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When do you give it more gas... and when do you downshift?

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Pookster

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Ok, so.. I've always had this question. Say your towing 8000 lbs of load behind ya. And you reach a nice grade. Not a super grade which makes you wonder if your driving up the side of a building, but a nice even grade.

Your engine is starting to bog a little.

In a 350TBI 700R4 with 3.73 gears and 33" tires would you:
Give it more gas, since if it wanted to downshift, it would do it automatically, or
Shift into D, slow down to normal RPM speeds, wait until the grade passes

Ok, now if it was the same combo but with a 6.2, would you do the same? or lug it through?

Swap combos, lets say you have a manual tranny (in my case a nv4500) would you tow in 5th? Or never go past 4th? Or would you just keep it in 5th and just pedal to the metal?
 
With a 700R4 and 8000lbs behind you, you should be in D on a grade or flat straight aways. Not to many people tow in OD /forums/images/graemlins/tongue.gif It will fry your tranny pretty quick.

You should look into a tranny temp guage and big tranny cooler. Your tranny will love you for it /forums/images/graemlins/thumb.gif /forums/images/graemlins/peace.gif

Not sure on the diesel as I've never had one /forums/images/graemlins/frown.gif
 
Lol. Yeah, sometimes I run too high RPM in D though, so I have to use OD. /forums/images/graemlins/smile.gif But I auctally have 3 tranny coolers in my truck. the in radiator one, the factory Auxiliary finned one, and a big honkin stacked plate cooler 12x12" square?)

Lets just say my tranny gets cooled before I do /forums/images/graemlins/rotfl.gif AC works a lot less /forums/images/graemlins/smile.gif

Anyways, its just hypothetical nowadays- since I got my pickup to do the towing work now.
 
I used to tow in OD all the time, have a tranny cooler though, that helps out a bunch, when the engine would start to slow down, "lug" if it didn't do it already, i would go ahead and downshift it manually, Now with diesels, they are capable of pulling the weight alittle better while lugging a bit, i know they are not the same, but the same principal, i used to drive big trucks otr, used to let them lug down to where i guess it sounded alittle low, then shift into a higher gear. although, i have found that keeping the rpm a little higher has always seemed to help out just alittle bit more. Diesels torque range is quite abit lower than the gas engines though, and much more.
 
I know it's just hypothetical, but you aren't going to be pulling 8,000 lbs. in O/D with 33's and 3.73 gears unless you have a very healthy engine. With the 700r4 you should just be in D anyway pulling that much, and there is no way you will too high of a RPM with the 33's and only 3.73 gears.

Anyways, on an older truck with an overdrive auto trans I would probably manaully shift into D as soon as it started lugging. This would prevent the problem of the trans shift-hunting (constantly shifting back and forth between D and OD).

My '03 2500HD has the "tow/haul mode" you turn on and I then just leave it in OD. If I start losing speed on grades I can just keep giving it more throttle until it downshifts, and then it will stay in D until you get back on flat ground.
 
Ok, but the question I have then is.. when you lugged it until it got low, were you giving it more gas? I guess that is my ultimate question- Do you give it more gas or do you downshift? I am only assuming a certain amount of lugging is ok, but too much lugging just puts unnecessary stress on the engine and tranny.

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I used to tow in OD all the time, have a tranny cooler though, that helps out a bunch, when the engine would start to slow down, "lug" if it didn't do it already, i would go ahead and downshift it manually, Now with diesels, they are capable of pulling the weight alittle better while lugging a bit, i know they are not the same, but the same principal, i used to drive big trucks otr, used to let them lug down to where i guess it sounded alittle low, then shift into a higher gear. although, i have found that keeping the rpm a little higher has always seemed to help out just alittle bit more. Diesels torque range is quite abit lower than the gas engines though, and much more.

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I don't know. I just load 'er up, stick it in drive, turn the box down so I can keep the EGT in line, speed up to 75, and engage cruise control until I need to stop for fuel. It's fun passing cars that can't hold speed when I'm still running OD with a trailer and the cruise set...

But when I was towing with the 1500 Ram 360, that was a different story. I basically put it in Drive rather than OD and let the trans do it's thing. It will shift down when it needs to, and then you pretty much run against the redline till/unless you back out to give it a breather. Not much fun, but it got the job done and it was paid off. In any case, I don't think there is much point in manually shifting down.
 
If you are on a grade and don't give it any more throttle, it will stay in O/D and just lose some speed...how much speed depends on how steep the grade is and how much power the engine has.

If you keep applying more throttle in an attempt to maintain the same speed it will eventually downshift on it's own. Basically it won't let the engine lug that much before downshifting.

After all, it is an "automatic" transmission.
 
Well you have to give it more gas to climb the hill, granted you will lose some speed climbing, i believe thats just a feel for your truck on how much you want to "push" it up the hill. I always downshift my truck when climbing hills with a load, as mentioned, to prevent shift searching. But yes you give it more gas when climbing but only to a certsain degree, you don't want to hold it to the floor, let the truck and trans do the work, don't force it.

You will know when your forcing it, when it doesn't want to do anymore, just takes the touch, knowing how your truck is setup and paying attention to the trucks performance when towing or whatever.
 
