Just got home from trying to get a dyno tune in OKC, was going great until something caused a break in the transmission case which locked it up...scattered my brand new built 4l60e and snapped the driveshaft which knocked a hole in my floor and ruined the exhaust.

I was using a stock style driveshaft resized and balanced. It's starting to look like that is a no no. The last time the car was on the dyno it broke the tailshaft housing on the 2nd pull, but when I took the transmission apart to rebuild it we found it had also cracked the case a few inches in front of the tailhousing in the same place this new tranmission just busted.

What else should I check when I get this thing back together? Is it likely just an issue with high speed balance of the shaft or something else?

The car has been street driven and drag raced for over a year, it's only an issue when on the dyno running to 6400rpm in 3rd.

 

Wow, sorry to hear that.

Did you have any vibrations before it broke or did it just let go?

 

Get a new shaft

My guess is a balance issue or bottoming the yoke in the trans.

I use www.dynotechengineering.com for my stuff and the quality is top notch I recive them in about 2 days of ordering.

Tim

 

U have slicks on the car when on the dyno??

 

What kind of engine and trans mounts do you have?

 

I would think that if it were a balance issue you would feel it greatly. I would first check to make sure the driveshaft is not to long and "pushing" the output shaft under acc. or high speeds, bet then again wouldn't this cause more of a problem during the launch.

Make sure you have very good poly mounts all the way around, maybe get an all new aluminum driveshaft, and make sure noting is loose in the rearend thats causint the axle to push on the driveshaft..pushing on the tranny. Oh also replace the tailhousing bushing.

I run an aluminum driveshaft in my 424 hp 4l60e with a 3600 stall, pulls 1.50 60's. A good aluminum driveshaft will behave at higher speeds much better.

 

trans engine mounts are rubber stock type but new

didn't have a noticeable vibration at normal speeds, but I do know it was not too long at all

the first time I had street tires, this time Nitto drag radials

some people have been telling me the chevelle driveshafts are so long that it becomes an issue at high rpm

 

Who is building the transmissions? If something is put together wrong it could cause the internals to "grow" at high rpms. Where is the case breaking at the center support? I have had a ton of Chevelles and the only thing I ever scattered was 4 speeds.

 

My stock aluminum driveshaft has a dampner on the tranny side...Maybe look into this of use an f-body slip yoke with a good quality aluminum driveshaft.

No matter what you do I bet your stomach will be turning on the next dyno pull...

 

First transmission was factory 4l60e from a 98 ls1 car but looked like it was either low mileage or had been rebuilt. We had just added a trans go kit.

This was a built transmission with BW red lined clutches, wide red lined band, no yo-yo pump upgrade, beast sunshell, yadda yadda yadda...all the good stuff minus billet pieces and 5 gear planetaries.

Nothing inside was damaged but the band, the sunshell, and the case. It was a case failure, not a transmission failure.

The car has been driven on the street as a daily and I go WOT several times most days. Has been raced and driven hard without issue, same with the old transmission. The problem seems to only show itself at PEAK rpm in 3rd gear. Highest I have ever had the car on something besides the dyno was around 130mph.

 

Wow...nice pic...check out my latest thread on me re-freshing up my 4l60e. I run a 10.89 with minimal issues on this tranny. Something isn't right, or you are creating much more power then you claim....any track times..60' foot, etc.

https://ls1tech.com/forums/automatic...resh-pics.html

I doubt a driveshaft would do this, but consider all options. it seems as if the output shaft wanted to force its way from the input shaft inside the tranny. Get a diagram of the inside of a 4l60e and make sure it was assemble correctly.

I did purchase the tq arm relocation bracket for my 2000 z28 to get the load off the tailshaft on my car. I only heard of this tailshaft breaking on 6 speed cars, so I wanted to not see the problem.

 

I've had my car at 7,000 rpm in 3rd on the dyno hitting the limiter, on the street at about 130 ish, no issues with the case. 3.73 gears. 3600 stall. similar build on the tranny.

