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Open Roads Forum  >  Tow Vehicles

 > 3.31 gears at 40,000 lbs gross.

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ShinerBock

LVTX

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Posted: 05/24/21 06:35am Link  |  Quote  |  Print  |  Notify Moderator

RoyJ wrote:

ShinerBock wrote:

Is this driver error? There are arguments for both sides, but I, like the OP, choose to change the gears myself based on what I am pulling. However, there are many out there that don't and just let computer do all the work. These are the people will generally have transmission clutch issues later on.


I'd call that design error - the input side of the transmission should always be sized for the max tq output of the engine.

Here're some charts I made a while back, 45 mph grade @ near full throttle. The 3.31 truck does it in 4th, the 4.30 truck does it in 6th:

The tq input with both gears are the same. In fact, the 3.31 is a bit lower, purely a fluke of course. At another speed the 4.30 might be a hair lower.

Point is, rear end ratio makes zero difference in RV application. In a commercial under-speed case, it may be difference because they're purposely lugging the engine down to 1100 rpm cruise. Whereas we're agreeing to lock out 9th/10th so both trucks cruise the same.


I am not sure if I would call it a design error and more like forced to in order to meet regulations. Most people think that longevity is the main concern for vehicle manufacturers. While it may be high on their list, meeting fuel and emissions regulations is priority number one since you cannot sell a vehicle unless you meet these regulations.

Many times, these regulations force the manufacturers to make things less reliable and counterintuitive to their purpose. From adding spent exhaust gasses back into the intake to reduce NOx, installing a less reliable VG turbo to better control the EGR flow, and even installing taller gears just to meet CAFE fuel requirements. The same thing happened in the heavy-duty industry when we had to turn to downspeeding in order to meet 2016 regulations. The manufacturers did not have time to do the research to see what effect downspeeding had on components and it wasn't until after a lot of fleets started complaining about premature driveline and clutch failure that they started to research it.

In the case of the OP towing 40k combined with his 3.31 axle, the truck's computer will put it in 10th as clearly seen in the video. My truck will put me in 6th even with towing close to 17k. We both are experienced enough to manually take out these gears to put less of a strain on our transmissions and driveline. However, most people out there have a "the computer knows best" mentality and lets their truck do all the shifting. It is these people that will generally have overdrive clutch issues.

Is this the fault of the owner for not being knowledgeable enough to know when to lock out gears? The manufacturer for being forced to make the truck this way to meet EPA and CAFE regulations? Or the EPA and NHTSA for forcing auto manufacturers to make trucks that are less reliable for their purpose?

* This post was edited 05/24/21 07:22am by ShinerBock *


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Jarlaxle

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Posted: 05/24/21 07:35am Link  |  Quote  |  Print  |  Notify Moderator

One of the tractors at work will lug down to 1000RPM on grades before downshifting-it regularly will start pulling (even loaded to 50K) at 900RPM. There's nothing I can do-the driver has zero control over the transmission gears in that truck.


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RoyJ

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Posted: 05/24/21 01:03pm Link  |  Quote  |  Print  |  Notify Moderator

ShinerBock wrote:

Is this the fault of the owner for not being knowledgeable enough to know when to lock out gears? The manufacturer for being forced to make the truck this way to meet EPA and CAFE regulations? Or the EPA and NHTSA for forcing auto manufacturers to make trucks that are less reliable for their purpose?


I'd say that answers this:

dodge guy wrote:

Ok let’s make this simple once and for all, if gearing does not matter, then the engineers at any manuf. would not have different ratios for towing higher weights. But to tow an XXXX lb trailer you need the next lower gear, and so on. It can’t be made any simpler than that. If you don’t understand that then all you are doing is arguing just to argue!


OEMs have to cater to the masses, so no, they can't expect owners to lock out OD and over-ride computer shift points. Thus they lower the tow rating on taller geared trucks. As enthusiasts, we're often surprised how many people don't know what a tach is in the "general driving public".

The counterpoint being raised is given an enthusiast driver who cares about his truck (not a fleet driver), towing heavy with a 3.31 puts very little additional stress on components other than the driveshaft / u-joints.

This is made possible by modern 8/10 spds with tight gear ratios that easily overlaps differences in 3.31 vs 4.30. I showed it takes TWO gears to bridge the gap, so technically the 10 speed can emulate a 3.8x gear ratio as well. Note, I would've never said this in the old 48RE / 4R100 days. Back then, a proper rear end was crucial as gears were so few.

ShinerBock

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Posted: 05/24/21 01:47pm Link  |  Quote  |  Print  |  Notify Moderator

RoyJ wrote:


OEMs have to cater to the masses, so no, they can't expect owners to lock out OD and over-ride computer shift points. Thus they lower the tow rating on taller geared trucks. As enthusiasts, we're often surprised how many people don't know what a tach is in the "general driving public".


