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Discussion Starter #1
So first day at the dragstrip after boosting. Eased into launching from idle then seeing how hard I could go, balancing grip vs power. Left around 2600 and it bounched and shuttered like wild. I backed out and stopped for the day. So driving home, when turning it feels like the wheels are going to fall off. Pretty much a 180 in a parking lot at idle speed is brutal. Took it to a shop who put it on a lift and said something is broke in the diff. All I could really get for free on short notice. Drove it two hours home. In a straight line it felt fine. Would kind of sway and feel like the wheels would spin for no reason but straight line driving was ok. But ANY type of turn the wheels shutter, bounce, etc. So is my diff likely destroyed, partially destroyed, maybe axles popped out a little? I won't know till monday but just trying to see my options here. Visibly nothing appears broken and no fluid leaks.
 

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That's pretty wild risking driving it back home like that. Could've been much worse if it decided to lock up at highway speeds. If it's a stock diff I wouldn't be surprised if it broke like that, seen it happen before at the track. Luckily replacements are plentiful and the job isn't too bad.
 

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Discussion Starter #3
I was puckered the whole time. But didn't have much of a choice. But you think though it's possible to have basically grenaded the diff but still be driveable like that?
 

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I can't be for certain, but I do believe it would still transmit power having a few broken teeth somewhere in the unit. Hopefully the shop could visually identify the axles not being fully seated if that was the case.
 

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Discussion Starter #5
So I took it to a pep boys. Being they were the only place open. The put it up, said everything visually looked ok. They couldn't rotate the wheels though while it was in the air and could hear stuff in the diff. It also looks as if my rear wheels are toe'd inward a lot too.
 

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Discussion Starter #6
So the diff is broken. I went an ordered a stock 2.92 with BMR bushings. Yes I know, should have gone camaro diff but it wasn't in the cards financially for me. I likely won't be drag racing it again with the stock diff or at least not launching above idle speeds. I found a used diff with 60000 miles for $150. Question though, what oil should I use to fill it up with?
 

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Factory. It has the additive for the carbon disks.

Of coarse, internet engineers / facebook gurus will state to load it with RP and send it.

Make sure you loosen the fill plug before pulling ths drain plug.

Caveat Emptor.
 

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Fwiw the 2.92 is actually a stronger unit then the 3.27/3.45. Hard to believe but they seem to hold up much better.
 

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Fwiw the 2.92 is actually a stronger unit then the 3.27/3.45. Hard to believe but they seem to hold up much better.
That’s some funny **** right there! My 2.92 lasted one track day, granted I broke a 3.27 as well after multiple events, but 3.45 is still going strong years later!
 

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That’s some funny **** right there! My 2.92 lasted one track day, granted I broke a 3.27 as well after multiple events, but 3.45 is still going strong years later!
Haha i hope it lasts forever! Ive had great luck with my 2.92 and seen plenty of failures with camaro pumpkins.

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Haha i hope it lasts forever! Ive had great luck with my 2.92 and seen plenty of failures with camaro pumpkins.

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Ya I've seen a bunch of each broken, normally its from wheel hop. I only installed the 2.92 because I broke the carrier on the 3.27 and I had the 2.92 laying around. All I got from the 2.92 was worse 60', less MPH and didn't withstand a day of racing. I rebuilt the 3.27 case with OEM 3.45 gears and a truetrac, cant beat it for the price. The 3.45 has held up to violent manual launches off the two-step so I don't think an auto on proper tire will give it much grief.
 

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Discussion Starter #12
well now I don't know what to believe...
 

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Hey man, sorry for the bad luck. Just curious what tires you were running out back when this happened. Drag radials or street tires?
 

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So first day at the dragstrip after boosting. Eased into launching from idle then seeing how hard I could go, balancing grip vs power. Left around 2600 and it bounched and shuttered like wild. I backed out and stopped for the day. So driving home, when turning it feels like the wheels are going to fall off. Pretty much a 180 in a parking lot at idle speed is brutal. Took it to a shop who put it on a lift and said something is broke in the diff. All I could really get for free on short notice. Drove it two hours home. In a straight line it felt fine. Would kind of sway and feel like the wheels would spin for no reason but straight line driving was ok. But ANY type of turn the wheels shutter, bounce, etc. So is my diff likely destroyed, partially destroyed, maybe axles popped out a little? I won't know till monday but just trying to see my options here. Visibly nothing appears broken and no fluid leaks.
based off the 2600 starting line leave its stick shift?
 

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Discussion Starter #15
bf goodrich drag radials, and I have a higher stall torque converter which is how I was able to leave at a higher rpm.
 

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That shuddering when you left the line sounds like wheel hop to me. Here's a quote by ZIm from a thread on wheel hop.

