Rear brake issues with IRS 16 in rotors 15 in wheels

[Garyc]

My rear brakes are dragging I can spin wheel by hand but it’s almost impossible
I’m probably overlooking something but can’t figure it out
I’ve done everything. Extra shims. No shim’s e brake cable on and off
Plus caliper only covers 1/2 of the rotor
FFR says if I followed directions they are ok

[Papa]

When you first installed them, did the pads slip over the rotors without significant resistance? It could be that your MC are not fully relaxing after letting off the pedal. You'll want to see if the pedal is resting on the chassis cross brace in the foot box. Have you shortened the push rod(s) at all? I had to trim mine about 1/8" for the front MC. Last thought is pulling the calipers off and winding the piston back.

[Papa]

Looking closer at the picture you posted, the rotor looks like it's too large for the caliper and the pads look like they aren't correct for the caliper. Something is definitely a miss. I'm also confused by the title of this thread -- obviously a 16" rotor is not going to work with a 15" wheel, but a 16" rotor would be massive. My big M-Sport brakes on my BMW have a 14" front rotor with a massive caliper.

https://thefactoryfiveforum.com/attachment.php?attachmentid=150103&d=1625102013

[Glen Davis]

Looking at your picture it looks like the caliper is touching the rotor which is not correct

[Rdone585]

Check your caliper bracket and the mount to make sure it's mounted correctly and positioned properly.

[NAZ]

The caliper and rotor don’t look like a good match to me, most calipers will cover more of the rotor. Are you sure these are a matched set (check part numbers and manufacturer’s specs)? More pad contact area does not have much effect on cold brake torque but does have a significant bearing on wear and heat transfer properties. More contact area will make the pads last longer and they will be a much bigger heat sink.


I see what appears to be a burnished area on the rotor about the height of the pad. How long have you run these? Or were they bed-in from the manufacturer?


Is any part of the caliper (not pad – caliper) touching the rotor? The caliper should have a goodly amount (technical term) of clearance so it will never touch the rotor.


Are the calipers compatible with the rotor thickness? Check the part numbers against the manufacturer’s specs to be sure. If the rotors are too thick the pads may be dragging on the rotors instead of releasing.



What happens if you open the bleeder valve? Will the rotor turn easier? If so, ensure your M/C piston is returning all the way home. If the piston does not return to the home position you can trap fluid between the caliper and M/C and the system will retain pressure (read that as clamping force) causing the brake to drag or even completely lock.

[rich grsc]

You do realize that the pistons need to be turned to move them in, you can't just push them in. A few more pictures at different angles would help.

[Garyc]

No I don’t know how I came up with that
They are 12 inch rotors

[Garyc]

Yes I do do and the emergency brake adjust the brakes

[Hoooper]

I would definitely say that caliper looks like an awful match for the rotor size, hopefully thats not really the right selection of parts from FFR. That said, you have the IRS and the axles in, its going to be hard to turn by hand with just the brake rotor size leverage. Have you driven the car yet? It looks like its either been driven or the brakes applied while running the rotors at a reasonable speed.

[Garyc]

No driving yet. That is just turning with a long pry bar

[Garyc]

Well I’ve spent another day on the rear brakes and
Calipers slide off and on easily however
When I tighten the mounting bolts. It locks up
I’ve tried 1 shim. 2 shims. No shims. Same action
When you tighten them
FFR has seen the pictures and his comments
We’re. If I followed their directions then the engineers
Did it right. I don’t like how they look either
Something is not right with the design or I have
The wrong calipers

[NAZ]

Gary, if you have clearance when loose and not with it tight regardless of the spacers you use, that sounds like the mating surfaces are not aligned. Make sure there are no burrs or debris on the faces of the mating surfaces.

So, again -- is the caliper touching the rotor at any point? Or when it gets tight is it binding on the pads -- both pads or one pad.

Have you confirmed with the manufacture that your set is compatible? I'd suggest you do that before you put a lot of effort into troubleshooting.

Hard to troubleshoot an issue over the internet sight unseen so the better you can describe what is happening the better help you will receive. And lots of photos can really help.

[Jeff Kleiner]

Gary,
Our mutual friend Joe H. asked me if it was OK to put you in touch with me. I told him of course but now that I see you're here maybe we can figure something out. The 2015+ Mustang IRS uses a 13" rotor. This is too large to allow 15" rims so FFR came up with the #16765 rear brake package which uses an 11.65" rotor along with caliper relocation brackets to accommodate the 15" wheels. From the photo it appears that your caliper is too far outboard, and in fact you've mentioned that it's not covering the entire rotor. I have to wonder if you have assembled it with the caliper brackets for the 13" rotor---this would explain why the caliper is so far away from center and not covering the rotor. It may be that the 11.65" rotor is offset a bit farther in or out in relation to the 13" one (this would be taken into account with the proper caliper brackets) and may be why you're getting the bind when everything is tightened. I suggest that you take a good look at the caliper mounting brackets. Here's a quick check---if you have the caliper on the mounts for the 13" rotor you won't be able to get the 15" rim to go on.

Let us know and good luck,
Jeff

[Railroad]

Put 2 lug nuts on the rotor.

[Garyc]

Thanks Jeff. I appreciate anything you can do
I’ve heard nothing but wonderful things about you
And then to have a mutual friend.
I completely disassembled calipers, brackets , cleaned
Turned pistons back in measured distance from brackets
To rotor top and bottom by the mounting bolts
I changed the spacers between caliper and brackets as I was just
Using flat washers and to me they still feel like they are dragging
I have 15 universal wheels which do fit without rubbing
Bias bar seems to be adjusted properly and everything has been bleed
Successfully The other brackets FFR sent clearly would not work
So I am confident in my work. I am going to jack my Shelby up
And spin rears and see what I get. I know they are or seem to be tight
But I blame that on the posi trac.
I’m going to continue my struggles and I will let you know
I would like to come and just visit and see some cars sometime
Let me know what is convenient for you
Thanks again. Gary Clingler. 317-626-3734