Transaxle gear swap - my experience getting to a 3.42

[PAK XLR8]

I have seen several people on this board asking about swapping gear ratios on their XLR's. I recently completed a switch on my 2005 base and thought I would
share some of my "lessons learned".

First thing you need to know is that it is not easy or cheap. I had assumed that I could use a Corvette Getrag pumpkin (c6 only) and it would be a simple "bolt on" - wrong. Even though they look the same on the outside, the interface to the transmission is different - you have to use your old pumpkin and just swap out the gears.

I bought a nice C6 3.42 pumpkin with ~41K miles for the job, not realizing the issues with the bolt up. Ended up taking both pumpkins to Unitrax (company in So Cal) to swap the gears and get it all squared away this was about $600. Luckily, my car came with a 2.93 ratio and the 3.42 gears barely fit. If you have the 2.73 or 2.53 ratio, it will require machining of the internal casting to allow the extra large gears to fit (bearings will be OK). The Z06 gears have larger bearings and will not swap easily.

Then, I had D3 do the install. This went pretty smooth, mechanically. The problem was that they could not program my ECU or TCU (they both need to be programed for the new gear ratio). If you have a 2006 or newer, supposedly they are easier to program. I ended up sending my ECU and TCU to PCM Performance ($600) - they had the software to get the speedo changed, as well as do a "hot tune" and modify the shift point and shift firmness settings - BIG DIFFERENCE!

While the 17% ratio difference does not seem like a lot, it is directly proportional to the torque at the wheels. Add the performance tune and I feel like I can keep up with the Corvettes.

I did lose a mile or two per gallon, and probably my top end speed (only been there once anyway), but it made a world of difference.

All said and done, it was about $2300 and a few weeks to complete.

So, for all you guys out there that have been asking - yes, it can be done.

Send me a PM if you want more details.

Hope this was helpful...

PAK XLR8

 

[madcurl]

Dude, where's the side profile of your car? I like to see it!

 

[ckrause333]

3.42 Gear Swap

I have seen several people on this board asking about swapping gear ratios on their XLR's. I recently completed a switch on my 2005 base and thought I would
share some of my "lessons learned".

First thing you need to know is that it is not easy or cheap. I had assumed that I could use a Corvette Getrag pumpkin (c6 only) and it would be a simple "bolt on" - wrong. Even though they look the same on the outside, the interface to the transmission is different - you have to use your old pumpkin and just swap out the gears.
View attachment 4032
I bought a nice C6 3.42 pumpkin with ~41K miles for the job, not realizing the issues with the bolt up. Ended up taking both pumpkins to Unitrax (company in So Cal) to swap the gears and get it all squared away this was about $600. Luckily, my car came with a 2.93 ratio and the 3.42 gears barely fit. If you have the 2.73 or 2.53 ratio, it will require machining of the internal casting to allow the extra large gears to fit (bearings will be OK). The Z06 gears have larger bearings and will not swap easily.

Then, I had D3 do the install. This went pretty smooth, mechanically. The problem was that they could not program my ECU or TCU (they both need to be programed for the new gear ratio). If you have a 2006 or newer, supposedly they are easier to program. I ended up sending my ECU and TCU to PCM Performance ($600) - they had the software to get the speedo changed, as well as do a "hot tune" and modify the shift point and shift firmness settings - BIG DIFFERENCE!

While the 17% ratio difference does not seem like a lot, it is directly proportional to the torque at the wheels. Add the performance tune and I feel like I can keep up with the Corvettes.

I did lose a mile or two per gallon, and probably my top end speed (only been there once anyway), but it made a world of difference.

All said and done, it was about $2300 and a few weeks to complete.

So, for all you guys out there that have been asking - yes, it can be done.

Send me a PM if you want more details.

Hope this was helpful...

