FX4362

So finally stepped up to 4.56 from 3.73. Tires are 285/75/r18, effectively 35". The good news is I have my power back. I can get up to speed without the sluggishness and I can pass people on the highway again when I need to. At 70mph I'm at 2100-2200 RPM where as I used to be at ~1800. It's too early to tell the effect on my gas mileage, but it's not looking good

Now for the bad news. There is no additional noise when accelerating or under load. When cruising or off the gas pedal, the is hum. It's not what I would describe as a high pitched whine, but definitely a hum that wasn't there before. The guy that installed them gave a 2 year/24k mile warranty so I'm not too worried. I'll run them the 500 miles for break in then change the fluid and see what's up with the noise.

eggejm11

What was the cost to have both diff's regeared?

marknissan

That noise you are hearing is the gears not being setup right. I did a few gear installs in the past on some old trucks and had that happen. I would call the shop that did it do fit it before they wear in wrong.

TJPlatinumEB

Agreed. I've done gear swaps on F-body's a number of times myself and if there is noise they either didn't set the pinion depth right, backlash is wrong, or wrong fluid.

Either way it needs to be looked at before it becomes worse.

FX4362

Thanks for the feedback on the nose. The cost was 2100 parts and labor.

PerryB

It's not necessarily the set-up (although it's entirely possible). I went through this on my 05 a couple years ago. Assuming you have a 9.75, the only gears available are Indium or Chineseium. The machining/finish/lapping quality is mediocre at best. I tried Sierra, Yukon and Dana SVL. The Sierras were disappointing, the Yukons hideous and the Dana SVL were acceptable but they have a bit of a coast whine at 42-50 and a soft but perceptible whir at high speed. I've set up a lot of diffs and did these by the numbers.

FWIW, as a GENERAL rule, (assuming the backlash and pinion preload is correct) a coast whine comes from too much pinion depth and a drive whine means too shallow. A float whine may be too much backlash.

Eric M

Time for bigger tires.

MikeyZ

Get it fixed ASAP, or you risk ruining the set.

RTM

I have roughly a 34 inch tall tire and want to change from 3.31 to 3.73. My fear is 4.10 gears would be a bad choice with the 6 speed auto trans. I'm afraid the first two gears will shift so quick it would yield them almost useless.

How is your truck from a stop? Does it shift more like it should with a factory tire?

marshallr

Gears 1-4 in a 6 speed are basically the same as gears 1-4 in an old school 4 speed. The difference is that gears 5 and 6 are both overdrive.