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  •  » Rear disc question

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    3/17/2014 6:38 PM  #1

    Alan
    I FYI 24-7

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    From: Axtell KS
    Registered: 4/03/2013
    Posts: 478

    Rear disc question

    My rear brakes do not seem to be square with the rotor. They are wearing on the outside part of the rotor on the outside and the inside part of the rotor on the inner. The PO put them on and as near as can find out they are off of a early 90s lincoln or a grand marquis. They are mounted on a 68 cougar 9" rear end. I can't see anything wrong with how they are mounted. Both sides are doing the same thing. Does anyone know of a way to square them up, or do I just let the pads wear in to the rotor. They might have about 1000 miles on them so far.

    67 Coupe, 5.0 EEC IV Fuel injected. T5, 3:70 rear
     

    3/17/2014 7:14 PM  #2

    GPatrick
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    Registered: 4/01/2013
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    Re: Rear disc question

    On this link I was reading step 5 about grinding the axle flange.  If that step was skipped, the bracket may not be sitting square even with the bolts cranked.  I would mount the caliper without the pads and use a straight edge to check the caliper to rotor squareness and to ensure that the caliper is centered around the rotor.  I think that continued use is putting a side load on the piston which will make it more prone to wear and leakage.  http://ynned.tripod.com/crown_vic_discs/index.html  If the PO didn't do the job correctly, I would also be concerned about the bearing spacers as well.  Maybe a picture of the caliper without pads taken straight-on would help.  Others on the site have much more experience with this swap.

     

    3/17/2014 7:33 PM  #3

    GPatrick
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    Re: Rear disc question

    Here is a thread on some of the concerns with the swap - http://www.stangnet.com/mustang-forums/threads/crown-vic-rear-discs.717933/

     

    3/17/2014 7:59 PM  #4

    Alan
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    From: Axtell KS
    Registered: 4/03/2013
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    Re: Rear disc question

    GPatrick wrote:

    Here is a thread on some of the concerns with the swap - http://www.stangnet.com/mustang-forums/threads/crown-vic-rear-discs.717933/

    Thats a lot of reading, I do have the bearing spacers installed so the play in the axle is taken care of. I will pull the pads out of the calipers and install them tomorrow nite to see if they are centered.
     

    67 Coupe, 5.0 EEC IV Fuel injected. T5, 3:70 rear
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    3/17/2014 8:45 PM  #5

    MS
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    From: Canyon Lake, Texas
    Registered: 1/24/2013
    Posts: 11,728

    Re: Rear disc question

    Are the brackets bolted to the exterior of the axle housing flanges or the interior side.  The outside is the only suitable place to mount them because it is machined so it is square to the axle centerline.  The back side is sometimes pretty uneven.  Not sure what they used for brackets, but I would not think you would want to leave them mounted at an angle like that.  It is putting uneven forces on it  that try to bend the caliper bracket when you apply the brake.

    Money you enjoy wasting is NOT wasted money... unless your wife finds out.
     

    3/18/2014 5:22 PM  #6

    Alan
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    From: Axtell KS
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    Re: Rear disc question

    MustangSteve wrote:

    Are the brackets bolted to the exterior of the axle housing flanges or the interior side.  The outside is the only suitable place to mount them because it is machined so it is square to the axle centerline.  The back side is sometimes pretty uneven.  Not sure what they used for brackets, but I would not think you would want to leave them mounted at an angle like that.  It is putting uneven forces on it  that try to bend the caliper bracket when you apply the brake.

    The brackets are on the exterior of the axle. The calipers look square when I mounted without the pads in them. The calipers ride on a smooth bolt shown in the picture and have about 3/16 of rubber all around that bolt so they have a lot of play in them.
    The caliper can slide about 7/8" back and forth on the shiny bolt

    I don't think the caliper bracket is going to bend from uneven force because the caliper can move alot in the rubber mount.
    I noticed ultrastang had started the one thread that gpatrick had shown. I was wondering if he had seen anything like this before.
    I do have the bearing spacers and the centering rings installed that he had talked about in that thread.