But this is not the case with Ford. The only rear gear option with the SRW trucks is a 3.31 and 3.55, and both are rated to tow the exact same amount in every configuration with a max of 22k in the F350. With the DRW trucks, you only have 3.55 and 4.10 as an option. The 4.10 is rated to tow just 3,400 lbs more at a max of 35k and the 3.55 at a max of 32k. That is A LOT for a 3.55 even with a 10-speed.

RoyJ wrote:

The counterpoint being raised is given an enthusiast driver who cares about his truck (not a fleet driver), towing heavy with a 3.31 puts very little additional stress on components other than the driveshaft / u-joints.


This is where we disagree. I know that the added stress put on the driveshaft/u-joints is also placed upon the output shaft of the trans which in turn is being held to the input side of the trans via clutches. I don't see how anyone can say that there is added stress on the driveline, but not added stress on a clutch and output shaft that is connected to that same driveline.

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Posted: 05/24/21 03:43pm Link  |  Quote  |  Print  |  Notify Moderator

ShinerBock wrote:

RoyJ wrote:

ShinerBock wrote:

Is this driver error? There are arguments for both sides, but I, like the OP, choose to change the gears myself based on what I am pulling. However, there are many out there that don't and just let computer do all the work. These are the people will generally have transmission clutch issues later on.


I'd call that design error - the input side of the transmission should always be sized for the max tq output of the engine.

Here're some charts I made a while back, 45 mph grade @ near full throttle. The 3.31 truck does it in 4th, the 4.30 truck does it in 6th:

The tq input with both gears are the same. In fact, the 3.31 is a bit lower, purely a fluke of course. At another speed the 4.30 might be a hair lower.

Point is, rear end ratio makes zero difference in RV application. In a commercial under-speed case, it may be difference because they're purposely lugging the engine down to 1100 rpm cruise. Whereas we're agreeing to lock out 9th/10th so both trucks cruise the same.


I am not sure if I would call it a design error and more like forced to in order to meet regulations. Most people think that longevity is the main concern for vehicle manufacturers. While it may be high on their list, meeting fuel and emissions regulations is priority number one since you cannot sell a vehicle unless you meet these regulations.

Many times, these regulations force the manufacturers to make things less reliable and counterintuitive to their purpose. From adding spent exhaust gasses back into the intake to reduce NOx, installing a less reliable VG turbo to better control the EGR flow, and even installing taller gears just to meet CAFE fuel requirements. The same thing happened in the heavy-duty industry when we had to turn to downspeeding in order to meet 2016 regulations. The manufacturers did not have time to do the research to see what effect downspeeding had on components and it wasn't until after a lot of fleets started complaining about premature driveline and clutch failure that they started to research it.

In the case of the OP towing 40k combined with his 3.31 axle, the truck's computer will put it in 10th as clearly seen in the video. My truck will put me in 6th even with towing close to 17k. We both are experienced enough to manually take out these gears to put less of a strain on our transmissions and driveline. However, most people out there have a "the computer knows best" mentality and lets their truck do all the shifting. It is these people that will generally have overdrive clutch issues.

Is this the fault of the owner for not being knowledgeable enough to know when to lock out gears? The manufacturer for being forced to make the truck this way to meet EPA and CAFE regulations? Or the EPA and NHTSA for forcing auto manufacturers to make trucks that are less reliable for their purpose?


I think you have a point regarding how the manufacturers have introduced poor design into their engines in order to meet EPA regulations. I also think those issues have been largely addressed. There is a possibility that poor driveline design is being forced apon us now but, I'd probably be willing to bet that my 2021 will be more reliable than was my 2003 but it is obviously to soon to tell.

While towing with 4.30 gears in the F450, high torque gets transmitted through the overdrive gears on every hill. So I would call it design error if the overdrive clutches of the 10R140 can't handle the full torque output of the Powerstroke at 2000 rpm.


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4x4ord

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Posted: 05/24/21 04:01pm Link  |  Quote  |  Print  |  Notify Moderator

ShinerBock wrote:

RoyJ wrote:


OEMs have to cater to the masses, so no, they can't expect owners to lock out OD and over-ride computer shift points. Thus they lower the tow rating on taller geared trucks. As enthusiasts, we're often surprised how many people don't know what a tach is in the "general driving public".


But this is not the case with Ford. The only rear gear option with the SRW trucks is a 3.31 and 3.55, and both are rated to tow the exact same amount in every configuration with a max of 22k in the F350. With the DRW trucks, you only have 3.55 and 4.10 as an option. The 4.10 is rated to tow just 3,400 lbs more at a max of 35k and the 3.55 at a max of 32k. That is A LOT for a 3.55 even with a 10-speed.

