Torque Limiting

[HBarlow]

I'll have to admit I was wrong about torque limiting on the late model trucks, at least the ISB6. 7s. It appears to be a fact.

Steve St. Laurent mentioned it in his article about the new Ram torque numbers and towing limits. He indicated a Ram engineer spoke of it and said he didn't think full torque was applied until the transmission was up in direct drive fourth gear.

 

[Bob V]

I also think this is one of the reasons the higher torque is for the automatics only. The computer can better control under what circumstances full power is allowed, like higher gears, locked converter and then detune at shift points and then slowly ramo the power back up.

 

[craiggo]

Sorry, I hate to sound ignorant here but what's the significance of limiting it? Why would they do this... transmission?

 

[RustyJC]

The weak link could be the transmission output shaft, but it could also be in the driveline from the transmission back (U-joints, rear axle, etc. ). Remember, in the lower gears you're multiplying the torque by the torque multiplication of an unlocked torque converter (up to 2. 5:1 in the converters I'm familiar with) as well as the gear ratio of the transmission, so 800 ft-lb of torque could wind up being 800 ft-lb x 2. 5 torque converter multiplication x 3. 23 first gear ratio = 6460 ft-lb being applied to the output shaft and driveline. Multiply that by the rear axle gear ratio (4. 10 in my case), and you have almost 26,500 ft-lb of torque being split between the rear wheels and transmitted through the axle shafts if no torque limiting were present in 1st gear.



The engineers have determined that, in the interest of longevity, they don't want to accept the risk of that much torque. As the transmission shifts into the higher ratios, the driveline torque drops, so they don't have to limit the torque from 4th gear (1:1 gear ratio) on up.



Rusty

 

[craiggo]

Ok, I get it..... being fairly new to Dodge/Cummins, I'm seeing that they err on the side of caution (longivity) which I greatly appreciate.

Craig

 

[AH64ID]

It has been used since the MY00 trucks to improve the drivability and to reduce the strain on the drivetrain/driveline.



IIRC the VP trucks use speed, as do the manual 3rd and 4th gens. The newer auto's use direct gear to go unrestricted.



Some of the tuners (Smarty and H&S for sure) can reduce the tq management. To take full advantage of it you need a fully built auto or a good clutch.

 

[opjohnny]

I always wondered how they did it(speed) on the manual trucks. I knew they did (you could tell by driving) saw it in print someplace but could never find it again.

John

 

[HBarlow]

Sorry, I hate to sound ignorant here but what's the significance of limiting it? Why would they do this... transmission?

Ram answered your question indirectly when they announced the driveline upgrades that will be included with the torque increase to 800 ft. lb.

Apparently engineers considered the torque converter, universal joints, and rear differential assembly of prior models not up to handling the increased torque.

 

[AH64ID]

Apparently engineers considered the torque converter, universal joints, and rear differential assembly of prior models not up to handling the increased torque.

Which is amazing to me. Rear end failures are very very rare.



I wonder what GM did, considering its the same axle.

 

[NIsaacs]

Sorry, I hate to sound ignorant here but what's the significance of limiting it? Why would they do this... transmission?

I have to kind of agree, why have it if you can't use it? Is it safe to say that 4th might/could pull harder then 3rd? Might Dodge advertise 800 lb tq, then limit the power all they way through 6th? How would the average owner know if Dodge limits the power 5% all the time? Computers can be very subtle, even sneaky!



Nick

 

[HBarlow]

I've never heard of a rear end failure either . . . with the old Dana or the current AAM axles, even from the guys with major power increases who have apparently disabled the torque limiting programming by using aftermarket black boxes.

Hotshotters have been running overloaded Ram duallies for many years without problems I've ever heard of.

 

[RVTRKN]

Which is amazing to me. Rear end failures are very very rare.



I wonder what GM did, considering its the same axle.

The Alison was the first to use torque management in its programing, and one of the reasons I don't like auto's.

 

[SBall]

I think Rusty's math is right on and is certainly an eye-opener. I believe the reason there are so few rear end failures is that the tires cannot transmit all that torque to the ground without slipping or burning up. Once tires start slipping, torque across the driveline is limited to that required to overcome the slipping tires + driveline inertia.

 

[HBarlow]

The Alison was the first to use torque management in its programing, and one of the reasons I don't like auto's.

Yeah, I don't like torque limiting much either but didn't even know my engine was doing it other than during shifts until I read Steve St. Laurent's report.

How do you feel about Joe Donnelly's report in TDR Issue #71 about the weakness and failures of the G-56?

