73-87chevytrucks.com
73-87 Chevy _ GMC Trucks => Brakes, Frame, Steering & Suspension => Brakes and Braking Systems => Topic started by: ehjorten on June 03, 2019, 09:23:30 AM
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Tore into the rear brakes on my Crew Cab. I had redone the brakes, but before the LS swap the Driver's side Rear was dragging heavily and would get hot! I would dial back the adjustment and it was just like it was over-adjusting! I couldn't understand why it would keep adjusting tighter and tighter. I have never had that happen before. The only thing that I could find was a little bit of weeping brake fluid on the forward cup of the wheel cylinder. So...I replaced the wheel cylinder. I had replaced it when I did the brakes about 30k miles ago.
The secondary shoe was cracked in two places across the rivets and there was some missing lining material. I can only guess that that happened because of the heat and was not a cause.
(https://lh3.googleusercontent.com/DdEhKvfNA4eTW4i3I5GwPcVc867epYVi2F7SyJnDrdTwgHXreA8_PSziQdWeJO7RP4LH_RO-K9VC1nPUDATnipdClCBtAwcsSGlJHfvY7vfVWPh7dfXCyVCZrwPENzXGRUgbwmYKuR5erJhjVKFUpQnJuOQXGoP2j8vLuoc2VlBoCtAOTCvWqER_gmDsgXtHvXNUHV82tmN-YPpfttCsy4ISQKb7v2ejrEzpoSOgqcIL_XP_S1megP2pgFUoNvotN5tfTOQECV-Eps9JsqrBfHDZLJ2v2Fz1mSFfXjBX1BQXkkRuvMR7ZzQqwgPthNx-LIMtutN9rJVE599WO63sxFKASpUJGbzMM-ITK3VzHTiTSIfC4EWVgDgTSHQhWuMpFg0fU3o7HSIeTNWKDt2nV_nqlNaZE3f0JrefC0zn9g5Ohr1jpker73-iINZoYZwDf77HXoXzzHzJa06BBemPB41fxo2gFtBpzxvE1RuJLzMjm4rv7EKe1TS2GhRk9onqcKBP4bC64KX1f6IjQnK1cOQ7U-FqinoB1_cEIv3M3PDnjR38pyobxNxA7BLXClIrXgr2-cbE_kZ4uYLpi1ntFgu_p2FUqm67ry8VrVcwC8BOo44hn0tTEqInz4kbmV8P0RvUJWCqcdv-TT2QcQi9nxzYN47Dg6jevZ_SoY2jwp7uN5pT3yfS9T6wKClHgPvFE6lhkxrHtdoGKF0HCEKJuIu5=w636-h1129-no)
Brakes Redone!
(https://lh3.googleusercontent.com/P0wdYHgUk1KFtBxidCyC62FIxL1izK_KKlxKbqoQRe-p29T4G3Be4vdcZivQ9AjcCOTf6moPUAXaPTninReRUGTelVHvTltHvREkfCJq7ApSHVDFnNzj1tyNLIY0paOU069BfL_tG-oRurRytwVpWc9ABF8qFJSRhf6z-Lve5SXNwfTU-7KXTuza5j4nySCdKHWa4r7DstX6cqdUk-CRIxfw2ohHgI1qf7wZxLVesiT4JIKLQcfgzvDeMhcfS3opDTlofDyH7DtOlZaulcuSPpF1g1V-HYnn8YLmYNCKMkEngEEHjH3DIM0yp5pg22QMW2L2_KK4vZPVbsD0CjB981GUO-A4Pi1ZP1niXYOzyT40Vt9XqnQOhd2lFYCoEyKUrjYxskke2vpxsQA6En5bV-OdjbI2UyWNYVNXdDLOy4Wu4nF0z7CxIyxyrT2q9wsr-umEo9qlckECkqUOqrLJTmPfjK8GD-uPl_LQe7Rc7rX97QsHlrbo5INWj12RlU_VRgBR-5JjxzMsHrqahJUAbmSoPSCj0HiR8QPaLLqIzseb_tVxMqv03yEYbh4w4tQykOKviDlhpHK_8Snn-9I_UabnMl2IVXXcvqsH6NbpONMxg8MdkgayEorlvANb2aHOFUhmCU5UJ2NiII9Bp_a810nU-Lu5v_C7vEW5i3vD_Zw5dAq3y1fOZmfGbxPX5pgL9LjURIZwB1CwF7LcpytbjL3J=w859-h1129-no)
My guess is that the leaking on the primary shoe side of the wheel cylinder was causing some uneven application of the brake shoes, that was activating the adjusting lever and slowly ratcheting the star-wheel more than it should have been. I have never had something like this happen before.
