I’m going nuts with 3.21s and 35” tires

[Agitated]

I knew when I installed the 35s I would lose some cruise rpm and effective gearing but I really did not expect the truck to be hunting between 7-8th gears on flat ground. This is killing me. I am aware I can just get some shorter tires but the current stance I have is important to me. I asked my dealer to price out a loaded 3.92 new rear housing and front section but they arent even sure it is available and if so what the cost will be. This crazy there is no aftermarket support for these axles.
I think my best bet here is to either find someone to switch and pay for the labor, or trade in on a different truck. But my truck is a good one so i hate to roll that dice. For now i have to keep hitting the steering wheel gear limit button and lock out 8th gear.
I made a big mistake.

 

[Jared B]

Yeah, unfortunately, the added height and weight of the 35's on a 3.21 geared truck puts the RPMs right in the hunting zone between 7 and 8th on the highway at cruising speed. Unfortunately if these trucks are like the later 4th Gens you can't just swap the gears in the front diff either because the carrier is welded in, you have to swap the whole front diff itself.

I know that's unfortunately probably not the news you want to hear.

 

[Billy James]

I knew when I installed the 35s I would lose some cruise rpm and effective gearing but I really did not expect the truck to be hunting between 7-8th gears on flat ground. This is killing me. I am aware I can just get some shorter tires but the current stance I have is important to me. I asked my dealer to price out a loaded 3.92 new rear housing and front section but they arent even sure it is available and if so what the cost will be. This crazy there is no aftermarket support for these axles.
I think my best bet here is to either find someone to switch and pay for the labor, or trade in on a different truck. But my truck is a good one so i hate to roll that dice. For now i have to keep hitting the steering wheel gear limit button and lock out 8th gear.
I made a big mistake.

That's too bad. Hopefully you can find someone to trade/sell with. I've seen a lot of Jeep people make the same mistake with the higher gears; it works ok with a manual but really takes it toll with an automatic.

 

[wthomps79]

I was wondering how you were getting along with the 35s. I noticed a very noticeable reduction in pulling power when I put on your old 34s and I have 3.92s! At least more than I was expecting. The truck downshifts on small hills where it didn’t before, but that was somewhat expected. I couldn’t imagine hooking up to my 20ft equipment trailer with it now. Luckily I still have my 2ton truck. The best gear ratio you could get would be 4.56 with the 35s as even 3.92 is marginal IMO.

 

[Agitated]

It was livable with the 34s and a/t tread. The 35s with m/t tread and wider width have taken some enjoyment away from my truck. I’ll figure something just not sure yet. I really just need a way to permanently lock out 8th gear really. I dont have a power complaint.

 

[Lettika]

Put it in tow/haul mode until someone puts out a tuner that will allow you to play with the shift points. If you are going to swap out the gears eventually it could pay off to deal with it until someone puts out a higher gear than the 3.92 also. Call Eaton and let them know you need one.

 

[Doc]

I knew when I installed the 35s I would lose some cruise rpm and effective gearing but I really did not expect the truck to be hunting between 7-8th gears on flat ground. This is killing me. I am aware I can just get some shorter tires but the current stance I have is important to me. I asked my dealer to price out a loaded 3.92 new rear housing and front section but they arent even sure it is available and if so what the cost will be. This crazy there is no aftermarket support for these axles.
I think my best bet here is to either find someone to switch and pay for the labor, or trade in on a different truck. But my truck is a good one so i hate to roll that dice. For now i have to keep hitting the steering wheel gear limit button and lock out 8th gear.
I made a big mistake.

Please forgive my ignorance if i'm way off on this. Could you get an ECM tune to up the RPMs for that trouble zone?

 

[Agitated]

To my knowledge that capabity doesn’t exist yet.

 

[Hackmunch]

i have the 3.21 gears and 33" a/t tires. no issues at all and get great gas milage on the freeway.

 

[grinch72]

I knew when I installed the 35s I would lose some cruise rpm and effective gearing but I really did not expect the truck to be hunting between 7-8th gears on flat ground. This is killing me. I am aware I can just get some shorter tires but the current stance I have is important to me. I asked my dealer to price out a loaded 3.92 new rear housing and front section but they arent even sure it is available and if so what the cost will be. This crazy there is no aftermarket support for these axles.
I think my best bet here is to either find someone to switch and pay for the labor, or trade in on a different truck. But my truck is a good one so i hate to roll that dice. For now i have to keep hitting the steering wheel gear limit button and lock out 8th gear.
I made a big mistake.

Why not try the new Pulsar ECM programmer that gives you the ability to change your tire size and effectively change the RPM and shift ratios? You get a 30 day return window. I know they are pricey but it could solve your issue.

 

[Agitated]

I have a Hypertech that already does that. Having said that I got in the Pulsar group buy and it should be here next week. Still doesn't give me the ability to reprogram shift points/rpm though.

 

[grinch72]

I have a Hypertech that already does that. Having said that I got in the Pulsar group buy and it should be here next week. Still doesn't give me the ability to reprogram shift points/rpm though.

I was under the impression that changing the wheel size effectively changes the RPM and MPH readouts which should effectively change your shiftpoints if they are based on the RPM, etc? I could be wrong though with my understanding of that.

 

[AnthonyD1978]

My truck hunts 7th and 8th too with 34" tires at 75+MPH with any slight elevation change. It's annoying to me and I bet it's worse for you.

Keep us updated on the pulsar.

 

[RPeezy]

I was under the impression that changing the wheel size effectively changes the RPM and MPH readouts which should effectively change your shiftpoints if they are based on the RPM, etc? I could be wrong though with my understanding of that.

The MPH reading will change, RPM won't. RPM isn't calculated, its mechanically determined by the speed the wheels are turning and the gearing, regardless of how much ground you're covering per revolution.

 

[Bboyce536]

Correct me if I'm wrong, but isnt 7th gear in a 3.21 truck essentially 8th in a 3.92? The cheapest route would be to just lock out 8th gear.

 

[RiverRacerX]

I just ordered 33x12.5x20s and I have 3.21s. Hope it runs fine.

 

[AnthonyD1978]

My truck hunts 7th and 8th too with 34" tires at 75+MPH with any slight elevation change. It's annoying to me and I bet it's worse for you.

Keep us updated on the pulsar.

Just want to reiterate that with my 34's it's barely an issue and I only notice it when I'm traveling in Arizona and it's 75mph speed limits. I'll probably still go with a 35" tire when it comes time to replace my 34" tires since 99% of my driving is in the city. On my next trip I'll throw it in tow mode during the sections it does this. See if it helps.

I just ordered 33x12.5x20s and I have 3.21s. Hope it runs fine.

Should be fine. 33" tire is available as a factory option and standard on the Rebel I believe.

 

[Jagertank390d]

What about switching out to 35x11.5's? I remember there being a significant weight reduction doing this. Like 12-15 lbs per tire.

 

[Dontfront82]

I have 3.21s with 35s on 22 inch stocks and have zero issues. maybe the wheel you are using is extremely heavy?? But these trucks can easy handle 35s or 33s. Now if you are trying to haul *** everywhere on 35s vs stock tires/lighter, that's diffrent, they truck will respond to how how u treat it

 

[aimlowrobin]

My 19 is my second ram with 321s and 35s. I don't really notice any difference between stock and the 35s with custom wheels and lift.