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  •  » Rear disc brake problems

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    7/18/2013 3:12 AM  #1

    67CougarTom
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    Registered: 7/07/2013
    Posts: 5

    Rear disc brake problems

    I will start this off short. I had a long story that I thought I posted, but it never showed up. I am very new to this so I will try again. In short, I have a 67 Mercury Cougar that I had a Ford 9 rear and 31 spline axles and added rear disc brakes. Everything is fine but the brakes. They are Wilwoods and wow do they run hot. The place that did all the work left everything stock. Long story short, when I got home after the first drive I had no front brakes. The rears were very hot and thus my adventure has begun. We removed the valve at the rear axle and added a proportion valve. Now I have front brakes, but the rears still get much warmer than the fronts. The brakes feel good, but the rears are much hotter than the fronts. The car had original front disc, and rear drum. I replaced the MC a couple years ago. We pulled the MC a couple weeks ago looking for a residual valve. There was none. What else could be causing the brakes to be so much hotter.  

     

    7/18/2013 4:38 AM  #2

    GPatrick
    Senior 24-7 FYI Addict

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    Registered: 4/01/2013
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    Re: Rear disc brake problems

    Did some of the cars have a residual pressure valve in the rear of the line rather than at the MC?  How do you have your e-brakes cabled up?  Any chance that cables are causing the e-brakes to actuate when the car is sitting on the ground or over bumps?  Could you have bearing issues that are heating the rotors?  And last, are the calipers truly centered over the rotor or are you rubbing on one side?  Sure sounds like a RPV but I fought a incorrect cable install on a car as well.

     

    7/18/2013 6:36 AM  #3

    67CougarTom
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    Re: Rear disc brake problems

    Mine had one in the rear by the axle. It was for the rear drum brakes.The E-Brakes are brand new, they were part of the install. They are located on the inside of the rotor. They are sort of like a rear drum. I had to have the driverside rotor replaced and the passenger side turned because they were warped. Keep in mind, that this was with about 35 miles on them. I believe they were warped from the start. They are Wilwoods, but that does not mean that they were good. In fact, I even recorded video of the rotors in motion and sent to Wilwood and they have yet to get back in touch with me. The shop that did this job replaced the driver side rotor dur to it being so bad and had the passenger side turned. Its much better, but still too darn hot to me. I can put the car up on a lift, put it in gear and run it for 30 minutes not touching the brakes, and everythying stays cool as can be. I believe they have the E-brake correct and the caliper centered. I have the proportion valve adjusted as far as it can to allow the front brakes to do as much of the work as possible.

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    7/18/2013 6:46 AM  #4

    MS
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    From: Canyon Lake, Texas
    Registered: 1/24/2013
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    Re: Rear disc brake problems

    It sounds like you installed an adjustable proportioning valve in the rear brake line.  Is that correct?

    Did you remove the  original proportioning valve from the rear axle?  If not, then you have created a situation where the pressure is contained becaue of two valves.

    Another thing to look for is the master cylinder or booster output shaft length.  If it is adjusted too long and is not letting the master cylinder return to its static position, then it will hold pressure.  Since the rear brake portion of the master cylinder gets pressureized first, the rear brakes would drag if that is the problem.

    Only other thing I could think of is the parking brakes adjusted too tight, but when you said they did not get hot running on a lift without touching the brakes, I discounted that idea.

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

    7/18/2013 6:53 AM  #5

    67CougarTom
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    Re: Rear disc brake problems

    Yes it is installed to the rear brakes only. Yes that valve that looks like a small cigar in the rear of the car has been removed I did that right after I got it home. I was surprised the shop left it on, and did not plumb in a proportion valve. The shaft on the master cylinder is the original one it came with. Perhaps it is too long? I did not know that they can adjust. How is that done? Makes sense. Or what length should it be? 

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    7/18/2013 8:42 AM  #6

    MS
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    From: Canyon Lake, Texas
    Registered: 1/24/2013
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    Re: Rear disc brake problems

    Is it power or manual brakes?  The manual rod is not adjustable, but if the master cylinder has a 1/2" deep hole in it instead of the normal 1" deep hole, it could be pushing the pedal back farther and limiting the ability of the mc to return to static.  If that is the case, it would also present a dangerous problem of the rod being able to fall out the back of the mc.

    To test for this problem, simply back off the master cylinder attaching nuts a couple of turns and see if the problem persists.  Unless someone made a serious blunder, that is usually enough to get clearance.

    IF it has a power booster, you remove the mc and adjust the output rod length to fit the mc, with just barely a bit of clearance.

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

    7/18/2013 10:15 AM  #7

    67CougarTom
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    Re: Rear disc brake problems

    It is power brakes. I will try the test you suggest. It all makes sense to me the way you are describing it. The first chance I get I will look into it. The "top end " project is now underway. It may be a little while before we get back to the brakes. But I will update my findings with high hopes that this is the solution. If it does solve the problem others will need to know this most valuable information!!!  Thanks so much for your time.  

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    7/18/2013 11:39 AM  #8

    McStang
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    From: Benicia, CA
    Registered: 4/01/2013
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    Re: Rear disc brake problems

    Just thinking out loud: have you checked the rotor runout on the rears? How is the prop valve adjusted? I would run it all the way down to the minimum pressure to the rears setting as a starting point - most valves have a range of somewhere around 60% to 100% from fully 'closed' to fully open. At full open you might be doing a lot of your braking with the rears before the fronts get a chance to really engage, which you might not really notice so much if you've only been driving around town a little bit.

    (Pinto!)
     

    7/18/2013 11:21 PM  #9

    67CougarTom
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    Registered: 7/07/2013
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    Re: Rear disc brake problems

    Thanks for all the help.I am going to check a few of the suggestions as soon as I can. I am banking on the problem being the shaft. I have already adjusted the proportion valve several different ways, and it makes very little or very unnoticeable differences. I will post something to this as soon as I'm able to get back into it. again thank you very much for your time and effort

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