Disc Size Issue
 

I put the ssbc 123a disc kit on the front of my 68 last yr and then ordered the a125-26 ssbc rear disc kit from Summit and we pulled the rear and installe the kit they sent us with no problems. Both kits went on with no problem at all.

However we did not look at the size of rear disc at all in relation to the front disc setup, it just was not on our mind. We did notice the difference though once we putthe rear wheel on and stepped back to look at all we did in 1 saturdays work.

They sent us the 13' rear disc kit not the 11' kit. So now the rear brakes look HUGE compaired to the front.

I am not that knowledgable in this area at all, will this be a problem to run 13 disc in rear and 11 in the front on a manual disc brake setup? I know its the norm to run bigger/same size in the front but at the moment it is opposite thanks to summit sending the bigger kit by accident.

You need to get the 11" rotors coming. For multitude of reasons, car control being number one, since front brakes, especially on front engine cars provide the majority of your stopping power. Summit made an error on the order but it is ultimately the mechanics responsibility to verify the parts are correct before installation.

Besides.........it looks backasserds! :D

yeah i know it does not LOOK right... but i am not asking visual oppinions thanks. I am looking for technical reasons. A proportioning valve handles the balance of stopping power from front to rear.

All the prop valve does is regulate line pressure from the master cylinder to the calipers. Simply put stopping power comes from surface area, caliper design, rotor and pad material.

Consult the component manufacturer for accurate technical info. :thumbsup:

hmm i thought this was a discussion board with a section for brakes... i must be in the wrong place... thanks for the input though.

Since the above poster clearly does not have any input other than pumping his post count...

I am working under the following beliefs...
Front to rear bias only really matters when you reach braking threshhold and one end or the other locks up. To maximize the braking power, you start with more rear and adjust proportioning valve so the rears don't lock up before the fronts.

Is that a correct assumption, and that my prop valve will equalize out the diffrence until the front is replaced?

I will upgrade the front rotors/calipers later but at the moment the $$ needs to be allocated for other areas.

You win.

your bout as useful as tits on a bull my friend

:rofl: BOOM! ROASTED

I think you answered your own question, however you won't know until you tune your proportioning valve. You are correct that a prop valve can be used to tune the rear brake bias, however it is meant to fine-tune a system, not fix major component mismatches as these are limited to a maximum pressure reduction to the rear of 57% the full line pressure by design. If you can achieve lockup at all four wheels with the rear locking just before the fronts, then you're good to go. If not, then you may need to make other changes to get there.

The larger rear rotor is increasing your rear brake torque by about 20%...you can make more of a difference than that in brake torque on either end by swapping out the pads. Lower CoF in the rear or higher in the front can and will shift your bias around back in your favor for not a lot of money.

Tobin
KORE3

"Lower CoF in the rear or higher in the front can and will shift your bias around back in your favor for not a lot of money."

Thats kind info I was looking to verify, thanks mucho! I can follow that olgic and work with the setup with tuning the prop valve and different pad types alot cheaper than new brake setup for the front at the moment.

I am learning things every day sadly knowledge can sometimes be costly!

If you can wade thru my lengthy post my questions are at the end.

I pulled the trigger on upgrading my front brakes to 13's to resolve the original size issue I had. I went with ssbc 13' rotors and their caliper bracket so I could keep my existing SSBC calipers. They were very helpful and I was stoked when the new parts arrived.

Well we mounted the new parts and everything went on smooth, that is until we we to mount the wheels. :eek:

The calipers were hitting the outer rim on my 17' Coy's c5 wheels. I have learned the hard way that there are Reverse Mount wheels out there and that Coys is one of them.

So I loaded up the studs with washers etc... to see how far out the wheel would need to be spaced to clear the back lip. I would need a 1' spacer and thats not going to work for me, it would push that front tire out to the fender lip edge.

I took the SSBC caliper apart (3 part caliper) and machined off 1/2 an inch off the outer/front caliper part and put it all back together. I could not go back/down further as the bolt hole threads just became exposed and I also needed to leave at least 1/2 of metal for the bolts to keep some strength.

I then put a 1/2 spacer on the wheel and it will turn with out rubbing now, but I only have about a credit cards thickness between the caliper and outer rim.

Excuse my poor paint skills in the pix below, but this is what the caliper looked like and the colored lines are items i just described. The green lines are represent where the bolts run thru the calipers, the yellow line is where the caliper is pieced together, and lastly the black lines represent the area i milled out 1/2 down. I will try to take pix this weekend when i get back down to the garage.

Have I ruined the one caliper by taking off so much metal? I did not lessen the amount off material further back than where the ends of the bolts are.

If the caliper is not ruined just lightened a bit, will a credit card thickness be enough clearance for the rim/caliper?

I called the brake co and they are going to see if they have any calipers with less material that would resolve the issue and they are researching. They couldn't tell me that my clearance would work or not, which I understand from a legal perspective.

I don't know how thick your credit cards are, but mine measure about .75mm [.03"]. I wouldn't be very comfortable running that little clearance on anything but a trailer queen. As soon as you start pushing any car hard, everything moves more than you probably think it would. We typically recommend .100" to .120" clearance between the wheels and calipers/tie-rod ends/etc, however we've have had customers get away with .06" to .08" in certain applications. Almost without fail though, they were running stiffer spindles/hubs/calipers/forged wheels...basically everything, but they never had issues.

Since you're running a .500" spacer, why not just run a .540" to .580" spacer instead? Can you not afford the extra width or are you trying to stick to an off-the-shelf nominal thickness spacer?

Tobin
KORE3

Tobin,

At the moment I am torn between the 2 options, because I agree that slight space does not fill me with warm fuzzies.

1. get a new caliper to replace the milled down one and go with new wheels all around that are not reverse mounted.

2. find a new caliper/disc setup for the front that is under 7.5 inches from center to outer caliper that is a 13' disc.

The ssbc caliper brackets supposedly put the caliper in oem position, but I am out of my comfort zone in this area. I may give you guys @ Kore3 a call soon. I should of done that in the 1st place from what I have seen on here and your website, but let someone close to me's opinion guide my brake selection. I see where your c5/c6 325 mm front kit for short spindles is 7.75, which is .25 larger than the inside diam of my rim. So sadly either option I take is going to most likely cost me around 1k to resolve the issue and allow me to run 13's up front, since I have 13's out back also.