I am coverting drum brakes to disc brakes on my 79 F350 Scab 4x4. I am using the front rotors from a 1984 chevy k20 4X4. The problem is the chevy rotor uses a 9/16 lug bolt compared to a 1/2 lug bolt from by ford hub. Will the ford 1/2 incg lug bolt work? Do I need to replace the ford lug bolts with longer 9/16 lug bolts?

Thanks, appreciate your comments

 

Your options are to drill out the axle flanges to use the front studs from the chevy. There are also studs out there that have the base of a 9/16" stud but have 1/2" threads. They will allow you to use your existing lug nuts. Or re-drill the rotors to the axle flange size holes. I wouldn't trust the ford studs being smaller diameter than the rotor holes.

 

Thanks for the info about the different size lug bolts. I have searched various threads concerning disc brake conversion and see no mention of changing out lug bolts. What am I am missing? The various Threads tell you you press the old lugs into the new 8 lug rotors/hub. Did I use the wrong rotors (9/16 vs 1/2)?

 

As far as I can tell Ford used both 1/2" and 9/16" (4x4 got 1/2" and 2x4 got 9/16"). Chevy doesn't seem to have used the 1/2" studs on any 3/4 ton or 1 ton. So I would say your best bet is to drill out the axle flange.

Anyone have input on doing this by hand? I would think you can but I don't really know.

Another option would be to get the axle shafts from a 2x4 Dana 60 with 9/16" studs.

Depending on the bracket kit you have or if you are building your own brackets you could run the f350 front rotor. It's pretty much the same as the chevy one except for it will place the caliper about 1" closer to the differential. The ford rotor is .06" bigger dia. and has a new/discard thickenss of 1.25/1.18 vs the chevy which is 1.29/1.22.

 

I did this on the rear of my chevy 14 bolt FF. but the front already matched. Have you thought about switching the whole truck to 9/16s? might be the easiest thing.....IF their isn't a '*******' stud that will work.

 

Summit racing lists a stud that has the chevy knurl and a 1/2" stud with the similar length of the chevy front studs so it should work but that doesn't address the difference in the hole size between the Ford axle and the chevy rotor (.625 and .608 knurl diameters)

There's nothing that says you can't have 9/16 on the rear and 1/2 on the front, they should all fit the same wheels. If you are running bigger tires or wheels the 9/16 might be worth it for peace of mind though.