Help Needed.. Swapping A 3.73 For My Current 3.23 Please Advise...

GMC_BOI · December 7, 2009

Hello everyone. Firstly, please excuse my ignorance in regards to the rear ends of these trucks. I am learning more and more everyday.

I have learned that my 2WD 05 Sierra 5.3 has the GU5 3.23 gears, and the G80 limited slip. I would like to have a 3.73 gear swapped in. Guys, I absolutely NEVER tow with my truck. I use it as my family daily driver. I do not own a boat or anything. My Sierra is just my family vehicle and I commute to work everyday in it. Its an extended cab so my kid and car seat fit nicely in the back, leaving me tons of room left for myself since Im a pretty big guy...

With that in mind, I wanted a 3.73 gear just to "wake it up" around town. I dont race it or anything, but I do have a heavy foot. I think I would enjoy the added ooomph with the 3.73 gears rather than these 3.23.

Im having a friend or shop do the install for me, but my main problem is where can I buy a set of 3.73 gears, and what exactly should I ask for? Do I simply ask for "3.73 gears for a 05 Sierra 5.3 2wd", or should I ask another way?? Can I get a used set somewhere cheaper? How about Ebay? When I search Ebay for 3.73's, I get tons if varying sizes and I dont want to buy the wrong size...

Once again, please pardon my ignorance here. Your help is greatly appreciated..

One last thing, and again please excuse my ignorance, but is there anything special or extra I would need to buy for the swap? Or do I simply just need the 3.73 gears and thats all. Am I missing something else?

jblakeney · December 7, 2009

Hello everyone. Firstly, please excuse my ignorance in regards to the rear ends of these trucks. I am learning more and more everyday.

I have learned that my 2WD 05 Sierra 5.3 has the GU5 3.23 gears, and the G80 limited slip. I would like to have a 3.73 gear swapped in. Guys, I absolutely NEVER tow with my truck. I use it as my family daily driver. I do not own a boat or anything. My Sierra is just my family vehicle and I commute to work everyday in it. Its an extended cab so my kid and car seat fit nicely in the back, leaving me tons of room left for myself since Im a pretty big guy...

With that in mind, I wanted a 3.73 gear just to "wake it up" around town. I dont race it or anything, but I do have a heavy foot. I think I would enjoy the added ooomph with the 3.73 gears rather than these 3.23.

Im having a friend or shop do the install for me, but my main problem is where can I buy a set of 3.73 gears, and what exactly should I ask for? Do I simply ask for "3.73 gears for a 05 Sierra 5.3 2wd", or should I ask another way?? Can I get a used set somewhere cheaper? How about Ebay? When I search Ebay for 3.73's, I get tons if varying sizes and I dont want to buy the wrong size...

Once again, please pardon my ignorance here. Your help is greatly appreciated..

One last thing, and again please excuse my ignorance, but is there anything special or extra I would need to buy for the swap? Or do I simply just need the 3.73 gears and thats all. Am I missing something else?

Pretty much any NAPA has these gears readily available. Also, the Dealer has them to. You will need a new crush sleeve (might want to get 2 in case ur buddy F#*%s one up).

No way I would do it with out a bearing and seal set.

You will have to get the PCM reprogrammed for the new gear. GM Tech II will do this and some aftermarket programmers.

You do know this is going to adversely effect your mileage (ie down). 3.73 is a good gear ratio on a truck.... You might consider meeting the middle a 3.42.......

Jbo

GMC_BOI · December 7, 2009

Thank you so very much. Wow, I had no idea I would have to reflash my PCM. I dont have a hand held programmer. So now I either must get a programmer, or just take the truck to a reputable custom shop, correct? There is a really big custom car shop near my home so perhaps I will pay them a visit. I bet they would have everything needed.

Anymore suggestions? I did not want to buy a programmer because I have read that Blackbear is better. I would hate to waste money on a programmer just to reflash my PCM.

One last thing.... I believe that autozone sells basic hand held units for pretty cheap. Do you suppose one of these units may work?

Thanks again!

Nytemare · December 7, 2009

Its not going to affect anything other than your speedo and odometer if you drive around without having the ratio changed on your PCM.

