Rear brakes dragging

[SteveP]

I think my rear brakes are dragging too much but I'm puzzled about how much drag is acceptable and how to reduce the dragging. My brakes are the standard Mustang brakes with 11.65 in the rear on 2015 IRS. The front brakes have a little drag and I expected that approximate amount. The rear had much more drag on installation. First I discovered the rotor inner chamfer did not clear the shoulder on the hub. We cut a deeper chamfer and the rotors now seem to mount tight on the hub flange. It takes considerable effort to rotate the hub without the e brake cable attached and with no brake fluid in the system. Of course, both hubs are turning because of the limited slip differential but it still feels like too much drag. I can measure the torque it takes to rotate the hub but I don't have a baseline for the amount of drag that is acceptable. Does anyone have any idea how much drag is acceptable on initial brake installation? Perhaps things will improve once I go cart a few miles but I'd rather fix a problem now then deal with it when access is more limited.
Also, access to the lower bracket mounting 12 point bolt is severely limited by the e brake cable. Are there any tricks to improve access other than ovaling the cable mounting hole?

[65 Cobra Dude]

Steve, a couple things I would check. Make sure the rotors are centered on the hubs. Also make sure the calipers are centered on the rotors. Do that by tightening the rotor down and turn it looking for interference at the end of the caliper and rotors. Lastly, I would make the the pads are retracting and the ebrake is not too tight.

Henry

[GFX2043mtu]

The rear brakes defiantly won’t spin as easy as the fronts will due to the fact that you have the rear gear set to spin with possibly the drive shaft and trans gears. It should be difficult to spin by hand if you try by just grabbing the flange. Try spinning the rear end with no brakes on it. Then install the rotor with lug nuts and try. It should be the same if not something is rubbing that shouldn’t. Check for rotor clearance. Once this is good check to make sure that the caliper slides easily on the guide pins connecting to to the mount (no pads at this point. If this is good check brake pad fitment. They should easily go on by hand and be able to move around easily with little clearance. If not find where they are binding and clearance the pad backer to fit. I find I have to do this on cheaper pads nowadays. If all of this is good reassemble the rear brakes. Recheck to make sure there isn’t any binding. If there is then it’s more then likely a caliper issue.

[SteveP]

Thank you gentlemen. It looks like the rotor is centered in the caliper but the caliper seems to be at the end of it's sliding range. I'll disassemble every thing and start checking everything step by step as I reassemble. By clearancing the pad backer I think you mean grind some of it away. How much can you take out? Maybe a millimeter? I will also put some lube on the pins. The kit included some spring clips to install in the calipers but there was nothing in the instructions about using them and I didn't see where they would go. Are they used? Also, the pad kit included some bolts I didn't see a use for. Are they used for something?

[GFX2043mtu]

Only grind what is needed to make them freely slide and just fit in the mount. You don’t want lots of additional clearance, and I would say 1 mm clearance is way to much. Your looking at a fraction of that as you want them tight to the mount but loose enough to be able to float. Take a little off and try it, then repeat till it goes in and slides easily in the mount (make sure the stainless clips are in the mount when fitting pads. See below). The spring clips if they are what I’m thinking about are for anti rattle and go on the mount. They clip on the top and bottom of the mount and are sandwiched between the mount and pad backer. They are stainless and provide the pads a rust free surface to move on. They also have a spring feature that prevents rattling. Lastly pics of the bolts would help on determining which ones your talking about.

[CraigS]

I would pull the sliders out and maybe add more grease. This will also allow you to check that they do slide freely. Not sure which calipers you have but the most common ones need to have the piston rotated and pushed at the same time for them to retract if the emergency brake has been used. You might want to install the pads as a test w/o any of the spring clips. this way you can determine if they slide in and out freely (just looking at their thickness) or if the pistons have been extended.

[rich grsc]

If you can install the pads and calipers without have to force either in place, all is good.

[SteveP]

Since we in Washington are sheltering in place, I have lots of time to fool with the brakes. I didn't realize the pistons had to be rotated for full retraction. I'll try that too. Thanks.

