Eaton LSD with 4.56 gearing

[schwang_11]

I have a 2001 Tundra ex cab with a TRD supercharger I am looking into installing an Eaton LSD with 4.56 gearing (because they have them for pretty cheap at performanceproducts.com) i was wondering how much of an RPM increase am i going to get with 265-75-16 tires (how do you calculate this), is this a bad setup, if so what do you recomend.

[Triple BB]

Bad idea in my opinion with the gears. Can't go wrong with the LSD. With 265's and 4:56's, you'll see your mileage go crap and you'll lose something on the top end.

[Imdone]

LSD cool
4.56 w/that tire size, bad.

4.56 are good w/a 33 x 12" tire and wheel combo. If you regear to anything then go 4.10 or 4.30. You may find that this gear ratio will cost more than it's worth. Rockymtnray is the only one I know of with 4.30 gears and it cost him more than my 4.88 w/powertrax locker installed. He also got a deal on the gears used from a member at TTORA.

[RockyMtnRay]

Originally Posted by schwang_11

I have a 2001 Tundra ex cab with a TRD supercharger I am looking into installing an Eaton LSD with 4.56 gearing (because they have them for pretty cheap at performanceproducts.com) i was wondering how much of an RPM increase am i going to get with 265-75-16 tires (how do you calculate this), is this a bad setup, if so what do you recomend.

Your 265/75 tires reduced your effective gear ratio by about 3%, the change from 3.91 to 4.56 gears will move things about 17% the other direction with a net change of about a 14% increase in RPM for the same true highway speed. By true highway speed, I mean the speed after you recalibrate your speedometer (which will be necessary). A 14% increase in RPMs means that where you used to drive 2300 RPM for a given speed, you will now be driving at about 2600 RPM. 2500 RPM will become almost 2900 RPM. There will be significant increase in torque but you will also notice a big increase in engine sound.

The effect on gas mileage is a bit hard to predict...but it won't be much (maybe around .5 mpg). Everybody believes that numerically high axle ratios will "kill" the gas mileage, the actuality is they don't have all that much effect and can actually slightly increase the mileage if you do a lot of hilly/mountainous driving because the transmission doesn't downshift as often. After I regeared to 4.30 (for towing), I'm actually getting slightly better (maybe .3 mpg) than I was before the regearing...the exact opposite effect that most people would have predicted.

So, bottom line, you will get noticeably better acceleration though the truck will run out of top end quite a bit sooner. At highway speeds, the engine will be turning 300 to 500 RPM higher for the same road speed. You'll notice quite a bit more engine noise inside the cab. You will have to get a speedometer recalibrator. And there's likely to be some loss of gas mileage.

As the guys note above, 4.30 gears are really the optimum for maximizing torque with 265/75 tires...but 4.30 gears are quite pricey and it will cost a lot to have both ends of a 4WD truck regeared. Athough it's an optimum ratio, I believe member Imdone is correct that I'm the only guy here who has regeared with 4.30. That's probably because everybody else who has regeared is running 33 or 35 inch tires and just about had to regear (with 4.56 or 4.88) to get back stock torque for daily driving. Whereas I have basically stock tires (265/75) and merely wanted to optimize the torque situation for towing.

[Agent WD-40]

Originally Posted by RockyMtnRay

Your 265/75 tires reduced your effective gear ratio by about 3%, the change from 3.91 to 4.56 gears will move things about 17% the other direction with a net change of about a 14% increase in RPM for the same true highway speed. By true highway speed, I mean the speed after you recalibrate your speedometer (which will be necessary). A 14% increase in RPMs means that where you used to drive 2300 RPM for a given speed, you will now be driving at about 2600 RPM. 2500 RPM will become almost 2900 RPM. There will be significant increase in torque but you will also notice a big increase in engine sound.

How can you correct your speedo and Odo to read correctly with changed gearing? How difficult is it?

[RockyMtnRay]

Originally Posted by Agent WD-40

How can you correct your speedo and Odo to read correctly with changed gearing? How difficult is it?

There are two companies that make speedo/odo recalibrators. One is Superlift TruSpeed; the other is Jet Accuspeed.

