Ram 1500 v6 - axle swap 3.21 to 3.55

[gallobg]

About a year ago I purchased a 2020 Ram 1500 with the v6 off the dealer lot. It has the standard 3.21 rear axle, which provides 6400lb tow capacity. That was fine at the time. Now I'm looking at occasionally (2-3 times per year) towing some bigger stuff and would like more tow capacity.

I've shopped around to change out my truck for the Hemi but this market is just brutal. Different dealers have now quoted me between $12,000-18,000 MORE than I paid one year ago to get the exact same truck but with the v8. It's the supply-chain stuff and I get it. But I'm not paying that.

I have seen forum posts about changing the axle ratio and would like to know more information. I understand that in "normal" times it wouldn't be worth it due to cost but it's now an appealing option in this market. My truck is the 4x4, so I believe that I need to change both of the front and rear axles.

I called a few dealers to inquire but this is not a common request so they're all a bit stumped on exactly what parts I need. Can anyone point me in the right direction?

 

[Vilas15]

Isn't 3.55 the only option with the v6? I would find your build sheet online or take a look at the differential before trying to get something you may already have.

 

[gallobg]

No, 3.21 is the default for the v6. 3.55 was an option. My window sticker says I have the 3.21.

 

[Jako]

I'm not a mechanic but have been on the forum for 3 years. This has been discussed on the forum and I believe you are correct about changing both the front and back.

 

[Moosefire66]

The most cost effective solution would be to find a wrecked truck and buy the pigs (or pumpkins, or center sections, etc) makes the swap much easier and cost effective. If you have 4wd you would definitely need to do the front and rear axle otherwise you wouldn't be able to run it in 4wd. Otherwise you can take it to a shop and get it done but you're probably looking at 1500 at a minimum, but I'd guess closer to 2500

Sent from my SM-G991U1 using Tapatalk

 

[IvoryHemi]

You’re only adding 1,000 lbs of towing capacity by going to 3.55 on the V6

You’ll never recover that expensive at resale time. Not worth it IMO

 

[gallobg]

Thanks for the advice everyone. I understand I'm only gaining 1,000lbs towing capacity and the cost will be around $2500. Normally I'd just swap the truck for a Hemi but in this market the cost differential is crazy high (~$15,000 from multiple dealers) and it seems like it will stay this way for awhile. So I'm trying to explore the next best option.

Does anyone know how I locate the correct part numbers for these 3.55 front and rear axles?

 

[silver billet]

You have to remember that you're really just changing the tow capacity "on paper". The 3.55 can accelerate under WOT faster, so if that's all you're doing (towing from 0 to 60 under WOT) then the gear change will certainly give you that paper win.

However, while actually using your truck for towing, the biggest place you probably need power is on "on ramps"; you're already well underway at that point, probably in 2n'd and/or 3rd gear and the transmission has lots of room to downshift; so therefore you gain nothing with the gear swap.

On the freeway climbing hills or trying to pass someone, same thing; your transmission will downshift into whatever RPMs you need, as long as you have gears left to downshift into, your truck is capable of making the same power numbers as the 3.55 is.

So my advice; don't waste your money for a paper win (accelerating faster from a dead stop under WOT). You're not going to see any improvements out in the real world for the 98% of the time you're towing.

 

[Dr. Jim]

Also, the front gear set is welded to the carrier. Check out "Anyone convert a 3.21 to 3.92?" in the search at the top of the page.

 

[Andymax]

For the few times per year, and assuming the larger loads are less that the thousand pounds you would gain, I think I'd try just towing the load first and see how it does...it may surprise you.

 

[GKIII]

Even if you change your gears you aren't changing your truck's tow rating in a LEGAL sense. So if you get into an accident with a trailer outside of your truck's maximum listed weight, you could be setting yourself up for some legal liability risk. Just my .02

 

[Whoa_Ram]

If you get the cost of changing them over let us know. I don't think I would cough up that money, but curious how much it would be.

I think for the front you can just buy the complete differential and swap it out right?

 

[gallobg]

Thanks for the advice everyone. I think you’ve talked me out of it.

 

[gallobg]

You have to remember that you're really just changing the tow capacity "on paper". The 3.55 can accelerate under WOT faster, so if that's all you're doing (towing from 0 to 60 under WOT) then the gear change will certainly give you that paper win.

However, while actually using your truck for towing, the biggest place you probably need power is on "on ramps"; you're already well underway at that point, probably in 2n'd and/or 3rd gear and the transmission has lots of room to downshift; so therefore you gain nothing with the gear swap.

On the freeway climbing hills or trying to pass someone, same thing; your transmission will downshift into whatever RPMs you need, as long as you have gears left to downshift into, your truck is capable of making the same power numbers as the 3.55 is.

