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Hi, my Kurtis Locost uses pontiac solstice brakes (spindles, etc) The front brakes are large vented rotors with cast iron calipers, sliding type. The rear brakes are 10.9: non-vented with aluminum sliding calipers, built in parking brake.

My issue is that with the replica halibrand wheels, i need to use a 5/8 wheel spacer on the front to clear the larger calipers. The rears fit with just 1/8 spacer. The front spacers exposes the calipers and upper ball joint, which ruins the look and makes the front too wide. I could make shorter control arms, but that won't solve the exposed caliper/ball joint issue. I am also planning on having the wheel widened 2" inboard which will hide the brakes better, too

My plan is to put a set of rear brakes on the front, get rid of the spacer, and everything is happy again. I machined the parking brake lever off the caliper and I'm going to plug with a 3/8 pipe plug. The thickness after machining is 0.750", which is the thickest part of the caliper. I attached pic prior to removal of parking mechanism.

Im looking for input regarding this. The Solstice is a much heavier, faster car (I'm not going 150 mph in a car i built) The front brakes are also used on chevy malibu, which is >4000lbs with 4 fat guys riding in it. I think the rear brakes will be large enough to work on the front, but looking for others experiences. This is going to be a street car, maybe a few autocrosses, but no track days.

FYI - i was looking a pipe plugs on McMasters site. They come in 150psi rating and 3000psi rating. It appears that the high PSI plugs have more full threads before taper starts. Just a heads up to anyone looking to plug hydraulics. I was completely unaware of this. Obviously , i bought the 3000psi plugs

In terms of rotor diameter 10.9" is plenty for a street/autoX car. The non-vented part is what is the biggest concern as they are much easier to overheat. Sealing with NPT is not great with brake fluid.
Also keep in mind the aluminum threads won't take 3000psi even if the fitting will.

If cost and/or using as much of the donor car is a factor I'd say go for it. But honestly I think you may do better to Frankenstein a better brake option. Solid rotors and lack of pad selection (I assume) are not something I would want to build into a modern car. For example I converted my Seven from rear drums. It was a lot of poking through parts lists, and buying/returning a few things but end results was a good sized rotor that is cheap/easy to buy, great pad selection, and OE calipers (with Ebrake) for not a lot of money. ~$300 iirc.

Cheers.

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Build log: viewtopic.php?t=9291

Thanks Corey. $$ not the issue. I am using Solstice spindles which limits my caliper selection. I called SSBC (Stainless Steel Brake Corp) to see if they had smaller front brakes or rear brakes without parking in caliper - he laughed. I don't think Wilwood makes any low profile cripplers either. Everyone wants BIGGER brakes. I looked online at other GM calipers that might bolt up - didn't find any. Most of the cars use the same parts in typical GM fashion.

Any other caliper suggestions???

I bought another set of rear spindles and calipers to put on the front. The brake bolt pattern is different but the geometry is otherwise the same. If the small brakes do not work out, i can swap back to the original front vented brakes.

I see a lot of scrub. I assume the 5/8 spacer is in addition to the bolt circle adapter from 5x110 (4.33) to 5x4.75 wheels? I will also assume you don't want to change spindles and then have to change the frame points and control arm lengths so I have an alternative.

Take light duty brake option G6 front rotors, have them machined to fit over the 110 circle solstice bearing hub by drilling them to 110bc and opening the bore slightly to fit the hub. Then make a bracket that offsets the caliper enough to bolt on about 0.4 closer to the hub. Your picture is of the wrong side of the wheel to show where it is hitting but I will make another assumption that the contact to the rim is on the radial edge of the caliper and not the outboard face. The g6 rotors are close to the same thickness and offset to work with your solstice caliper and bracket (if it were closer, which is why you need the intermediate bracket).

You could make a new upright that accepts c4 vette bearings, calipers, and rotors (assuming you have 15 inch wheels). Not enough material in the hub to drill to 5x4.75.

