well it will sure as hell be easier to swap out the full assembly... and you'll even be able to sell the old one to someone in need...

Either way they will prolly end up being the same...

 

Cool thanks again

 

Speedo calibration is not effected by gear swapping.
Wheel size will alter it.
Al.

 

Hello from another pittsburgh guy!

i'm also doing 4.56's in my rig. i debated back and forth but my truck is a tow rig primarily and a 3rd vehicle for when i need a truck. so i'm not too stressed about the revs. this whole 1800 rpm at 70 BS has to go!

anyway, laborwise a decent shop will usually set up gears for 250-350/axle. pittsburgh driveline has a good reputation though. And i haven't priced out the locker you're having put in.

are you on pgh-offroad or any other local sites? is your rig an off roader or a street truck?

just curious.

also, your speedo is going to be off with new gears but the same size tires. it won't affect the shift points though. it hits 3k rpm (or whatever) when it hits it, regardless of the gearing.

 

What are the wheels connected to again....? (rhetorical question with tons of sarcasm...)

 

In past posts from people who have actual first hand experience of doing this, all have stated that speedo cal was not an issue.
Let me research this further and ill get back to you I zero..... Without the sarcasm you imply, that's just not needed or required when people only want to help. Which keeps the forum healthy and friendly with people wanting to come back without fear of being bullied or intimidated!

 

Does your speedo run off the tcase or off the ABS sensor like the newer trucks?

if it runs off the ABS sensor then changing the gears in the axles won't change the speedo. If it runs off the tcase then it will.

 

Ryan Dunbar

Mine runs off the ABS sensor.
But when mines done next week.....I'll post up actual results on what I find.
Oh and BTW....I was correct in saying speedo will only be affected by wheel size with ref to my and the op particular trucks.....read the link posted by a forum member in an earlier post or better still...here it is.

"In order to grasp the concept you need to know what a RING GEAR IS. The RING GEAR is bolted to your CARRIER. Your CARRIER turns ONE revolution each time the TIRE turns ONE revolution. This means the RING GEAR also turns ONE revolution for each full revolution of the tire. So if the SPEED sensor is taking the reading from the RING GEAR then it does NOT matter what the gear ratio is... because ONE revolution of the tire will ALWAYS be ONE revolution at the RING GEAR. If you have 3.26 gears the ring gear will only turn ONE REVOLUTION per the tires... If you have 5.86 gears the ring gear will only turn ONE REVOLUTION per the tires... so gear ratio has ZERO effect on the CHRYSLER 9.25 SPEED READINGS".

And the Wamo underlining my key principal without the unhelpful "(rhetorical question with tons of sarcasm...)".............

"NOW when your tire hight changes the distance the tire covers per revolution changes with it.

So If ONE revolution = 5 feet on a tall tire but you put a shorter tire and it covers 4 feet you will effectively be moving SLOWER but the SPEED sensor would read FASTER... Because ONE REVOLUTION is ALWAYS one REVOLUTION".

Thanks Air_Ram

Al.

 

Abarmby, I stand corrected. I re-read that all and read some more before you posted and was about to post.

Reason I am disagreeing is because I was watching Power Block last weekend (not a serious follower but I watch when they have a dodge ram to work on). They were changing the gear ratio for their customer from a 3.55 to a 4.10 b/c he wanted to pull a big camper w/ a small car behind it, so they suggested a tuner b/c the change in gear ratio would mess up the shift points due to unexpected RPM increase as well as affect the speedometer reading, and even the odometer readings.

Now I don't take their word as the gospel of mechanical knowledge, but I do understand the physics behind it all, which made me dig a little more into how the system works. I know that I've seen threads on here that show people have problems when they change gear ratios.

I looked into it a little more, and I understand the speed/abs sensor is inside the rear diff (and at the front wheels), and counts revolutions so by nature if they are measuring the output gear/ring that goes to the rear wheels then I admit that I am wrong.

But I did read that if the ring & pinion gears are changed that you will see some or all of the following changes as a result:

Incorrect Speedometer
Incorrect Odometer
Incorrect Shifting under part throttle (<100% aka WOT)

Due to the fact that the sensor reads the actual revolutions of the axle/gear that is spinning the wheel, I will agree that your speedometer will likely not be affected. BUT, I will bet that it WILL change your odometer readings.

So grab that GPS, reset your Tripmeter on the truck, and take a drive... lets see how different the GPS reads from your tripmeter.

I'll have to research some more and find out how the odometer on our trucks calculates distance, because if it uses the speed sensors then it might not be affected, but that seems unlikely because if you get some wheelspin here and there the odometer will suffer some serious inconsistency over time. So my guess is that it reads calculates by taking tire size, gear ratio and the actual input vs output gear speeds to determine distance.

From what I remember about the odometer system from when I worked in the automotive industry, I recall that most manufacturers were using an SAE J1850 type system in order to reliably count the pulses caused by electromagnetic waves formed by reading the magnets of the teeth on gears, so by changing the ratio if it is actually just reading these pulses then the odometer wouldn't be affected, but there would be a considerable amount of error achieved and the reading would not be a "true" distance reading, because the estimated error would be greater than the +/- 2% that automotive regulations require as an "acceptable error" for odometers.

So that's why I think there are some error correction calculations because the PCM usually stores the expected gear ratio as well as other important information.

That is why the OBD-II system has the following error codes:

• P0730 Incorrect Gear Ratio
• P0731 Incorrect 1st Gear Ratio
• P0732 Incorrect 2nd Gear Ratio
• P0733 Incorrect 3rd Gear Ratio
• P0734 Incorrect 4th Gear Ratio
• P0735 Gear 5 Incorrect ratio
• P0736 Reverse incorrect gear ratio

so that leads me to believe that my thinking is correct that the odometer & shift points will be affected.


To summarize:


Yes I looked into it, and I ADMIT that I am WRONG, and I humbly accept the flaming and retract my sarcasm in previous post.


And I add that changing the gear ratio MIGHT change the Odometer reading and also change the shift points under part throttle.

 

Will do
But either way....I think I'll be happy when they're installed next week (fingers crossed the noise isn't too bad)
Al.