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Wow, that is really bizarre.
Normally the star is only moved as the result of reverse torsion on the entire assembly.
But I get your theory; maybe the shoe would grab and release, causing the assembly to oscillate between forward and reverse torsion.
Not a usual suspect, but I would have the drum checked out too.
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Drum and bearings were brand new when I last did the brakes about 30k miles ago. Drum was pressed-on, new bearings and races inserted, and a light clean-up pass was taken on the drum to true up the braking surface! The drag from the shoes has always been nice and even.
The drum brakes that we have on our vehicles (Duo-Servo Drum Brakes) automatically adjust when the brake linings wear down to a certain point that when you actuate the brakes and the shoes come off of the top anchor pin, they rotate enough from the spinning action of the drum and the friction between the linings and drum. I am thinking that if one side was not being pushed off of the anchor the same as the other, then it would look like there was more distance between the linings at their resting point...which would activate the star wheel. That is all that I could find in there was that brake fluid that was leaking from one side of the wheel cylinder. Prior to re-doing the brakes everything worked fine, and the passenger's side still does work fine.
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Was there enough fluid leakage to actually reach the shoe? Because of the rotation of the secondary shoe away from the anchor pin (CW on the driver side; CCW on the passenger side), which more effectively tugs on the adjuster levers, self-adjusters are more apt to tighten when backing than when moving forward. Do you consistently turn the steer wheels in the same direction while backing and then braking, for example, out of your driveway or parking spot at work, etc? This can result in differential over-adjusting of one rear brake, left vs right.
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(https://lh3.googleusercontent.com/DdEhKvfNA4eTW4i3I5GwPcVc867epYVi2F7SyJnDrdTwgHXreA8_PSziQdWeJO7RP4LH_RO-K9VC1nPUDATnipdClCBtAwcsSGlJHfvY7vfVWPh7dfXCyVCZrwPENzXGRUgbwmYKuR5erJhjVKFUpQnJuOQXGoP2j8vLuoc2VlBoCtAOTCvWqER_gmDsgXtHvXNUHV82tmN-YPpfttCsy4ISQKb7v2ejrEzpoSOgqcIL_XP_S1megP2pgFUoNvotN5tfTOQECV-Eps9JsqrBfHDZLJ2v2Fz1mSFfXjBX1BQXkkRuvMR7ZzQqwgPthNx-LIMtutN9rJVE599WO63sxFKASpUJGbzMM-ITK3VzHTiTSIfC4EWVgDgTSHQhWuMpFg0fU3o7HSIeTNWKDt2nV_nqlNaZE3f0JrefC0zn9g5Ohr1jpker73-iINZoYZwDf77HXoXzzHzJa06BBemPB41fxo2gFtBpzxvE1RuJLzMjm4rv7EKe1TS2GhRk9onqcKBP4bC64KX1f6IjQnK1cOQ7U-FqinoB1_cEIv3M3PDnjR38pyobxNxA7BLXClIrXgr2-cbE_kZ4uYLpi1ntFgu_p2FUqm67ry8VrVcwC8BOo44hn0tTEqInz4kbmV8P0RvUJWCqcdv-TT2QcQi9nxzYN47Dg6jevZ_SoY2jwp7uN5pT3yfS9T6wKClHgPvFE6lhkxrHtdoGKF0HCEKJuIu5=w636-h1129-no)
Incidentally, this type of friction material failure can also result from improper curing during manufacture.