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Open Roads Forum  >  Tow Vehicles

 > 3.31 gears at 40,000 lbs gross.

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Devo the dog

Moved out of crazy California

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Posted: 05/22/21 07:24am Link  |  Quote  |  Print  |  Notify Moderator

ShinerBock wrote:


Well then by all means teach us "sophemores" which is correct. Does a taller gear ratio add more stress to the driveline?


Define driveline and pick a spot where you draw the FBD.

The crankshaft? The bolts at the TC? A shaft in the transmission? A spline on a gear? A rod on a U joint? The splines in the U joint? Driveshaft? Axle? Leaf springs? Is the truck in 4WD or 2WD? etc.

BTW, you misspelled sophomores. LOL. That's a great example of being sophomoric.

ShinerBock

LVTX

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Posted: 05/22/21 07:50am Link  |  Quote  |  Print  |  Notify Moderator

4x4ord wrote:

^^^^Part of the problem with this discussion is in the terminology being used and how it is understood. For instance you use the term “stress” and I believe you’re thinking stress and wear are synonymous. I believe you’re thinking like this:

1.Taller gears increases the stress on the driveline components
2. Increasing stress increases wear
3. Therefore taller gears increase wear on the driveline components.

Furthermore, not only do I believe you’re thinking like this, but, I also believe you think this reasoning is so obviously sound that you can assume we should all understand how you’re thinking without any explanation.

Can you spot the problem with this reasoning as far as how it relates to our discussion on transmitting power through a driveline? I’m challenging you to think about this to help you and others who might be reasoning like this to come to a clearer understanding of things.... I’m not simply wanting to argue.


It is not just thinking, it is fact. As I stated before, this was an issue in my industry when the OE's started to adopt "downspeeding" back in the early 2010's which is essentially putting even taller gear ratios on over the road class 8 trucks so that their cruising engine speed is dropped from around 1,400 rpm to around 1,100 rpm. This was all done to meet the upcoming fuel economy standards for class 2B and up vehicles and is likely why we are seeing it done in our trucks since they will also fall into these new standards.

Shortly after this, fleets started to have major driveline issues due to the added stress downspeeding was putting on the drivelines, shortening the lifespan of these components. Clutches and u-joints where all failing a lot sooner than normal. So much so that it led Dana(one of the worlds largest class 8 driveline manufactures) to research the issue.

At first, manufacturers started de-rating the engines, but that still did not fix the issue. Dana had to come up with a whole new driveline system with more robust parts to cope with the added torque stress of downspeeding with these taller axle ratios just to get the component to last as long as they did with the shorter gears sets that were used previously.

If you want to read more on this research and what they did to combat this then you can in this (LINK)

So I am not basing this on what I "think". I am basing it on what I know and have experienced in my own professional industry. And yes it is a fact that taller axle ratios put more stress on the driveline gear for gear than shorter axle ratios. And yes, I would trust Dana's research(which I have to study and keep up to date with in my profession) over what someone is stating on an internet forum , especially when they are not providing any data or research to back up their theories.

* This post was last edited 05/22/21 08:57am by ShinerBock *   View edit history


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blt2ski

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Posted: 05/22/21 08:24am Link  |  Quote  |  Print  |  Notify Moderator

