Axle Shaft Flex Question

[smallblock]

Has anyone here running slicks induced enough lateral G's on the rear that the axle shaft flexed enough for the rotor to contact the caliper mounting bracket? In other words, caused the wheel and rotor to go positive camber (no longer perpendicular to the axle housing) to the extent that they actually made contact?

I'm dealing with a bit of a mystery here.

Thanks,

John

 

[TMSBOSS]

That's a lot of flex.

Warped rotors or a build up of brake pad residue is a common problem when rotor are contacting pads. Turning does flex components. With the excess build up or a slight warp in the rotors, contact occurs.

Wear on the end of the axel, where the axel contacts the differential cross shaft can also be an issue. A worn Posi clutch pack can also be a problem.

Share a few more details and maybe someone has had the same experience and has a fix for you.

 

[smallblock]

I talked to Kohr Racing. It's a problem with running 13.8” GT500 rotors. The Caliper brackets aren’t wide enough to accommodate the surprising amount of flex of the axle shafts that is amplified by the larger O.D. rotors. The guys a Kohr were extremely helpful.

 

[TMSBOSS]

I run the same set up. I have Blowfish racing mounts. Steve includes direction with his part explaining this issue and the fix. The brackets need to be relieved.

 

[smallblock]

I ended up buying the Performance Friction rear Caliper brackets and 2 piece 12.9" rotors from Kohr's World Challenge car. If it was good enough for their race car it will be good enough for me. I installed new axles as well just to be sure.

Witnessing the amount of flex in the axle shafts has really shown me how unsuited a fixed caliper is on the rear of these cars if you intend on seeing high cornering Gs.

I'm going to Grattan this weekend so we'll see how it goes.

 

[ArizonaBOSS]

In for field report.

 

[Swiss Boss]

What's the difference between the Performance Friction rear caliper and the stock one?

Also where can you buy those?

 

[smallblock]

What's the difference between the Performance Friction rear caliper and the stock one?

Also where can you buy those?

The kit is only the caliper mounting brackets and 2-piece rotors. The stock caliper is reused. The bracket bridge is slightly wider to allow more flex and positions the caliper for the 12.9" rotor.

You would have to ask Kohr where to buy, it's not on Performance Friction's website.

 

[antman450]

It's only the caliper mounting bracket, it reuses the stock caliper. The bridge is slightly wider to allow more flex and positions the caliper for the 12.25" rotor.

You would have to ask Kohr where to buy, it's not on Performance Friction's website.

If it is just the bracket, I wonder if it would work on stock calipers with the 13.8 inch rotor. I get brake wine in reverse and stuff like that but only since I put race pads on with no grease anywhere. Before that, with street pads, there was no noise at all.

 

[smallblock]

In for field report.

It seems to have fixed the issue. I don't see any signs of rubbing.

 

[Swiss Boss]

It's only the caliper mounting bracket, it reuses the stock caliper. The bridge is slightly wider to allow more flex and positions the caliper for the 12.25" rotor.

You would have to ask Kohr where to buy, it's not on Performance Friction's website.

Thanks. I will pass on this for now.

My plan is to save enough $$ so I can afford the Cortex cambered axle

 

[smallblock]

Old thread but i came across a photo over the weekend illustrating the axle flex described above. The wheel has clearly gone positive camber due to axle and wheel flex. This causes the rotor to contact the caliper bracket. The tires appear to be DOT, so one could expect grippier slicks to exasperate the problem.
Photo credit goes to a Mr. Karigan on Corner Ponies facebook page
Untitled by smallblock, on Flickr
Untitled by smallblock, on Flickr
Untitled by smallblock, on Flickr

 

[smallblock]

I also found some literature for the Performance Friction rear brake package I am using:

https://s3.amazonaws.com/ccommunications/Build+Sheets/20150408_LAT_Mustang+Build+Sheet+F&B.pdf

 

[Grant 302]

Tough to see how much is the wheel vs. the tire carcass at the tread. The face of the rim doesn't look too bad, but they're really working that tire!

 

[smallblock]

Tough to see how much is the wheel vs. the tire carcass at the tread. The face of the rim doesn't look too bad, but they're really working that tire!

I just scribbled some reference lines to help illustrate how extreme the issue is. Cortex should have an image like this on their cambered axle page

 

[Grant 302]

I took another reference line from the bottom of the LCA brackets and got about 2.47º

This reference line would eliminate the difference in tire compression. Though I'm not sure I can actually see the point for the top edge of the rim without more resolution.

 

[smallblock]

I Built a cambered axle on Cortex’s site. Price of entry is around $7000.00, guess I’ll have to live with it