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Discussion Starter · #1 ·
This pretty much describes what happened when I detonated my rear diff at my last autocross event of the season. :(

Let this be a warning to those that drag race or do hard launches at autocrosses. Here is the sceanario: It was a somewhat cool Maine day, temps only reaching about 60 degrees, the concrete surface was cool but still grippier than pavement. The particular event this day had what we would call "a drag strip" start...a long straight right out of the start box to the first cone...not normally something that has occured at past events (fyi). We had a problem on course after our first run and a small section of the concrete was breaking up for some reason. We had to do a small course change which meant a safety run after implementing the change. The event chair asked if I could run that section at speed to determine if the change was subtle but safe. I made two passes with the chair in the car. Now my tires (Hoosier A6s) have heat in them and thus more grip...a detail I had forgotten about.

On my first run of the morning I had minor tire spin at the launch because the tires and surface were cold so launching wasn't a problem. When I got back in line to do my 2nd run I launched hard because I wanted a more aggressive start than my first run and also wanted to improve my time. The warm tires hooked up, spun, hooked up, spun, etc. which started a "hopping" feel in the rear end. Rather than back off the throttle I stayed in it thinking that the tires would eventually just hook up and I'd be off...WRONG! About the fourth or fifth "hop" there was a loud BANG. I knew right away what it was...a blown rear diff. I started to limp the car back to the paddock and heard some rather disconcerting crunching noises and then silence...the car was dead in the water. Got some buddies to push the car up onto the trailer so I could get it home but my autox day was finished.

I have yet to disassemble the rear diff to have a look inside but can imagine that I will find bits and pieces of the internal gears everywhere. Will take pictures when I do get it disassembled.

So as a warning to others...when you launch hard at a light, drag strip, autocross run, etc. and you start to get rear wheel hop...do yourself a big favor and back off the gas, otherwise you will be getting towed home!
 

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Ouch! Those A6s will also make a difference since I autocross in street tires (Michelin Pilot Super Sports).
 

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reminds me of the old days where we had rear leaf springs and the rear end would hop and chop like that unless you had traction bars which didn't completely cure it. Sorry for your loss but coming from a fellow racer, you aren't trying hard enough until you crash or break something.
 

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Discussion Starter · #4 ·
Well if there is any good that will come of this mishap it's the fact that the rear diff I had in the car was from a GXP with the 3.73 rear diff. I want to replace it with the stock 3.91 diff with the LSD installed. When I had the original stock 3.91 open diff installed my 0-60 launches were around 4.8-4.9 seconds (using the Dashhawk). My launches with the 3.73 diff with the LSD were between 5.4-5.6 seconds (using the Dashhawk) which means that the taller gearing in the GXP diff was costing me tenths of a second on the autocross course since most courses that I have been competing on are generally around 60mph or less anyway. The GXP taller gearing doesn't "shoot you out of the hole" as fast as the 3.91 rear end.
 

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That's why we used to rip out the 3.23's out of our 70's cars and run 4:11 or even 4:56. I did have one car with 3:90's and that's a good gear for 1/4 mile and light highway driving. Ofcourse, this was old school 3 and 4spd tranny's.
 

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Sorry for your loss. :devil:

I get a lot of slip but no hop. You must have hit just the right conditions to get this result.

I have been told previously that the weakest point of the drive train is the rear axel splines. How did yours look after your experience?
 

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Well if there is any good that will come of this mishap it's the fact that the rear diff I had in the car was from a GXP with the 3.73 rear diff. I want to replace it with the stock 3.91 diff with the LSD installed. When I had the original stock 3.91 open diff installed my 0-60 launches were around 4.8-4.9 seconds (using the Dashhawk). My launches with the 3.73 diff with the LSD were between 5.4-5.6 seconds (using the Dashhawk) which means that the taller gearing in the GXP diff was costing me tenths of a second on the autocross course since most courses that I have been competing on are generally around 60mph or less anyway. The GXP taller gearing doesn't "shoot you out of the hole" as fast as the 3.91 rear end.
Anyone have a schematic of the rear diff on our cars, what kind of LSD is used in them, clutch pack deal or torsional gear driven? I'm not technically proficient with our cars, but I can tell you generally that if you blew the diff you likely toasted the LSD in it. If the Sol diff is pretty much like any other diff, then you could pull the whole LSD carrier that's in there and drop it in your stock diff (assuming the LSD carrier does not have a carrier gear change between 3.91 and 3.73 gearing, in which case the LSD carrier would only be meant to bolt up to a 3.73 ring gear). But if you had pieces flying around in the diff and heard a lot of grinding, ring/pinion, bearing, and LSD carrier are all likely damaged.

Edit: This is probably most likely to occur I'd think with a very hard manual tranny launch, not likely with an auto. And unlike braking wheel hop I'd doubt this would have anything to do with stock 2.4 softer springs/shocks (if you are still using them), but perhaps with some sticky rubber and just enough power I suppose a stock suspension could have also added to this (looks like you are supercharged, which delivers power very quickly).