Many of you are also forgetting about the tranny gears. 4x truck in reality has a lower overall gear ratio than the F450s shiner had drivetrain issues with.
4x set has granted 3.31 in axle, he has iirc the 10 auto has a 4.54 1st gear. F450, 4.33 axles, and a 3.08 first gear. 4x has approx 100-150 more ft lbs if torque to work with too. Along with he uses 4low pulling the trailer out of the field.
Shiners 450s, if they are rwd, doing local delivery in a city like Seattle, San Francisco with many local roads, granted a block long are in the 15-25+% range, they are probably doing many more 100% throttle starts to move 30-35000 lbs if truck and trailer.
I blew up TH400 auto trans like clockwork every 30,000 miles. Due to the super tall 1st gear in the trans. I had 4.10 gears. Reality, needed 5.xx gears to keep the drivetrain in tack. This is probably the issue with the Allison trans jaraxle mentioned a few posts back, why those trucks are geared too low for freeway driving. First is to talk, so compinsate with a lower axle. Shiners 450s really needed 4.88s for how they were driven, assuming my swag on how they are used us correct.
My new used to me GM 1500 has better towing gears than my 2000 C2500, and it has 4.10 gears too. Like 4x, the low gear is first in trans at 4.1, axle gears 3.42. vs 4.10 in axle, and a 2.48 in trans. Overall low is lower, over all high gear for freeway is taller netting me double the mpg empty, and better the few times towing by 10-20%. With a 4.3L V6 vs a 5.7L V8.
For those thing axle gears are what makes a tow, I've found trans gears can be a BIGGER factor in the how well it does performance wise, how long parts last. GCWR usually means squat! Like my 96 K3500 with a manual blew the doors off the higher rated auto trans equals. Just because you can go 60 mph over the Rockies from Louisiana, you won't stall out in a 20% grade in Seattle. An 18wheeler moving tractor trailer had this issue one time in a housing development I was working in.
I can do more issues I've seen and had too where what you think would be best, us worst!

Marty


92 Navistar dump truck, 7.3L 7 sp, 4.33 gears with a Detroit no spin
2014 Chevy 1500 Dual cab 4x4
92 Red-e-haul 12K equipment trailer

4x4ord

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Posted: 05/22/21 09:36am Link  |  Quote  |  Print  |  Notify Moderator

ShinerBock wrote:

RoyJ wrote:

blt2ski wrote:

Roy,

Probably a good thing we can't get multiple transmission options, along with axle gears. You'd get some crazy like me, order the 3.31 gear sets, but put a 10 so with a single OD, but have lower gears than the on Ford uses. I would have the same overall low, but at the top end, not have to worry about the DOD and TOD blowing up!
We do have some different folks south of that line!

Marty


I believe that's actually the trend in Class 8s these days: ultra tall rear end, with direct or mild OD in the transmission.

Theoretically it would make slightly more power, as ring and pinion gears of lesser difference have lower parasitic loss.

Think We can agree a point: we can't evaluate the best rear end ratio, without also taking transmission ratios into account.

A lot of the "get 4.1 to tow, 3.55 to cruise" mentality dates back to the Turbo 400 days with emissions choked 170hp 350 SBCs. With modern diesels and 8/10 spd transmissions, a 3.31 can drag a house off a foundation, and sufficient for all but the harshest fleet duties.


This is called dowspeeding and it wreaked havoc on drivelines back when the trend first started for some of the same reasons I stated here. We sold a lot and I do me a lot of clutches during this time. Many of my customers found out that the fuel economy benefits were washed away by driveline repairs. In many cases it even cost more than what they would have saved in fuel.

"Dana claims a downsped engine at cruise speed increases torque in the driveline by 57%. Fortifying the driveline is the only way to protect it against the resulting long-term torque stresses."

Downspeeding can Destroy Driveline

And for those who claim it is only engine torque that goes through the driveline. The max engine torque from these class 8 engines is 2,050 lb-ft and the added torque is way more than that.

[image]


This is for class 8 trucks that generally cruised between 1,200- 1,400 rpm.
[image]

These are all things we found out many years ago in my industry and is the main reason why I say taller axle ratios put more stress on the driveline.


I find this interesting. I just replaced the transmission in one of our class 8 trucks at just under 1,000,000 miles. Was it worn out? I don't know. The bearing on the input shaft failed. The truck has 3.36 gears with a double overdrive 18 speed transmission. I haven't had to change a U=joint yet, but i've broken all four axles. Maybe if I had had shorter gears the transmission would have lasted longer .... I know it would have used a lot more fuel.


