Steep grades / Gears / 4HI

Hi,

(I realize there are other posts on the topic, but I could not find 4HI question).

I had a bit of a stressful experience going done a 7% grade with 6500 lbs trailer (GCVW 13200). I started going to S4 and S3, but to remain at about 40mph and feel secure I went to S2.

Will I destroy the transmission / torque converter in S2 going down long steep grades? Also, could I use 4HI to increase stability and divide the transmission load?

(I have weight distribution hitch, e-rated tires , TRD sway bar, sumo springs and Bilsteins).

Thanks,

 

No risk of damaging the transmission.

I don't see how 4Hi would help and would potentially cause damage to your drivetrain if you don't go completely straight or don't have reduced traction.

 

Don’t use 4hi on a dry road.

What speed are you trying to maintain? Use engine braking, which you are.
Make it a good practice to use your truck/trailer brakes appropriately as well. If you are trying to maintain 55 mph all the way down, let the truck get to 55 then firmly press on the brakes to slow down to 45ish. Process should take just a few seconds, then back off the brakes fully, let the truck speed back up to 55 (using engine brake still) then repeat the process. This will keep your brakes cooler and truck under control.

 

Yeah I would stay out of 4hi. keep the gears low and utilize the truck and trailer's brakes.

 

As long as you don't slam it down in to second, holding S2 down the grade will not hurt it. Don't ride the brakes, though. Instead, apply firm braking to slow the vehicle down below your desired speed, then hold S2 until your speed has increased 5 MPH past your desired speed (as long as that speed still feels safe, then apply the brakes again.

As for using 4Hi in this situation DO NOT DO IT. If you are snowy or gravel or limited traction roads - sure, use 4 Hi. But don't use if for the reason you mentioned. It won't divide the load in any way; your trailer should have brakes at that weight, and your truck has brakes. The braking system is smart enough to apply braking to the right wheels when towing.

When I was a kid, my dad read in the manual about the transfer case being able to increase torque via the gear reduction (of 4Lo). He'd never owned a 4wd so mistakenly put in 4WD while climbing a steep grade pulling a camper trailer to the middle of nowhere for our family vacation. The road was paved and it ended up overheating the transfer case and cracking the actual case. They owned that vehicle for another 20 years and the transferase always leaked when under a heavy load or in the summer. I believe they repaired it at least 3 times including when we got home from vacation. It took out the automatic locking hubs as well.