95' Junker Drag Truck

I didn't know that was the junker when I posted on FB about it, that's a bummer man.


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that spiral break is exactly how it is supposed to break under torsional loading to fatigue.
 
that spiral break is exactly how it is supposed to break under torsional loading to fatigue.

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It has to have been shock load failure if the shaft is rated for 2700 ft lbs and my truck makes a measly 1600 ft lbs.

I ran some numbers and it looks like this TCS Canada 300 maraging steel shaft measures 1.034" in diameter with a 0.254" diameter bore in the center. This leaves 0.789 square inches of material to handle the work load.

Comparing that to a TCS Arizona 300m shaft, it measures the same 1.034" diameter but has a smaller 0.192" diameter bore in the center. This leaves 0.811 square inches of material or 2.8% more material.

I'm going to try a TCS Arizona shaft this time around, hopefully it performs as expected.

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How many passes did you say were on that one shaft? Who knows, it could have outperformed every other shaft by 100% LOL
 
How many passes did you say were on that one shaft? Who knows, it could have outperformed every other shaft by 100% LOL

I'd say 100-150 passes by me. It came out of a local low 12 second 2wd common rail so it might have had 100 or more passes on it before I got it. It was straight when I installed it, had a slight twist about 3/4 of a spline offset when I installed the quad disk, and had zero 1/4 mile runs with the quad disk conveter, maybe 2 gallons of fuel, all street use, mostly with converter unlocked, mostly short burnout sessions and roll-on power burnouts to see where it would hook vs spin in 3rd gear.
 
The steel doesn't lie. I am also saying the selling literature of the company may not lie either. What I am saying is this shaft broke exactly how it is supposed to break under torsional loading past fatigue (for a hardened steel shaft/rod), and you need to find out what was present that allowed this to happen well below the rated 2700ftlbs.

few things i see there. on the main shaft piece on the table, is the hardening (darker outside part) equal in distance around the circumference? the lower right part of the piece you are holding in the zoom has red. is that rust? or after failure induced color? I see some marking inside the bore of the shaft. a line perpendicular, another rising up to the right at 45*. are those consistent all the way up the shaft?

The manufacturing process of this shaft, does it go initial machining, hardening then finish machining? Or do they do the more common practice of hardening the part form rough point and machine one step after. I ask this because if your particular blank was off center and hardened, during machining back to round you could have lost 1/2 your hardness in a section of the shaft.
 
This is also not to say this failure also didn't have help from a few shock loads that might have caused some micro fracturing at the starting point of the torsional break. BUT, that is speculation and the pictures and history of the part provided doesn't back it up.
 
Easily one of the best threads I have ever read. It was like reading a good book, I couldn't stop turning pages!
 
I agree, 2 thumbs up on the tale of the Junker Drag Truck.
There is so much valuable information in this thread, I wish I could remember it all.
Keep up the good work.
 
Will is on his way to Montana to compete at the nhrda event tomorrow. With his latest round of mods he thinks he picked up some power. He is hoping to run 11.90 and 10.90.
 
I was really checking this out in Montana but was wasn't sure haven't checked in on it since March. What happened in Montana didn't get to see you run
 
Will said the injection pump hung up and ran away during a 4500 rpm free-rev in the parking lot before he made any passes at the track. The motor ran away and hit 5500+ rpm for a few seconds before he got it shut down. Needless to say, no track times from last weekend and lucky it didn't happen mid-pass, could have been disastrous!
 
Will said the injection pump hung up and ran away during a 4500 rpm free-rev in the parking lot before he made any passes at the track. The motor ran away and hit 5500+ rpm for a few seconds before he got it shut down. Needless to say, no track times from last weekend and lucky it didn't happen mid-pass, could have been disastrous!


What is causing these issues? What supply fuel is on the truck now
 
Will said the injection pump hung up and ran away during a 4500 rpm free-rev in the parking lot before he made any passes at the track. The motor ran away and hit 5500+ rpm for a few seconds before he got it shut down. Needless to say, no track times from last weekend and lucky it didn't happen mid-pass, could have been disastrous!

Again? Maybe he's better off sticking with the 160 pump!
 
The motor is fine, luckily I went back with a .020" oversized headgasket this time around to gain valve/piston clearance.

It appears that something came apart in the governor this time and it wasn't a fuel-related issue.

I will say this, it sure sounded mean with 30+ degrees timing and 5500 ish RPM. It pegged the tachometer around to the zero peg so I really don't know how high it revved....
 
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