Dbl Edit: nevermind on the suspension it appears you are not stock there...lowering springs and Koni's, so if all that is fine and nothing broken the suspension should not be any issue.
 

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Discussion Starter · #8 ·
Update to answer some questions. It appears that the rear diff held up! What I thought was a detonated ring/pinion gear turned out to be something different. The dealership had the car on the lift and was prepared to change out the rear diff like I wanted but then noticed that I had blown the left rear axle at the CV joint. That was the loud bang I heard and the crunching noise, then nothing at all.

So I had them change the rear diff anyway as I wanted the original 3.91 gear ratio back, plus I wasn't going to take any chances on something possibly wrong with the rear diff short of taking it all apart and inspecting it. I ordered a new rear axle which took awhile to come in...I guess there aren't too many people out there blowing rear axles on Solstices. Lol. They installed the axle and rear diff for me. Then another problem arose.

Apparently if you don't drive your car all winter and leave it outside in the wet, snow and humidity for a few months, then the ceramic metallic clutch disc will rust to your flywheel preventing you from being able to disengage the clutch! Ugh! Translation: pull the tranny and replace the clutch and pressure plate!

Turns out the rusting of the clutch disc to the flywheel was a hidden omen. The disc was worn to the point where it would have needed to be replaced soon anyway, and the lightweight flywheel was slightly warped (as apparent by only 2 out of 3 sets of disc pads rusting to the flywheel) and it had hot spots in it. Got the flywheel ground down and ordered another Exedy Stage II disc and pressure plate. Also decided to put in a new slave cylinder as well while I had it apart.

Long story short, car is back together and running strong and I'm back in business for autocrossing for the summer!
 

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You can get disc corrosion on normal clutch discs with high ferrous content as well. One of my cars, a 6 cylinder MG, needs to have the clutch pushed in and the engine turned over about once a month all winter while in storage, otherwise it will stick to the flywheel.

If it does stick, it isn't the end of the world, I just warm it up in neutral, then stop it, put it in first and start the engine again and it moves off. Hold the clutch down and if necessary give it shots of throttle and the disc always pops loose sooner or later (0nce took a half a block). The disc was nothing special as it is a street car, but I guess it just has enough ferrous content to cause this issue.

Sounds like it was just as well you did take yours out, though.

I used a ceramic button clutch on my turbo Fiero and never had a single problem with it. I think Centerforce has these for the Kappas.....
 

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This makes me feel slightly better since I am autocrossing my Sol and am experiencing wheelhop.

Still learning on how to modulate the clutch release to be quick, but smooth :)
 

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Hmm, I thought this was common knowledge what happened to the OP. Wheelhop equals busted half shafts/CV joints. When you start getting wheelhop you let off the throttle, not roll into it some more.
 

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Discussion Starter · #13 ·
Sorry for your loss. :devil:

I get a lot of slip but no hop. You must have hit just the right conditions to get this result.

I have been told previously that the weakest point of the drive train is the rear axel splines. How did yours look after your experience?
Splines were fine. The CV joint was obliterated.
 

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Discussion Starter · #14 ·
You can get disc corrosion on normal clutch discs with high ferrous content as well. One of my cars, a 6 cylinder MG, needs to have the clutch pushed in and the engine turned over about once a month all winter while in storage, otherwise it will stick to the flywheel.

If it does stick, it isn't the end of the world, I just warm it up in neutral, then stop it, put it in first and start the engine again and it moves off. Hold the clutch down and if necessary give it shots of throttle and the disc always pops loose sooner or later (0nce took a half a block). The disc was nothing special as it is a street car, but I guess it just has enough ferrous content to cause this issue.

Sounds like it was just as well you did take yours out, though.

I used a ceramic button clutch on my turbo Fiero and never had a single problem with it. I think Centerforce has these for the Kappas.....
When I broke the axle at the end of the autocross season I had some guys push me up onto my car trailer and left the car in first gear while I cinched it down onto the trailer. I apparently forgot to take it out of gear. Couldn't even start the car without it lurching forward as the car was stuck in 1st gear.
 

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Discussion Starter · #15 ·
Hmm, I thought this was common knowledge what happened to the OP. Wheelhop equals busted half shafts/CV joints. When you start getting wheelhop you let off the throttle, not roll into it some more.
I suppose it would be common knowledge for some who have owned cars with enough HP to generate enough force to create wheel hop or sheer CV joints. I have never had a car that had enough power until I supercharged the Solstice. Had I been on the street I probably would have backed off the throttle, but due to my competitive nature in Autocross I stayed the course and learned the hard way. It won't happen again, trust me. It was an expensive lesson to learn.
 

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Discussion Starter · #16 ·
I want to know if you use any of the settings on the traction control, specifically what do you leave it on when you do a launch? ESCT on or off or Aggressive setting? Or do you not have this option at all?
I have a NA Solstice with the DDM Works Stage II supercharger setup. I don't have traction control on my car other than modulating the gas pedal myself:)
 
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