truck - 2014 Ford F250 Super Duty 6.2 3.5" lift 37" tires
I recently had the gears changed from factory 3.73's to Yukon 4.88's. Drives much better, shifts better as well... also no longer hunts around.

Anyway, everything is perfect except - once I get over 50 mph it starts to devlope a loud noise in the cab, and by 55 - 60 mph it's much louder. Once I get to, say 60 mph, and let off the gas to coast, the noise all but goes away. There is also a slight, best way to describe it is, rumbly feeling that accompanies the sound. The sound is not a whine, but a deeper sounding rumble.

None of the sound is tire related road noise however.

I am not sure if this is gear related, or something else, but it seems pretty strange to me. It's going to the dealer next week for an oil change, tire rotation and NYS inspection, so I was going to have them check bearings.

any thoughts?

thanks in advance

 

Not sure about our trucks, but with the Ford 8.8 it is mandatory to use Ford gears or else there are usually noise issues. This is especially true with the IRS versions. I am sure that leaf spring set up will help isolate some of the noise though. I suspect that most people that switch to lower gears and big tires have little regard for NVH issues, so what you are experiencing could be more the norm rather than the exception.

 

hope they set the gear backlash and pinion depth correctly and used quality pinion and carrier bearings.

 

Thanks for the feedback.

He's a reputable shop that does all the gear swaps for a local offroad shop. Having said that, if there was an issue with gear backlash and pinion depth, would that be constant all speeds, rather then the 50+ mph issue I am experiencing? I've never dealt with this before... all new to me.

 

 

I had an outfit billing themselves as "..the 9 inch experts" do the 9er in my old van. After 5 attempts, they finally installed one that didn't whine. The low rumble is not good. Since your driveshaft speed is increased, examine/inspect/replace anything that moves from the transmission tail shaft to the diff, in addition to the diff itself.

 

Hopefully Pirate4x4 camo will chime in here. I think this is right in his wheelhouse.

 

Talked to him just a little while ago. Taking it to him tomorrow to have him listen to it. WTF... you know, I thought about just leaving the 3.73s with the 37" tires, but thought I was doing the right thing by going to 4.88's. ugh

 

Sounds like a pinion may not be set right. Mine did not make a sound difference from before, even during break in. I also went with 4:88s.

 

Thanks brother.

Perfect.... Figures. Just my luck lately.

 

You absolutely did the right thing replacing the 3.73's with 4.88's. There is something else going on. Hopefully the installation wasn't too long ago and your mechanic will stand by his work if there is something that needs extensive attention. If you get things sorted out you will love the lower gearing.

Good luck. Hopefully it turns out to be something simple and inexpensive.

 

Just had them done last week Wednesday/Thursday. Drove it home and it seemed fine. Drove it work Friday and around town over the weekend a little bit, and it seemed fine. It was Monday on the way to work that I noticed it.

It drives, shifts gears and has much better performance then before (with the 3.73s), it's just loud at highway speed. Almost wondering if there is something in the tranny or driveshaft. But the only thing that changed was the gears. So I'm taking it back tomorrow.

 

I'll be headed back to the shop this afternoon to have them take it for a ride with me.

Question: What I am experiencing happens at 50+ mph and gets worse around 60mph+, and seems to been a little less if I put it in TOW mode (button on the shifter). All the while the drive quality is great (acceleration, shifting etc), even at 50+ (other than the deep rumble sound and slight rumble from under the cab at hiway speed). Could it be something else, like tranny or drive shaft? Could the lower gears be amplifying a problem that I was not really noticing before?

The truck has 78k miles, and nothing has been replaced until the gear swap last week.

It always made a funky rumble when I would take my foot off the gas... say going 55mph, take foot off the gas, it would make a slight rumbly sound and vibration then clear up in a second or two.

I guess I'll know more when I get it to the shop.

I appreciate everyone's input so far...

 

Sorry I'm late to the show. It sounds like an issues with pinion preload to me, or maybe they damaged a bearing during install?

But I do want to ask about your 3.5" lift. Did you have it installed at the same time? Do you have a 1 piece or 2 piece drive shaft? And did you verify the part number for your truck through ready lift? I found several online venders selling the kit for the 2 piece driveshaft that were trying to list that part number as correct for the one piece driveshaft trucks. I guess they just assumed you didn't use the carrier bearing shim. I contacted readylift about this. And their tech support told me the taper on the rear lift blocks are different. That if I ran the blocks for the 2 piece drive shaft, I could experience driveline vibrations. Something for you to check and confirm anyway.

 

Thanks Ron.

I had the 3.5" Readylift installed by the same shop, but 3 years ago. My truck is a supercab (suicide rear doors) with a short bed, so I have a one piece driveshaft, not the 2 piece. I purchased the lift kit directly through Readylift, not on line either, I called them directly when I ordered it.

I'm going to head over shortly, but I will ask them about the pinion preload, as well as backlash.

Thanks again for the help...