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I am relatively new to Corvette ownership and I had an unfortunate accident this week. When getting on it, I mis-shifted from 2nd to 1st at just under 60 and the diff case cracked in two (dumb, I know). Engine seems to be unharmed thankfully, and I plan to investigate the trans when I pull the diff, but I can still roll through the gears when the car is off so that is a good sign.
For some background, the car came modified with a pretty large cam and stronger push rods, stronger forks/LS7 clutch in the trans, and drag radials, but I believe the diff was stock. Previous owner claims 416 whp, which seems accurate.
While the mis-shift was no doubt bad for the driveline, the speed I was going was less than 10 mph over the max rated speed for 1st gear, and I was only pushing it a bit above half throttle. For these reasons, the larger power and sticky tires, and the high likelihood the car was driven hard before I bought it, I think a diff upgrade was in store regardless of this incident, but I'd love to hear all of your thoughts on this.
I've scoured the forum for the last week for differential info and I've gathered some different solutions. I've heard lots of good things about RPM diffs, as well as ECS trans/diff braces and HPI diff braces. I plan to use this car primarily on the street, with maybe a drag/track day or two a year.
I am all for spending the money to get the best parts, however I am on a bit of a budget so I don't want to go overkill if I can avoid it. The three options I'm considering as of now are 1. New stock diff with a brace, 2. RPM stage 2 diff, 3. Both RPM diff and a brace. I am happy to hear any other options you may have as well, and all options include hope for no more mis-shifts lol. I would like to hear from your experiences which option you think is best for me.
Thanks, and I'm excited to be a new member of the Corvette community!
Just to be clear you do not need a c6 transmission to run the diff. The differential will bolt up to the 4l60e and also the T56.
You will need either offset mounts or the c6 rear cradle to mount though. RPM, RTK and ECS can all hook you up with the right parts regarding the C5 or C6 setup
As far as breakage goes it doesn’t matter what you buy. If you down shift the way you did your lucky that’s all you broke.
Now you mentioned drag radials so your drivetrain may have lived a tough life. Aside from what you did the main killer of drivetrain parts is wheel hop. If you’re launching from a dig it’s the tire chatter and rattle you feel before it hooks. It’s is absolutely hell on parts. You may have already had a stress cracks and you just finished it off. You can get a take out 3:42 and a ECS differential brace for about $1000 total. If your transmission is ok then you’re good.
Half shafts $125 and stock differentials $500 are cheap compared to transmissions etc. Once you beef up those parts & wheel hop bad or high rpm mis shift to 1st….Pop goes the next weakest part. That part may be a lot more expensive.
Thank you all for the help and advice. I finished pulling the diff today and found that it was an RPM diff, not stock (I’m surprised the previous owner wouldn’t advertise that). It was also a 3.73, not a 3.42. I also drained the trans fluid and there was no metal in it so thankfully the trans is okay.
I’ve started looking at both c5 and c6 z06 used diffs online, and the c5s are definitely more plentiful (and cheaper) than the c6z. As of now, I’m leaning towards a stock c5 diff with the addition of a brace. That being said, I’m weary of putting “downgraded” parts into it if the last owner thought it needed a beefier rear end. I’m in favor of lowering the gear ratio back to stock, being that I currently get no traction in 1st and minimal in 2nd, but I don’t want to have any issues from lesser stresses than a miss shift, like hard use or the occasional launch. Do you all think a brace would be sufficient, or should I look into another RPM diff?
Thank you all for the help and advice. I finished pulling the diff today and found that it was an RPM diff, not stock (I’m surprised the previous owner wouldn’t advertise that). It was also a 3.73, not a 3.42. I also drained the trans fluid and there was no metal in it so thankfully the trans is okay.
I’ve started looking at both c5 and c6 z06 used diffs online, and the c5s are definitely more plentiful (and cheaper) than the c6z. As of now, I’m leaning towards a stock c5 diff with the addition of a brace. That being said, I’m weary of putting “downgraded” parts into it if the last owner thought it needed a beefier rear end. I’m in favor of lowering the gear ratio back to stock, being that I currently get no traction in 1st and minimal in 2nd, but I don’t want to have any issues from lesser stresses than a miss shift, like hard use or the occasional launch. Do you all think a brace would be sufficient, or should I look into another RPM diff?
I bring genuine right now.
It sounds to me like you need to learn some left foot control and what kind of feel a car makes before your breaking parts. Now sometimes stuff is just going to come apart I get that. The reason for what I’m saying is your talk about lack of traction. You have plenty in all gears as long as you know the limit of power you can apply with your foot. An example being you can’t mat the pedal in first gear but you can in third.
The number one destroyer of rear ends is wheel hop combined with a manual transmission. I suspect when your trying to feather the throttle out of the hole in first gear your chattering the tires of maybe when you finally hook in second. In a drag car you add power or raise launch RPM.
Now if I’m off base and you know that’s not happening no problem. I’m trying to help.
I’m not saying you should or should not buy part XYZ your a grown man spend how you want. I’m just telling you that you can’t spend your way out of an issue and will break whatever you have. That RPM diff is most likely using c6z stub shafts anyway.
