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Engine alignment (centerline to axle)

4

45acp

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How close to perfect alignment have others been able to get the tail shaft of the transmission aligned between the frame rails? I have the engine (Cad 500) mounts set in place and I'm mounting the cross members for the TH400/Doubler and find the tail shaft is off by .020" to center line of the rear differential. The engine is setting level side to side and 5 degrees sloped to the back and looks parallel to the frame. The frame has so many twists and bends at this point it is hard to tell where to measure from. Any one with experience, I would appreciate your input as to how close you got the tail shaft centered.
/forums/images/icons/confused.gif
 
I'd be surprised if GM got it any more accurate than that. 20 thou ain't much...

Rene
 
I'm not sure how you could quanitfy that...but I am sure there is more lateral deflection in your spring bushings than .020".

There is also torsional deflection in the engine and tranny mounts due to torque.

Lastly the datum you are measuring from is also not the most reliable.Too many variables in manufacturing as well as 20 plus years of service means the edge of your frame is not a reliable enough datum to use. Ideally I would drop a plumb line from the center of the front balancer, another plumb line from the center of the tailshaft and a third from the center of the diff. All three points should line up on the floor when everything is centered. Make sure the truck is sitting level front and rear though.

I am pretty sure that 20 thou isn't worth worrying about though.

Rene
 
I agree with what Rene said about the engine and tranny mounts.

Over time and the years, the stock rubber mounts are subjected to much wear and tear, no just to the weather but also to the oils and other fluids from the vehicle.
These fluids such as the oils, etc. are/have been known to soften some of the rubber compounds. Such softening and all the vibrations they are accustomed to will make the motor/tranny/t-case all settle in different locations than what the factory had spec'ed them to.

So your .020" is not much at all to worry about. That's basically like what, a dime or smaller? I doubt something that thin can or will affect the driveline any worse than if it was sitting dead-on straight as the factory. /forums/images/icons/wink.gif
 
I doubt they were ever that straight from the factory Wes...GM getting the drivetrain aligned within 20 thou? /forums/images/icons/smirk.gif I wouldn't bet on it.

Rene
 
Rene, Thanks, I went ahead and finished the crossmember that I was building and left it about .020 to .030 off center. If I tried to get the last little bit it would have put a bind on the front engine mounts. I just didn't want to get down the road a year from now and wish I had done a better job.
 
Human hair is .004 so you're only off 5 hairs or so.... /forums/images/icons/wink.gif /forums/images/icons/grin.gif /forums/images/icons/cool.gif
 
a tenth of a quarter inch, hmmmm. You get almost an inch just turning, I don't see a problem, as for angles, that's what a driveline is for /forums/images/icons/grin.gif
 
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