Gears (4.10 to 3.42) front diff info?

[Big Red Suburban]

I've looked into a Gear Vendors for some time now, but decided the cost is just too much. I don't ever tow heavy loads, at most the suburban is fully loaded with the family pulling our boat which is less than 3000 lbs.

So I've decided to swap both axles to 3.42 gears (maybe even a limited slip of some kind in the rear). I've done my share of gear changes before but no chevys. The 14 bolt FF looks easy with the backlash adjustment nuts (no shims), however I'm unsure how much work it will take to do the front diff.

Can someone provide some info on what all has to be removed to get the front diff apart to swap gears? How long did it take you (for those that did it themselves)?

I understand I can alter some jumper connections somewhere to recalibrate the PCM for the different gear ratios, however the TC lockup is based on the trans speed sensor. I've read here that my TC won't lock up until like 53 mph instead of 45 mph with this gear change. Can I do anything to correct/alter this? Or is it really a problem?

Any other problems I should be aware of?

[moondoggie]

Good Day!

One of the years of reprint articles contains an article that is extremely good about altering your VSSB to make everything have the correct speed signals. It's really pretty simple.

Without altering your VSSB, your TC still will lock at 45 mph indicated, which will actually be ~ 54 mph. I'm surprised your TC will lock this low - mine won't lock until 48 mph if I'm REAL easy on the footfeed, although I have noticed it will lock at 45 mph if I've previously set the CC at a speed lower than 45.

If memory serves, your OE tires were 245/75R16's. What's the effective rolling diameter of your tires? If it's much different than 30.47", you're already experiencing speedo & odo errors.

I hope you get your parts cheap. You're unlikely to pick up much more than 2 mpg, IMHO. ;)

Blessings!

Brian Johnson

[JohnC]

Red:

Contact me if you're interested in a 10.5" FF axle with 3.42 gears and factory locker with 51,000 miles on it...

cooperjr at access4less.net

[Big Red Suburban]

OE tires were 245/75R16's (30.47"), new ones are 265/70R17's advertised at (31.4"). This works out to be a 3% difference from stock, however after the tire swap I checked the odometer and it was right on with the mile markers? I remember being upset it was the same. I really wanted that 3%, can you tell? Anyways, 4.10's are way too steep for my rig, I can't wait to cruise down the interstate at 2100 rpms instead of 2500 rpms to keep up with everyone ;)

Even if I only gain 2 mpg, thats a 13% improvement in mileage, less wear on everything (including my ears), and a more pleasant driving experience on long trips. I won't feel like I'm revving the crap out of it running down the interstate. I know I could always slow down, but with four kids in the vehicle on long trips, the time saved by running 75 is worth the $1000 or so to swap the gears smile.gif

Am I the only person to justify a gear swap for this reason?

[moondoggie]

Good Day!

You ought to hear these trucks with the Gear Vendors Aux. OD. That, plus my slightly oversized tires (235/85's), & my effective overal ratio is 3.08 (~ 1750 rpm @ 70 mph). If Scotty beamed you into my pickup at 65 or 70 mph, you wouldn't be able to guess it's a diesel.

Ditto on the mpg - it's my only hobby.

Blessings!

Brian Johnson, # 5044

[DA BIG ONE]

Originally posted by Big Red Suburban:
Am I the only person to justify a gear swap for this reason? I did mine 4.10 to 3.42 front and back last April. I have an uncommon (for 1999) burb w/NP246 AutoTrac t-case, having 3 speed sensors calibration can only be done w/fact VSSB.

The stock tire size is ok, but I am going w/19.5" 265/70, 33.5" dia so I will an overall ratio of about 3.09:1 making highway driving more enjoyable.

As for towing? Rarely tow anything over 3,000 lbs, so w/heavy towing I can go w/smaller dia tire if need be.

[Big Red Suburban]

Anyone have a full service manual that they would be willing to copy the applicable pages for the front end gear change and fax/mail to me?

I checked with the local dealer and if I absolutely have to, I can resort to letting them do it (I would take the housing in to them). They said it would be 4 1/2 hrs at $44/hr (not too bad I guess).