C30, do I need center clamp rings on rear

[71swb4x4]

I have a 67 C30 with front brakes and wheels from a 75 dually. The front came with the center clamp rings that go between the wheel and the lugnuts. Do I need that ring on the rear too? I have not seen those rings on the older duallies, but I have seen them on the rear of newer duallies. I did upgrade the rear to 9/16" studs which is what the 75 would have had.

[Tx Firefighter]

I'd believe so. The lugnuts are tapered seat and you'll need the clamp rings as the wheels offer a flat surface that wouldn't jive with the tapered nuts without that ring. I've had three duallys myself, a 78, an 88 (square body) and a 94. They all had clamp rings on all four corners.

[71swb4x4]

My 67 had flat lug nuts, not tapered. That must have changed after 67. I will find two more rings.

[Tx Firefighter]

PM me your mailing address. I got you covered.

[71Dually]

The C30 clamp rings were introduced I believe in 1973 on the square body trucks. They also introduced longer wheels studs at the same time to accommodate the extra thickness of those rings. I do not know why GM engineers switched to this set up.

Be careful using these clamp rings with the earlier 67-72 shorter wheels studs, you may not get the lug nuts full thread engagement. Dorman studs 610-182 (front) & 610-193 (rear) will provide the extra length needed to use the plates. However they are the larger 9/16"-18 studs so as you probably already know stock 67-70 1/2" factory wheel stud hubs will need to be drilled out to accommodate these wheel studs and their larger .622 shoulder knurl diameter.

I used a set of 73-91 GM hub centric chrome wheels on my 71 C30 dually. I believe the wheels are aftermarket. I excluded the clamp rings that I pulled off the same truck and instead used my stock flange lug nuts without any problem. 1,600 miles so far and no loosening of the applied torque specs yet.

Here's a few pics:

There is a longer 73 up wheel stud in the picture for comparison to the shorter studs. I'm going to put some Alcoa classics on my 71 truck and have been researching wheels studs thus the longer stud on my front hub. The wheel in the picture is a 73 up hub centric chrome one.


The 73 up hub centric chrome wheels installed without clamp plates on my stock shorter wheel studs:




P.S. Tx Firefighter, thank you for all the great tech posts. Very helpful with the things I want to do to my truck. I've followed a few of your posts and my research leads me to them quite often. You do good work. Please don't be surprised if I hit you up someday about a set of 86 spindles and rotors you may have on your shelf.

[jdean]

The 14 bolt out of my 74 had two piece wheels with flanged lugnuts on it. But the front end has tapered lugnuts. Front of the 69 has flat nuts on it with the 1/2 studs. I think the p30 vans run clamp rings in the back. Seems like they had 5/8 studs though? I'll be running 19.5 wheels from one, but i'll probably see how they fit with the flanged nuts.

[71swb4x4]

71Dually we did drill out the jobs for 9/16" studs. There's a lot of metal there!