TruSpeed sells a kit (pricey, around $180), Jet is just the part (not so pricey). The TruSpeed is allegedly waterproof so can be installed under the truck, the Jet isn't and must be installed inside. Both get wired in between the sensor at the back of the transmission and the ECU. Both have adjustment screws to change the ratio of pulses coming out of the sensor to the pulses going to the ECU.

For a variety of reasons, more people have gotten the TruSpeed (including me though mine is not yet installed...hopefully this week it will finally get nice enough to be able to work on my truck).

[Imdone]

Originally Posted by Agent WD-40

How can you correct your speedo and Odo to read correctly with changed gearing? How difficult is it?

I used a Truspeed from superlift. was about $180 and took about 3 hours to install.

I wasn't breaking any install records this day I can tell you. I just putzed along and got it done.

it was easy, running the wires and soldering were the hardest part. there is only 1 wire you have to cut and 1 power wire and 1 ground wire that has to be perished.

pretty easy, works like a charm.

[Agent WD-40]

Thanks for the info guys. How hard is it to adjust? Is it a guess and test type thing or are there easy settings to choose from?

[RockyMtnRay]

Originally Posted by Agent WD-40

Thanks for the info guys. How hard is it to adjust? Is it a guess and test type thing or are there easy settings to choose from?

There's some guidance in the manual regarding how much to turn the adjustment screws to get a desired ratio but most who do it have the adjuster in the cab and do a series of short tests with a GPS unit until the speedo and GPS indicated speed match up. GPSs are so common these days that you should be able to find someone who has one...even the kind that folks go hiking with will work perfectly well.

[TwinStop]

Originally Posted by RockyMtnRay

There are two companies that make speedo/odo recalibrators. One is Superlift TruSpeed; the other is Jet Accuspeed.

TruSpeed sells a kit (pricey, around $180), Jet is just the part (not so pricey). The TruSpeed is allegedly waterproof so can be installed under the truck, the Jet isn't and must be installed inside. Both get wired in between the sensor at the back of the transmission and the ECU. Both have adjustment screws to change the ratio of pulses coming out of the sensor to the pulses going to the ECU.

For a variety of reasons, more people have gotten the TruSpeed (including me though mine is not yet installed...hopefully this week it will finally get nice enough to be able to work on my truck).

Are you planning on taking pictures and doing a write up on the install?

[mustang67408]

Heres a few pics of my TRUSPEED. They are not very clear , but it gives you an idea.
Attached to speedo wiring
Truspeed mounted to my air compressor
Wiring secured to tunnel
It all depends on the year of the vehicle as to where it goes.

DISCONNECT BATTERY BEFORE DOING ANY OF THE WIRING.

The TruSpeed is installed in-line with the speed signal wire coming from the speedo gear (speed sensor). The easiest place to tap into this is under the vehicle. You can find it inside the cab, but will need the wiring diagrams to find the junction connectors.

The TruSpeed has two calibration settings and allows you to set the speed for two different sets of tires with the flick of a switch. The adjustments are done by turning a small screw on the side of the box.

The TruSpeed unit has 4 wires on it:

BLACK - Ground
Red - +12V
Green - to the speedo gear encoder (speed sensor)
Yellow - to the speedometer

The black/red wires are tapped to a ignition +12v source and ground. The green/yellow wires are spliced in-line with the speed signal wire. I cut the harness to a suitable length to install, and use the excess to tap into the car harness.

I chose to actually install the unit on the frame next to my air compressor, with sufficient wire on the harness to remove to do the tuning and then stick it back on the velcro pad.

The final calibration was done with my GPS.
This is for a 2002 Tundra
It will fit many years.
It all depends on the year as to where it goes and which wires you tap into.
-V-

[kylant1]

Ray,

Do you think 4.56 gears would be the best for towing and regaining lost torque from up moving up to a 285/70-17 tire? My truck works pretty good when towing my boat.

This truck definately does not tow like my 8.1L Big Block Chevy did

Thanks

[kiokenTUNDRA]

i just got my truck lifted w some 35's and lost some power, what gearing would i have to go with to get back the stock torque?