I am in the process of swapping in a 355 into my 89 IROC with a t-5 what would be the first thing to go on this tranny? I have heard of a guy here in Minnesota that is/was running a T-5 on his 406. I am just kind of curious what parts would go first so that I may increase the longevity of this tranny. I do not have the money for a T56 that is why. Thanks for all of the help. I also tried the search and could not come up with anything so if this has been posted before I do apologize in advance.

 

The first thing that will go is the T5. It will not hurt the 350, I guarantee.

The part of the T5 that fails will depend on exactly how you go about tearing it up, and which version of T5 you have. If it's the 1st design, the case will stretch and all the fluid will leak out around the front countergear bearing. The trans will either eat the clutch gear & countergear, or eat 5th gear (it runs dry first because it's up the highest in the case). If you dump the clutch or speed-shift it, whichever gear gets nailed the hardest will tear up; 3rd seems to be the more likely victim. If it's the 2nd design, the stretched case won't cause the fluid to all leak out, but the bearing will still allow the clutch gear & countergear to misalign and they will munch each other; or you will strip the teeth off a gear, again usually 3rd. It's possible with either trans that you will snap off the mainshaft between 5th gear and the speedo gear.

Want to know how I know these things? I have a 400 also, and a T5; I have torn up so many I lost count, I know it's at least a dozen. Several of them were with the original 305. I finally learned that (surprise!) it's possible to lift my foot off the gas in between the gears while shifting a manual trans, a totally alien concept to me after decades of driving 4-speeds; now I get a fair lifetime out of them, although the car isn't quite as fast.