Low Range vs Brakes for downhill descents.....

[Chance]

Originally Posted by haywoodphotomaccom

Yes, using the tow/haul, low range 4x4 and 1st gear. Van was revving to 4800 the entire way down the hill and still needed the brakes almost the entire way down...

Although I had the Tow/Haul on does it do anything in low 4x4 1st gear?

Just curious -- how fast are you going under those conditions? Are you over 10 MPH? Is it possible your transmission is not dropping down to 1st because the revs are too high?

With your gearing it would seem like speed would be very slow (although I have no idea how slow you want or expect). My only experience with 10-cylinder and tow-haul was with large and heavy rented RV and sometimes I had to brake hard to slow enough for transmission to downshift, otherwise engine would have gone over 6000 RPM easily. These were paved roads with limited slope but I didn't have a low-range transfer case either. I'd guess weight around 14000 pounds. First gear would certainly keep speed extremely low -- plenty safe for paved road.

[haywoodphotomaccom]

Not sure on the speed. When I was in Low Range First Gear it was reading 30-40mph or something like that. I started off in Low Range First Gear at the top of the hill so it was definitely in first. Worked through the gears on different roads throughout the trip. If I had to guess it was in the 5-8mph range that I kept it at but as mention I was on the brakes the whole time to keep it that slow. This particular road I would like to have been going half that for most of the time.

[rionapo]

Originally Posted by haywoodphotomaccom

Not sure on the speed. When I was in Low Range First Gear it was reading 30-40mph or something like that. I started off in Low Range First Gear at the top of the hill so it was definitely in first. Worked through the gears on different roads throughout the trip. If I had to guess it was in the 5-8mph range that I kept it at but as mention I was on the brakes the whole time to keep it that slow. This particular road I would like to have been going half that for most of the time.

Is there any chance the hubs or the axle aren't fully engaging? You could test drive in low with only the front or rear axle engaged to confirm they're working.

Don

[BajaSportsmobile]

Front hubs being locked or not would not effect the vehicle speed or RPMs as long as the rear had traction and traction was not the problem.

[deserteagle56]

I don't think that people realize just how steep the road in Silver Canyon really is. In just a few miles it drops from nearly 11,000 feet in elevation down to about 4,000 feet at Laws. We're talking standing-on-your-nose grades! Heavy as the van is, there's no way of coming down a grade like that without riding the brakes. About all you can do is stop every so often and let them cool.

Don't know about this particular van, but on mine the speedometer is not accurate in low range. You have to divide the indicated reading by 2.7 to get the actual speed.

A few years ago when I went from my old van to this new one I was hoping to have the automatic hold back a lot better going down hill. No such luck. Even though the 5R110 has a lower first gear and the transfer case ratio dropped from 1.96 to 1 to 2.7 to 1, steep downhills still mean riding the brakes. Of course, the new van is a bit heavier!

Manual transmissions still have the advantage in these situations. This past February I traded pickups; my new ride has the 6 speed manual. Whereas the previous pickup with an automatic had the same problem as the van going down hill, this new one with the manual, in low range low gear, will not run the tach over 2 grand no matter how steep the hill. But then I imagine that could be because the manual has a 6:1 low gear and the 5R110 is 3.11 to 1.

[rionapo]

Originally Posted by BajaSportsmobile

Front hubs being locked or not would not effect the vehicle speed or RPMs as long as the rear had traction and traction was not the problem.

I agree that rear low by itself will slow the vehicle but how would front low operate if the hubs aren't locked?

Don

[BajaSportsmobile]

Originally Posted by rionapo

I agree that rear low by itself will slow the vehicle but how would front low operate if the hubs aren't locked?

Don

Not sure I understand your question exactly, but...

Hi or Low Range is selected in the transfercase for both front and rear outputs and cannot be different one form the other. So that if in Low Range with the front hubs unlocked, the front drive shaft would still be turning at the same speed as the rear shaft but the front wheels/tires would be free wheeling. While the front tires would not be aiding in compression/engine braking, the rear would be doing it all as long as there is no traction loss (sliding) of the rear tires.

[Viejo]

Baja is correct about the traction on the rear and RPMs.

The problem with having the front unlocked in low range is that it can overstress the rear end and rip up your differential.

Been there - done that.

[rionapo]

Originally Posted by Viejo

Baja is correct about the traction on the rear and RPMs.

The problem with having the front unlocked in low range is that it can overstress the rear end and rip up your differential.

Been there - done that.

Does that mean engaging the front axle in low range is irrelevant for speed control? Or, just locking the wheels?

Don

[Viejo]

As long as your rear wheels don't skid or slip, you're getting the full advantage of engine breaking in low range.

The problem comes because in low range you can generate more torque than the rear end alone can handle. It has to be spread across all 4 wheels.