sohc5.4

I just got my 2014 FX4 back from the off road shop, had 4.56 gears put in. Went with Sierra gears as the shop installs a lot of them..not sure..cost a small fortune. Following Sierra's break in procedure listed on the site.

Shop put in Royal Purple 75w-140 w/limited slip modifier in rear and 75w-85 front, $1 difference in price from Ford synthetic. Changing after 500 miles. Went with complete master install kits front and rear.

Vibration and whine has me wishing I had the dealership do this job. Warranty is still good with offroad shop, but I got a sick feeling something isn't right. Maybe the drive shaft and rear yoke isn't lined up as before or they mounted my wheels and tire backwards as far as vibration goes..just guessing now..hoping they got the mesh and backlash correct more importantly.

The 9.75 rear differential takes smaller pinion bearings to fit the Sierra pinion, front are 8.8 reverse cut that have been around.

Think this will wear in and be fine? I can handle the whine but the vibration isn't going to fly we me. Anyone experience this before and it turn out just fine or do I have a bad install /ticking time bomb?

Thanks for any input.

jhelrey

The whine is due to the gear mesh up or bearings. Did you purchase a bearing shim kit and a pinion shim kit? Setting up a rear end isn't difficult but it takes a lot of in and out to get it perfect. My buddy has been a mechanic for 30+ years and it still took us a 6 hour day to get it right with a lift. In my case, my truck had 225K miles and the bearings were bad. He suggested replacing bearings, ring and the pinion gear. I put in Yukon stuff.

Vibration can be from the driveshaft not being clocked correctly. I marked mine before I removed it. You could also have bad U joints.

I had no issue when the job was complete

sohc5.4

The off-road shop used the master install kits sold by sierra including plenty of pinion shims that was $500 of the cost not counting the R&Ps. Truck only has 18000 miles. The installer has a lot of experience. I called today and he wants to take a look at it. The vibration can be felt in the steering at 55 mph. Also a hi pitch whine at 30mph in 4x4 high. Haven't tried the e-locker yet.

Installer took 4 days to install. 4hrs charged for R&R the front lift.

WXman

What size are your tires? You have to remember that your driveshaft is spinning much faster now. Sometimes you get vibes because the shafts are now spinning beyond factory parameters. Might look into that. Obviously, the preload on the bearings could be incorrect or the shimming could be incorrect. You are finding out first hand why I don't do gear swaps anymore. Too many other cans of worms get opened.

sohc5.4

BFG 325/60 r20 KM2, went from 3.73s, drive shaft should be spinning faster but closer to stock with those tires. I just drove it a few miles on smooth payment and can feel the vibration pulse every few seconds at 55mph in the floorboard and steering wheel. Almost seems like the tires are out of balance. Got an appointment tomorrow, most likely will leave it with them to sort out. Hope it's not another week with no truck.

paintballdude05

What are the chances that they could have dropped the driveshaft?

jhelrey

You can unbolt the drive shaft and swing it out of the way and bungee it up.

sohc5.4

Chance is pretty slim they'd admit to it, judging from the quote for the gear swap vs what it ended up costing. There could be many things that went wrong like dropping the brake calipers and crushing the rubber brake lines, did that myself years ago and it caused vibration and a burnt up rotor. They had the lift apart ball joints apart, who knows.

One thing I know is they have been great to deal with and I'm confident they will resolve the issue.

sohc5.4

Met the installer today, guy knows what he's doing. He showed me the specs on backlash as being .010/.015 from sierra for that 9.75 an 4.56, crazy. He uses a snap on pinion torque wrench to get the crush spacer correct. He's trying to rotate the drive shaft first 90 degrees at a time first. Had to leave it overnight, hopes to have it figured out by tomorrow.

cbr600rx7

Keep us up to date. Some times things don't go right with gear installs. I had a 12 bolt that killed three sets in 5000 miles.