Looking for a 3.73 rear & front end

[BrentN]

Hey All,
I have had my truck for 2 weeks. It indeed has the GT5 option of a 4.10 rear end, the rpms bear out as well 1750-1800 @ 55.

I tow a 4000lb 23 foot total length trailer. Add probably another 1000lbs for water and stuff.

My mpg (unladen running down the freeway @ 65-72mph + a mixture of intown driving)is I feel respectable at 15.5 to 16. I have only put a few tanks through it, but seems pretty stable...I think the effect of having a 4:10.

Given my trailer loading and the fact that the truck sees far more non towing highway miles than with the trailer, I am thinking I want to slap a 3.73 in the front and rear. Anyone disagree with this plan?

I figure that will pick up about 1.5-2.0 mpg on the highway, plus just get the rpms down and make my engine (gm goodwrench replaced in Feb 2004 with 7k miles on it) last all that much longer.

Does anyone have a recommendation as to where I should go for good quality gears as well as what should be a going rate for a shop to install?

Thanks,
Brent

[Dieselboy]

New 14FF gears from Precision Gear will go for around $235. An install kit is another $150. A typical install fee is anywhere between $350 and $500. I also have a set of used gears for sale.

I can't speak for the IFS front though.

[moondoggie]

Good Day!

Assumptions (for your truck):

* 4.10 gears
* 4L80-E AT (0.75 OD)
* 245/75R16 tires (30.47" OD, 95.72" circumference)


rpm @ 60 mph = (60 mph) X (1 hour/60 minutes) x (63,360 inches/mile) / (95.72 inches/tire rev) X (4.10 driveshaft rev/tire rev) X (0.75 engine rev/driveshaft rev)

rpm @ 60 mph ≈ 2035 rpm

Substitute 3.73 gears:

rpm @ 60 mph ≈ 1852 rpm

I picked up ~ 2 mpg by changing from 3.936 effective ratio (4.10 gears, 4% taller tires) to 3.08 effective ratio (4.10 gears, 4% taller tires, Gear Vendors Aux. OD [0.78 ratio]). (I have a spreadsheet

[Keith Richards]

Brent, just curious about what happened to the motor in such a new truck.Do you know what happened?

[moondoggie]

Good Day!

I should have checked my calculations - my previous post is wrong. I put the wrong data in the spreadsheet I used to calculate the miles to payback a gearset change like the one you're considering.

Actually, with the above assumptions, it would take > 154K miles to pay back $1000 of upgrades. :(

Blessings!

Brian Johnson, #5044

[BrentN]

Hi Keith,
I dont know what happened to the original motor per say. I bought the truck a few weeks ago, had my local Chevy dealer run the vin in the warranty system before I signed on the dotted line.

Here was the history:
2001- new injector pump
Feb 2002- Left and Right Heads replaced
Feb 2004- Entire engine replaced.

I actually have information as to the original owner. However, I would have to contact the widow as the husband died April 9th. (Found this out when I got all the title paperwork from the dealer I purchased it from). I dont feel right about calling the widow and trying to pick her brain, as the truck was titled and registered to her husband...If he were alive, I am sure he would have a detailed history as to what it was doing...He was a 64 year old Orthopedic surgeon...

What I did find after I got it home and put it through its paces was it was smoking like a banshee when I put my trailer on and started towing some decent hills out here in Oregon. About that time I picked up a PO 236..Turbo boost problems...That led me to find that the vacuum pump had gone south...thus no turbo. Apparently when a new GM engine is put in, the vacuum pump is transfered from the old...I suspect it was bad when they transferred it. You'd think that they would have checked it...but ya never know.

So my theory (looking for group input here)was that the previous owner may have had the vacuum pump die early on...leading to high egt...thus cooking the heads once and then twice (getting a new engine then).

I rejuvenated the pump and am getting good vacuum to the turbo...all is good now.

Any comments on my theory?

In any case, my Sub has 92,000 miles now. 9000 on the new engine...It runs and drives great. Tows my 18 foot 4000lb trailer like it wasnt there.

I really love this truck...I have never really raved about any vehicle I have owned...It is such a delight to drive.

I have put a K&N on it..The original filter was completely plugged as well.

As time and funds permit...I will start modest upgrades. Sounds like, gauges, exhaust, remote FSD w/cooler. I have the 4.10 rear end, I think for what I tow, it is way over kill, but I want to get some good data as to mpg and performance towing with it before I make any changes.

Living in Oregon, we definately have some 6% grades to climb. This summer I took my 93 Gas Burb with trailer to Los Angeles...1000 miles @ 6-6.5mpg. Even had a CHP pull up along side me and gave me the 55 signal with his hand..With the 4.10, 55 mph puts me right around 1750-1800 rpm.
Since out here, officially cars or trucks with trailers are limited to 55, maybe I should leave the gearing alone and spend my money elsewhere.

We plan on heading back to Rushmore next summer and probably back to LA (family down there). So, as a matter of operation, my truck will see the tallest passes in the US as its normal towing duty cycle.

But, like I said, I love this truck. Diesel Suburbans are the shiznit!

[jdmetcalf57]

I have a 99 k3500 (45wd) cc drw that I made the change to 3.73 and 265/85 tires that made the equivalent change to about 3.55 gears. I only saw maybe 1mpg difference. I pull about the same load you do 4k but usually have about 2k in the truck. I would make this change again though if for no other reason than it is much nicer driving with the rpms at a more reasonable level at 70-75 mph. Also now you can drive in 3rd at a reasonable speed.

I think I bought the gears from Randys ring gears which you can find in 4 wheel drive magazines. They were from Yukon gear. Front and back ring gears with install kits w/o new bearings run about $500. I did the work myself as it is not to difficult especially on full floating rear axles. It does take some time though and I think I spent most of a Saturday to get it done. The instructions that came with the gears were pretty decent. I did though just take the front differential (ifs) out as it made it much easier to make the gear adjustment.

[Dvldog 8793]

Howdy
I did the Gearvendor thing about two years ago. I was considering a gear swap, by the time I did both tfront and rear, the money would have been close(new parts). The deciding factor for me was that I can have my cake(4.10s) and get fat also(highway gears and good mileage) :D
One simple fact that people sometimes forget to mention, the truck gets the same mileage at any given rpm. Not considering wind drag. I can now keep up with the flow of traffic on the big roads, and my truck gets about 19-21 MPG. Also less wear on the engine and driven components. If you want great mileage you need to keep the engine at around 1600-1700 RPM. The Gearvondor has been a GREAT unit for me. They ain't cheap! I got mine new but I think people have found them used on Ebay.
Have fun!
L8r
Conley Janssen