Newish with lug nut questions

[Thom]

Hello all,
I have a 1987 R20 suburban. My father-in-law gave it to me as a "you can have it if you can get it to run" deal (in the woods 10+ years). He has passed now and I drive it all the time. When I was working on the brakes I noticed my front and rear lug nuts were different sizes. They are very rusty and I want to replace them but the parts stores look at me crazy when I tell them the rear has larger lug nuts than the front. Does anyone know what the sizes are so I can just order them online? BTW, it's a 2 wheel drive. I think the 4x4s have all the same sized lug nuts but idk.

 

[PrairieDrifter]

Pretty much every vehicle ever has the same lugs on all 4 wheels. Maybe one or two European cars that don't, i don't know lol.

You have a case of mismatching. I'm sure the thread pitch is the same size just the physical size of the nut is different.

I believe that would be 7/16 with a 60 degree seat. You'll have to wait for another to chime in, as 87 was a transitional year newer than I am used to. So it could also be 1/2. Also what wheels do you have?


Orrr it could be a case of a blown up 10 bolt that was 7/16, and they put in a different axle with 1/2 studs.

 

[Thom]

The stock bullet hole wheels.

 

[idahovette]

Your avatar says R20.....3/4 ton right? 8 lugs?

 

[Thom]

Yes, it's a 3/4 ton.
I can remember right now, but I think I tested to see if the front and rear lugs would screw on the other studs and they were different inside too. It is in the shop now getting a new a/c system so I cant check right now. I do know the rear hubs are HUGE.

 

[HotWheelsBurban]

You have any pictures of the lug nuts and the wheels, that would show the hub in the center of the wheel? A 3/4 ton "should be" 9/16" fine threads, or possibly metric equivalents. The half ton square body pickup and Burb used 1/2" SAE threads, with a 13/16" hex. The newer models (OBS/GMT 400) use 14mm threads on the lug nuts, even on the half tons. So actually my C1500 Burb and C3500 crew cab use the same lug nuts, crew just has 3 more per wheel! These use a 22mm socket which is very close to 7/8".

 

[PrairieDrifter]

Shoot I totally glanced over 3/4 ton. It would be 9/16, but that being said if they actually don't fit on all four I would be pretty confused, don't be hard on your parts people for it.

Fine thread would be news to me. But my family has either had half tons or c50 and up. The only 3/4 ton was our 98 and we only got that in 2012ish.

Also don't those aluminum wheels have the lugnuts with the collar on them? That slip into the lug hole in the wheel? Or a lug nut with a washer?

 

[HotWheelsBurban]

Could be at some earlier time in the truck's life, someone replaced the rotors and used the wrong ones? Are they 8 lug like the rear wheels?

 

[squaredeal91]

I bet like you might have the" SD " metric 8 lug. Send a picture. Is the face of the wheel flush?

 

[Thom]

You must be registered for see images attach

 

[Thom]

The lug nuts do have the collar, not the washers.

 

[HotWheelsBurban]

You must be registered for see images attach

Aftermarket mag wheels will use different lug nuts than stock. GM didn't have a factory alloy wheel on the 8 lugs till the 2000-2006 generation.

 

[Mr Clean]

It sounds like someone in the past it a brake job and used the wrong rotors. The lugs would be 9/16. I would replace the rotors, and replace the rear lugs. That way you have piece of mind knowing they are all the same.

 

[84GMCSierra]

I replaced both rotors , pads etc on my 84 C2500, as the studs were stripped, and doing the studs and lug nuts on both back axles as well as they are stripped too. Getting all the stuff from Rock Auto