There are online calculators that will tell you how much you are out by on the speedo..and drive accordingly. I wouldn't do it too long though, I dont know what the law would be regarding not having your speed and odometer working correctly. Than when its time to get a Blackbear tune, you just tell him you have 3.73's and whatever size tire you have and he will fix it for you. You know he has PCM's for your truck...all you have to do is pay for a core charge and send back your old PCM for a core refund when you get your new one.

I would also look at some scrap yards and see if they have a whole 3.73 rearend sitting there...it may be cheaper than cracking yours open and putting 3.73's in there.

Those basic handhelds at auto zone are just code readers most likely, and can do nothing more than read a code. Gm will do it for you for 38 bucks, or Justin will do it for you when you get your tune.

GMC_BOI · December 7, 2009

Its not going to affect anything other than your speedo and odometer if you drive around without having the ratio changed on your PCM.

There are online calculators that will tell you how much you are out by on the speedo..and drive accordingly. I wouldn't do it too long though, I dont know what the law would be regarding not having your speed and odometer working correctly. Than when its time to get a Blackbear tune, you just tell him you have 3.73's and whatever size tire you have and he will fix it for you. You know he has PCM's for your truck...all you have to do is pay for a core charge and send back your old PCM for a core refund when you get your new one.

I would also look at some scrap yards and see if they have a whole 3.73 rearend sitting there...it may be cheaper than cracking yours open and putting 3.73's in there.

Those basic handhelds at auto zone are just code readers most likely, and can do nothing more than read a code. Gm will do it for you for 38 bucks, or Justin will do it for you when you get your tune.

Thank you for your post! Im definately going that route with Blackbear because he will be no where near Michigan within the next few months...

I understand now what you are saying in regards to the speedometer after the swap. totally understand now...

And GM will only charge me $38 to flash my computer? Wow! I had no idea it would be so cheap. Hell, they charged me like $100 just to reflash a remote key fob for my new STS Caddy... Im gonna check into this with the closest Chevy dealer in my area. Thanks so much again....

By the way, the person who says they can do the swap for me is a certified Semi Truck Mechanic. Do you suggest that he could handle this job? He says he has never messed with a truck, but swaps gears on Semi trucks all the time. He said he would do the job for $150. I thought that was pretty cheap????? But I honestly have no real clue...

Nytemare · December 7, 2009

Its not going to affect anything other than your speedo and odometer if you drive around without having the ratio changed on your PCM.

There are online calculators that will tell you how much you are out by on the speedo..and drive accordingly. I wouldn't do it too long though, I dont know what the law would be regarding not having your speed and odometer working correctly. Than when its time to get a Blackbear tune, you just tell him you have 3.73's and whatever size tire you have and he will fix it for you. You know he has PCM's for your truck...all you have to do is pay for a core charge and send back your old PCM for a core refund when you get your new one.

I would also look at some scrap yards and see if they have a whole 3.73 rearend sitting there...it may be cheaper than cracking yours open and putting 3.73's in there.

Those basic handhelds at auto zone are just code readers most likely, and can do nothing more than read a code. Gm will do it for you for 38 bucks, or Justin will do it for you when you get your tune.

Thank you for your post! Im definately going that route with Blackbear because he will be no where near Michigan within the next few months...

I understand now what you are saying in regards to the speedometer after the swap. totally understand now...

And GM will only charge me $38 to flash my computer? Wow! I had no idea it would be so cheap. Hell, they charged me like $100 just to reflash a remote key fob for my new STS Caddy... Im gonna check into this with the closest Chevy dealer in my area. Thanks so much again....

By the way, the person who says they can do the swap for me is a certified Semi Truck Mechanic. Do you suggest that he could handle this job? He says he has never messed with a truck, but swaps gears on Semi trucks all the time. He said he would do the job for $150. I thought that was pretty cheap????? But I honestly have no real clue...

They don't reflash the PCM...just the gearing portion...it takes 15 min...so they charge you 1/4 hr labor and tax. Unless they have a 1hr min charge...some shops do...my local dealer charges actual time to the nearest 1/4 hr

I'm not saying that the swap is hard and 150 for a gear swap is cheap....just that it may be cheaper and even easier to get a whole diff with 3.73's in it already...something to look into before you bite the bullet and buy the gears.