I'm going to visit my parents this weekend, and while there I will be doing some wheelin' on a road that goes from an elevation of 4000' to about 10500'. I've done quite a bit of off roading in the past, but only in vehicles with manual trans. This trip will be in my 99 150 w/ 4.2 and auto trans. My question is when coming down this road (often quite steep, narrow and rough) will I hurt (overheat) my trans by using low gear in the trans (tranfer case in 4L also) to slow the truck, or am I better off using the brakes primarily. My truck is equipped with a factory aux trans cooler, the air temp will be in the 80's. Thanks for any advice...I CAN'T WAIT TO GO!!!!

 

Depending on how big your tires are you're going to be travelling quickly down a hill if you try to use only your transmission while in 4lo. I would leave it in 4hi when going downhill (there is monster torque in 4low) that way your brakes won't be screaming trying to slow your truck down in 4low (your truck will be trying to accelerate down hill with gravity, and in 4low your truck will be accelerating down hill faster than you want to be going and will be hard on your brakes). 4hi does not have a ton of torque and I'm not sure if you have a "coastable" transmission or you can just go in neutral. I'm coming from 37's so that will change a few variables (namely speed) but either way your brakes will be hardpressed to overcome the torque in 4lo.

 

Thanks for your response. I've only had this truck about 4 months, so this will be my first real trip with it. I have a couple of steep hills in my yard which I ran up and down and I got the impression that the trans didn't hold the truck back all that well. The road I'll be driving has several sections steep continuous downgrade 4-5 miles long. I'll try 4hi and see how it goes.
BTW with a 4.2, you can bet my tires aren't a whole lot bigger than stock!

Come on Friday...I can't wait to be casting for a trout and breathing that cool Sierra air!!!

 

Use 4 low, put the tranny in 1st gear (so that it won't shift into 2nd) and use the brakes too. My truck crawls along pretty dang slow in 4 lo in 1st gear only. Plenty slow enough for a steep steep decent if using the brakes. The RPM's will be up there if you go too fast, but at that point you'll also have engine braking (not fighting torque unless your RPM's are lower than idle, which would be VERY slow in 4lo!) along with the regular brakes.

Cliff notes: transfer case in 4lo, gear selector in 1st, foot on the brakes.

 

See now why can't everyone do that...

 

While going downhill you want little to no torque applied against your brakes so as said before if your tires are not larger than stock 4lo and 1st gear might be fine, you're already multiplying the 6,000lb vehicle and the torque multiplication from our transfercase in 4lo is absurd. Your brakes will not handle this stress for an entire duration of a descend so make sure 4lo is slow enough (depending on how bad of a hill), and if they fail you can thank stng. There is an absurd amount of torque in low range, it's probably something like 3.5:1 (3.5x as many teeth). I said before I'm on 37" tires and low range is probably around a 2:1 effective ratio when factored in, so it's pretty quick, you will notice how much easier it is to brake when you are in neutral as opposed to in 4lo (your brake pedal will feel much better). If it was granny low that would be another story. You'll have to make the decision on the trail but try them both.

Also something to keep in mind, the abs/engine firing do not retard when in 4lo so what are you talking about while in idle, :rollseyes:. That is the main reason 4lo in 1st on most vehicles will do a number on the brakes. If you would have read I asked whether he had oversized tires or not, makes all the difference in the world.

 

If he is in 4lo and NOT giving it any gas, the FASTEST he will go on a flat surface is idle speed, which is very slow in 4lo, 1st gear. That's my point...once he's ABOVE idle speed, there won't be ANY torque being applied from the engine, because he won't be giving it any gas. Get my point? On a downhill decent, if he's ABOVE idle speed, the ONLY force he's fighting against is gravity pulling the weight of the vehicle down the hill. He won't be fighting against torque because he won't be giving it any gas.

 

I agree I have done this many times and it will slow you down to a crawl on even a very steep grade.

 

I know exactly what you're getting at, but if it's a decent trail it is going to have rocky descents and @ idle it was nothing like a granny low. If it's a typical dirt hill descent he'll have no problem, sure. Like I said before if idle speed is too fast you're going to have a hard time on your brakes.

 

4low, 1st gear, you won't need to brake at all... there is no better way to do it. I don't follow Josiah's logic.

 

By using 4low and 1st gear, you reduce the amount of torque needed on the brakes. Many times you need no brakes. If you use 4 hi, you will have to ride the brakes all the way down, thus causing them to heat up and fade.

 

Once again, if 4lo in 1st is too quick for the descent you'd be a fool to keep it in 1st, you're braking against the trucks weight and engine and you may cause warpage if it's sustained (it's an absurd amount of weight put on the stock brakes, @ frank raines I waisted about 1/4-3/8" on my pads doing so). If it's not too quick, 1st would work great.

To understand where I'm coming from, low range is much too quick for the 37's I now run (in first it's at the least 4-6mph), and was too quick at times on my stocker 31's, depending on the hill. If you're braking a lot downhill try putting it in neutral and you'll feel a huge difference, there is no longer a boat (that'd be the torque in 4lo) attached to your truck. I have not once said it's a bad idea if it's slow enough, in fact I said the opposite. Depends on the trail and it is in fact a good way to descend a hill, but that is why I asked if you were on stock height rubber. You will be fine using 4low and 1st but like said before, I had trouble keeping the truck stopped downhill and in first in low range, it had my foot aching to stop the truck (a lot of pressure on the pedal). I've replaced my rotors (what a pain), have Akebono's in front and raybestos in rear. Have fun on your trip and I don't mean to cause a debate but you'll only learn more this way, hope your options are clear.

It's a simple test anyone can do, brake going downhill while in 4low and 1st gear, then put it in neutral and try braking again. Extreme difference in braking power and stress, thats why I said if you're braking a lot down hill(s) (if it's a difficult hill you definitely will be) do not keep it in first. Try it for yourself and let us know what happens.

Exp03, you're absolutely right, in 4hi on stock rubber you will be riding the brakes but just think about being in 4lo and the amount of torque you're pushing your brakes against (if you are indeed braking downhill often). Try not to doubt until you try it.

 

I agree with that. IF idle speed in 4lo, 1st gear is too fast, then you'll have to go 4hi with lots of brake.

 

You guys are arguing about two completely different circumstances for no particular reason. If you're trying to SLOW the truck to a crawl (which is what a hill descent is), the 4 low and 1st or 2nd gear as necessary. If you're trying to STOP the truck, then yes, shifting to neutral may be beneficial so that you're not riding the brakes to maintain the slower-than-idle speed.

The bottom line is that there is no right or wrong answer. It will vary based on the trail conditions and the truck equipment. In any case, no, you will not be hurting the engine or trans to slow it either way. Of course, the less you use your brakes, the less wear you'll put on them. That's not rocket science.

 

Thanks for all the responses. I just returned from the trip, and found the truck actually held back very well in 4 lo in either 1st or 2nd depending on the steepness of the hill. Portions of the road had deteriorated quite a bit in the 6 years since I had driven it, so I found my self crawling along in 4 lo over rock piles...great fun! I'll post a few pictures in my gallery if anyone is interested.