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Miata UBJ: ES-2074R('70s maz pickup)
Ford IFS viewtopic.php?f=5&t=13225&p=134742
Simple Spring select viewtopic.php?f=5&t=11815
LxWxHt
360LA 442E: 134.5x46x15
Lotus7:115x39x7.25
Tiger Avon:114x40x13.3-12.6
Champion/Book:114x42x11
Gibbs/Haynes:122x42x14
VoDou:113x44x14
McSorley 442:122x46x14
Collins 241:127x46x12

Hopefully this pic will help. Use a high strength, low profile head fastener between the caliper rail and the spindle boss to minimize grinding of the rail for clearance.The intermediate bracket will clock or rotate the caliper rail around the hub about 1.25 above or below the original location on the spindle and 0.4 closer to the hub. The clocking allows the fasteners (and bosses/wall thicknesses) from the spindle to the intermediate bracket and the fasteners from the intermediate bracket to the caliper to clear each other. The intermediate bracket can also compensate for any small differences in rotor offset. After you have a rotor that will slip on the hub and a spindle that will accept the hub, use the rotor as a jig for the intermediate bracket. You want the caliper bolt on to the rail and have clearance on the new rotor with new pads and a fully seated piston.

2006 G6 2.4L standard brake option, Raybestos 580244R, 10.86 od, 1.025 thick, 1.685 height.

Compare to a 2006 solstice rotor, Raybestos 580367R, 11.65 od, 1.027 thick, 1.705 height.

The g6 rotor is a little smaller than the rear solstice rotor (10.94 od) but that will not be an issue if you use an adjustable proportioning valve in the line to the rear.

I should mention that c5 bearing hubs can be used with some minor machining of the solstice upright bore, but most of the vette slip on rotors are too big with too much offset and the g6 rotors probably won't be large enough on the id to clear the od, much less drill to 5x4.75.

You asked about using the rears on the front, and the solid rotor is the number one reason not to imho. I'm also fuzzy on why you would need to plug anything but i should probably reread your post. Doubling up spacers and adapters is also a bad idea since tolerances can stack against you. I assume you were intending to widen the rear when you widen the front.

_________________
Miata UBJ: ES-2074R('70s maz pickup)
Ford IFS viewtopic.php?f=5&t=13225&p=134742
Simple Spring select viewtopic.php?f=5&t=11815
LxWxHt
360LA 442E: 134.5x46x15
Lotus7:115x39x7.25
Tiger Avon:114x40x13.3-12.6
Champion/Book:114x42x11
Gibbs/Haynes:122x42x14
VoDou:113x44x14
McSorley 442:122x46x14
Collins 241:127x46x12

Thanks MV8 - i guess i need more info for you. The wheels are 18"x6". The caliper hits on the outboard side, not radially. I remachined the hubs for 5 x 4-1/2 BC. There is a 5/8 spacer but no adapter. The rear rotors that i am planning on using on the front are only 1/2" thick with calipers to match - that is where the gain is, rather than the decreased diameter.
By removing the spacer, then having the wheel widened 2"inboard, most of my scrub will disappear.

I had to machine the parking brake off the caliper - there is a .450 hole that needs to be plugged where the actuator screw was.
I bought high pressure 3/8 pipe plugs to plug. Would i be better off using a bolt with copper washer? I have some old wildwood caliper that have extra ports plugged with pipe threads, so i figured it was a viable method.

When i was growing up, my father had a bunch of vintage brit cars - Jag mark 9 and XK150, Healey 3000, Morgan +4, etc. All of these had large solid front rotors which were never a problem. OF course we never drove them in rain and snow where the rotors would get hot then rapidly cooled. Obviously, vented rotors were invented for a reason though.....

Thanks for providing more info. I don’t know how you determined the required spacer thickness so I will tell you how I would do it. In your pic of the front wheel assy it looks like there is a lot more room than needed.
Removed the pads, install the wheel without a spacer, then push the caliper outboard until it makes contact. Measure the caliper position at the slider pins with a dial caliper (measurement A).
Install a new outer pad. Pull the caliper inboard. Measure the caliper position at the slider pins (measurement B).
B plus .250” minus A is the minimum spacer thickness.

In using the rear calipers on the front, you may have to use a universal master to find a suitable smaller bore to comp for the leverage loss in going from a 60mm caliper piston to a 40mm.