RoyJ wrote:

The counterpoint being raised is given an enthusiast driver who cares about his truck (not a fleet driver), towing heavy with a 3.31 puts very little additional stress on components other than the driveshaft / u-joints.


This is where we disagree. I know that the added stress put on the driveshaft/u-joints is also placed upon the output shaft of the trans which in turn is being held to the input side of the trans via clutches. I don't see how anyone can say that there is added stress on the driveline, but not added stress on a clutch and output shaft that is connected to that same driveline.


It could be that if the 10R140 can only handle a 35000 lb trailer behind an F450 a guy should be careful towing any more than about 26,000 lbs behind his 3.31 equipped F350. In my case I don't tow over 26,000 lbs that often and when I do it's usually on fairly level roads.

RoyJ

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Posted: 05/25/21 11:48am Link  |  Quote  |  Print  |  Notify Moderator

ShinerBock wrote:

RoyJ wrote:

The counterpoint being raised is given an enthusiast driver who cares about his truck (not a fleet driver), towing heavy with a 3.31 puts very little additional stress on components other than the driveshaft / u-joints.


This is where we disagree. I know that the added stress put on the driveshaft/u-joints is also placed upon the output shaft of the trans which in turn is being held to the input side of the trans via clutches. I don't see how anyone can say that there is added stress on the driveline, but not added stress on a clutch and output shaft that is connected to that same driveline.


I'll start by saying we're talking RV use, NOT commercial under-speed cases. In the latter case you would have higher average torque in the transmission input side, because you're purposely lowering the cruising speed. So with a fix cruising hp requirement: we drop the rpm by 25%, up goes engine torque by 25%.

In the RV case, we're locking out 9th / 10th. So if cruising rpm is identical, engine output HAS to be identical. Engine does not know what rear end there is, only the total gear reduction ratio.

If you look at my chart earlier, both 3.31 and 4.30 truck engines are putting out ~420 hp and ~800 lb-ft of torque. The only difference is the 3.31 truck in 4th, and 4.30 truck in 6th. The flywheel / TC clutch would not know the difference.

RoyJ

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Posted: 05/25/21 11:59am Link  |  Quote  |  Print  |  Notify Moderator

Let's be fair to Ford and look at what Ram uses (I'm a big Mopar fan just to be clear):

3.75:1 Aisin 1st speed ratio, 4.10 axle ratio, 37,100 lbs tow rating. Works out to be 15.375 total ratio, or "2413 lbs per total gear ratio"

Ford: 4.615:1 1st gear, 3.55 axle ratio, 35,000 lbs towing. 16.383 total ratio, or 2136 lbs per gear ratio

So starting out in 1st gear, the 3.55 Ford has a 12% gearing advantage over an Aisin Ram running 4.10.

Grit dog

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Posted: 05/25/21 07:21pm Link  |  Quote  |  Print  |  Notify Moderator

RoyJ wrote:

Let's be fair to Ford and look at what Ram uses (I'm a big Mopar fan just to be clear):

3.75:1 Aisin 1st speed ratio, 4.10 axle ratio, 37,100 lbs tow rating. Works out to be 15.375 total ratio, or "2413 lbs per total gear ratio"

Ford: 4.615:1 1st gear, 3.55 axle ratio, 35,000 lbs towing. 16.383 total ratio, or 2136 lbs per gear ratio

So starting out in 1st gear, the 3.55 Ford has a 12% gearing advantage over an Aisin Ram running 4.10.


Never heard "lbs per gear ratio" unit of measure, but I'm tracking and your assumption is solid.

What you're confused about is the argument was never, is the trans (OD clutches, whatever) being overstressed. But rather higher final ratios put "more" stress on the trans, (OD clutches, driveline, whatever) and the answer is still resoundingly yes.
Oh, and I'm a Dodge guy too and they're again (sorry, still...) s ucking hind teat in the transmission department!


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RoyJ

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Posted: 05/25/21 09:38pm Link  |  Quote  |  Print  |  Notify Moderator

If Ford shoved a beefed up 4R100 in the new dually, paired it with a 6.15 rear end ......... are we all going to say "oh, ah, what an amazing tow rig Ford made!"

On the other hand, if Ford used a military 7 speed Allison or 18 spd Fuller, but a 2.23 rear end, are we getting out the pitch forks and crucify Ford for using a "car" rear end?

See my point? All this talk about gear ratio, no one even mentioned the transmission ratio. As for component stress, I think I've bored people with enough math already [emoticon]

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