    67 Coupe, 5.0 EEC IV Fuel injected. T5, 3:70 rear
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    3/18/2014 5:45 PM  #7

    GPatrick
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    Re: Rear disc question

    Are you using wheel spacers?  Is there any chance that the rotor itself is not sitting flat against the axle flange?  If the OD of the axle flange is too large, the rotor may not sit flat.  If you were to crank down on the lugs it could potentially cause the rotor to "mushroom" for lack of a better description.  This distortion would cause the OD of the rotor facing the wheel to move towards the wheel causing the pad to hit the rotor on the OD of the wheel side and the ID of the inside.  I think it must be more simple than this but it is something to look at.  You could prove/disprove by installing nuts on the studs without the wheel and spacer if a spacer is used and seeing if the rotor distorts when tightening.  Or, you could just mount the rotor on to the axle with a little clay on the mating surfaces to see if is fully compressed.  You may also be able to simply see if the rotor was able to be rocked.  You can see what appears to be some fretting corrosion around the ID of the rotor where it mounts to the axle flange which would be consistent with some metal to metal surface movement if the rotor is not sitting flat.

     

    3/18/2014 6:16 PM  #8

    Alan
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    From: Axtell KS
    Registered: 4/03/2013
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    Re: Rear disc question

    I am using wheel spacers, but I am thinking that what you described is a very long shot at what is happening. Possible, I guess. I do torque the spacers to 100 ft lbs when I install them. I  will install them tomorrow and see if I can see any movement. The spacers are flat on the back, so I can't see how the outside would force the (mushroom shape).

    67 Coupe, 5.0 EEC IV Fuel injected. T5, 3:70 rear
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    3/18/2014 6:30 PM  #9

    GPatrick
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    Re: Rear disc question

    If they are not the same OD as the mounting face of the rotor, they would potentially pull the rotor in at the center if the rotor is not sitting correctly on the axle flange.  If the OD of the axle flange hits the radius of the rotor mounting surface, the rotor mounting face will have a gap between it and the axle flange.  I know that this is an issue with some of the front brake conversions where the OD of the drum brake flange is larger than rotor mounting surface.  The OD of the drum brake flange must be turned down or the rotor will not sit flat.  In the case of the rotor you are using, because of the drum parking brake it may be more likely to mushroom or distort.  It is remote but I am just trying to think what could cause the pad to hit unevenly.  If the brake caliper is square and true to the axle centerline then about the only other thing it could be is the rotor itself.  As I said, it is probably something much more basic.  If you look at you bottom photograph in your initial post you can see the coloring of the mounting face is different between the OD and the ID which can mean that only a portion is in contact.  Could be paint overspray too, I suppose.  Anyway, let us know what you find.

     

    3/19/2014 7:02 AM  #10

    Bolted to Floor
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    From: Houston, Texas
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    Re: Rear disc question

    Your first sentence says it all. It’s not square. The caliper mounting bracket needs to be on the same plane as the face of the axle shaft. To me, the best reference point is the flat spots where the caliper mounting bolts connect to the caliper mounting bracket (white arrows). Also, the slides on the caliper mounting bracket (yellow arrow) that caliper ride across as the brake pads where should form a right angle to the face of the axle shaft. How about some pictures of the back side showing where the caliper mounting bracket is bolted to the axle?


    John  -- 67 Mustang Coupe 390 5 speed
     

    3/19/2014 4:37 PM  #11

    MS
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    From: Canyon Lake, Texas
    Registered: 1/24/2013
    Posts: 11,728

    Re: Rear disc question

    Not sure this is even relevant, but I just did a complete brake job on the rear of my RAM 1500.  It has discs and I installed new rotors and pads.  The old stuff was worn very evenly with no tapered pads or anything.

    Since you made this post, I have been keeping an eye on the wear pattern.

    They are showing a pattern very similar to what you are seeing on your disc brakes.  Maybe it is a big concern about nothing, as I am certain the truck's parts were working fine previously and were reinstalled properly.

    So, unless that wear is really severe, you might just want to do a WAIT AND SEE thing...

    Money you enjoy wasting is NOT wasted money... unless your wife finds out.
     

    3/19/2014 7:09 PM  #12

    Alan
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    From: Axtell KS
    Registered: 4/03/2013
    Posts: 478

    Re: Rear disc question

    I think i have figured out what is going on. The pads have an anti rattle spring on that pushes only on one side of the caliper. With the surface rust on the rotors from sitting a couple of years, the pattern on the wear is really pronounced. I looked at this for several hours, tearing down and reinstalling everything and it comes out the same. When I looked at the pads, I can see the outer pad is further away from the mount than the inner from the spring pushing it away. I think they will wear in, it just hasn;t had enough miles and wear yet.
    The spring is only on the outside so it pushes the whole caliper out of square, being that it floats on the rubber mounts.

    67 Coupe, 5.0 EEC IV Fuel injected. T5, 3:70 rear
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