PAK XLR8
View attachment 4034

This info is very helpful. I live in AZ and want to make the swap in my 07 XLR Base. (I know - I shoulda bought the "V") I have some questions: 1) What gear set did you actually use? 2) where did you purchase it? 3)Have you heard of Mark McPhail? he is supposed to be a great tuner in Costa Mesa. Thanks for your input. ckrause333

 

[PAK XLR8]

More details about gear swap

First, let me say this, to address your comment about "shoulda bought the "V"

While the V does have more HP, and all the other upgrades, it is a ~$10K upgrade. Only you can decide if that is worth it. And, for what it's worth, the gear swap made my "little red" quicker off the line, than my current V (with a 2.56 ratio).

As mentioned in my write-up, I had assumed that since the XLR was built on a C6 base, and the pumpkins look exactly the same, I could just get a used Corvette (3:42 comes with the manual transmission) pumpkin and bolt it right up - wrong! Because they use different transmissions, the actual bolt locations are different on the interface to the transmission. So, to answer your question, I had a gear shop take the gears out of the Corvette pumpkin and put them in the XLR pumpkin, with new bearings and seals. I could have purchased a brand new set of gears, for just a little more than in would have cost me to use the Corvette used set - lesson learned. Any good gear shop will be able to get you a new set of gears that you can use (3:12 is the ratio used in the automatic version of the Corvette, which you may want to consider). The comment about machining the inside of the pumpkin was given to me from the gear shop, since he assumed that the 2:56 and 2:73 may not have as much space inside. The only thing you need to make sure is that the tranny pinion gear is a match for the gears you choose.

I have not heard of Mark McPhail, but if he specializes in GM or Northstar programming, he is probably a good option. Luckily, you have a newer year XLR, which is supposedly easier to program.

I have considered changing the ratio of my V, but I know that it could degrade the value of my rare Dark Cherry, taking it away from stock. I can tell you from experience, you will never get your money out of these upgrades when you sell, you only get the enjoyment out of them while YOU drive it.

Good luck with your upgrade, if you decide to do it!

This info is very helpful. I live in AZ and want to make the swap in my 07 XLR Base. (I know - I shoulda bought the "V") I have some questions: 1) What gear set did you actually use? 2) where did you purchase it? 3)Have you heard of Mark McPhail? he is supposed to be a great tuner in Costa Mesa. Thanks for your input. ckrause333

 

[ckrause333]

First, let me say this, to address your comment about "shoulda bought the "V"

While the V does have more HP, and all the other upgrades, it is a ~$10K upgrade. Only you can decide if that is worth it. And, for what it's worth, the gear swap made my "little red" quicker off the line, than my current V (with a 2.56 ratio).

As mentioned in my write-up, I had assumed that since the XLR was built on a C6 base, and the pumpkins look exactly the same, I could just get a used Corvette (3:42 comes with the manual transmission) pumpkin and bolt it right up - wrong! Because they use different transmissions, the actual bolt locations are different on the interface to the transmission. So, to answer your question, I had a gear shop take the gears out of the Corvette pumpkin and put them in the XLR pumpkin, with new bearings and seals. I could have purchased a brand new set of gears, for just a little more than in would have cost me to use the Corvette used set - lesson learned. Any good gear shop will be able to get you a new set of gears that you can use (3:12 is the ratio used in the automatic version of the Corvette, which you may want to consider). The comment about machining the inside of the pumpkin was given to me from the gear shop, since he assumed that the 2:56 and 2:73 may not have as much space inside. The only thing you need to make sure is that the tranny pinion gear is a match for the gears you choose.

I have not heard of Mark McPhail, but if he specializes in GM or Northstar programming, he is probably a good option. Luckily, you have a newer year XLR, which is supposedly easier to program.

I have considered changing the ratio of my V, but I know that it could degrade the value of my rare Dark Cherry, taking it away from stock. I can tell you from experience, you will never get your money out of these upgrades when you sell, you only get the enjoyment out of them while YOU drive it.

Good luck with your upgrade, if you decide to do it!

I'm working on it. Thanks again for your input.

