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

[BajaSportsmobile]

Originally Posted by rionapo

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

Don

As long as the rear tires have traction, and they are not slipping, the front does not come into play. Of course on a steep dirt or low traction decline, one would want the added traction that comes with the front hubs being locked.

Another interesting point is that when in 4-wheel drive, the front and rear axles are "locked" together so that the front brakes are also braking the rear axle and the rear brakes are also braking the front axle so you actually end up having better braking control as well as power control when in 4-wheel drive.

[86Scotty]

Hmmm, I never thought about that but excellent point.

[carringb]

Here's one possible solution:
http://www.dbrake.com/liquid-cooled-...system-faq.php


Also very popular for the E-series:
http://www.telmausa.com


Note.... There's probably some programming changes that can improve engine braking on the V10, such as forcing the Torque Converter to lock, or forcing the throttle body to close all the way. On drive-by-wire vans ('05+) the throttle body stays open slightly when coasting to reduce engine drag, to allow you to coast further while its de-fueled, therefore slightly improving fuel economy for your typical driving conditions.

[rionapo]

Originally Posted by BajaSportsmobile

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.

Edit: [s:e7gq9hw7]You understood. Does the front drive shaft assist is slowing the vehicle under those circumstances?[/s:e7gq9hw7] Missed the other comments on the thread. I think I understand now. Engaging the front axle doesn't increase braking but it does disperse the energy and protect the rear end if the hubs are engaged. Thanks for the comments.

Don

[Steve_382]

We drove down that canyon last summer. Very steep down hill. Wish I had driven up it instead and then back down the blacktop. Our van is only 8,000 pounds, so it didn't seem like the brakes were smoking, but we needed to ride them quite a bit. Beautiful view though when you pull over the top and look down into the valley. Clearly, 4x4 low isn't low enough.

[Chance]

Originally Posted by carringb

Here's one possible solution:
http://www.dbrake.com/liquid-cooled-...system-faq.php


Also very popular for the E-series:
http://www.telmausa.com


Note.... There's probably some programming changes that can improve engine braking on the V10, such as forcing the Torque Converter to lock, or forcing the throttle body to close all the way. On drive-by-wire vans ('05+) the throttle body stays open slightly when coasting to reduce engine drag, to allow you to coast further while its de-fueled, therefore slightly improving fuel economy for your typical driving conditions.

The only issue I would question with either of those add-on brakes is whether they can do enough good to be worthwhile at the very low speeds being discussed here.

If limited by braking torque, for instance, the 100 HP at 50 MPH would only be worth 10 HP at 5 MPH. Anyway, you get the point. They may work great at highway speeds to prevent a runaway situation but may not do much a crawl speeds.

Modifying the engine and transmission sounds more promising to me.

Another option would be to install external brake cooling since much less is available at low vehicle speeds. Personally I'd look at much lower gearing if doing this kind of trail often.

[Pschitt]

Just my two cents...

I've 4.1 tcase ratio on VivaLaVida which weight almost 11,000 lbs. To try to show the comparison with the 2.7 ratio, your 1st gear low is about my 3rd low.
With such a ratio, even on VERY steep off-road path - definitely steeper that the Silver Pass I drove up last Spring - you don't have to touch the brakes in 1st gear low, even to keep your foot on the gas pedal to maintain some speed despite diesel having less engine brake. I had some brake issue two weeks ago and drove 35 miles of steep mountain road without brakes at all, it was ok with such a ratio (only had to use 3rd low).
On the other side, when off-roading uphill, 1st is to short. I almost always drive in 3rd gear low to avoid to much torque on differentials. It's also easier to manage the throttle than in 1st low.

[BillPa1]

In my old (2011 V-10 SMB), when I put it in low range the RPM and MPH doubled. And I am assuming miles on the OD double too.

[daveb]

Originally Posted by BillPa1

In my old (2011 V-10 SMB), when I put it in low range the RPM and MPH doubled. And I am assuming miles on the OD double too.

Yeah, it does change the odometer on my SMB conversion just like going larger or smaller with tire size. Makes it difficult to measure mileage.

[Pschitt]

The same for me. But if you know the ratio of your t-case, mileage is not too difficult to calculate... ;-)