: How hard is it to convert a 3.11 transaxel to 3.73?

07-15-10, 04:33 PM
Is this doable? Convert a vin y transaxel to vin 9 by swapping the gears inside? How hard is this?

07-15-10, 05:26 PM
3.11 to 3.71 is a final drive swap - internal transmission work = remove the transmission.

BUT, the VIN Y engine (cams) and its power management systems would probably need to be reprogrammed to take advantage of the higher engine rpm vs. wheel rotation afforded by the 3.71 gearset - the management systems will see an engine speed/transmission gear/vehicle speed mismatch and you'll probably wind up with either torque limiting or speed limiting or transmission speed codes, or all three.

Just as we had to manually retune an older engine for a gear change - carb and ignition - we now must reprogram the electronic management system.

07-15-10, 05:36 PM
Well said Sub -

I do believe the gearset could be changed in the car- GM quotes 2.4-3 hours I believe depending on the car, this same procedure was used to repair the fluxuating speedometer on 98-99 4T80 equipped cars.

07-15-10, 06:15 PM
Cool. Maybe I'll check into that then. I'd sure love to make use of that low mileage tranny I have. So ready to be off work. So much to do so little time

07-15-10, 06:56 PM
You will need Lynden Wester or AJ to reflash your PCM to accept that final drive gearset. A Tech2 or Cadillac dealership cannot do it- I believe AJ is just as capable as Lynden, he's a member of the forums here. AJxtcMan-

07-15-10, 08:43 PM
Cool. I may look into that. If I change the gears it's my understanding that it would be basically the same tranny. I spoke with a transmission tech here. Actully a couple. Consensus is that switching the gears would make it run like mine. Maybe a fresh torque converter too. Didn't get into the actual dealings of the tranny tho. I could utilize the 311 ratio with a retuned PCM from my understanding. Not sure which is best

07-15-10, 11:20 PM
Keep in mind that the engines mated with the 3.11 and the 3.71 final drives (LD8 & L37) also have different intake cams.

07-16-10, 07:24 AM
I think there was some confusion. I was trying to swap the gears because my original tranny has 3.73 gears. I have a low mileage 3.11 gear ratio vin y tranny I would like to use if mine starts giving me problems. Keeping it Asa backup. So take out my original vin 9 tranny. Swap the gears in my low mileage vin y extra tranny to make it a vin 9 tranny (along with possibly a new torque converter). My PCM should already be programmer to accept 3.73 gears as that's what it has from the factory.

07-16-10, 07:28 AM
Sometimes I miss stuff when I'm reading the posts on my phone. Hard to see the big picture on a little screen. Lol

07-16-10, 07:58 AM
OK - make the used VIN Y into a VIN 9 by swapping in the 3.73 gearset. If you put that rebuilt transmission into a VIN 9 car you should have no problems.

While you're in there, replace the 1-2 and 2-3 shift solenoids with the new upgraded GM kit and also replace the TCC solenoid. Better safe than sorry.

A new/rebuilt converter would be nice, but if you had no problems before, then the extra expense isn't warranted. A somewhat higher stall setting might be fun in the stoplight parade, but really won't make a world of difference.

07-18-10, 09:46 AM
Sounds like fun!! That will most likely be my next big task once I have this other stuff finished with the engine. In no hurry b/c the original transmission works. Thanks for the info. Very helpful as usual!! :-)