 

3rd gear should be the 3-4 clutch pack and the forward clutch applied. Get a good driveshaft...aluminum with the ls1 slip yoke/dampner. double check the ds lenght. Look at dennysdriveshafts.com

If both transmission cracked in the same spot then I wouldn't blame the tranny, unless you went inside both. I do know there is a clip that goes in a specific position in the low/roller clutch area, and the snapring has to be in only one position as well.

 

My d/s supplier told me that about 90% of the stock shafts brought to him for vibration problems, are found to be bent. [F bodies being the most frequent].
I've seen tire failures, driveline failures, caused by running slicks at low psi on a chassis dyno...In yur case???

 

Is your u-joint binding? I know it sounds stupid, but if it is, the trans is shifting to compensate and causing it to snap. Does not take much, just look at the tollerances for the aftermarket bellhousings to keep the input from snapping.

SWS

 

I know this is slightly different but it's just something to think of...

I worked on a Tahoe that did the same thing on the highway. The theory everyone came up with was the transmission mount gave out dropping the tail shaft angle enough to create a small vibration (which the owner was living with) which caused the U-Joint to slide inside it's almost finger tight straps. This created a larger wobble which got worse with speed and he ignored it, got on the highway and it took out the tail shaft of the transmission. The damage looked almost exactly the same as yours only his was smaller due to less power.

This leads me to my next question and theory on your situation. I know there is something called "critical speed" on drive shafts. This is the point where the speed of the drive shaft causes it to oscillate and eventually fail. It has to do with tubing diameter, tubing thickness and overall length. My drive shaft guy was talking about it and he said the larger the diameter tube the higher the critical speed is. But he also said the longer the tube, the lower the critical speed is. Factory drive shafts are usually long, skinny and not good for much power because of this. You mentioned something about running "stock style" drive shafts "resized," what did you mean by that? If it is stock diameter that may be an issue.

 

Stock driveshaft in a Chevelle is good for 450 horsepower. At least that is the highest stock HP a 70 came with. My 70 SS Elcamino has a longer driveshaft and my 461 is probably at that level. No issues at all and I drive it like I stole it including 25 trips through the auto cross course at Chevelleabration 09.

 

I'm thinking it might be by driveline angles combined with the supposed weak shaft.

My angle up front might be off enough to cause some u joint bind, but it hasn't been wearing them out or giving any vibration I could feel at normal speeds.

As far as power, it was 360 unlocked with cutouts closed. Had it been a locked pull with open exhaust I am 99.9% sure it would have been within 5hp +/- of 400rwhp.

It was a factoy type driveshaft from a driveline shop cut to the length I needed. It was not out of my chevelle, I still have that one sized for a smallblock/th350 trans.

We did not go inside the stock tranny, and this one was built by my dad who happens to be a mechanic and his specialty is GM transmissions. He has never seen one fail like this before as this is a small rural area he mostly gets worn out ones and the occasional offroad 4x4 disaster, never any high rpm/speed stuff.

Bowtie70SS: I drive mine like I stole it too. Street, strip, and twisty mountain roads...never misses a beat. Done very few high speed runs though and like I said the failures always occur almost immediately at above 6200rpm in 3rd gear which should equate to about 145 mph tire speed. This is the biggest clue I have to my problem...and IMO it leaves 2 primary suspects: driveline and driveline angle. I'm not sure what rpm you turn your big block or what speeds it sees, let me know and that might help.

But like I said, technically it wasn't a "chevelle" driveshaft so much as a chevelle length driveshaft from who knows what that was ready to accept the same u joints I use (1330 IIRC), I just had it shortened to fit the car. Size was great with plenty of slip, but not too much.

Thanks guys, keep it coming and I'll keep digging up some research.

 

Do you have a pic of the driveshaft? If it was shortened and the didned weld the yoke in phase with the other end then that would cause the u-joint to bind.

 

I'll get 1 today, I had left it in a different truck (had to trade my little brother out of his to tow the trailer, so the new trans core and old shaft were left in my truck.