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final drive gear swap



I'm mainly looking to get better gas mileage to help with the rising gas prices and my daily commute. Its easier on the budget to get 30+mph rather than 24-26mph depending on weather. All the research I have done through the www. and my Haynes how to book say the GTP of the same year had the 3.05 ratio. Is it possible to just change out the computer with one that's already programmed for the 3.05? On a side note... I had an 03 Impala with basically the same drive train only the 3.05 ratio and it was still pretty snappy.
 
No GTP ever came with anything other than 2.93 gearing from the factory.

Therefore you can't swap the pcm. You need it reprogrammed.
 
Is that strictly a dealership job or is there any other way (other than having to be tech smart and able to download and do it yourself)?
 
BillBoost37 by chance do you know the chain ratio for the GT and if its different from the GTP can that be changed out without a reprogram?
 


NA motor drive gear (chain) ratio is 1:1 aka 35 tooth drive and 35 tooth driven.
SC motor drive gear is 1:1.121 or 37:33
 
I think things are getting confused here.

You currently have a GT aka NA car. So it's a 1:1 chain ratio and a 3.29 diff aka final drive. Gives you an overall gear ratio of 3.29.

You want to replace/rebuild your trans which would be a 1:1 chain and a 3.05 diff. Gives you a 3.05 overall gear ratio.

Going from 3.29 to 3.05 would cause a reprogram. Has nothing to do with swapping the drive/driven gears.

From your rebuilders point of view a diff swap is as easy as putting it in the case instead of the 3.29 diff. If you wanted to do it later down the road, we can definately point you to the post by TripleEdgePerformance where Dave detailed it.
 
My apologies. Don't mean to be confusing in any way. What I meant was instead of going from the 3.29 to the 3.05 could the drive/driven gears be changed to the 37:33? Guess I'm kinda looking for the easiest way to reach my goal = better gas mileage.
 
all 4t60/4t65 final drive ratios and convertor codes based on the transmission ID tag, just incase anyone who cares doesnt already have it...lesabres, park avenues, bonnevilles, olds etc. could have any number of ratios including 2.86, and 3.05 depending on the engine and coding


GM FWD Transmission ID charts
 
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I'm starting to think if I do need a rebuild I would be better off remaining stock due the lack of resources in my area. Basically I dont think I would be able to due any computer reprogramming or have someone due it for me.
 
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Buy HPTuner..... best money I ever spent on my car.... Dont like the shift points? You can change them!
 
I got in touch with Triple Edge Performance out of Indiana and they will reprogram the pcm so it won't run in limp mode when and if it ever gets rebuilt. It doesn't need it yet even though some decent sized pieces of what was believed to be torque converter and shims were found in the filter. I'm just gonna drive it til it stop moving.
 
Do you have a picture of said pieces?

FWIW it's impossible TMK for TC to end up in the pan. The TC feeds into the valve body which has little filters etc.
 


No pictures but the mechanic that told me what he thought it was has been building transmissions for 30+ years told me what he believed they were and said there was no telling how long the transmission would last and since there was no tranny codes to drive it til something actually breaks. The fluid and filter change seems to have solved the occasional whining and hard shifting so it gives me more time to explore some modifications. I'm even considering going from N/A to S/C and exhaust upgrades. Just waiting for the right time to tell my wife.
 
Reason I asked is frequently our differentials let go. If you caught it now, you might be able to swap another in w/o replacing the whole trans.
 
I think even if the differential went I would still have the whole thing rebuilt and with the GTP chain ratio. I just need to make sure its not gonna be too doggy without a S/C. The pieces found though weren't in the tranny pan. The magnet just had normal crap on it. The bigger pieces were found inside the filter itself. They dissected the filter when what I told them what them what it was doing and nothing was in the pan or on the magnet to explain it. The mechanic doing the work though did say he didn't like the smell of the fluid when he dropped the pan. I don't really know what thats supposed to smell like since I've done very few tranny filters.
 
In the filter is the same as in the pan IMO. The fluid is lifted from the pan into the filter.

On the gear ratio of the SC not being dogging with an NA motor. Would you like a vid of my stock L26 Regal GS with 2.93 gears?

Drunkie rode in it this weekend and said "if that's what NA guys have, that's pretty darn good". Then I explained it should be slower than an NA with the 3.29's.
 
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