Nope no problems there. Guess we should look elsewhere...

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2004 Impala LS - got some mods
NAIOA Moderator

Making you think twice before picking on Impalas

Unless your drive and driven sprockets were replace with the correct ones it will throw an incorrect gear ratio code as I mentioned above. Did you check the "Current gear ratio" in 3rd gear yet? Without knowing the data here there is no reason to look into anything else yet.

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4T65E Transmission Info
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Trannyman... the transmission builder tells me "the gears have 33 tooth drive and 37 tooth driven" for a ratio of 1.1212. The HD differential has a 3.29 ratio. This leads me to believe that the transmssion has a final drive ratio of 2.93 (3.29/1.1212=2.93). Is that correct? If it is correct... then I will have to send back to the transmission builder because I asked him to build me a HD transmission with the GT gearing so that I would not have to change my PCM. If the transmission had the GT gearing then I would assume the drive and driven gears would have the same tooth count - right... say at 35 (half way in between the 33 and 37)?

Question... how do I determine the differential ratio? Do I take the tooth count from the ring and divid by the tooth count of the sun gear?

NOTE. I have not changed the PCM from the stock GT.

If you truely have a 33 Drive and 37 Driven then your builder went in the wrong direction!!! This will give you a 3.69 overall ratio. The HD transmissions have a 37 Drive and 33 Driven, giving you a 2.93 overall ratio. The GT / NA 3800 cars had a 35 Drive and 35 Driven sprocket arrangement. Again, PLEASE check the current gear ratio on a scanner in 3rd gear, there is nothing more to talk about until you check that number unless your builder admits to putting in the wrong gears, which will be proven with a scanner.

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4T65E Transmission Info
Voted GPF.net Community Hero

Trannyman95. You were correct, my math was wrong. They did put in a 33 Drive and 37 Driver for a 3.69 overall ratio. The builder gave me the option of changing out the gears or putting in a new PCM from zzperformance. I went with the new PCM, because I kinda like having the stronger acceleration with the new gears. Everything is working perfectly now.

Glad to hear you got it sorted out and everything is working right now

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4T65E Transmission Info
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Trannyman95... there is one odd behaviour that I am assuming has to do with changing the stock torque converter with a 2800 stall torque converter. When cruising on the highway at 60 miles an hour... at the slightest change in grade (going up hill and I do mean slightest) it seems the transmission slips because the revs will go up about 500 rpm for about a second and then back again, and I can feel the car get weighted back. It will continue to do this untill the grade levels off again. Is this PCM again or something else?

If it is not a stock / OE converter then it likely doesnt have the correct woven carbon lockup clutch lining and isnt holding like it should. Most aftermarket pcm suppliers up the TCC duty cycle to overcome this. It is normal opperation for the rpms to come up a bit and the pcm will catch this and quickly up the duty cycly of the tcc solenoid to drop the slippage to a desired level but if it seems a lot farther off then it did with the stock trans then you will likely need to make some adjustments to the tune.

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4T65E Transmission Info
Voted GPF.net Community Hero

Stock slippage is about 15-30RPMs at cruising speed, right? (that's how much I see with the stock tune)

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2004 Impala LS - got some mods
NAIOA Moderator

Making you think twice before picking on Impalas

The pcm wants to see between 2 and 50 rpm of slippage so your numbers are right in line. Without a graphing scanner or scope it is near impossible to see the real time variations and the averare is normally where it rides in between the two values.

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4T65E Transmission Info
Voted GPF.net Community Hero