Towing with Auto on Steep Grades

[NC_Mog]

I had an "opportunity" to haul my trailer over some steep grades (9%) a few months ago, and have a question about proper towing technique.



The trailer and load total out to approx. 11. 5k. My '03 is stock with 3. 73 gears and 315-70-R17s. The larger tires have had some effect on the flat, but not that bad. My question stems from the steep grade and the temperatures I encountered. My speed dropped to approx. 15 mph, the transmission temp gradually crept to 220F and the engine temp started to rise. When the transmission got to 220F, I pulled over, dropped to neutral and let everything cool off for 20 min or so. I had tried to keep as light a throttle position as I could while still maintained some forward momentum. I believe the transmission was in first.



This just par for the course? Does the transmission ever lock the TC in 1st or 2nd? If not, has anyone ever dropped to 4 low and allowed the transmission to move up to a higher gear so the TC can lock up? (Normally I wouldn't consider this because of gear wind-up).

 

[Reb.B]

if you are going slower than 30 up a grade it would be adviseable to put the truck in 4 LO, because it is easier to take off and it will lock up very soon. If you have a custom built Valve body and a lock up switch then you can just stick it in first and lock the converter. The problem that you were having was the converter was not locked and all you were making was heat.

 

[BHolm]

I think the big tires are your problem. I live in the mountains and have towed a whole lot more than that with either of my '03s and the '05. I had the 416 Mog and a swb G-wagen on a 36ft gooseneck and my '03 dually 4x4, 3. 73 auto was able to maintain 40 mph coming up Monarch pass with a good 15 miles of 6-7% up grades. That was with 20k lbs behind it. Good thing you had a transmission temp gauge and enough sense to let the transmission cool. Those low speeds are tough, first will never lock, my '05 I think locks in second but I don't think the '03s do. Of course you have to be around 35-40 mph before second gear will lock and you probably didn't have enough room to run that fast. I think you pretty much just operated in a very extreme condition and the big tires exacerbated it. With stock 265s or even 285s like my srws have I bet it would have fared better. I don't see where you did anything wrong though. These convertors are just way to loose from the factory IMO.

 

[Bertram65]

The auto with 3. 73s is less than ideal if you towing heavy, add 315s and you are really working the trans hard when the TC is not locked. I would get rid of the 315s. I would not want to run of dry pavement in 4 lo either, even if you never turn you will still get gear wind up as the front and rear diffs can never be exactly the same ratio as they are differnt sizes.

 

[CLAYTON]

If you put it manually in to 2nd gear the TC will lock up after a second or two. What you need is to let your truck breath with a free flowing exhaust and intake and some extra HP's to get you up the hills. Also a better trans cooler would help along with a bigger pan to keep those trans temps down. Upgraded transmission wouldn't be bad either

 

[TFucili]

Take the time to compare the revs per mile of your 315's versus the stockers and the actual final drive ratio. You'll probably find you need 4. 10's to get back to the same final drove ratio. If you NEED the tires, regear. If you don't,lose 'em. IMHO

 

[NC_Mog]

I didn't think that the TC locked in 1st. I'm not inclined to swap the tires as I only tow a half dozen times a year. A 6 to 7% grade is typically the max I see, and the truck has no problems at all. The 9% was atypical... it was either 9% grade & 1-1/2 hr to hook back up with my convoy. Or a 4 hr detour, I miss the group, and get home at 5 am. Now I'll admit, I didn't know the route was going to be that steep before I took it.



I admit the tires are the only form-following-function item that I've got. Regearing for crappy mileage on my daily commute is not what I'm looking for. Increased transmission cooling and transmission upgrades are more the ticket. Thanks for the feedback.

 

[BHolm]

I think about the best dang upgrade for the auto trucks is an aftermarket convertor. I bet you would see better economy and lower trans temps. I am sure it would also greatly improve acceleration. You know what it feels like to hit it hard with a load on, seems like the truck just sits there and makes a bunch of noise (and heat) for the first few seconds. I'm still too cheap to do it though