Computer mod for 37" tires....

What is the best and easiest (and cheapest) way to calibrate the transmission on my 2008 F250 (6.4) for better shift points once I get my 37" Toyos put on??

I am scared the 37's will make the truck run like hell without doing something.

 

Definitely not the cheapest, but a SCT Livewire system would do wonders for your car and you can adjust many thing including shift points whenever you would like. It definitely would not be your cheapest option though.

 

realisticly ur should prolly lookin to a gear swap..

not only will u regain the lost power from turning such larger then stock tires but ur tranny will have less load on it ...

def. not the cheapest method but it is without a doubt the best way to go...

otherwise a tuner like the above mentioned is really ur only option, i dont think the Ford dealer can tune for tires as big as 37...least id be surprized if they could...

 

The dealers should be limited to 35" tires or there about. A lot of the tuners have up to 44" tire options available. Superchips makes a tire paq for just doing the tire size change, or you can do a true speed or similar specmo, or get a tuner which will do that plus many other fun options.

 

Yes proper gearing helps, and I would definately recommend regearing for larger tires, especially 37's.

But just a side note to remember, swapping gears doesn't correct the speedo. The tone gear is identical for all gearsets (3.73, 4.10, 4.30, 4.56, etc). So no matter what your final drive ratio is, the speedo will still need adjusting according to tire size, not gear size.

Ford will only reprogram for up to a 35" tire. As has been mentioned, there are plenty of aftermarket alternatives to calibrate the speedo.

 

What gears do you have in the truck now?

 

3.73

To the best of my knowledge (which is limited), a lower ratio gear will give me better power and less fuel economy BUT WILL IT help my transmission shift points?

I would LOVE to hear from DCSPecial on this as I know they modified many 2008's with 37" tires.

 

I'd install 4.30 gears and get a SCT X3 tuner to address the speedometer and transmission.

 

SCARED to void my warranty.

 

Ha! It's only by the grace of your extremely friendly dealership that you haven't already voided your warranty with the BDS lift kit and 37" tires. That considered, you can use the SCT X3 tuner to just set you speedometer and transmission shift points/firmness. You don't have to use the "performance" aspects of the tuner.

I believe that you have a 100K powertrain warranty. That's a long time to be putting undue stress on your transmission due to the larger tires. Ask the dealership if they will void your warranty if you install new 4.30 gears. You may even want to pay them to do the install. It will cost more $$$ than having them replaced by a shop but if it enables you to keep the powertrain warranty, then it's worth the extra $$$.

I'm just thinking about the long-term affects of the larger tires on the reliability of the truck. If you plan on selling it in a few years, then there's no issue. If you plan to keep this truck for the next 10-15 years, then you are sacrificing long-term reliability by keeping your current setup. Just my opinion... btw, did you post pics yet?

 

They won't void the entire warranty. Dealerships cannot do that.

However, there's certain things that "might" happen. First, if you don't regear and your transmission fails, there's probably a 99.9% chance the dealership will not repair the transmission under warranty due to the lift and tires. Second, if you do regear, and if your dealer is nice and even understanding, you may have a better chance of having the transmission covered in the event of a failure.

Some dealerships use lifts and larger tires as an excuse to not honor warranties. Other dealerships are "mod friendly" and understand that many folks will add a lift to their trucks. These dealers also understand that if the work is done correctly, then there shouldn't be much added strain to the driveline. But if they see that something was skipped or not done correctly in their eyes, they will not honor repairs under warranty. Most dealers that are mod friendly will still require that correct gearing goes with the size tires you choose, especially when it comes to the transmission and driveline.

I've had 5 different warranty repairs with my truck while it had a lift and larger tires on it, and the repairs were done at 3 different dealerships. None of them even questioned the lift, and all honored the warranty. I know lately some dealerships have tightened the reigns a bit, but there are still mod friendly service techs out there.

The dealership in town is selling Superduties brand new off the lot with 6" lifts and 37" tires, and all under warranty.

 

A gear swap and calibrated speedo will help your mileage. Until the speedo is calibrated don't bother checking your mileage, it will be way off because the 37" tires travel much further per revolution than the stock. Once you have the speedo corrected, the shift point should return to a stock feel and you should notice kind of poor mileage because the engine is having to work harder to turn those big tires.

 

I like the Superlift True Speed Speedo Calibrator. You can find it for around 200.00 if you shop the internet. It also ties into the ABS system wiring. Only a 4 wire hookup. It is only a speedo calibrator but it does correct the trans shift points as delivered from the factory.

 

I really can't tell any differents in the shift points with the 37x12.50x20, speedometer is about 8 mph off, I have 3:73.

 

Okay, a gear swap won't help your shift points. With larger tires your shift points are actually at the same RPM if you don't correct the speedo because they are based on axle speed from the rear ABS sensor. If you put in lower gears without reprogramming the ABS module for them it will raise your shift points. The dealership can program the ABS module for gear changes and tires up to 35". For larger tires you can either run a tuner to fix the shift points (won't correct speedo), or you can get a module like the Superlift TruSpeed which will correct the speedo (and make your shift points a little lower because it shifts on speed). I wouldn't swap gears unless you lost your low end and want to spend $2k. If I were you, just have the dealer set the tire size to the max (601 revs/mile) and you'll be a lot better, speedo will be off by only 5% and shift points will be just slightly lower than stock.