Broken input shaft on 700R4

[PROFESSORSK5]

I have an 89 K5 with an 8 1/2 inch lift, 36 inch Super Swamper IROK's, 14 bolt ff and 3/4 ton 10 bolt, The transmission shop rebuilt the trans (700R4) about a year ago and at just about three months, the input shaft (the shaft that goes into the troque converter) broke just inside the bell, they fixed it, and now after about nine months the input shaft broke again and this time they said it broke at the weld on the outside of the bell. Does anybody make a stronger replacement or is there something wrong with the transmission.

 

[DPI]

There is something wrong with the tranny. I am not a tranny expert, but that shaft should not break unless something is not aligning right. What weld broke? That input shaft should not be welded. Did the weld the shaft to fix it the first time? If so, that is the problem.

Other things I would check to make sure they are not bent or warped are the flex plate and torque converter.

 

[sickquad]

If it happened two times it sounds like something isn't lined up right. Could the entire transmission casting be warped? Therefore it isn't bolting up to the motor straight? I'm not sure how you would check that though.

-Chris

 

[big83chevy4x4]

i would count the splines on the shaft, the 27 spline used to break, but they changed to 30 spline in mid 84 and i have never heard of a problem. i have heard of some tranny shops stealing the 30 spline shafts and putting a 27 spline shaft in its place.

if the shaft is 30 spline, something is deffinetely wrong inside the tranny. the only thing i can think of is if the hub that the shaft sits into is bent a little then the converter can be putting a side force on it and causeing it to break.

there is no weld on it, the shaft is a 1 peice hardened steel and the hub it sits into is aluminum.