_________________
Miata UBJ: ES-2074R('70s maz pickup)
Ford IFS viewtopic.php?f=5&t=13225&p=134742
Simple Spring select viewtopic.php?f=5&t=11815
LxWxHt
360LA 442E: 134.5x46x15
Lotus7:115x39x7.25
Tiger Avon:114x40x13.3-12.6
Champion/Book:114x42x11
Gibbs/Haynes:122x42x14
VoDou:113x44x14
McSorley 442:122x46x14
Collins 241:127x46x12

MV8 i had a bunch of AN washers that were .105" thick Kept adding them til i had clearance. Only about 3/16" clearance at the tightest point. It is the fixed part of the caliper that is most prominent, though the sliding part with new-ish pads is close behind.
I have a Tilton pedal set up - i can use a large MC for the rear and a small for the front...maybe 1-1/8 rear and 3/4 front.

Here are 2 pics of the front big brakes, with 5/8 spacer. I am going to remove the whole spindle, brake,caliper assembly as a unit and replace with my rear brake set up minus parking brake. If i don't like it, i can easily swap back.
Just bought a set of front and rear calipers and a set of OEM rotors. I already had a set of 4 (2 F 2R) spindles that i got a killer deal on (for the next project)

That is tight! You have another option. 2000 mustang GT rear rotors are the same OD at 11.65", are 5x4.5bc, have a deeper offset by 0.3", and are thinner by 0.3" for close to 5/8" overall offset. I was looking for a larger rotor with a greater offset to clear the bosses on the id of the swept area but didn't find any.

For the caliper brackets, you'd need to thin the spindle bosses enough to clear a thin bolt head between the rotor and boss, drill new holes in the caliper rail radially outboard of the bosses, trim off where the rail overlaps the boss, then make a bracket to fit laterally inboard of the bosses to lap the bosses and the caliper rail. Since the od is no different, the bracket is much simpler to make. Also need to fit a shim for the caliper; basically a 60mm thick wall tube turned down to fit snug in the piston, leaving .30" at a full 60mm to protrude from the piston.

In hind site, you could have saved all the machining by having 16mm thick adapters made from 110mm to 4.5" with a 65.1mm bore to fit the hub's concentric ring. The price of trail blazing.

If you are looking at refitting unmodified hubs, know that the adapters and spacers all over ebay use non-standard thread studs and nuts. Not a problem unless you need replacement hardware. I ran into this when fitting late magnum 17" wheels to a 80s D100 to get the offset right for the rear fender wells in the bed.

_________________
Miata UBJ: ES-2074R('70s maz pickup)
Ford IFS viewtopic.php?f=5&t=13225&p=134742
Simple Spring select viewtopic.php?f=5&t=11815
LxWxHt
360LA 442E: 134.5x46x15
Lotus7:115x39x7.25
Tiger Avon:114x40x13.3-12.6
Champion/Book:114x42x11
Gibbs/Haynes:122x42x14
VoDou:113x44x14
McSorley 442:122x46x14
Collins 241:127x46x12

I've been looking at how to adapt smaller rotors/calipers to my solstice spindles as well. Here is what I've been able to deduce based on posts online and matching some pictures...

The solstice hub bearing assembly uses the same 3 bolt pattern as the Chevy Cobalt, which is available with a 4x100 lug pattern. This allows for far more wheel selection. I've yet to try it, but will soon be ordering the cobalt hubs to confirm fitment. At that point, you can also use cobalt front rotors which also fit under 15" wheels. As far as calipers, the cobalt caliper bracket MIGHT fit, but I have no easy way of determining this short of buying the calipers and trying. I was planning on finding a better 4 pot option and machining adapters to mount to the solstice spindles.

With all that said, I still need to get home today and double check that a 15" diameter wheel will even fit over the solstice control arms.

I re-drilled my hubs to 5 x 4-1/2. It was close to the original pattern - I used an endmill in my milling machine and drilled oversize with a 4mm offset (something like that)
Be aware that all 4 uprights are different. The rear use different caliper spacing than the front. The spindle/pin is offset from the kingpin axis ("built in caster") so you need to pay attention when swapping them around