Big Brake kit question (mainly 2 piece hat question)

[Shoaz]

Buy the correct 13" rotors and be done with it. I know you're trying to keep the 2 peice rotors, but either replace them, or deal with it

The 12.5" kit uses different knuckles (pre-93) with a much different rotor offset than the Cobra 13" kit. You'd need a 13" deep-offset Corvette rotor, not a Cobra rotor, and modify either the caliper bracket or the adapter bracket, and you'd still have the same clearance issue with the LCA.

 

[1993MTXSHO]

Nick

Aren't these Michael Olsen's old rotors? If so, they are the TCE 2 piece replacements. I don't think that Michael spec'ed them out differently than Todd (TCE) would have offered them but you may want to check with Michael to make sure. You are using the correct caliper brackets for the 12.5" setup, correct?

Ian

yes they are, he said it was a shoshop kit that he had modified to fit under slicers. I had spoke with him about this problem and all he said he did was grind the LCA (this is why I am thinking it is because of my moog control arms). I used to have this same problem with my old 12.5" kit (same sound and everything) but I didn't have to put a 3mm spacer behind my rotor to make the LCA clear (do you remember what heikki did to the LCA on this thing when he installed his 12.5" kit before he sold the car to me years ago?). I am going to have to take a closer look at this whole thing and see if maybe something else is grinding. Is there anything else that could grind during a slightly harder then your grandmother would take turn? I am going to check the caliper squeelers or w/e they're called and then take another look at he LCA and brake rotor. I actually just remembered I had painted my LCA after grinding it down. I'll look at that and if the paint is ground off I know that's my problem, if not, I know it lies somewhere else.

 

[SinisterSHO]

Bracket deflection.

 

[1993MTXSHO]

Bracket deflection.

you'll have to excuse me but I have to ask, what is that?

 

[SinisterSHO]

Every Cobra based kit does it. You take a hard turn and the rotor rubs against the control arm. The bracket is actually flexing (deflecting).

Eventually it goes away. But its real awesome the first time you hear it on a track.

If you're only hearing this noise when you take "semi hard" turns and now when your just going down the road, I'm willing to be thats whats happening. And with your custom hat size its happening more than your typical Cobra based kit.

 

[K-Dawg]

Every Cobra based kit does it. You take a hard turn and the rotor rubs against the control arm. The bracket is actually flexing (deflecting).

Eventually it goes away. But its real awesome the first time you hear it on a track.

If you're only hearing this noise when you take "semi hard" turns and now when your just going down the road, I'm willing to be thats whats happening. And with your custom hat size its happening more than your typical Cobra based kit.

The noise is from the hubs flexing, which causes the rotor to contact the bracket. The noise goes away after the rotor wears the bracket down.

Doesn't sound to me like this is his issue.

 

[1993MTXSHO]

Every Cobra based kit does it. You take a hard turn and the rotor rubs against the control arm. The bracket is actually flexing (deflecting).

Eventually it goes away. But its real awesome the first time you hear it on a track.

If you're only hearing this noise when you take "semi hard" turns and now when your just going down the road, I'm willing to be thats whats happening. And with your custom hat size its happening more than your typical Cobra based kit.

it's not even semi hard turns, sometimes it happens on turns I wouldn't even expect, like turns I would have no problem taking in my F-150 daily.

 

[K-Dawg]

Sure its not the dust/water shield? 3mm is a lot when you are talking about moving parts.

 

[Shoaz]

The hub flex issues being described are not an issue with the 12.5" kit, which is based on pre-93 knuckles. That's one advantage with that kit...the bracket mounting and rotor offset are quite different than the SN-95 knuckle Cobra kits and that particular problem doesn't seem to happen with this kit.

 

[gmorrell]

it's not even semi hard turns, sometimes it happens on turns I wouldn't even expect, like turns I would have no problem taking in my F-150 daily.

If you have the time, pull the spring from a front strut, disconnect the anitroll-bar link, reassemble the suspension and brakes on that knuckle, and then use a jack to move the suspension through it's full range of motion - you have to remove the spring to do this. Pay particular attention to the clearance between the ball joint and the inside edge of the rotor, especially as the suspension goes through bump, and you'll rapidly understand why you need to cut a chamfer on the back side of the rotors.

 

[gmorrell]

The hub flex issues being described are not an issue with the 12.5" kit, which is based on pre-93 knuckles. That's one advantage with that kit...the bracket mounting and rotor offset are quite different than the SN-95 knuckle Cobra kits and that particular problem doesn't seem to happen with this kit.

Perzactly. Hub flex is not an issue with the Baer/SHOShop 12.5" high-offset rotor brakes. It's not caliper bracket flex either, and if you take the time to sketch up a force-reaction diagram of the knuckle, rotor and caliper bracket, and then use your head to insert side loading from a tire, you'll see that if there were an issue with the rotor contacting the (fixed) caliper bracket, the primary culprit is hub flex. Distortion of the knuckle is another matter, but it's secondary or less to hub flex issues, and causes a different set of problems.

 

[Shoaz]

If you have the time, pull the spring from a front strut, disconnect the anitroll-bar link, reassemble the suspension and brakes on that knuckle, and then use a jack to move the suspension through it's full range of motion. Pay particular attention to the clearance between the ball joint and the inside edge of the rotor, and you'll rapidly understand why you need to cut a chamfer on the back side of the rotors.

Another way around that when ordering replacement rotor rings is to get the "eye" I.D. at least 8 7/8". IIRC much more than that and you'll be eating into the pad firepath, as your pics show, which would be bad.

I'm also trying to sort out what the rotor O.D. needs to be. I still get a fair amount of "unused" rotor face around the edge.

 

[1993MTXSHO]

ok thanks guys, I have a lot to go look at and will do so as soon as I am home. If it see the paint rubbed off my LCA I will pull the rotors and get them machined and see if that fixes the problem. I would love to get that 3mm spacer out of there, but I have a feeling a big part of my problem is the moog control arms, so the spacer may have to stay for now. I don't like the idea of that spacer being there stressing the lugs more then hey should be. I realize they have the same tinsel strength throughout, but having it further away from the hub should make it easier to snap a lug no? So I think I may have to go get some new stock control arms and use them to have the safest possible setup.

 

[SinisterSHO]

The noise is from the hubs flexing, which causes the rotor to contact the bracket. The noise goes away after the rotor wears the bracket down.

Doesn't sound to me like this is his issue.

I knew it was one or the other.