C5 Corvette Transmission Removal/Install & Z06 VS Base Trans

After my 34th Track day at the ridge, I started experiencing problems going from 3rd to 4th gear at higher rpms. I noticed if I waited a bit for my shifts between 3rd and 4th, it would be fine, as I assume the transmission revolutions would slow down allowing the synchros to better mesh between the gears when shifting. This was costing me time on the track, and I was also concerned I was going to fully destroy the transmission if I kept going.

Fast forward to the next week, and I'm researching options. Fully rebuilt C5 transmissions are 3-4 months out, and cost $5-6k. There's also a lot to research. RPM does their stage 5 build, which sounds great, but Tick has their own stuff and installs mechanical pumps on front billet plates and... there's just a lot to research. Plus there's the DIY option, which... is really diving into the deep end and would surely take a bunch of time along with quite possibly ruin my transmission AND stress me out.

My solution was simple enough: A local auto-wrecker had three Z06 transmissions good to go. One hit the sweet spot of mileage and use and cost me $1500. I would swap the transmission in with the hopes it lasts even half as many track days as the original base transmission (17 track days being half of 34) and that would buy me a year of time. In that time I could research and ponder rebuilding the base transmission, or perhaps send it out to be rebuilt.

A quick conversation on base vs z06 transmissions and gear ratios:

One thing to note, is that folks will surely point out that the Z06 transmission and gear ratios are less desirable than the base model transmission. With this mentality in mind, had I access to a base model transmission I'd have gotten that instead. Unfortunately, all that was available locally was a Z06 transmission. For what it's worth though... I actually found the gearing of the Z06 transmission much more useful on my first day out with it at the track. Specifically I could stay in 3rd over go to 2nd in a lot of turns, which in turn saved me time on a shift and resulted in an increase of 4mph in my top speed. I also felt like going to 5th the car didn't fall flat on it's face nearly as much, which was also a nice improvement.

Above is a graph shared with me by a fellow named Mark Nunnally over on Trackable Corvettes on facebook. It's a dyno graph showing the acceleration run of a base models trans with 3.4 gears (in Red) versus a Z06 trans with 3.9 gears in green. As you can see, the green is largely quicker at accelerating from the getgo... right up until you grab 5th gear in the Z06 trans and then the losses of overdrive put it beneath the longer 1:1 4th gear ratio.

I've got a way nerdier spread sheet comparing all of these details, The big thing for me was comparing speed ranges of a given gear ratio and diff ratio, with 3000rpm being minimum usable speed IMO, and 6200rpm being redline. This makes 2-3-4 for a basemodel trans and 3.4 diff 37-138mph, which is surely right in the sweet spot for me at most tracks. With my base model trans and 3.7 ratios, 2-3-4 gave me 34-126, which just wasn't quite ideal. With the Z06 trans and 3.7 gears 3-4-5 gives me 46-151mph, with 3-4 being 34-126 and covering the vast majority of my speeds at a track.

Would a base model trans and 3.4 diff be better? Sure seems like it. They aren't what i've got though, and thus this is the reality in which I shred!

There were some benefits to be had here too though, as the Z06 transmission is a later model transmission (01+) which means it has slightly better internals. The early C5 T56 transmissions all had paper blockers (see what RPM transmissions had to say about it), while the 01+ transmissions all had upgraded carbon fiber blockers. In the picture above you can see the difference in, with the ring in the background/left being carbon fiber, while the one on the right/front is the paper blockers, that being the ring on the inside. I'm hopeful that with the slightly upgraded internals the transmissions will last longer, especially as these are renowned for holding up better to modern synthetic fluids.

A possible plus as far as gearing as well is that I've found that I often am faster if I carry a gear instead of downshift. Some of that is my imperfections heel toe-ing, some of that is just time lost on a shift that instead could have been putting down power, and also some of it is that being that traction is a bit easier to manage when carrying a gear higher. The Z06 transmission has a higher 3rd gear ratio (1.43) which means I can use it from a lower speed with better power, saving me from some 2nd gear downshifts. However, I'll run out of 3rd sooner and have to grab 4th earlier, which given the wide power range of these Corvettes should be fair. Also, it brings fifth a bit down in it's overdrive ratio to help make it a little but more useful at the rare track where I find I grab fifth gear.

How the Actual Transmission Swap Went

So I'm actually working to wrap the transmission swap up either today or tomorrow. In the meantime though I uploaded pictures I took of the project underway, and I'll come back and update the article with tips, tricks, lessons painfully learned, and all taht sort of stuff!

As you can see above, cutting out the rear tube greatly increases access to the transmission!

This is my transmission and diff removed from the car. As you can see, it's quite dirty compared to my new transmission. This gives me hope that the new transmission has a bunch of life left in it compared to the one I am pulling that needs to be rebuilt.

Here is my base model transmission separated from the diff.

Here's a plug on the Diff that got severed during removal. Nobody mentioned this in any of the removal videos so I figured I'd call it out for you. Right on the top of the diff.

Here's the transmission and diff reinstalled into the Corvette and mated up to the torque tube. We stopped trying to get it perfectly lined up and shoved in and just switched to using bolts to pull it together. It worked like a treat and went together with minimal resistance. Way easier than trying to hump it in there from either below or that nice access hole I cut into the rear of the Corvette.

The rear Subframe re-installed fairly reasonably. I did find I had to back all the way off and go at it one more time to get the orientation of everything right. Trying to do just the rear of the subframe and swing the front up into place simply didn't work as the diff mount didn't line up. Still, this was not the most difficult part of the job by any means and it all bolted up fine. Be sure to check your torque values when reattaching all of this by the way!

So I did make a bit of a mistake perhaps reinstalling my rear subframe but not putting the brake lines back into place. I disconnected the lines at the caliper though and ran them all back into place. Unfortunatley, none of the old clips for holding anything in place survived the removal process. Such is the life of 25 year old plastic it would seem. So I routed everything as best as I can (not as in the picture above) and zip tied it all quite copiously in place.

How the Tranmission Reinstall Worked For Me At the Track

So I wrote about everything in great detail over at my track report on track day 35, but the short version for here is that it worked amazingly. The transmission clearly was in much much better condition and shifted smoothly. Having added the anti-venom mod to this Transmission right from the getgo all of the notchiness of my previous transmission was gone. I also found that I had zero issues between gears, which was a nice feeling. I wrote about it as well above and in my article, but the Z06 gearing actually felt preferable for me at this track in this car.

I am still having issues getting into reverse, which apparently is not so uncommon with a short throw shifter. Apparently, you can change out the bias spring for quite cheap. I've got no idea why this is the first I'm hearing about this... but reading the description for the part, it totally makes sense with a short throw shifter and may be where my reverse problem comes from!

Long Term Plan with the Transmission

So now that I have a transmission out and removed, I intend to research what other folks due to upgrade their transmissions, and perhaps this winter I'll tear into mine on my own and upgrade it with the combination of the best parts I can ascertain that various folks install into these. It's tough to say though if i'll bother though since I really like this Z06 gearing... so it's all to be determined!

One thing I do intend to add to my Z06 transmission is this softer reverse lockout spring. On both transmissions with my short throw MGW shifter, I've struggled to get into reverse. If this product is as described... it should make my life notably easier and the car that much easier to live with!