The Stovebolt Site Forums The Parking Lot Big Bolts Clamp Plates Purpose and Placement

48 Loadmaster w/Dump Bed

I have taken the dump platform off and will be refinishing. Some of the beams are indeed in bad shape but the majority are useful. While the bed is off I am doing some brake work on the rear wheels and replacing a leaking axle seal. I have a question about the clamp plates that I removed while taking off the wheels. The clamp plates were in the inside next to the brake drum "two deep" on both sides. It appears they were put there for spacing as the tires are 10" and require additional clearance from the springs and frame.

According to Grigg Mullen's(Bolter # 6590) in the Tech Files mentions the clamp plates purpose is to "add strength at the center of the wheel". It is my thought that the clamp plates purpose is also to act as a "spring" tensor between the lug nuts (which are not tapered) and the wheel/hub setup and if so then order of placement could be important. Do any maintenance/service manuals speak to placement?

There are two types (see pictures below) of clamp plates one with a concave rise at each hole and one that is flat. I would like some insight on the placement of both types. I hope to change the tires back to spec so that I will not need the 10 inch spacing.

Click here for picture file

The ones with the tapered hole are for using nuts tapered on the side that fits the taper in the plate. The flat ones are for nuts flat on the nesting side.

Ed

Hy Burgy, welcome, the true clamp plates are the ones with the small counterbore around each bolt hole, the other ones you found are spacers someone has made up to give you clearance between the tire and wheel and the springs or frame or possibly to space the wheels farther apart to get clearance between the two tires, hope that helps.

3B has told you the correct information.
I will add that the clamps with the counterbore go on the out side of the wheel before the nuts are installed
If your particular wheel/nut combo. requires them. Not all trucks used them.
The other spacers are not factory and not needed unless someone has the wrong wheels.
Personally I don't like spacers of any kind.
Tom

The original clamp plates for the AD trucks, and I'm sure other years, do not have countersinks and do use flat bottomed nuts. The clamp plates do however have some shape, raised portions under the nuts such that the clamping pressure provided by the nut is spread over a larger area/diameter.

Some of the plates in your picture look like may be torched out centers of old wheels used as spacers for whatever reason.

Clamp plates used with this same 10 lug on 7.25" circle (but 5.25" bore) from the 80's and later (possibly earlier) do have countersinks and do use 90* lug nuts.

Same details as above are true for the 1 ton wheels and the corresponding 8 lug clamp plates.

If necessary I could take pictures of both types.

As to using them or not.. if you read the Accuride wheel catalog the modern equivalent of these wheels require use of clamp plates and they provide the GM part number for them. Similarly, if GM used them on our old trucks when new it's safe to assume that they did so for a reason and it'd be smart to continue using clamp plates.

Thank you all for your input. It is nice to have this valuable resource.
So what I am learning from your replies is that the clamp plate should be on the outside of the wheel with the convex (raised) side of the plate toward the lug nuts. This makes more sense than the way that they were positioned when I acquired the truck because the plates were on the interior being used as spacers. I now also notice that this matches what you (Grigg) noted in your article in the section titled "Note on the 10-lug wheels with 7.25” bolt circle[b][/b]' regarding the front clamp plate which is on and in the correct position.Picture of front left wheel with clamp plate

Next - some of the wheel bolt holes are wallered-out on two of the wheels. With the clamp plates and spacers in this more of a problem, less of a problem, critical, fixable (welding) or just need replacement? I have attached pictures of the wheels in question.
Wallered-out wheel #1
Wallered-out wheel #2

Since the wheels are "Hub Centric" it is less important regarding centering. But is it structurally safe?

The wheels and the clamp plates register on the hub, not the studs, however, with wallowed out holes, upon braking hard or a hard pull, the wheel might rotate to the extent the wallowed hole(s) allow, never a good idea.

Ed

Hy Burgy, I can't access your photo's

Sorry about the link to photos. I was trying to target individual pictures and in doing so it seems I restricted the user file.
Here is a link to the photo album. 48 Chevrolet 1 1/2 Ton