Took the car to XP racing in OKC this morning for dyno tune. Got the idle sorted out great, found out a bunch of **** was turned off in the pcm that didn't need to be, all was going well...

Strapped onto the dyno for drive tuning and after a while he even had all that good. All was going swell, so he tried a WOT pull.

At 6400rpm it looked like someone threw a hand grenade under my car...literally. There was fire, there was an explosion like sound, and there was shrapnel as the car chunked pieces of my brand new transmission and ripped the driveshaft in half.

It chunked the slip yoke half onto the floor, the other half slapped the floorboard and ripping a fist size hole in that, then it slammed into the exhaust pinching the passenger side nearly closed. Oh boy.

So Bret climbed out of the car, might have **** himself (I can only imagine what it sounded and felt like inside the car) and we watched it bleed transmission fluid.

We rolled the car forward onto the lift and raised it to look and found pieces of the low/reverse planetary among the guts, transmission case is busted all the way around about 4" in front of the tailhousing.

I'm thinking that the driveshaft had a high speed balance issue, causing the planetary failure, causing transmission lockup (at 135+ mph dyno speed). I will be having a better shaft built at a race shop this time and it will be high speed balanced. Also going to thoroughly inspect my driveline and pinion angles for issues. Last time the car was on the dyno it broke the tailhousing.

Also going to have to get new exhaust so I might take the chance to order a 3" x pipe with built in cutouts from Pypes exhaust.

So, in the end it made 358 rwhp/ 340rwtq through the mufflers (cutouts closed) and the converter unlocked and it was still rich, he needed at least 1 more pull to finish up the tune then we were going to lock the converter to get final numbers

I already picked up a new transmission core while we are here in the city, waiting on my brother to get here with his truck, rent a uhaul and carry it home tomorrow. Pics of the slaughter will follow.

 

Dang man, good numbers to start, but bad ending. Well, just time to build it better.

 

wow sounds crazy

 

If it's in that Chevelle it doesn't surprise me the shaft fell apart.The angles and shaft balance have to be perfect because the driveshafts are too long for high speed. They are just like truck shafts which are rated to only 98mph.Anything above that and they can litterally break in 1/2.

I wonder if you could fit a 2 piece shaft in that car?

 

I'm going to look into what options I have. If nothing else I guess I could get a quality drive shaft and just have him dyno it in 2nd next time to finish the tune.

It's really frustrating because this transmission just went in a couple months ago and was very well built from a good core. I just hope the converter is ok.

 

Damn, that sucks, dude! I've heard stories of driveshafts coming apart on the dyno but luckily haven't seen it yet in person.

The numbers look good so far for what you have! What were the previous numbers and what are the new mods?

 

old numbers: 325rwhp/339rwtq with cutout open, unlocked stock converter (power fell off HARD at 5600 rpm)

switched from ls1 intake to FAST 90/90 ported by me, built transmission with yank3600, larger air filter

new numbers: 358rwhp/340rwtq closed cutouts, unlocked stall, peak power at 6000 slowly falling until run ended at 6400rpm (air fuel not 100% dialed in yet, not sure if he was happy with the timing I didn't ask)

the torque curve looked great, very flat from 3000 on

I was suprised with the numbers for closed exhaust because right now I have 2.25" with no H or X pipe all the way out the back. At the track I pick up just under 2 tenths and almost 2mph with them open.

 

looks like the busted case was the culprit of the other trouble, nothing in the transmission failed...everything but the beast sunshell (mild crack) and the band (friction material was scraped off and scarred during the failure) seems to be in perfect shape, even the output shaft surprisingly

now I just have to find out the cause of the vibration that is causing these cases to fail for me