 

[ckrause333]

3.42 Gear Swap

I have seen several people on this board asking about swapping gear ratios on their XLR's. I recently completed a switch on my 2005 base and thought I would
share some of my "lessons learned".

First thing you need to know is that it is not easy or cheap. I had assumed that I could use a Corvette Getrag pumpkin (c6 only) and it would be a simple "bolt on" - wrong. Even though they look the same on the outside, the interface to the transmission is different - you have to use your old pumpkin and just swap out the gears.
View attachment 4032
I bought a nice C6 3.42 pumpkin with ~41K miles for the job, not realizing the issues with the bolt up. Ended up taking both pumpkins to Unitrax (company in So Cal) to swap the gears and get it all squared away this was about $600. Luckily, my car came with a 2.93 ratio and the 3.42 gears barely fit. If you have the 2.73 or 2.53 ratio, it will require machining of the internal casting to allow the extra large gears to fit (bearings will be OK). The Z06 gears have larger bearings and will not swap easily.

Then, I had D3 do the install. This went pretty smooth, mechanically. The problem was that they could not program my ECU or TCU (they both need to be programed for the new gear ratio). If you have a 2006 or newer, supposedly they are easier to program. I ended up sending my ECU and TCU to PCM Performance ($600) - they had the software to get the speedo changed, as well as do a "hot tune" and modify the shift point and shift firmness settings - BIG DIFFERENCE!

While the 17% ratio difference does not seem like a lot, it is directly proportional to the torque at the wheels. Add the performance tune and I feel like I can keep up with the Corvettes.

I did lose a mile or two per gallon, and probably my top end speed (only been there once anyway), but it made a world of difference.

All said and done, it was about $2300 and a few weeks to complete.

So, for all you guys out there that have been asking - yes, it can be done.

Send me a PM if you want more details.

Hope this was helpful...

PAK XLR8
View attachment 4034

It sounds as though you are quite pleased with this upgrade. I live in AZ and have been talking to Mark McPhail in Costa Mesa for the tuning and Unitrax in Anaheim about the 3.42 gear swap. In your research did you come across either one of these guys? I have an 07 Base XLR.

Thanks

ckrause333

 

[PAK XLR8]

Unitrax Gear Swap

I did use Unitrax to change out the gears in my swap. I dealt with a Devin King, who was very helpful. They can put new gears or used gears into that pumpkin. I had D3 install the pumpkin, after the swap - I needed it to be right and it requires dropping the everything from the torque tube, transmission and suspension, back (and reinstall).

I have not heard of Mark McPhail, but the newer XLR's are much easier to program, so you should be good. Along with the Transmission Control Module (TCM), to account for the speedometer and shift point changes needed after a swap, you need to get the Engine Control Module updated. I recommend getting it to a "hot tune" to accept 93 octane, along with higher shift point (RPM), and quicker delay between shifts.

The only thing I can suggest you research completely, before doing a swap, is making sure that you have enough space in there for the 3.42 gears. I think yours has a 2.73, or something close. While the casting is the same on the outside, the internal machining for gear diameter clearance may not allow an installation without additional machining. You may not know until they open it up. When I went from the 2005 2.92 ratio to the 3.42, they said it "barely fit". There is also a 3.12 ratio available (standard on C6 automatic transmissions).

I don't have my 2005 base any more - had to sell it when I bought the 09 V early this year. With that 3.42 rear end, the base was faster off the line (and could burn more rubber), than my V model with the 2.53 ratio I currently have. Would lose in a 1/4 mile, but the 0 to 60 would be very close.

Let me know if you decide to do the swap, and if you are in the Orange County area when you do. Best of luck!

Paul

It sounds as though you are quite pleased with this upgrade. I live in AZ and have been talking to Mark McPhail in Costa Mesa for the tuning and Unitrax in Anaheim about the 3.42 gear swap. In your research did you come across either one of these guys? I have an 07 Base XLR.

Thanks

ckrause333