is a manual transmission), the recommendations of the group was to get a little speed at the bottom of the hill in 4-Hi and the JK should carry us up.

Numerous tries and numerous failures. Speed was not a real issue, although channels at the bottom of the hill made it difficult to find any more speed. The limiting factor was engine RPM and power. Starting out in 1st or 2nd didn't (appear) to make a difference. We finally decided to try 4-Lo against other recommendations, and we were able to start out in 1st, building some speed and RPM, and then upshift to 2nd. (If I wasn't carrying enough speed I would sometimes need to downshift back to 1st just to keep the RPMs up.)

I believe that the problem concerns 1st gear while in 4-Hi. Is there anything that prevents the JK from starting out in 1st gear in 4-Hi? I am reasonably certain that I was running fast enough in 4-Hi to kick the RPM up; but, I didn't note what the RPM was at the time.

Thanks for any input.

Jeff

 

I haven't played in the Sand with my Jk....yet, but I've had two other 4x4s, and for the bigger hills I found that low range was the better place to be. In fact for both, 2nd gear low range was the best "climbing" gear.

Anyone offroading with an auto trans should understand that when the engine rpm is below the stall speed of the torque convertor ( usually about 1500) rpm the torque convertor generates a lot of heat, and you will over heat the tranny. So unless you are running fast all the time you are better off in low anyhow.

I've played a lot in the sand. Unless you have a lot of horsepower, you need to be in low range with an automatic. Your buddy with a manual trans has much lower first and second gears, so he could stay in high range first gear. You needed low range.

Tire size and air pressure and tread pattern and load ( number of passengers) will also impact your ability to climb in the sand.
At the end of the day no two rigs are identical and you needed low range, don't sweat it, you are better off in low anyhow.

Tom
I have had a jk for 7 days, but I've been wheeling in the sand since 1980

 

Short answer, yes.

Long answer, yes, lack of power. The 3.8 doesn't make any power down low, which is exactly what you need to get going. Add to that the 35" tires I see in your sig line and that leads to disaster.

Run it in low range and you'll be fine.

Just noticed you have a Rubi- hate to say this to ya but the low range in the rubi sucks in the soft sand too. Geared too low when added to a juice tranny which makes gear selection difficult. Sorry! That's why I didn't get a rubi. Do most of my wheeling in the sand and the rubi xfer case is too low for sand running.

 

Hi Guys,

Thanks for the replies.

I realize the limitations...

I am planning to regear to 5.13s in the near future; but, I'm not sure if that will help, or hurt, this situation.

I'm still curious about starting out in low gear in 4-Hi. Is there something in the electronic controls that would prevent this?

Sand was interesting... but, there's only one run each year to Silver Lake. The rest of the runs are dirt, rock and mud.

(As further clarification, the gearing at that time was 4.10s and the tire pressure started out at 12 and was reduced to 10.)

Thanks again for your input.

Jeff

 

I think some posts skipped this, but

Turn off the traction control...

 

Yes, the problem is that big gerbil-powered hamster wheel that says "3.8L" under your hood. The JK can't do sand properly in high unless it has a blower, or you swap the engine. Switch to low. If you have a rubi then you're screwed because you won't be able to get the speed you need in many instances in sand. Be sure to deflate your tires properly too if you're digging into the sand.

Also, like Goody said, you have to turn ESP off, but do it completely. Pushing the ESP button once isn't good enough, neither is pushing it during 7 seconds. You have to the turn the wheel right then left then middle chicken dance, anything else will make sand driving hell and heat up your brakes and tranny.

 

Second that.

 

I don't think there is anything that would prevent selecting 1st in 4hi.

Try it on level ground when you are not preoccupied with running a hill.
Select 4hi, 1st, and note rpm at a certain speed.
Select 4hi, 2nd, and note rpm drop when it shifts from 1st to 2nd.
Select 4hi, D, and not rpm drops as it shifts through the gears.