For what it’s worth my car was shaking the tires hard. I just knew to get out of the throttle immediately so I haven’t broken a rear “yet”. I changed my rear diff mount to a AMT double barrel solid mount and it helped. You may want to take some pictures and contract RPM and ask them what direction to go. They have seen it all and will give you better guidance than the forum can.
BTW I said it before and it’s worth repeating. You may not be doing anything wrong and the previous owner was beating the guts out of the car. I suspect the RPM was installed after breaking the stick diff. You may have just finished off what was already on its way out. I doubt the 3 rib case just suddenly split. It probably had stress cracks that have been widening over time.
I bring genuine right now.
It sounds to me like you need to learn some left foot control and what kind of feel a car makes before your breaking parts. Now sometimes stuff is just going to come apart I get that. The reason for what I’m saying is your talk about lack of traction. You have plenty in all gears as long as you know the limit of power you can apply with your foot. An example being you can’t mat the pedal in first gear but you can in third.
The number one destroyer of rear ends is wheel hop combined with a manual transmission. I suspect when your trying to feather the throttle out of the hole in first gear your chattering the tires of maybe when you finally hook in second. In a drag car you add power or raise launch RPM.
Now if I’m off base and you know that’s not happening no problem. I’m trying to help.
I’m not saying you should or should not buy part XYZ your a grown man spend how you want. I’m just telling you that you can’t spend your way out of an issue and will break whatever you have. That RPM diff is most likely using c6z stub shafts anyway.
For what it’s worth my car was shaking the tires hard. I just knew to get out of the throttle immediately so I haven’t broken a rear “yet”. I changed my rear diff mount to a AMT double barrel solid mount and it helped. You may want to take some pictures and contract RPM and ask them what direction to go. They have seen it all and will give you better guidance than the forum can.
BTW I said it before and it’s worth repeating. You may not be doing anything wrong and the previous owner was beating the guts out of the car. I suspect the RPM was installed after breaking the stick diff. You may have just finished off what was already on its way out. I doubt the 3 rib case just suddenly split. It probably had stress cracks that have been widening over time.
I appreciate the advice! I’ll admit I could use improvement on stick. I have driven stick a good amount before, but this is the first stick car I’ve owned and driven this frequently. I had the car for about a month before the miss shift and I was still taking it easy for the most part. I haven’t experienced any wheel hop yet, the lack of traction has primarily been from the tires breaking lose and I can usually feel the car start to get sideways rather than hop. In first gear this happens at pretty much anything above half throttle and at any speed. I’m from Michigan though so that could be a combination of cold roads and tires with the big power. My main point with that part of the diff comment was to say I wouldn’t mind “downgrading” the axle ratio so the car is more usable for street driving.
I am more concerned with “downgrading” to a stock c5z diff with less rigid hardware than the RPM diff that was in the car. I know that another miss shift or something similar would break anything I put in there, I’m more worried about it breaking from hard driving and launching when I’m more comfortable with the car, due to the larger power, drag radials, etc. It’s good to know that’s primarily from wheel hop though, thanks for that info.
Contacting RPM is a great idea, I’ll call them tomorrow to see what they suggest. Thanks again for the advice!
How much power is the car making ? A C5 diff from rpm or even stock might benefit from the brace.
The early C5/ had the single rib case then they upgraded to the 3 rib. Im sure they did that for a reason.
I don’t know if a stock c6z is an upgrade from a RPM diff or not. In any case good luck with it. Seems like you’re having fun with the car and that’s what it’s about.
How much power is the car making ? A C5 diff from rpm or even stock might benefit from the brace.
The early C5/ had the single rib case then they upgraded to the 3 rib. Im sure they did that for a reason.
I don’t know if a stock c6z is an upgrade from a RPM diff or not. In any case good luck with it. Seems like you’re having fun with the car and that’s what it’s about.
The previous owner claims 416 wheel horsepower but I haven’t had a chance to dyno it and double check yet. Based on driving it that seems accurate to me.
I’m hoping I can get away with a stock diff with a brace. That’s a lot cheaper than the RPM stuff. I’ve seen it’s around $3k for the RPM and a stock diff plus brace would be about half that.
416 hp at the wheels is by no means excessive for the stock Z06 rear. I'm guessing the car was probably used to its potential and possibly beyond by the previous owner. Just how much tread was left on those drag radials?
Nothing wrong with spending the money on a new RPM rear but keep in mind the $4K or so price tag requires a core.
I have no info to offer as to the aftermarket braces.
My 3.42 C5 diff was rebuilt locally with C6 internals and it's working great during HPDE stresses.
You may also want to get a better shifter. Consider MGW or a nice TMOD unit.
I have a stock 2002 C5Z diff with as many upgraded internals I could get my hands on and a brace. I'm putting either 600whp or 700whp depending on what I'm doing with the car. The car get's used for standing mile racing and circuit use. This was my first season with it but the oem build held up surprisingly well. I've only run the car a couple of times on a prepped surface on drag radials.
416rwhp with a stock diff is fine more so if you put a brace.
Do you have the factory diff mount? It’s a big hunk of flexible rubber. If so ditch it and get yourself a AMT double barrel mount and a ECS brace.
You cracked the case which would make me think you had the stock mount.
Modified Z06 Differential Options
