SMG Built Race Trans & 06' TCM don't mix
 

I brought the last SMG Motoring 4T45E race trans for their old cavy project. The trans was installed on my 2006 LT and should have been a plug in play swap.

Well the trans works, however the stock TCM fails to electronically control the transmission. I thought there was a fault with the TCM so I had my buddy Mike drive over to my house with his 2009 G5 auto and we swapped his TCM for mine and it worked where as my stock TCM would not work at all. This was about 3 weeks ago. Since then I brought a new 2006 LT TCM and installed it last weekend. I thought that this TCM would solve my problem and I find I have the same issue with this TCM as well, it does not work at all.

So, I had Mike come back over with his car and we did the swap again and what do you know it works like it did before. We went for a longer drive and noted some issues, but these seem minor compared to the overall problem. The up-shift and down-shift points are off and the speedometer does not work. Other then that his TCM does electronically control my new trans.

I'm lost on this matter because Mike owns a 2009 G5 and my car is a 2006 LT Cobalt. My new trans from SMG did come out of a cobalt but at this point I don't know what model year it came from. The transmission will work with my new TCM, but it's purely in a mechanical aspect as there is no electronic control.

Like I mentioned to you over the phone yesterday, Put your TCM back in a try swapping the nuetral safety switch on the top of the trans with a new one. Its possible it got damaged when the mechanics swapped it from your old trans to ours. If the trans upshifts and down shifts ok in Drive, but doesnt manually down shift when you move the gear selector to 1 or L then that could be your issue, as mechanically the trans is shifting ok. The 2009 G5 computer is not the same as your 2006 and the TCM and BCM will not communicate which is why you had no speedo with his computer. Also, the shift times may be a little off until you get a reflash with the correct gear ratio as remember this trans has a much different gear ratio that the stock trans had.

Fred, I did test out your theory yesterday and sure enough when I mashed the gas a little it did downshift and begin to accelerate. I ordered a neutral safety switch last night and I'm hoping this gets my build back on track.

Just curious why not do an manual tranny?

cause it would have cost way more in time and money making the conversion.

problem solved. it's always the simple shit. we just needed to set the 3.91 final drive ratio in the TCM adaptives and we now have trans control again.