Rear wheel rubbing issues

CoyoteCobra · #1 (**permalink**) 12-13-2020, 08:58 AM

Hello

My cobra has bullitt replica 17" wheels that I ordered from Vintage Wheels. Vintage said they've sold the same wheels I bought to many A&C customers without clearance issues. I'm running 315/35/17 tires on the back. I noticed as soon as I put them on that the driver side rear tire was hitting the fender on just the slightest bit of deflection/articulation of the springs. The passenger side has clearance and I've checked the centering of the axle vs. the frame a bunch of times. It is definitely centered.

I am assuming that the reason why I have more clearance on the pass vs the driver is either I mounted the body off by a tiny amount, or that the body's driver side wheel well is slightly smaller. I've measured the axle's position vs the frame and it is definitely centered properly. I can't really see anything on the body that looks like it was mounted wrong either.

As a temporary fix I tried adjusting the 4 link to set the axle back just a tiny bit and added a 0.25" spacer which seems to have resolved the issue from what I can tell. It no longer has any rub when going over a bump or driving over something where it causes the rear axle to articulate (such as approaching an incline at an angle).

The thing that bothers me is that with the axle moved a tiny bit I think this is causing a some amount of bind from the triangulated 4 link being in a stressed position. Maybe that isn't an issue but I think it would make more sense to move the axle back forward a tiny bit and get wider spacers.

I'm curious if anyone else ran into rubbing issues with 315s on their A&C and if so what did you do to fix it? The 315s I have are NT-05 and I'm unsure if they tend to run a little bit wider than other tires.

saltshaker · #2 (**permalink**) 12-13-2020, 01:45 PM

couple questions; do you have adjustable control arms? If you do, have you checked to make sure your wheel base is 90”? This was a big issue on my A&C
Another question; are you using their panard bar? I found removing it gave the diff a lot more travel and less bind.
Jon

CoyoteCobra · #3 (**permalink**) 12-20-2020, 07:34 AM

Hi Saltshaker,

Yes the wheel base was at 90 and I extended it a tiny bit past that to get the clearance.

I am not using their panhard; it seemed very redundant to me when it already has triangulated 4 link setup. Ideally I'd like to have a non triangulated link setup with a panhard as that seems like it would have much less inherent bind. Maybe I can change it someday.

saltshaker · #4 (**permalink**) 12-21-2020, 07:53 PM

I always wanted to convert mine to a 3 link. Factory 5 and Hurricane both made
3 link Cobras
Jon

xb-60 · #5 (**permalink**) 12-22-2020, 03:03 AM

Quote:

Originally Posted by CoyoteCobra

Hi Saltshaker,

Yes the wheel base was at 90 and I extended it a tiny bit past that to get the clearance.

I am not using their panhard; it seemed very redundant to me when it already has triangulated 4 link setup. Ideally I'd like to have a non triangulated link setup with a panhard as that seems like it would have much less inherent bind. Maybe I can change it someday.

CoyoteCobra, how would a panhard rod work on a triangulated 4-link setup without binding?

Cheers,
Glen

CoyoteCobra · #6 (**permalink**) 01-01-2021, 03:39 PM

Quote:

Originally Posted by xb-60

CoyoteCobra, how would a panhard rod work on a triangulated 4-link setup without binding?

Cheers,
Glen

It would not work. That is the reason why I didn't use their panhard option with the 4 link. I suppose the idea of 4 link + panhard may have been to try to help limit whatever deflection is in the bushings, but even then the panhard (or even a watts) still seems like it would be bind city!

Plus with a light car it seems the deflection on the 4 link has to be pretty minimal.

Something like a 3 or 4 link (not triangulated) with heims or poly bushings + panhard seems like it would be nice simple, non-binding, and reliable config. Well, heims may not be the most reliably but given the millage these cars see it might.

Quote:

Originally Posted by saltshaker

I always wanted to convert mine to a 3 link. Factory 5 and Hurricane both made
3 link Cobras
Jon

Yeah, something like even a stock s197 rear geometry seems like it would be pretty good.

daverascal · #7 (**permalink**) 01-15-2021, 08:16 PM

I had the same problem while building my car. I built my own panhard bar, the longer the better. I could not get the rear end centered. Found the brackets on the rear end for the arms were welded in wrong location.The panhard bar is to control side to side movement. You can tweak the rear end side to side by changing the length of the panhard bar. Local shop builds promod cars taught me a bunch about getting a car square, amazing how much you can change the way a car handles by adjusting the 4 link arms.

CoyoteCobra · #8 (**permalink**) 01-24-2021, 07:45 AM

Yeah at a normal ride height the LCA are not ideal for anti-squat, too. Maybe I will relocate them and change to a panhard at some point, but I just wish it wouldn't rub for now.

CoyoteCobra · #9 (**permalink**) 02-28-2021, 04:51 PM

Has anyone modified the LCA on the 9" housing or modified the mount on the frame?

When mine is sitting at what I think should be normal ride height the LCA is past center and basically anti-antisquat. Raising the mount point on the frame or extending the brackets on the 9" housing could correct this geometry. I'm leaning towards the brackets on the 9" being the better of the two solutions but am curious if anyone else did this.

saltshaker · #10 (**permalink**) 02-28-2021, 07:20 PM

I raised the lower control arms to change the anti squat . The way the geometry is set up the anti squat is in front of the front wheels. This makes the rear wheels push into the ground ... not good for max acceleration. Raising the front of the control arms or lowering the rear of the control arms will move the anti squat farther back. I also have a 9” rear from a A&C with lowered lca brackets sitting in Nj....
Jon

CoyoteCobra · #11 (**permalink**) 03-05-2021, 08:08 AM

Interesting. Thanks for commenting. How much did you lower your LCA mounts on the housing? I'm thinking of doing this sometime this season.

hauss · #12 (**permalink**) 03-05-2021, 09:02 AM

I would say binding is not good and not what you want. what about different offset rims or shortening the rear end.

CoyoteCobra · #13 (**permalink**) 03-06-2021, 08:28 PM

Well, narrowing the axle would make the issue worse since that would make the rim get even closer to the inner fender. I added a small spacer to push the track out, and that's largely fixed the issue but I hate using spacers if I can avoid it. Replacing the custom welded wheels would be an option but it would be much easier to cut the fiberglass and tweak the inner fender a bit (something I may end up doing).

CoyoteCobra · #14 (**permalink**) 04-03-2022, 05:59 AM

I ended up doing a few upgrades to the Cobra that will hopefully help-

1.) Cut out some of the inner fender and re-glassed it to a different shape to clear the 315s. It is barely noticeable in the interior and there's plenty of room behind the seat still. This change allowed me to put the wheelbase back to 90" without rubbing the inside of the tire.

2.) Replaced the adjustment joints on the upper and lower control arms with Rock Jock joints to allow much smoother motion and articulation without the inherent bind of a triangulated 4-link with short arms.

4.) Relocated the LCA brackets on the 9" to correct the incorrect anti-squat geometry. As SaltShaker mentioned, the geometry from A&C is way off. With a normal ride height, the stock config of the LCAs are tilting down towards the front- producing anti-anti-squat! The only way it could try to have somewhat reasonable angles on the LCAs would be if the car ride height was high in the rear (which would also make the driveshaft angle a challenge) and then the UCAs would be incorrect.

Hopefully when I button a few other things up I can take it for a drive to see how it handles.