He describes the scenario pretty well and offers suggestions on how to eliminate it.


The above mentioned items will help some, but will not eliminate it unfortunately ....as I have all the items installed and can attest.

A lot of people don't know why wheel hop occurs, which often leads to them throwing the incorrect parts at the car in an effort to eliminate the issue. Fortunately understanding (and correcting) wheel hop is not difficult. Here is what happens. When a car accelerates, you can picture the forces involved as something (the ground) pushing the driven wheels of the car forward. Obviously if you push the wheels forward, the car is going to move forward also. However, the wheels are not rigidly fixed to the chassis, so when the ground pushes on the wheels, they move forward a bit in the wheel well. Normally a car's acceleration is so small that this motion is negligible, but when a car accelerates quickly, especially during a launch, the wheels can move forward quite a bit in the wheel wells. As the wheels move forward, significant toe changes occur. Now, everybody knows that a tire can provide the most grip when it is perpendicular to the ground, parallel with the acceleration, and pressurized to provide the optimal contact patch. That being said, if the toe of the driven wheels changes during acceleration, the grip of the tire must be changing. Wheel hop is a result of this change in grip. Here is the sequence of events:

1.) Acceleration begins with good grip.
2.) The wheels move forward, toe changes, and available grip is reduced. Wheelspin occurs.
3.) During wheelspin, acceleration is very small. The wheels move back again, toe changes back, and the tire regains grip.
4.) Acceleration begins again, and the process repeats itself.

This rapid switching between grippy acceleration and wheelspin is wheel hop. My above description of the wheel hop process sounds tame, but the frequency of the grip changes and the magnitude of the forces involved is what makes wheel hop so violent. Race tires can prevent wheel hop since they have more grip (i.e., they don't lose grip even with the toe change), but cars that wheel hop with race tires will do so in a much more violent fashion.

Getting rid of wheel hop really isn't difficult. If you can limit the motion of the wheel with respect to the chassis, then the toe changes during acceleration will be small and the tire will not suddenly lose grip. If the tire does lose grip (common on a high-HP car of course), then it won't suddenly regain grip due to the wheel moving back to it's static position. How do you keep the wheel from moving with respect to the chassis? Well, assuming your car has reasonably rigid suspension arms, then all you need to look at are the suspension bushings! The wheel can move with respect to the chassis because the bushings flex...especially old, stock rubber bushings. Sometimes simply replacing old rubber bushings with new rubber bushings is all that is required. However, on a modified car that posesses more horsepower than the designer's intended, upgrading to stiffer materials like nylon or polyurethane may be required. The ultimate solution is to use rod ends or spherical bearings at every suspension joint, but that is unreasonable unless your car will never again see public roadways. Anyway, by simply upgrading your bushings, the suspension bushings will not flex as much under strong acceleration, the wheel will not move far forward in the wheel well, the toe of the car will not appreciably change, and your tires will not lose grip. Wheel hop will have been eliminated.

In some cases weak shocks can allow a perturbed wheel to continue hopping up and down since the motion is not damped. This is a less likely scenario, but shocks should not be ruled out as a potential culprit.


What gets rid of wheel hop?

As mentioned earlier, a lot of people throw the wrong parts at the car in an effort to eliminate wheel hop. First, springs and sway bars will generally not do anything to promote or prevent wheel hop. Additionally, suspension settings, such as camber and toe, will generally not help the issue. It is the change in toe that leads to wheel hop, not the static setting. Tires do not cause wheel hop, though they do determine the grip level at which wheel hop occurs. For example, race tires, with their increased grip over street tires, will not break traction until you reach a higher level of acceleration. Some people might think that race tires solved their wheel hop problems, but in truth they merely changed their "wheel hop acceleration threshold" from a level below their launch acceleration to a level above their launch acceleration. Once they increase their horsepower to the point where they can accelerate enough to once again reach that threshold, their wheel hop will return.

Limited-slip differentials will also not prevent wheel hop. They may increase the acceleration threshold at which wheel hop occurs (much like installing race tires), but once again an increase in horsepower will eventually reintroduce the problem.

Check your shocks. If they are not malfunctioning, then you need to increase your bushing stiffness.
 

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Discussion Starter #19
thanks nugz. and I was at no point wondering why it broke. I knew supercharging it and launching hard would strain it. also something important I guess I should have mentioned. before I raced I had installed UMI toe rod ends. I did NOT get an alignment done before the race. But idk if not aligning it coupled with the added power aided in breaking it. But I had been driving with the supercharger and new toe rod ends unaligned for about 3 weeks prior.
 

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Makes perfect sense Camo. If you're toe was out of spec I suspect your drag radials weren't able to hook up as they should on launch resulting in the violent wheelhop which led to broken parts in your diff.
 
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