So my advice; don't waste your money for a paper win (accelerating faster from a dead stop under WOT). You're not going to see any improvements out in the real world for the 98% of the time you're towing.

Based on the discussion here, I have decided not to pursue this. However, for the sake of my education, could you please help me to better understand the situation with axle ratios?

My v6 Laramie 1500 with 3.21 axle ratio has a max towing capacity of about 6400lbs, with a GCWR of 11,900.

The v6 Laramie 1500 with 3.55 axle ratio has a max towing capacity of about 7400lbs, with a GCWR of 12,900.

It is my understanding that the truck is exactly the same, except for the axle ratio (same engine, frame, brakes, suspension, payload capacity, etc.). The different axle ratio specs out at +1,000lbs of tow capacity "on paper" by increasing the GCWR spec. If, as you said, the main benefit of the 3.55 axle is the 0-60 towing situation (i.e., from a stop), then is the increase in tow capacity mainly a factor of getting the towed item moving? And that once moving at speed, the two axle ratios are essentially a non-issue?

Or perhaps said another way, is it that the base v6 with 3.21 axle ratio simply cannot get a 7000lb trailer up-to-speed at a fast enough rate to be considered safe?

Thank you for any insight you can provide.

 

[silver billet]

Based on the discussion here, I have decided not to pursue this. However, for the sake of my education, could you please help me to better understand the situation with axle ratios?

My v6 Laramie 1500 with 3.21 axle ratio has a max towing capacity of about 6400lbs, with a GCWR of 11,900.

The v6 Laramie 1500 with 3.55 axle ratio has a max towing capacity of about 7400lbs, with a GCWR of 12,900.

It is my understanding that the truck is exactly the same, except for the axle ratio (same engine, frame, brakes, suspension, payload capacity, etc.). The different axle ratio specs out at +1,000lbs of tow capacity "on paper" by increasing the GCWR spec. If, as you said, the main benefit of the 3.55 axle is the 0-60 towing situation (i.e., from a stop), then is the increase in tow capacity mainly a factor of getting the towed item moving? And that once moving at speed, the two axle ratios are essentially a non-issue?

Or perhaps said another way, is it that the base v6 with 3.21 axle ratio simply cannot get a 7000lb trailer up-to-speed at a fast enough rate to be considered safe?

Thank you for any insight you can provide.

"Safe" and "fast enough" are subjective for the most part; however, the ratings on your truck come from the SAE J2807 standard, which run through multiple tests to ensure that all trucks using the standard can be compared directly to eachother. If one truck under that standard is rated at 5000 pounds, it will pull 5000 pounds easier/quicker than a truck that is rated for 4000 pounds, regardless of manufacturer. This is relatively new, up til 2015(?) Ford and GM did not use that standard and they self rated their own trucks so nobody could compare an F150 vs a silverado with any certainty. They test stuff like truck understeer/oversteer, engine/transmission temps, and 0 to 30 + 0 to 60 etc. Since as you noted, the gear ratio is the only change between two otherwise identical v6 trucks and there is a 1000 pound GCWR difference, we can assume that the only tests which your truck would do worse on, are those tests where the gear ratio can make a difference; ie, acceleration from a stop.

There is nothing magic about a gear ratio, all it does (in combination with the transmission gears) is multiply engine torque. If your truck is revving at 4000 rpms in 3rd gear up a hill, a 3.55 will have to be roughly in that same RPM range, and if you do the math it will probably be between 3800 and 4200 RPMs but also probably in a different numerical transmission gear. But the gear number doesn't matter; what matters, is that your truck needs 4000 rpms (almost peak torque) to pull that load at that speed up that hill, so a 3.55 will need roughly the same 4000 RPMs; it might get away with 3800 instead, but it will be very close; it will certainly not be 2000 rpms, for example. And if you need even more power, your transmission will downshift.

The only place this doesn't work, is where your transmission has no room left to downshift, ie., first gear. If you're pulling such a heavy load that you need first, the 3.55 will do it easier/quicker. But once you are in second or third, the advantage of the 3.55 is gone; in the days of 8 and 10 speed transmission, rear axle ratio is pretty unimportant unless you're doing drag racing from a stop; if you need more power, the transmission has many gears to choose from. When you had a 3 or 4 speed auto back in the 90's, gear ratio was extremely important, every transmission shift was at least 1000 rpms change, but today it's far less important.

Another way to look at it; if your load is so heavy that a 3.21 makes you uncomfortable towing it, there is a very very high probablility that you will also not want to tow that load with a 3.55. It's not going to improve much. Moving up to a hemi, you will notice a huge change, but that's because the hemi makes loads more torque at every rpm, and every gear.