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4x4ord

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Posted: 05/22/21 09:48am Link  |  Quote  |  Print  |  Notify Moderator

ShinerBock wrote:

4x4ord wrote:

^^^^Part of the problem with this discussion is in the terminology being used and how it is understood. For instance you use the term “stress” and I believe you’re thinking stress and wear are synonymous. I believe you’re thinking like this:

1.Taller gears increases the stress on the driveline components
2. Increasing stress increases wear
3. Therefore taller gears increase wear on the driveline components.

Furthermore, not only do I believe you’re thinking like this, but, I also believe you think this reasoning is so obviously sound that you can assume we should all understand how you’re thinking without any explanation.

Can you spot the problem with this reasoning as far as how it relates to our discussion on transmitting power through a driveline? I’m challenging you to think about this to help you and others who might be reasoning like this to come to a clearer understanding of things.... I’m not simply wanting to argue.


It is not just thinking, it is fact. As I stated before, this was an issue in my industry when the OE's started to adopt "downspeeding" back in the early 2010's which is essentially putting even taller gear ratios on over the road class 8 trucks so that their cruising engine speed is dropped from around 1,400 rpm to around 1,100 rpm. This was all done to meet the upcoming fuel economy standards for class 2B and up vehicles and is likely why we are seeing it done in our trucks since they will also fall into these new standards.

Shortly after this, fleets started to have major driveline issues due to the added stress downspeeding was putting on the drivelines, shortening the lifespan of these components. Clutches and u-joints where all failing a lot sooner than normal. So much so that it led Dana(one of the worlds largest class 8 driveline manufactures) to research the issue.

At first, manufacturers started de-rating the engines, but that still did not fix the issue. Dana had to come up with a whole new driveline system with more robust parts to cope with the added torque stress of downspeeding with these taller axle ratios just to get the component to last as long as they did with the shorter gears sets that were used previously.

If you want to read more on this research and what they did to combat this then you can in this (LINK)

So I am not basing this on what I "think". I am basing it on what I know and have experienced in my own professional industry. And yes it is a fact that taller axle ratios put more stress on the driveline gear for gear than shorter axle ratios. And yes, I would trust Dana's research(which I have to study and keep up to date with in my profession) over what someone is stating on an internet forum , especially when they are not providing any data or research to back up their theories.


Does your reasoning work on engines?

1. Reducing the number of cylinders in an engine increases the stress on the engine components.
2. Increasing stress increases wear.
3. Therefore a 6 cylinder will wear out faster than an 8 cylinder.

ShinerBock

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Posted: 05/22/21 11:30am Link  |  Quote  |  Print  |  Notify Moderator

4x4ord wrote:


Does your reasoning work on engines?

1. Reducing the number of cylinders in an engine increases the stress on the engine components.
2. Increasing stress increases wear.
3. Therefore a 6 cylinder will wear out faster than an 8 cylinder.


Yes this fact does work on engines, but not in the way you are talking about. High load at too low of an rpm (aka lugging) puts a lot of stress on engine internals similar to how a high load at a low rpm puts more stress in the driveline.

All three pickup truck diesel engine manufacturers found this out the hard way when they switched from fixed geometry turbos to VG turbos. Ever notice how all three had head gasket issues the first few years after having a VG turbo? GM with the LLY, Ford with the 6.0L and Cummins with the 6.7l. Too much timing, fuel and boost at low rpms creates a lot of cylinder pressure which equals blown headgaskets or even worse bent rods.

This generally does not happen as easily on a fixed geometry turbos at low rpms because it is not creating a lot of drive pressure or boost like VG turbos do. All three had to reconfigure their fuel mapping(tuning) to decreasing timing along with turbo boost modification at low rpms and/or increase the head bolt and gasket strength to solve the issue. Same makes had it worst than others.

* This post was edited 05/22/21 11:41am by ShinerBock *

noteven

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Posted: 05/22/21 11:44am Link  |  Quote  |  Print  |  Notify Moderator

Good explanation here:

Clicky

RoyJ

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Posted: 05/22/21 12:48pm Link  |  Quote  |  Print  |  Notify Moderator

ShinerBock wrote:

[image]


They say a picture is worth a 1000 words! That's EXACTLY my point earlier:

RoyJ wrote:

That means the ONLY difference in stress between a 3.31 and 4.30 truck is the transmission output torque, or driveshaft torque (again, T-in must = T-out). Because on the same hill, a 4.30 truck may be in 6th and the 3.31 truck in 5th.