 

[rscurtis]

It's overhaul may be more user friendly than the 5600, but the cost of some of the parts is astronomical. Reminds me of what an Atlas Copco rep. told me once, "that's where we make our money, on the parts, just like the Gillette razor. "

 

[Bill Stockard]

I wonder what GM did, considering its the same axle.

I don't imagine GM did anything other than tell the axle vendor, American Axle Manufacturing, what torque numbers the engine would produce and the designers/engineers at AAM upgraded the components to match the torque requirements. I'll bet Dodge did the same.



With vendor engineering and manufacturing, any failures (warranty claims) can be dumped back on the vendor.



Bill

 

[AH64ID]

I have to kind of agree, why have it if you can't use it? Is it safe to say that 4th might/could pull harder then 3rd? Might Dodge advertise 800 lb tq, then limit the power all they way through 6th? How would the average owner know if Dodge limits the power 5% all the time? Computers can be very subtle, even sneaky!



Nick

The way gearing works it all works out okay. Honestly even 460 ft/lbs that the 03 SO's had was limited and you couldn't really tell unless you got a tuner that decreased the limiting, but 800 ft/lbs un-limited thru gearing would be very difficult to drive on the street. Ask some of the guys running aggressive tq management reduction, their wives won't drive the truck, too much power off idle.



IF you could obtain full fueling/power in each gear this is how much tq would be to the rear wheels assuming a locked converter (which we know won't occur in the lower gears, so the tq would be higher). 4. 10 gears were used.



1st 10,594 ft/lbs

2nd 6,035 ft/lbs

3rd 4,624 ft/lbs

4th 3,280 ft/lbs

5th 2,689 ft/lbs

6th 2,066 ft/lbs



As you can see you can limt it quite a bit and not really effect power to the wheels in the sence were its a "limiting" factor.



The 800 ft/lbs of tq is needed and available when your doing 45ish+ mph, where wind, weight, and incline takes it's biggest toll.

 

[AClayton]

The way gearing works it all works out okay. Honestly even 460 ft/lbs that the 03 SO's had was limited and you couldn't really tell unless you got a tuner that decreased the limiting, but 800 ft/lbs un-limited thru gearing would be very difficult to drive on the street. Ask some of the guys running aggressive tq management reduction, their wives won't drive the truck, too much power off idle.



IF you could obtain full fueling/power in each gear this is how much tq would be to the rear wheels assuming a locked converter (which we know won't occur in the lower gears, so the tq would be higher). 4. 10 gears were used.



1st 10,594 ft/lbs

2nd 6,035 ft/lbs

3rd 4,624 ft/lbs

4th 3,280 ft/lbs

5th 2,689 ft/lbs

6th 2,066 ft/lbs



As you can see you can limt it quite a bit and not really effect power to the wheels in the sence were its a "limiting" factor.



The 800 ft/lbs of tq is needed and available when your doing 45ish+ mph, where wind, weight, and incline takes it's biggest toll.

Which is the exact reason I detuned my truck to pull my 5th wheel toyhauler. A truck with 600hp will literally destroy the hitch and frame of any trailer you hook it to... ... ... ... if you're not careful. My truck dynoed over 1200ft. lbs with everything turned up and it quickly went through 2 transmission's that were supposedly built to withstand it. I have since detuned down to maybe 350hp and 750 or 800ft. lbs and it behaves much better pulling the heavy loads. With 1200, the truck shakes and NO hills slow it down, so the drivetrain takes the abuse. The Cummins is a real torque monster when stock but when they are BOMB'ed... ... ... . OMG! Just way too much power for towing.





Alan

 

[RustyJC]

I have since detuned down to maybe 350hp and 750 or 800ft. lbs and it behaves much better pulling the heavy loads.

My 2002 HO/6-speed set up as a mild towing rig dynoed at 347/762 at the rear wheels (Dynojet 246C) and never had a problem once I changed out the stock clutch to a Con OFE. In my experience, that's a pretty good target for a long term towing rig that won't tear up the drivetrain or the 5th wheel.



Rusty

 

[AH64ID]

My 2002 HO/6-speed set up as a mild towing rig dynoed at 347/762 at the rear wheels (Dynojet 246C) and never had a problem once I changed out the stock clutch to a Con OFE. In my experience, that's a pretty good target for a long term towing rig that won't tear up the drivetrain or the 5th wheel.



Rusty

That's about where I am shooting for as well. 400/800 is about as high as I want to go at the rear wheels.