With the 3.55 you may notice first gear is a little easier, but how much time do you spend towing in first? I tow quite frequently, and though I'll never turn down more power, I'm not terribly worried about first and second. I would love more on ramp acceleration, or more passing power, but those happen when your in 3rd and beyond, all the gears where the gear ratio doesn't change your acceleration because that's what the transmission does for you (downshifts).

 

[GKIII]

He's just saying you aren't going to see a noticeable increase in torque when it's all said and done. Here's a comparison of the final drive ratios between the two (with 3.92 gears thrown in as well).



Unlike the difference between the 3.92 and 3.21 where similar gear ratios are often an entire gear apart, the improvement between 3.21 and 3.55 is marginal...at best. It might help your truck go slightly faster up a long 8% grade in places like CO but honestly with a V6 the change just isn't worth it for edge cases like that.

 

[Richard320]

Based on the discussion here, I have decided not to pursue this. However, for the sake of my education, could you please help me to better understand the situation with axle ratios?

My v6 Laramie 1500 with 3.21 axle ratio has a max towing capacity of about 6400lbs, with a GCWR of 11,900.

The v6 Laramie 1500 with 3.55 axle ratio has a max towing capacity of about 7400lbs, with a GCWR of 12,900.

It is my understanding that the truck is exactly the same, except for the axle ratio (same engine, frame, brakes, suspension, payload capacity, etc.). The different axle ratio specs out at +1,000lbs of tow capacity "on paper" by increasing the GCWR spec. If, as you said, the main benefit of the 3.55 axle is the 0-60 towing situation (i.e., from a stop), then is the increase in tow capacity mainly a factor of getting the towed item moving? And that once moving at speed, the two axle ratios are essentially a non-issue?

Or perhaps said another way, is it that the base v6 with 3.21 axle ratio simply cannot get a 7000lb trailer up-to-speed at a fast enough rate to be considered safe?

Thank you for any insight you can provide.

The only thing that changes is the ratio between engine RPM and wheel speed. So acceleration may be slightly better with the lower gears, and compression braking may be marginally improved. But I don't see anyone pulling a load that they can't budge with 3.21s but can with 3.55s. That would be way too heavy. Maybe they're afraid the transmission will overheat with the torque converter working so hard?

 

[JimD007]

I agree with what you are saying, taking it easy with a 3.21 ratio for occasionally towing a heavy load is probably an OK alternative. 3.55 wouldn't make a huge difference and only in first gear. But wouldn't the 3.55 also help the transmission not downshift as much on hills on the highway? I'm getting used to it and it is also not a huge deal but it might be another benefit of the 3.55. I would have spec'd it if I had ordered one but I bought mine off the lot. You'd give up a little gas mileage but with limited torque, I think it might make some sense in general - as well as being marginally better for towing.

 

[silver billet]

But wouldn't the 3.55 also help the transmission not downshift as much on hills on the highway?

No it wouldn't. Best way to think of it (conceptually) is this. Let's say I have a unique truck with 8 gears, only I have a gear "0" that you don't have, and I end at gear 7. So my truck looks like this:
0, 1, 2, 3, 4, 5, 6, 7
and yours
1, 2, 3, 4, 5, 6, 7, 8

So you and I both have 8 gears, we share 7 of them, but our first and last gears are different of course.

On the hills, both trucks can use the same gears (1 - 7) and we will have the same power, torque, rpms, etc. Only when our trucks are starting from a stop, or running in our final gears, will there be a difference between our two trucks. For the rest, operation is identical.

That's basically what gear ratio does... it moves the shifts down or up, but the same gears can be found in every truck because our transmissions are identical. We're just changing the start and end points, so that's where the differences are, in the middle we don't get any extra power, or on the flip side, any extra mpg savings.

And yes, this is a "explain like I'm five" explanation, and it works better when comparing the 3.21 vs 3.92 because the math works so beautifully in that particular example, but it's the same sort of idea with the 3.55 vs 3.21. You don't gain any pulling power beyond first and maybe second. With the 3.21 vs 3.55 it's more like this:
1, 2, 3, 4, 5, 6, 7, 8 <--- 3.21
0.5, 1.5, 2.5, 3.5, 4.5, 5.5, 6.5, 7.5 <-- 3.55
0, 1, 2, 3, 4, 5, 6, 7 <--- 3.92

 

[JimD007]

Silver bullet,

I don't think what your wrote above is correct. With the 3.55 rear end, the engine is turning more rpm in every gear including 8th. That means it has more torque to carry hills. It is a minor point but in theory, I think the transmission will have less need to downshift. I think it's minor because the extra torque you need has to be quite small for this small change in rear end ratio to provide it. But the difference between 7th and 8th is also pretty small. I have not done the math.

But in each gear, a higher rear end ratio means more engine rpm and thus more torque.

Jim