Drilling out Lower Control Arm U-bolt holes for 9/16" U-Bolts

[RoyL]

Passing on in case others are going to upgrade your smaller 63-66 U-bolts to 9/16" when swapping to '73-87 C10 control arms for disc brakes or whatever reason.

Get a sharp bit...
Drill from the bottom and put a tight fitting bolt in the opposite hole to keep the saddle bracket from moving.

One of mine shifted a tad when the drill bit caught the bracket as it was almost thru. Before I realized it, I drilled out more of the bracket than needed, which caused the control arm not to want to seat in the alignment pin. So I had to line up the saddle and ream it out some more so the pin would line up.

I ended up using a 5/8" bit to get the 9/16 u-bolts through.

[PGSigns]

Actually you need to move the holes over along with making them bigger. I have done it in the past with a die grinder. The bolt in the other hole does help.
Jimmy

[RoyL]

Originally Posted by PGSigns

Actually you need to move the holes over along with making them bigger. I have done it in the past with a die grinder. The bolt in the other hole does help.
Jimmy

Agreed, a 9/16" bit would've worked if the 2 holes center to center was a wee bit more, going to 5/8" was enough to allow the ubolt to pass thru the holes.

[RoyL]

A question related to the U-bolt diameter used on the up to 66 C10s. My understanding is that for a stock C10 up to 1972, the LCA U-bolt diameter is 1/2" and 73 -87 were 9/16"
I thought PO had swapped the entire cross member with a 1980-something C10. But after having to drill out for the 9/16" U-bolts, I'm assuming that only the control arms, spindles were swapped.

Is this a fair assumption? Are there other differences in the cross members?