I have disk brakes installed on my street rod using G body disks. I tried to put an SSIII wheel on the hub but it would not clear. Are Gbody disks a larger diameter than earlier disks?

 

'69--'72 "G-body" is the same as the same years "A-body". Identical.

'82--'88 G-body, and '95--'11, I'm not sure about. I'd expect 11" rotors on the '82--88, but I haven't researched 'em.

 

The Olds rally wheels with the bolt on centers won’t fit G body rotors. If I remember correctly the calipers hit the rim.

Years ago I bought a badly wrecked 69 442. Typical “got drunk and wrecked into a tree” story, a fate that entirely too many of these cars seem to suffer. I bought it for the 425 Olds engine that had been swapped in. It also had a really nice set of Olds wheels with brand new tires. I swapped the engine/trans into a 78 Grand Prix. I planned to use the nee tires/wheels on the car, only to find the front wouldn’t fit.

 

That's news to me. The metric calipers are smaller than those on the 69-77 cars.

 

I need to clarify my issue. It isn't the outside diameter of the disk that is the problem, it is the hub diameter. The SSIII wheel wouldn't go over the hub because the hub was larger than the opening in the wheel center. 15 inch solid wheels fit just fine. The center hole is snug but does fit.

 

Are those really G-body discs, or are they aftermarket discs that use the GM bolt pattern? What is the exact diameter of the pilot on the hub? The OEM dimension should be 2.78". That dimension is the same from 1964 to 1988 on the A/G body cars.

 

Is this a bolt on or a snap on SSII/III wheel?

 

I have slept since then, so I may be wrong on what the actual issue was. All I know is the 14 inch rally’s with the bolt on center cap would not fit on the front of my 78 Grand Prix. They fit the rear just fine.

 

https://oldsjunction.classicoldsmobile.com/ssiii.html

It says in this article the 14x6 wheel hits the control arm on G body cars. I remembered there was some issue, just a little fuzzy on the details.

 

Snap on caps

 

Those wheels came on G-body cars from the factory. Your rotors are not machined correctly.

 

Here's the problem I have with that. Any interference with a 14x6 wheel at that point would be as bad or worse with a 14x7. The wider wheel projects further towards the LCA and tie rod end. Sorry, but this smacks of "headers don't fit supremes".

 

i don’t remember what the interference was. That was almost 30 years ago. I don’t remember if it was the caliper, control arm, tie rod, whatever. Maybe the wheels I took off that 442 were 14x7, they were definitely a Olds rally wheel with a bolt on center cap. The one thing I am absolutely sure if they did not fit the front.

A Grand Prix isn’t a Supreme. 🤑

 

Very likely the rotors are wrong, probably came from China. There would not be any other interference because it is a 15" wheel. Came off of a 76 Cutlass. However all other GM 15 inch wheels fit right on without any problem.

 

I'll bump this for relevance to something of mine.

I took the mounted wheels of my H/O last night and replaced them with 3 15 inch Chevy steel wheels with tires and a universal donut. 2 of the Chevy rims are (at least) 70-72 Chevy base option A body rims that are associated with my Monte Carlo (I have 6 rims for that car, so, two spares), and a third rim was a mid 80s Chevy truck rim, 15", same bolt pattern, late of my utility trailer. The universal donut is probably from the 80s, and was the spare of the Monte Carlo when I reactivated the car in 02 from its 15 year idle period after my granddad died in 87.

I started at the left front, jacked, pulled wheel, looked it all over, then put one of the Monte Carlo rims on, then lowered it. Jacked up the right front and the rim had been a tight fit on the hub. Normally, you just lift a little and pull the wheel off. I had to wiggle it off. I checked everything out, and grabbed the other Monte Carlo rim and it would not go on, the hub opening in the middle was very definitely too small. So, it got the donut, though, in hindsight, I should've tried the truck rim.

I will put a new battery in my calipers and shoot hub diameters as these rims have no center cap and I can get to them easily while it's on tires. I think I have an aftermarket rotor with a larger hub OD that is close to interfering with my ID of my SSIIs. I will also measure all SSII ID's as I pull the center caps for preparation for tire dismount/mount/balance.