Bad day...Dyno

[CSchafer]

Put my truck on the dyno today at the high school for the open house tonight. I wanted to get a baseline before the new injectors come in before I started tuning the smoke out of it so I didn't choke the crowd. I played with the throttle linkage on tuesday and got alot more travel out of it. I think maybe too much, It was still pullin at 3200rpm when I was just about to push in the clutch and hit the little red button a loud noise sent the crowd dodging parts. The driveshaft let go at about 110 mph sending u-joint caps and straps flying. It crushed the exhaust pipe, smashed the fuel tank to the point of shattering the sending unit out of the top and broke the transmission case all the way around it and not to mention made the driveshaft a 90deg bend#@$%! Made some decent power though, for stock gov. spring, timing and injectors. I guess it will be getting my nv4500, duel disk and fuel cell sooner then I thought

 

[OKish]

aww man, im sorry about that. good thing everyone is intact.

 

[CSchafer]

yeah we had everyone back up incase somthing happins . No one was hurt but a u-joint strap did break a window in the teachers office.

 

[daledozer]

Sorry to hear bout the breakage, but those are some good numbers! Yea, just pull the parts out of that 2nd gen. and get that 1st gen. back on the road, you gotta get those new injectors in.

 

[IC Smoke]

holy cow cade!!!!



time to fab up some driveshaft loops!!



Ian

 

[PToombs]

Glad nobody got hurt! Good HP & torque, too much torque? Too bad about the fuel tank and the trans. Hope you get it back together soon!

 

[woodsrat]

Uhhh not that it matters at the moment but your injectors will be there saturday. Hope you get everything back together. Might as well do the head now too:-laf

Chuck

 

[PToombs]

I was looking back thru the pics, and I noticed the trans oil was milky! It needed changing anyway! :-laf

At least you didn't break the dyno!

 

[rockjeep73]

Those are nice numbers.

What injectors are in the truck right now? What all do you have done to the truck?

 

[wtfd6]

wow Cade!

 

[CSchafer]

With the injectors hear it will give me some motivation to work on it. It probobly won't come back out before I do everything to it. Put in a fuel cell with my a1000 supply pump,nv4500 with mitchel twin disk, 96 head with o-rings and ported, build my twins,get the 14mm head and rotor put on and build some driveshaft loops



The dyno is still ok:-laf we checked it's pulse with a 99 ws6 trans am with only made 305rwh. And a late 90's v8 thunderbird with 175rwh. They may of been able to drive them home but I had top numbers anyway:-laf



It was manely a baseline run to get a number before I put in all my gofast parts. The truck has a HTB2 62/12 and banks intercooler but has stock ip timing, gov spring and injectors. However the full fuel screw is all the way in till it got hard to turn:-laf

 

[bgilbert]

That sucks. Too much lift:-laf. I need getrag parts :-laf.

 

[JLEONARD]

So what failed first? What caused everything to break?

Gotta find out so it doesn't repeat.

baseline run to get a number before I put in all my gofast parts

Yea, find the weak link before you juice her up. :-laf I think you were successful

 

[CSchafer]

I've come to the conclusion that the shaft had a slight bend in it. I sheared the strap bolts off once before in the yoke on a wholshot and tossed the shaft. After that it got driven around town some but no highway. Then it sat for a while and got a new clutch and differnt suspension and smaller tires. I took it on a trip and noticed a viberation above 70mph. I got home and found a pitted wheel bareing so I figured that was it. I ran it up on the dyno slow and felt nothing so I figured the vibration was in the front end anyway. I never thought about the driveshaft being bent from tossing it before because it didn't do it around town and it was about 3-4 months before I found the vibration so it was no longer on the top of my head. Well it went at 109mph so I think that is when the vibration got bad enough to break the u-joint straps and it snowballed from there. It wasnt from the lift Bill:-{} It was from racing a 03 powerstroke and trying to smoke him out of the whole . Oh well live and learn I guess.

 

[Babyfat]

chad sorry to here about the truck, but why did't you tell us you were having a dyno day? will training wheels fit?Oo.

 

[JLEONARD]

It wasnt from the lift Bill

Don't be too sure. When you lift the truck, you increase the u joint angles. That puts MUCH MORE load on the u joints. It also can induce a velocity error or magnify an existing velocity error if the ujoint angles are not both the same.

That makes things go crazy and fail.

I'll explain velocity error a little bit. As the shaft turns 360 degrees, each 90 deg one axis of the ujoint is accelerating, and one axis is decellerating. You will get a sine wave curve of each axis if this were plotted out.

As the ujoint angle increases, the force/curve gets higher... . ie it takes more force to make the rotation.

IF the ujoint angles are identical, the forces will cancel out perfectly... the acceleration (positive force) will be cancelled out by the decelleration (negative force) and the shaft will be perfectly "in phase" or balanced.

If the angles are not identical, then it will be out of phase. . ie it wil take more force to rotate for part of the 360 deg and it will happen 2 times in each revolution.

More rpm make this more unstable.

So the driveshaft will come from the factory with a certain angle and the yokes will be phased (orientation from one u joint axis to the other) for optimum operation ie minimal error.

When you change the angle, all bets are off.

Sometimes it doesn't adversely affect performance... sometimes it does. Any manufacturing error or out of balance condition will accentuate the problem.

You may be on the egde.

I do this for a living with steering shafts so I know what I'm talking about here. We just don't have the rpm and balance factors to deal with.



You can draw an analogy to this scenario by considering the junky steering shaft connector we have at the steering gear. The 2 wd ones last longer than the 4x4 trucks... because the angle in that coupler is much larger in the 4x4 version.



Sorry for the long post. hope I didn't cornfuse anyone.

Jay

 

[TWorline]

Hey Jay, great post! That makes perfect sense now that you have explained it so well. Now I know why you get a vibration when the u-joints are not lined up through the slip yoke, thank you.

 

[dpuckett]

TWorline- that is plain u-joint alignment, not the sine waves and loads Jay is talking about. The anlges in relation to (in this case) the transmission output shaft, driveline, and pinion into the diff have to be equal. For example (if I understand correctly), if the driveshaft angle drops 15deg coming out of the transmission, then the line/ angle needs to drop another 15deg into the pinion into the rear diff. So, if you put a 12" lift on, you SHOULD get your spring perches reset to better match your driveline anlges.



Jay, am I on the right path? Or have I just added to the murkiness?



Daniel

 

[PToombs]

I actually understood it! My ex-boss used to chew my butt for spinning the wheels on the plow trucks, with the front wheels turned tight. He said it tore the joints out. I proved him right! :-laf

 

[TWorline]

So the driveshaft will come from the factory with a certain angle and the yokes will be phased (orientation from one u joint axis to the other) for optimum operation ie minimal error. 

When you change the angle, all bets are off. 

Sometimes it doesn't adversely affect performance... sometimes it does. Any manufacturing error or out of balance condition will accentuate the problem. 

Jay[/QUOTE]





Daniel:



This is the part that I thought might pertain to the mismatch condition.