Twins4us07
Virginia
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Joined: 09/15/2008
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Ok I have been reading the forums and finally have decided to make the jump. I called my dealer and asked about swapping from 3.73 to 4.56 and the response I got was it can't be done. I called a local axle shop and was told I would need a new carrier and all. I called a gear distributor and was told I did not need a carrier. I called another dealer and was told it would just ruin the computer. Has anyone ever made a swap from 3.73 to 4.56 or 4.10 with a similar vehicle? If so how difficult was it? I am willing to spend about $2000.00 instead of buying a new TV so all help is appreciated.
1997 GMC Yukon, Firestone Airbags,K&N Intake,Flowmaster,Tekonsha P3, Hensley Arrow,Mckesh Mirrors,VR3 Rearview Camera.
2009 Cougar 29BHS X-Lite,Kippor 3000W Generator(quiet as a Honda but cheaper).
Twin Girls who hate hotels....
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BenK
SF BayArea
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Joined: 04/18/2002
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Find a 4x4 shop that does tons of diff work, as they get changed often
by serious off roaders and/or they break them more often.
The ring and pinion gears need to be changed, as they are a matched pair
The carrier is just that. The ring gear is bolted to that and the innards
of the carrier has the diff gears and clutches/cones/springs/etc if
a LS or locker.
Since the ring gear gets bolted to the carrier flange, the flange must
be in the right position in order for the ring gear to mesh with the
pinion. The pinion center line is fixed by the housing bore, so the
main adjustment is with the carrier, which rides on tappered bearings
bolted to the diff pumpkin housing.
If the carrier flange is not in the right position, the carrier must
be changed to one with the flange moved over.
So those shops could be telling the truth, or just don't know. They
should have opened up the diff pumpkin and measured. If they didn't,
then they are just going by whatever mental knowledge they have...or,
they are going by what they have in the stock room where as another
brand/model/etc might work without changing the carrier.
Going from a 3.73 to a 4.56 is pushing the limits and most likely
in need of a new carrier, but again, they should have opened it up
to measure. You'll have to pay for the new gasket and new lube if you
don't have them do the work.
Also note that this is on the extreme side of gearing and you won't
find much in any chart that has a 4.56 listed. Plus there is a down
side and is when not towing. The engine will be rev'ing about 20%
higher in all tranny gears (GM diff ratios are all about 10% apart
from each other per step).
Is this to make for larger dia tires? Note that if plans for a
suspension lift, it will reduce power delivered to the pavement.
-Ben Picture of my rig
1996 GMC SLT Suburban 3/4 ton K3500/7.4L/4:1/+150Kmiles orig owner...
1980 Chevy Silverado C10/long bed/"BUILT" 5.7L/3:73/1 ton helper springs/+329Kmiles, bought it from dad...
1998 Mazda B2500 (1/2 ton) pickup, 2nd owner...
Praise Dyno Brake equiped and all have "nose bleed" braking!
Previous trucks/offroaders: 40's Jeep restored in mid 60's / 69 DuneBuggy (approx +1K lb: VW pan/200hpCorvair: eng, cam, dual carb'w velocity stacks'n 18" runners, 4spd transaxle) made myself from ground up / 1970 Toyota FJ40 / 1973 K5 Blazer (2dr Tahoe, 1 ton axles front/rear, +255K miles when sold it)...
Sold the boat (looking for another): Trophy with twin 150's...
51 cylinders in household, what's yours?...
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bldrbuck
Boulder, Colorado
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Joined: 02/11/2001
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Try the auto salvage dealers. If they have the whole unit it probably will work. It may be expensive. It might be better to trade tow vehicles.
93 Ford F350 Turbo Diesel, DRW, Crew Cab. PullRite Hitch. 90 Nomad 28' 5er, 375 Watts Solar, 2800 Watt Yamaha Generator, 1750 Watt Inverter, 4 Trogan T105 Batteries, Spare tire and wheel and folding ladder. Me, wife and 2 spoiled Maltise furkids.
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Twins4us07
Virginia
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No tire swaps or lifts in the future and may go to 4.10. A new TV is out of the question my Yukon is perfect except for gears.
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BenK
SF BayArea
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Joined: 04/18/2002
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In my area (SF Bayarea CA) it ranges from $1K-$1.2K per diff. If 4x4, then 2x
If you need a new carrier, that will be more (guessing another $500
or more).
Best bang for the buck changing diff gears and as with anything, trading one
for another (more rev's, therefore less MPG running empty, but better towing and
maybe better towing MPG).
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mkirsch
Rochester, NY
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Joined: 04/09/2004
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Going from 3.73 to 4.56 gears is about the same as running in 3rd instead of OD.
IIRC the OD ratio for the 700R4/4L60/4L60E is .7, and the ratio of 3.73 to 4.56 is .8.
So close, it's not worth the time or the money unless you're drag racing and need the torque off the line.
If the rumors are true, you don't want to tow heavy in OD with a 4L60-series transmission anyway, due to the rumored weak OD clutches.
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SoCalDesertRider
SanDiego, CA, USA
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Joined: 12/14/2003
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Contact Precision Gear, Richmond Gear, Reider Racing, or Randy's Ring & Pinion. You should be able to find a 4.56 gear set for your axles. 4.56 is available for most truck axles. Dig deeper than what the sales staff are telling you. Those gears are out there.
I changed my F350 from 3.55 to 4.56 and I absolutely love it!  Your results may vary.
92F350 CrewCab 4x4 351/C6
LoadNGo service body
69Bronco ATC250R CR500
20' BigTex flatbed carhauler
B&W TurnoverBall g-neck Curt Magnum rr DrawTite ft
HD springs Rancho9000s Bilsteins poly sway bushings
285/75-16E BFG AT on 16x8 Stocktons
4.56's & Lock-Rite rear
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ThumperEXC
Crested Butte, Colorado
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Joined: 05/12/2008
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I swapped my 3.73's for 4.56's on my F150, but it was to offset the bigger tires, 265's to 315's. 4.56's with smaller tires...... not sure I would do that, you would be running some scary RPM numbers.
2007 Travel Star 21SSD
2004 F150
2007 Yamaha Grizzly 700
2001 KTM 520EXC
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BenK
SF BayArea
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Joined: 04/18/2002
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Twins4us07 wrote:Ok I have been reading the forums and finally have decided to make the jump.
snip....
Just checking back to see how this is going and realized made a big
assumption based on OPs comment in the above quote.
Assumed he has done his homework and knows the effects of this
re-gearing (higher rev's in all gears, speedometer going to be off
and in need of recalibration, etc). If a daily, then this change will
make it less fuel efficient running lightly loaded.
Also assumed he won't be towing in OD, as the manual says.
Both the 4L60E and 12 bolt diff are know weak links in the drive train
food chain when towing heavy.
Depending on the miles going to tow vs daily driver, it might be a
better way to go with an underdrive, IMHO.
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Twins4us07
Virginia
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Joined: 09/15/2008
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Underdrive?
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