[SteveP]

I spent today continuing my fight with the back brakes. Based on the good advice from the forum, I disassembled the brakes, added lube to the posts, bought a piston retracting tool and ensured the pistons were fully retracted, then I mounted the bare caliper and checked the rotor centering with feeler gauges. The kit came with shims to center the calipers and additional washers to supplement the larger shim. The instructions say the washers can be left out if necessary. Contrary to the instructions, I found it took additional washers to even the spacing on the lower caliper mounting point. I don't understand why it would take asymmetrical shimming to center the calipers when the part mating surfaces are machined at the manufacturer. Maybe I assembled something wrong but I don't know what it could be. Any ideas?
Before I put the brakes back on, I measured the torque to rotate the hubs. It's less than 10 ft. lbs. Then I put one brake on. It was a very tight fit and the pads had to be forced over the rotors. With this one brake on it took 40 ft. lbs. to rotate the hubs. I then looked at the pads. They have a thin, .025, plate loosely mounted on the back side. I took these thin plates off the pads of the last wheel. With the thin plates removed, the calipers fit over the rotors like I'm used to from changing pads over the years and it didn't take more torque to rotate the hub. So, what are the thin plates for? Do I need them?
Any ideas will be appreciated. I'm at a loss.

[CraigS]

Your caliper mounts should have equal thickness of shims at both positions. I just now noticed you have IRS so I am not sure which calipers you have. Stock Ford that came w/ your salvage yard IRS pallet? Provided by FFR? Do they look like this? And these (the red circles) are the mount holes you are shimming right?
https://live.staticflickr.com/65535/49696452023_fe982f3792.jpg (https://flic.kr/p/2iHviMH)Rear calipers 2 mod 1 (https://flic.kr/p/2iHviMH) by craig stuard (https://www.flickr.com/photos/152454123@N04/), on Flickr
You can leave those plates off the pads. They are there to help reduce noise but there are millions of cars w/o them. I 'think' what you may be dealing w/ is a stackup of manufacturing tolerances that are all in the wrong direction. If the calipers fit onto the car like you expect w/o those plates, I'd leave them off in a heartbeat. Save them though. It could be that w/ some driving and getting everything broken in, they could be installed later. I worked as a tech for most of my life so, if I were there and able to feel how much drag you have, I might say I think it's fine. But to be on the safe side, (dragging calipers overheat and often lock up the wheel til they cool) I am more comfortable w/ saying leave the plates off for now. The worst that could happen would be some noise once in a while.

[Railroad]

Any chance your master cyl push rod is too long? Do not know if this would affect the rear brakes more than the front on a single master cyl.

[SteveP]

Craig:
Thanks for the information on the plates, I'll leave them off. The picture you have is a picture of my brakes. They came from FFR. I am shimming where you indicated. My spindles are new Ford spindles from American Muscle. If you have seen the instructions, FFR has the builder cut a mounting ear off and bolt a laser cut mounting bracket onto the spindle. I did that but don't understand why the caliper needs to be asymmetrically shimmed to center the rotor. I added an AN960-8 washer to the stack on the lower mount. The aircraft washer is thinner than a hardware store washer, about .053, to center the caliper.
I really appreciate your input. I don't have much automotive experience and lack the confidence to just blunder ahead with out some experienced oversight. I want to avoid unintended consequences from my half baked ideas. Hopefully taking the plates from both sides will cure my problem. I'll be out to the shop in an hour or two, as soon as I get today's new snow shoveled.
Steve

[SteveP]

The push rod is free and not under any pressure when the brake peddle is not pushed. Also, I had the problem when there was no fluid in the system. The e brake cable is not attached. Good ideas, thanks for the input.

[initiator]

Hey Steve - you up near Bear Lake? Every year we'd come up US2 from Spokane on our way into N. Idaho.

[michael everson]

Make sure the little recessed area on the piston face is in line with the post on the back of the pads.

Mike

[SteveP]

We live just half a mile west of Hwy 395, about 5 miles west of Hwy 2 but we spend most of the summer at Priest Lake in North Idaho. Hope you can stop by for a visit. Maybe we will even be able to shake hands by then.

[SteveP]

Mike,
Thanks for the idea. I spend a few hours fooling with the brakes today and gave up because I ran out of ideas. Now I have something else to try.

