Help - Lower Control Arm Rubbing on Rotor

boblyon1 · #1 (**permalink**) 09-14-2007, 11:12 AM

I am a very recent third owner of a Superformance MKIII, originally titled in 2000, with about 3000 stated miles. I bought in about 5 weeks ago and still haven't been able to wipe the grin off my face.

I had my Cobra up on a rack this week and the mechanic noticed that the "knuckle" of the left lower control arm was rubbing on the rotor. I saw about a 1/8 inch path of bright metal on the inside track of the rotor, thankfully not anywhere near where the pad rides. Also, it is not a deep path at all, barely scratching the surface. The tire alignment seems fine and there does not appear to be any deformity or damage to the suspension. When on the lift (both weight bearing and not) you can slip a piece of paper between the rotor and control arm and it is close but not touching. The mechanic was at a loss to understand the reason why. He took a lot of mesaurements. He even measured the distance of the vehicle to the ground on both sides, and it was the same. I'm a heavy guy, about 240. Guess I will try to find an expert front end mechanic. Anyone have an idea what could be happening? Thanks.

bobcowan · #2 (**permalink**) 09-14-2007, 01:06 PM

There are always differances in manufactured components. How's the distance on the other side? About the same? If so, I don't think I would worry about it too much, as long as everything checks out OK.

CHANMADD · #3 (**permalink**) 09-14-2007, 01:57 PM

Did you check that there is no play in the wheel bearing?A loose bearing will give it enough play to rub.

CSX 4027 · #4 (**permalink**) 09-14-2007, 02:28 PM

Same With The Early 4000 Cars.
First, The Clearance Is And Will Be Close.
You Might Have To Grind The Ball A Touch But, Let An Expert Do It. There Is A Fine Line With Just Enough And Too Much.
Second, Wheel Bearings. If They Are Adjusted Right Then..
You Can Probably Be Experiencing Spindle Flex In The Upright.
The Spindles Have Been A Problem For A Long Time For Some Or All Of The Following Reasons.
Inferior Quality Material
Wrong Taper Or The Upright Taper Might Not Be Dead On To The Spindle.
Could Also Be Wrong Rotors

boblyon1 · #5 (**permalink**) 09-14-2007, 08:56 PM

Thanks all, for all your ideas.

Steve - I should have mentioned that the wheel bearings are tight - no wobble at all. That is the first thing we checked.

Hmm - the rotor is doing a good job of grinding the control arm - In fact, this problem may be self correcting.

Any other ideas?

Velox · #6 (**permalink**) 09-15-2007, 09:15 AM

I checked mine and measured a 0.462 inch gap at the closest point between the rotor and the lower control arm, well spaced IMHO almost half an inch. Maybe I misunderstand where yours is rubbing, can you post a picture? I would wonder if someone prior to you had changed that to a different rotor, otherwise can't see how they could be that close as the other geometry is fixed assuming no prior accident, nothing bent etc. I would be concerned about letting it self correct, something is clearly off if the rotor is grinding on the arm knuckle. Warped rotor?

boblyon1 · #7 (**permalink**) 09-18-2007, 12:04 AM

I finally took my beauty to a mehanic who knows Cobras. He looked at a more recent control arm from a newer SPF Cobra and noted that the lower part of the control arms are beveled away from the rotor in the same place where mine rub. (Obviously, mine are not beveled). He pulled the front wheels, brake assemblies and then grinded (or is it ground?) a bevel on the lower part of the outside of the control arms. I think we can assume that the beveling of later models fixed a design flaw.

Thanks to all those who emailed me or spoke to me. What a nice group of people you SPF owners are!!!