So here's the point that I'm at..... I have a 4T60E with a 2.73 final drive ratio,according to the tranny tag,but I would like to have a 3.33 final drive ratio or lower. I've researched as much as I possibly could using the forum,Google and calling transmission shops but I've yet to find an answer to my questions. I understand that the tranny has up to 12 different final drive ratios but I can't figure out if the ratios were spread out over the production years of the tranny in total or if 12 different ratios were available for each year. I understand that the internal sprockets and differential can be switched to change the final ratio but I can't find any information pertaining to the differential. What final drive ratios can be accomplished by simply changing the differential and leaving the internal sprockets alone?
I want my 4.9 to be a stump puller from red light to red light and I could care less about fuel economy so if I can wind up with a final drive ratio even lower than 3.33 I'm fine with that. The lower the better......
------------------ Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should. (Jurassic Park)
So here's the point that I'm at..... I have a 4T60E with a 2.73 final drive ratio,according to the tranny tag,but I would like to have a 3.33 final drive ratio or lower. I've researched as much as I possibly could using the forum,Google and calling transmission shops but I've yet to find an answer to my questions. I understand that the tranny has up to 12 different final drive ratios but I can't figure out if the ratios were spread out over the production years of the tranny in total or if 12 different ratios were available for each year. I understand that the internal sprockets and differential can be switched to change the final ratio but I can't find any information pertaining to the differential. What final drive ratios can be accomplished by simply changing the differential and leaving the internal sprockets alone?
I want my 4.9 to be a stump puller from red light to red light and I could care less about fuel economy so if I can wind up with a final drive ratio even lower than 3.33 I'm fine with that. The lower the better......
why not just get a 91-92 seville tranny from a junkyard? they come stock with a 3.33:1 overall final drive.
if you want to keep yrou existing tranny, i guess we can help yu figure out what to change.. whats your 4 digit broadcast code?
theogre...thanks for the link,it was good reading. Unfortunately,the writeup didn't give specific information as to what gears could be used along with different differentials to give specific final drive ratios. If it did,I misunderstood what I read.
Stickpony......I have two 4t60e tranny's and both have the 2.73 final ratio,unfortunately. I am merely trying to learn if I can change the final ratio by changing the differential instead of tearing the tranny's apart. I'm working with what I have right now. I have no problem finding another tranny if I have to but thought I would check on the differential option first.....thought there might be a quick fix to the final ratio issue. On the plus side....within the next week or so,I should be able to turn the key on my 4.9 car that you burnt the chip for.
I know that parts from different years can't be mixed and matched because of the way the gears are cut but I still haven't found information as to what parts can be matched up and give specific final ratios.....years,gears,differentials....etc.
Some basic info for you. Internal to the transmission, there is a chain driven by a gear set- one gear on the output shaft of the transmission, one on the shaft that holds all the clutches, etc. These gears come in three ratios- 37 driven / 33 drive for a 1.12 Ratio Overdrive, 35 /35 for a 1.0 ratio, and 33 driven / 37 drive for a .82 ratio.
On the rear of the transmission, where the passenger axle shaft is installed, sits the differential. The differentials came in several ratios. They varied slightly over the years, but were basically 2.84, 3.05 and 3.29. To get your final drive ratio, you divide the gear ratio above into the differential ratio. In your case, it is likely you have 3.05 differential and 37 /33 chain gears, so you end up with 3.05/1.12= 2.73 Final Drive Ratio.
Changing the internal gears, keeping the 3.05 differential, will yield either a 3.06 or 3.43 ratio ( 35/35 gears or 33 /37 gears) Changing the rear differential to 3.29, will yield either a 2.93 FDR ( your stock gears), or 3.29 or 3.69 (35/35 gears or 33/37 gears).
I'm considering doing this change on mine. The gear change is not too hard, and I hear ( although not researched ) that the differential swap is not too hard either. I think the most difficult thing is the getting the PCM reprogrammed to understand the new gears- not a simple task, and one I will certainly need Ryan's help at GMTuners.com.
For the gear swap, Here's a pretty good write up that shows changing the 4th gear clutches. If you get this far, all that's left is to pull the two gears and replace them. http://www.grandprixforums....ar-side-cover-access
------------------ '87 GT , '00 3800 Series II SC, 4t65e.
Originally posted by MadProfessor8138: theogre...thanks for the link,it was good reading. Unfortunately,the writeup didn't give specific information as to what gears could be used along with different differentials to give specific final drive ratios. If it did,I misunderstood what I read.
Yes it does in the 2nd chart. And work other way around to show what you have currently 2.73 is RPO FP3 w/ 3.06 final and 37/33 chain set
Go to any trans shop to get parts w/ tag data on the trans. Lost tag then likely have problems ordering parts. No one else have PN because Trans and year made of trans can change PN for parts. Every 4T60 and E version May look same outside but GM change internal parts over time on many units. Example: TH125c change gear set in ~86 to have wider chain. New parts won't work in older trans.
Changing final and/or chain set will make you to have ECM reprogram to shift right w/ new trans ratio.
theogre...thanks for the link,it was good reading. Unfortunately,the writeup didn't give specific information as to what gears could be used along with different differentials to give specific final drive ratios. If it did,I misunderstood what I read.
Stickpony......I have two 4t60e tranny's and both have the 2.73 final ratio,unfortunately. I am merely trying to learn if I can change the final ratio by changing the differential instead of tearing the tranny's apart. I'm working with what I have right now. I have no problem finding another tranny if I have to but thought I would check on the differential option first.....thought there might be a quick fix to the final ratio issue. On the plus side....within the next week or so,I should be able to turn the key on my 4.9 car that you burnt the chip for.
I know that parts from different years can't be mixed and matched because of the way the gears are cut but I still haven't found information as to what parts can be matched up and give specific final ratios.....years,gears,differentials....etc.
cool.. also keep in mind, if you change to a 3.33:1 final, your transmission shift points will need to be altered to match,
Would I be correct in saying that even with the best combination of sprockets and differential ,with my year tranny,that the 3.33 is the lowest final ratio that I can hope to achieve?
How are the guys on the ,I think it's the GTP group,achieving ratios in the 3.70's-3.80's with their tranny's? Is it because of the different years of their tranny's and more parts are available to them?
Stickpony.......yeah,I realize that any change I make to the tranny final ratio or even wheel size will affect the ECM. I have a spare chip that I might be sending your way to burn for me.
If you install 33 drive / 37 driven gears, AND change out the differential to a 3.33 differential, you will have 3.73 Final Drive Ratio. This is the highest you can likely get, and it assumes you can find the parts that fit your year of transmission. Be aware that as you make this change, Torque increases so that wear and tear on the trans increases. Some have reported Chain failures, and other related internal issues. If you are close to stock HP, I don't think you will have issues. I'm pretty much stock, and this is what I plan to do. As long as you're not doing power burnouts and hard launches, you should be OK.
The Chart in the Ogre's cave, referenced above, is pretty good at detailing out the options.
------------------ '87 GT , '00 3800 Series II SC, 4t65e.
About 10 minutes before I saw your post I found the info on the gmtuners website about the 33/37 sprockets and the 3.33 differential to give a final drive of 3.73......
Dabysan.....therein lies the issue for me...... The only reason anyone would want to change to a 3.73 ratio is specifically for hard launches....lol My engine is stock but I want lower gearing for the red light to red light torque.
At this point,I'm trying to research on the web where I can pick up sprockets and a differential that will work in my tranny.............anyone have anything laying around that would be of use? If I need to go with a different year tranny in order to get parts to fit then that's not an issue.
[This message has been edited by MadProfessor8138 (edited 02-02-2017).]
