2nd Gen Non-Engine/Transmission Anyone Who Changed 4:10s to 3:54s Please Read

[Motorhead]

I am going to help a guy change his '02, 4X4 automatic with 4:10s to 3:54s. We have another TDR member that is going to trade out the whole front and rear axel assemblies.

My question is with the automatic, are we going to experience any shifting problems? I had thought about exchanging the PCMs from each truck so the speedos are not affected. Is the speedo and the auto trans governed by the PCM?

 

[LSMITH]

Chris, take both trucks down to the dealer after the swap and have them flash the PCM for the gear ratio. Should only cost $40-60 each, and is the right way to go about it. The PCM stores the VIN, mileage and all sorts of stuff that you really don't want to lose if you just swapped them out.



Yes the speedo and the shifting for OD is controlled by the PCM.

 

[dlange]

gear swap

I am doing a similar swap next week. I'm getting his 4. 10s, and he is taking me 3. 5's. I'll let ya' know how it goes. But we are changing ring and pinions on both.

 

[Motorhead]

Thanks Howard, Chris

 

[Big White Beast]

No need for a flash.........

The only thing they can flash for is tire size. The speedo is driven from the rear end. Once you swap all will be fine. No problems with shift points or the speedo.



I've changed gears twice and it's been fine. Heck, the first time I went to the dealer and they didn't have a clue wether they had to do it or not. Typical dealer.



Went to a speedo shop and they verified eveything was fine.



Garrett

 

[LSMITH]

Garrett, good info. Thanks. I was thinking about mine, it does not have the tone ring in the rear diff.

 

[richardleonard]

Changing the ratios 4.11 to 3.54

I do have a question here,, does the speed/abs sensor key off the pinon gear or off the drive shaft?? changing the gear ratios will change the speed of the drive shaft - it will turn slower for a given speed,, however if the reading is taken off the pinon carrier, I would assume nothing would change as the axles will turn at the same rate for a given speed no matter what the gear ratio is... or am I all wet????

 

[Snow man]

We swapped an 01 4. 10 to 3. 54 and the dealer said it doesnt need to be flashed,since the sped sensor is on the ring gr,the speedo,and PCM will work fine. Its been 2 yrs since we did it,and its still working perfect. The truck has zero driveablity issues.

 

[Motorhead]

Big White Beast, Snowman, Make sense now to me. I thought the speedo was signaled by a sensor on the tail shaft of the trans thus 3:54s would turn the drive shaft slower that 4:10s.



AGAIN TO ALL ON THIS SITE... . THANKS CHRIS

 

[Hohn]

Re: Changing the ratios 4.11 to 3.54

Originally posted by richardleonard

I do have a question here,, does the speed/abs sensor key off the pinon gear or off the drive shaft?? changing the gear ratios will change the speed of the drive shaft - it will turn slower for a given speed,, however if the reading is taken off the pinon carrier, I would assume nothing would change as the axles will turn at the same rate for a given speed no matter what the gear ratio is... or am I all wet????

The tone ring on the rear diff (on trucks so equipped) provides ALL the data for functions that need wheelspeed info-- speedometer, trans shift points, ABS brakes, etc... .



Correct me please if i am wrong...



Hohn

 

[Hohn]

BTW, this is why it would be better if the sensor was at each wheel Then the ABS could respons better. With the sensor in the diff, you get pulsed braking to the rears if EITHER wheel is near lock up, reducing total braking force applied over a system that pulsed only the actual wheel that was near lockup.



These more advanced setups are called 4-channel ABS.



Hohn