I'm a new user, so please forgive my ignorance.

I've recently been towing a 3-horse trailer (~4500-5,000 lb with one horse) up and down several miles of steep switchbacks with my 1999 F350 V10 Auto, 4WD SRW. When coming down, the engine braking available with 1st gear is not enough to maintain a stable speed (I have to also use the truck or trailer brakes every 20 seconds or so). I've ended up using 4x4 Low in 2nd gear, which allows a nice, stable descent with no braking except for turns.

In reading up on the question of using 4x4 Low for this purpose, I ran across another site that suggested it is very bad (read "certain death") on the 4R100 to coast downhill in 1st. The claim was that the 4R100 under those conditions applies only about 10 psi to the 6 stack low/reverse clutch package, causing undue slip, heat, and clutch failure.

I've tried searching this forum for any related info but so far have come up short. If anyone has any info regarding the use of 1st gear for engine braking downhill, I'd appreciate it.

Thanks!

 

Welcome to FTE.

Just my general experience and advise, regardless of transmission.

--using 1st gear in an automatic for downhill braking would be limited to no more than 20-30 mph. It won't even shift down into first in most circumstances at higher MPH

--use of 4WD, high or low, on hard surfaces is prohibited. Driveline windup and hard part breakage is guaranteed. (unless you have manual hubs and can disengage the front hubs)

--brakes are cheap compared to transmissions and transfer cases

I would select 2nd if available for speeds below 40 and just do the "snub" method with hard brake application at intervals while not allowing speed above a safe maximum. This and the reason for it is described in the following. Note this is for air brakes, and the logic behind it is make sure all your brakes are taking part, vs. just a few that engage at lighter pressures. This is less applicable to hydraulic brakes, but I think it has some merit--get all the brakes to work, not just the fronts.

downhill braking,truck accidents,air brakes,runaway accidents

 

Thanks for the reply, 85e150six4mtod. Good info; just wanted to respond to a couple of the points:

- In this case, the road is pretty steep and narrow, with no guard rails and very tight turns, so I actually would like to run about 15-20 mph. 1st engages OK (I slow down to probably 10-15 mph before I pull it down), but doesn't hit equilibrium below maybe 30 mph or so, which is too fast for the road.

- Thanks for the info on 4WD. I have since read that if you want to use the low range for increased engine braking in this model, you must disconnect the wire from the ESOF solenoid to prevent the front hubs from automatically locking in. I'll figure on looking into that before the next such trip.

- Agreed--brakes are easy and cheap by comparison. My concern, and reason for not wanting to use the brakes much, was related to overheating the brakes and rendering them useless. With the disc brakes all the way around, maybe this isn't a real concern on this model?

Thanks for the link, also. I'd always thought it better to engage the brakes a bit more firmly and then let off completely, but hadn't considered this as a way to ensure they all do their part. The difficulty here is that with the horse, the driving rule is to minimize acceleration, which is at odds with a more aggressive application of brakes.

Still interested in whether there's a specific reason why not to use 1st gear for engine braking in the 4R100 when I need to go really slowly downhill.

 

Not as big a concern, but it is still VERY possible to overheat 4 wheel disc brakes to where you get a lot of brake fade. I recommend using the transmission.

I'd be very interested in this, too. This is the first I've heard of this issue, if it really exists.

 

Thanks for the reply, Mark. For what it's worth, the origin of the information in the other post I saw was reportedly Brian at BTS. Perhaps if someone knows him they could substantiate or get more detail?

In the meantime, I believe I've located the PVH Solenoid for the ESOF, so I'll try disconnecting it and verify the hubs don't lock if I need to run in low range for extra engine braking in the future.

 

If you want to disable the vacuum hubs, you can wire a switch into the solenoid wiring and control it from the cab, making it that much easier to disable. This would also be a good thing to have when maneuvering the trailer in tight spots, or pulling on high inclines, it'll help the tranny stay that much cooler as well.

Check the fluid in your transfer case and make sure it's in good condition. You don't want to fry your transfer case, as the 2.9:1 gearing in that will certainly heat it up under engine braking. Not a lot, but just make sure your fluid is good and up to the right level.

 

With the problems you have on this road. Why not add trailer brakes? with a trailer that heavy it would greatly help you slow down on those tight turns.

 

Good points about disabling the front hub locks with a switch, and using 4LO to maneuver trailers in tight spots, keeping the tranny cool.

Another good point about the transfer case fluid. The capacity is only a couple of quarts, so it's worth checking and changing more often, especially if 4LO is used often.

The reduction ratio in 4LO is 2.71:1, not 2.9:1. Hence, the name. The base (manual shift model) is called the NP271 transfer case. The ESOF versions are called the NP273.

 

Thanks for the input, Krewat, 6.2 V8 power, and Y2KW57. I hadn't mentioned it, but this trailer does have brakes. It's a double-axel, and has electric drum brakes all around. They work well, but I'm assuming that they will retain heat worse than my discs, and overall just don't want my brakes to be the only thing keeping me from freewheeling down the hill.

Good point about checking the transfer case. I'll do that as well.

 

Or another option is to install Warn manual hubs like I did which works equally as well...

 

That's what I did when one of my auto lock hubs failed at about 2 or 3 years old

Very true, not sure why I wrote 2.9, thanks for the correction

The NP205 in my highboy was 1.96, maybe that's where I got the "9" from ...

 

If I didn't already have manually locking hubs from Ford, I'd install Milemarker Selectro hubs. I had a set of those on my E-350 4x4 van (with a cast iron NP205 btw). Wonderful hub locking mechanism. You just grasp around the OUTSIDE of the large fluted cast aluminum collar and rotate.

No need to brush out the snow or pull off the gloves to fit freezing fingers tips inside that teeny tiny little slot that Warn uses for a dial, trying to get leverage with only 3/8" of finger tip purchase to work with in order to turn Warn's little dial. None of that. With the Selectro hubs, keep the gloves on, grab hold of the hub around the outside, and you've all the leverage of your entire hand and arm yank it around and lock em.

At least the Ford manual hubs offer a larger dial to turn than the Warns. But if my big dial Ford's ever fail, I'm going with the cast metal collar Selectro hubs.

I like Warn products, I really do, but those little hub dials?