well i just finished up my th400 swap today and hop on the dyno to tune it,

and te second pull...bammm, the driveshaft went out and craked the bell housing and case.

from the looks of it my rearu-joint split completely in half, I was told that my u joint couldnt handle the power cause it had the grease fitting which weaken the u-joint...

one expensive and upsetting night lol

 

I would be looking at pinion angles. I have seen in some cases this happening on the dyno and I often question what happens to the pinion angles when a vehicle is strapped down to the rollers. I personally would like to see both! The whole grease fitting theory is a new one to me unless the ujoint was not made properly. Don't most replacement ujoints come with a fitting? I don't know but good luck getting your car back up and running. Vince

 

I agree with Vince-check your pinion angle so this doesnt happen again. The "grease fitting" theory is that the cross part of a greasable U-joint is hollow and thus weaker than a non-greasable one which is solid.

 

You might want to check the length of the driveshaft and make sure it didn't bottom out the yolk in the transmission when they strapped the car down.

As for the u-joints most of the "high performance" joints don't come with grease fittings anymore because the "grease fittings make it weaker" theory.

 

Ya, I was thinking pinion bangle musta been off as well, i didnt really get crazy with the adjustment, and I guess the car wasn't loaded rightt with the front on jackstand and only rear suspension loaded when i set the angle , if I woulda had a ds safety loop it probly woulda saved my tranny too, just glad it didnt happen on the street or track cause i might not be here typing this if it did, so i guess we learn from our mistakes and negligence

Im looking to do an all out th400 this time with all proper stuff to handle the power, with ultrabell and aluminum drum..

Maybe a couple sponsers can quote some prices lol

BTW the rear pinion was the first to let go im sure because of the grease passages cause it completly split so you can see the entire grease passage on both halves of the broken pieces

 

My car did this, first time was just the tailhousing. Next time it spit the driveshaft out and busted the case 3 places.

Check:

1) Pinion angle
2) Angle of the drivetrain
3) Use a heavy duty high speed balanced driveshaft
4) If possible strap the car down by the axle tube or something besides the body (pulling it down loads the suspension and rotates the pinion even more

I seriously doubt the Ujoint was the first failure point. Even when mine broke the u joint survived...the rear yolk was ruined but the u joint was still in it. I would use solids in the future though.

Mine was a bad combination of trans angled down too much and a cut/spliced factory steel shaft (look up "critical speed") that was too long for the RPM I was turning.

 

When you say angle of drivetrain are you refering to side to side, cause it makes me worry, I used the bmr th400 crossmember with the torque arm relocation on it..and when I installed it I had to pry the tranny over about 1/8" for the trannymount to line up with the crossmember hole, and keep in mind I am running a motor plate on this car, but i installed and welded everything with the stock kmember and mounts still in

 

Well I jacked car up yesterday and seen that the ds broke the front ujoint first because it left a nice mark there and no mark in the rear, the entire bellhousing shattered, rear tailhousing cracked, flexplate cracked and looks like a couple converter bolts are unthreaded (i dont know what to think of this since I used red loctite on all 6 of them....

So now im a little lost on what may be the cause of this disaster, I will post some pics today that I took...

But my setup is a front motorplate with no midplate, ironblock 370, th400, yank converter, stock trans mount, bmr th400 trans crossmember w/ T/A relocation, steel 3" driveshaftmoser 12bolt with upgraded yoke

 

the main case looks like it may be fine, u think I can put a jw bell on it and change the tail..

Im just hoping it didnt mess up my main bearings or anything engine related

 

how the hell did it shatter the bell??? I dont understand that.

 

Not really sure but it makes me wonder if the driveshaft failed first or was it something else that failed first, and what caused it, because this is gonna run me atleast 3 or 4k to get back in business and i cant afford to do this again

 

Heres some pics of the driveshaft

 

I agree with the guy above, Are you sure that the DS wasn't bottomed out on the transmission?

 

Yours looks like the u-joint failed first....no????

My steel shaft broke last week while doing a steady 80mph.....we"re all stumped as to what failed first too. Wierd ****...

Sorry to hear your tranny got hammered.....I got lucky and it was fine, good thing to because it was completely rebuilt 2 weeks before this shaft failure.

with pics of what was left...........
https://ls1tech.com/forums/gears-axl...ing-80mph.html

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ill take pics of when I get the tranny out, I'll probly drop it tomorrow, but It had to have broke in the front first cause theres a mark there, unless the rear broke hit the ground, caused the beelhousing to brake and the front joint then hit the body

 

From your pictures....the front UJ is broke in half....is that right?

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Not uncommon for the case to break (including the bell) after a D/S failure.

 

ya the front u-joint split... but if lets say the front joint broke first, then how the hell would the tranny case break along with the bellhousing, I woud think the case would break only if the rear joint broke first and the ds hit the ground...

I seen the flexplate cracked as well and either the converter bolt is loose or it pulled the thread outta the converter because I can see threads between the converter and flexplate

I know for sure there was a vibration right before it happened

 

I don't know if you have a tailshaft mounted TQ Arm anymore......I still do....and I think in my case when the shaft broke, the inertia/momentum...whatever....caused the rear-end to want to rotate forward (with the wheels) and bent the hell out of my stock tq-arm...which in turn put pressure on my tailshaft housing......breaking it.

What TQ-Arm mount do you have........thats enough pressue at high rpm to put energy into the tailshaft housing and case, via the TQ-Arm, to break it. When my shaft broke the front 3 feet of the shaft fell out of the car, only that rear 18" piece remained attached to my rear-end. So the TQ-Arm is the only thing that had contact with the tailshaft housing to put any kind of force on it.....

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Crossmember mounted torquearm, do you think I could have messed my main/thrust bearings up