1. You're really putting a lot of stress with 33s and the 700R4 and 3.73 gears, so you should NEVER be in overdrive towing anything behind such a rig under any circumstances.

2. What do you consider too much RPM? I would probably shift to 2nd and pull the grade at whatever the speed limit is. 4,000 RPM isn't unacceptable--that's where your horsepower is anyway.

3. With a manual, yes, I would tow in O/D. A manual won't get hot from towing in O/D. As long as I was on flat ground and didn't have to floor it to keep going, I'd use O/D. If I hit a hill where it started to bog, I'd downshift immediately.

In my tow rig (C30 SRW with a TH 400, 4.10 gears, and 31.5" tall tires I have ran 65 MPH in 2nd gear before trying to pull a steep hill. If ya do the math that's over 4,000 RPM, but that's what it takes to maintain road speed on a steep hill with a lot of weight behind you.

Remember, RPM is your friend when you're towing with a gas engine that has no power. /forums/images/graemlins/rotfl.gif /forums/images/graemlins/thumb.gif
 
Not sure what the rpm was, it was up alittle high though when i pulled that Caddy from San Diego to Phoenix, but i was in 2nd gear and only pulling 45 mph up the hills, not overworking it, and not pushing it to keep up with the speed limit. When towing, the speed limit should be the last of your concerns, people will go around you, don't worry about them, they see your towing, they'll get over it. On flat ground, OD works fine as long as there isn't a harsh headwind, or slight upgrade, the auto shifting with a slight grade every now and then will not hurt the 700, mainly when it starts to "hunt" is when you definately need to downshift manually. I also have a fairly large cooler installed on mine though, if you do ANY towing with the 700 a decent cooler is needed. Hell on the flatter road areas, i was rollin about 75-85 on the open road, with my bro in the U-Haul right behind me. Interesting trip.
 
GM has never recommended that a 700R4 be used to tow in overdrive. The overdrive gear is not strong enough for such use and will fail even without, "gear hunting". That said, even if it was strong enough to pull with in O/D, with 8,000 lbs behind you, 3.73 gears, and 33s, there's no way any small block will have sufficient torque to keep something moving at a reasonable speed in O/D.

Without a cooler, you shouldn't be towing with any automatic. It's not just limited to the 700R4. I have a huge cooler on my TH 400 in my tow rig (B&M stacked plate, teh biggest they make).
 
Ok, Lets change the equation a bit then.

Say its a 3/4 ton with 4.10 gears and acutal tire outer diameter of 31". Lets change the equation a bit more, and say its a Nv4500. Lets also say its a 6.2 diesel.
So then.. do you tow in 4th? (1:1)? Are you then not supposed to use OD? I'd be awefully slow towing in 1:1.

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GM has never recommended that a 700R4 be used to tow in overdrive. The overdrive gear is not strong enough for such use and will fail even without, "gear hunting". That said, even if it was strong enough to pull with in O/D, with 8,000 lbs behind you, 3.73 gears, and 33s, there's no way any small block will have sufficient torque to keep something moving at a reasonable speed in O/D.

Without a cooler, you shouldn't be towing with any automatic. It's not just limited to the 700R4. I have a huge cooler on my TH 400 in my tow rig (B&M stacked plate, teh biggest they make).

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Could you elaborate your answer? Are you talkin about on the 700R4, or theNV4500, and you didnt answer my "OD" question. Yeah, I can do 70 in the 6.2 in 1:1 but thats pretty high up in the revs. Thats why im asking about the OD.

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I tow 70 mph with 31s and 4.10s, so I can't see what the problem is.

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As stated above, it's a TH 400. It doesn't have overdrive. It revs a bit but a tow rig is supposed to rev. That's how you keep a load going down the road.
 
With a stick, it's generally just a matter of watching your rpms and keeping the engine happy. Particularly important with a diesel. But the 6.2 is pretty gutless for towing, so getting it into OD with a load and keeping it there is going to be a problem anyway. From what I hear, on stronger "turned up" diesels like the Cummins or Duramax, the OD starts having longevity problems even in the NV4500 due to mechanical disadvantage placing strain on the input and the fifth gear shaft/gear. Same thing happens to the Allison auto with a turned up DMax. I have to watch mine in OD with the box turned up or I can hurt it…
 
Hey Timmay, why are you towing anything at 70 mph when the speed limit in Illinois with a trailer is 55 mph? Sounds pretty stupid to me, a lot worse that using grade 2 centering pin bolts.
 
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Hey Timmay, why are you towing anything at 70 mph when the speed limit in Illinois with a trailer is 55 mph? Sounds pretty stupid to me, a lot worse that using grade 2 centering pin bolts.

[/ QUOTE ]

I tow 70 mph because my tow rig will do it. /forums/images/graemlins/rotfl.gif /forums/images/graemlins/thumb.gif /forums/images/graemlins/thumb.gif

And I have peace of mind knowing my rear axle is firmly located on its centering pin as I do so.

Nobody said anything about towing in Illinois anyway. /forums/images/graemlins/deal.gif
 
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