Your only stress increase with taller gearing is driveshaft torque.

If anything else is burning up - that's drive abuse. Which granted, happens often with today's fleet drivers. But we're talking RV owners here.

RoyJ

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Posted: 05/22/21 12:56pm Link  |  Quote  |  Print  |  Notify Moderator

blt2ski wrote:

Many of you are also forgetting about the tranny gears.


That should be a sticky for any rear end discussion.

My old Dodge V10 has a 2.45 1st gear ratio, that's nearly as tall as 3rd on a 10R140! I have a 3.54 rear end. It would take a 6.23 rear end to match a modern F350 with 3.31 diffs.

Let's ask ourselves, if you bought an HD pickup 20 years ago, with a 6.23 rear end, would you honestly say: gee, this rear end is way too TALL, I'll burn up the tranny towing with it!?

A 4.30 F350 would be like by old Dodge with 8.10 diffs - heck, do they even make that? Even military Rockwells don't go that short IIRC

4x4ord

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Posted: 05/22/21 01:17pm Link  |  Quote  |  Print  |  Notify Moderator

ShinerBock wrote:

4x4ord wrote:

^^^^Part of the problem with this discussion is in the terminology being used and how it is understood. For instance you use the term “stress” and I believe you’re thinking stress and wear are synonymous. I believe you’re thinking like this:

1.Taller gears increases the stress on the driveline components
2. Increasing stress increases wear
3. Therefore taller gears increase wear on the driveline components.

Furthermore, not only do I believe you’re thinking like this, but, I also believe you think this reasoning is so obviously sound that you can assume we should all understand how you’re thinking without any explanation.

Can you spot the problem with this reasoning as far as how it relates to our discussion on transmitting power through a driveline? I’m challenging you to think about this to help you and others who might be reasoning like this to come to a clearer understanding of things.... I’m not simply wanting to argue.


It is not just thinking, it is fact. As I stated before, this was an issue in my industry when the OE's started to adopt "downspeeding" back in the early 2010's which is essentially putting even taller gear ratios on over the road class 8 trucks so that their cruising engine speed is dropped from around 1,400 rpm to around 1,100 rpm. This was all done to meet the upcoming fuel economy standards for class 2B and up vehicles and is likely why we are seeing it done in our trucks since they will also fall into these new standards.

Shortly after this, fleets started to have major driveline issues due to the added stress downspeeding was putting on the drivelines, shortening the lifespan of these components. Clutches and u-joints where all failing a lot sooner than normal. So much so that it led Dana(one of the worlds largest class 8 driveline manufactures) to research the issue.

At first, manufacturers started de-rating the engines, but that still did not fix the issue. Dana had to come up with a whole new driveline system with more robust parts to cope with the added torque stress of downspeeding with these taller axle ratios just to get the component to last as long as they did with the shorter gears sets that were used previously.

If you want to read more on this research and what they did to combat this then you can in this (LINK)

So I am not basing this on what I "think". I am basing it on what I know and have experienced in my own professional industry. And yes it is a fact that taller axle ratios put more stress on the driveline gear for gear than shorter axle ratios. And yes, I would trust Dana's research(which I have to study and keep up to date with in my profession) over what someone is stating on an internet forum , especially when they are not providing any data or research to back up their theories.




I thought we all came around to understanding that premise #1 is false? For instance it is true for u joints but not overdrive clutches or axles.
Premise #2 is something that I’d like to learn more about .... for instance if premise 2 is correct why would a 6 cylinder engine not wear faster than an 8 cylinder doing the same work? Also what is it about u joints that makes their wear rate so sensitive to torque load?

Edit: By the way thanks for posting the underspeed link. I haven’t read it yet but I will.

* This post was edited 05/22/21 01:24pm by 4x4ord *

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