[michael everson]

Sent you a PM
Mike

[CraigS]

Can you take a picture or 3 of your installation especially looking in at the edge of the rotor. I think you may not have enough posts yet to attach to this thread so email them to craigstuard at comcast dot net. I am still nervous about using different thickness shims. I think I made a small mistake in my picture w/ the red rings. I think your mating surfaces are actually the opposite side of those holes as indicated here by the green arrow.
https://live.staticflickr.com/65535/49700396636_9371cfc37b.jpg (https://flic.kr/p/2iHRwoh)Rear calipers 2 mod 2 (https://flic.kr/p/2iHRwoh) by craig stuard (https://www.flickr.com/photos/152454123@N04/), on Flickr
As you look at the calipers and brackets over all, you notice that most of the surfaces are as cast. There are just the critical surfaces that are machined. Example is red rings vs green arrow. The red ring side is as cast and the green arrow side is machined (I think as I can't see it). You may be looking at an as cast area when judging your caliper mount shims.

[SteveP]

Thank you for the interest Craig. As soon as I finish breakfast I'll head to the shop and get some pictures. FFR has instructions posted under parts for this installation, the 11.65 brakes on 2015 Mustang IRS. As far as I can tell, my installation is exactly like the photos there. Yesterday I experimented some more. When I loosen the mounting bolts one quarter turn or so, the rotors free up and turn with less then 10 ft. lbs. Loosening the bolts enough leaves a gap of .010 between the mounting surface and the shim. Even when I changed the shims around, I got the same result. Tightening the bolts closes the gap but also rotates the caliper a little as it pulls tight. I wonder if the slight rotation is the problem. I will also check to ensure the pins on the pad are in the recess on the face of the piston.

[SteveP]

Yahoo!!!!! After days struggling with my rear brakes, they work. After I followed the forum suggestions, CraigS called on the phone, helped analyze the situation and offered more good suggestions. Then a friend came over and we reassembled the brakes a piece at a time after taking the slider pins off so we could evaluate clearances as we went. It became apparent that the spacers and optional shims in the FFR kit were not enough. We doubled the number of washers used as shims and the brakes work perfectly. Thanks everyone who offered suggestions.

[initiator]

We live just half a mile west of Hwy 395, about 5 miles west of Hwy 2 but we spend most of the summer at Priest Lake in North Idaho. Hope you can stop by for a visit. Maybe we will even be able to shake hands by then.

Glad you got it figured out, Steve! That's a great feeling.

We had a place on Priest Lake until a few years ago. I spent part of every summer of my life up there. Our place was right next to Hunt Creek, between Cavanaugh Bay and Eight Mile.

[SteveP]

It's a great place, bet you miss it. We are in Reeder bay, North and east of Elkins. My kids and grandkids love it. Two grandkids are working at Elkins this summer.

[michael everson]

Have you got a solution for the parking brake cable? I had to remove the bracket that FFR supplied and countersink the hole and use a flat head bolt. I have extra bolts if you need them.
Mike

[SteveP]

Michael, I don't have a good solution for the interference between the pb cable and the brake mount bolt. When I asked Dan at FFR if there was anything more than ovaling the cable mounting hole he said no. I don't know how you would get a wrench on a flat head bolt in such a way to get enough torque on it. It is a really good idea because of the interference.
Can you give me a better description. Obviously FFR used the 12 point bolt because of the smaller head diameter compared to a hex bolt.

[MyBucketList]

Make sure the little recessed area on the piston face is in line with the post on the back of the pads.

Mike

Mike... very appreciative of this post in particular (as well as the entire string). We assembled our rear brakes and noticed the both sides were tight, but the passenger was particularly bad. After searching and finding this series, we pulled the brakes back off to check the piston positions. Sure enough, our PS was rotated slightly and the pad pin was bottoming out against the face of the piston instead of in the recess. Something really simple and easy to overlook (at least we did anyway). After correcting that and removing the clip-on plates on the back of the piston facing pad, we have even gaps on both sides and the rotors are now free to rotor as they should. Huge relief.

Thanks, so much. Now we one to our next challenge. :)