I have a 74 C3 with GM stocker crate engine (435hp/450lb) paired with TKO5. Rear differential is stock (3.08/1 ratio)
I have upgraded all four u-joints on halfshafts to nongreaseable one which I assume they should be heavy-duty.
Lately, my driver's side halfshafts/differential u-joints broke when I was making some smoke at my rear wheels and spinning end of loose halfshafts broke my composite spring and also one of differential cover spring boltsNow I am in process of changing the cover, spring and one of the halfshafts (the passenger side halfshaft and u-joints are fine). My existing halfshaft is 2.5" diameter and 12" long but all halfshafts I find in market (eckler, zip) are 3" diameter
here are my questions
1) should I change both halfshafts or I can leave the original (2.5") one paired with new (3")?
2) is there stronger un-joint than non-greaseable ones, it seems my upgraded u-joints were not standing my engine torque (I brought them from zip as heavy-duty)?
3) while differential is opened, do you recommend changing any thing in addition to oil, additive and cover gasket ( my differential was noiseless before this incident)?

Here is picture of differential after cleaning

 

1) should I change both half shafts or I can leave the original (2.5") one paired with new (3")? GM went to 3 x090 wall shafts in 75 and for service parts. The 63-74 shafts were 2.5 x 130 wall. You can run them mixed , there is no balance issue. The question is with your use, if you continue to beat up the car you will continue to break parts. If you need a replacement shaft and stronger then Tom's are the only ones I would use but keep in mind your shaft didn't fail- the u-joint did. Spicer solids are the best and they are 1350 size. They should not break during a burn out as yours did. They will break with enough power and launch applied. They are what I would use and are available from any Spicer dealer, 1000's across the country.



2) is there stronger un-joint than non-greaseable ones, it seems my upgraded u-joints were not standing my engine torque (I brought them from zip as heavy-duty)? Answered above

3) while differential is opened, do you recommend changing any thing in addition to oil, additive and cover gasket ( my differential was noiseless before this incident)? The picture shows a stock posi setup. You should check it for cracks, check the hardness of the axle faces, check or better replace the ring gear bolts with ARP brand. It is much easier to remove the diff from the car and service it then to break it apart in the car as you have - even though the old manuals state to do it as you did. Again usage will determine what needs to be done to the diff. Continual abuse will break the stock diff.

I would also invest in a good set of loops to protect the car in the future. Toms had the best but I don't know if they still offer them I would not use the ones that bolt to the T-arm- we used them and they broke along with the shaft when a joint broke. You want them about 1/2 way on the shaft not at the end. You can make them from flat stock - just have to figure a radius bending tool or method. A steel metal shop would bend them up as well.

 

@GTR1999 thanks for detailed recommendation
My driver side half shaft does not have any dent or crack but the C-clip grooves are badly scraped (as it is seen in theses pictures). Do you recommend keeping this half shaft and just install new set of Spicer u-join or I must replace it?

 

That yoke is pretty chewed up, you can find GM shafts in better shape for about $30 - I would replace it.

 

thanks for the hint. I just bought a used (very good shape) half shaft for $30 (your price estimate was right on). will pair it with Spicer (5-1350x) u-joint and put it back together