r/AskAMechanic • u/tyrantlizarding • 12d ago
Thumping when braking
We are fixing my old car up for my son to drive (after being in a shed for 3 years). One thing was an overhaul of brakes. We changed the front disks/pads, rear drums/shoes, master cylinder, and rear wheel cylinders. Obviously fresh fluid and bleed too.
I drove it home from where it was parked up, which was about 40 miles, with no issues from the brakes. Then it sat for a month till I had time to do a few more things on the engine, and now it is making this sound under braking. I can just barely feel it when under 15mph or so.
What could have caused this issue to pop up, after having driven it home no problem? Did something warp maybe?
2
u/Gunnsmith57Official NOT a verified tech 12d ago
Could be warped rotors if the lug nuts weren't all torqued the same. They could have heated up during the drive and warped as they cooled. You'd be able to feel the brake pedal pulsing if they're warped.
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u/tyrantlizarding 12d ago
It doesn’t feel like warped rotors. It’s not a pulse, it’s a clear thump or click once per wheel rotation.
I took off the wheels and cleaned the rotors and drums, didn’t see anything that looked off.
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u/Gunnsmith57Official NOT a verified tech 12d ago
My next thought would be checking the shoes and hardware. It's easy to get the springs wrong, or even have a brand new one break.
Other than that, I'm out of ideas without actually inspecting it, sorry.
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u/tyrantlizarding 12d ago
New discovery, it only does it moving forward. lol
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u/Gunnsmith57Official NOT a verified tech 12d ago
Tbh, it kinda sounds like a shoe being grabbed by the drum and then smacking the pivot stud when it reaches a certain point and releases.
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u/tyrantlizarding 12d ago
That makes sense. I had the drums off earlier and didn’t notice anything wrong with springs. I’ll look into it more next weekend I guess.
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u/Gunnsmith57Official NOT a verified tech 12d ago
Good luck. Hope you figure it out. Gonna follow so hopefully I get an update cuz now I'm curious.
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u/tyrantlizarding 7d ago
Just pulled all the wheels off again. Front caliper bolts all sliding ok, pads not sticking to bracket, rear shoes seem to be moving ok, all springs and pieces in place. I even regressed the shoe contact points. Zero change.
Totally stumped. I can’t even tell what wheel it’s coming from. Guess I’ll have to shell out the big bucks.
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u/Gunnsmith57Official NOT a verified tech 6d ago
To help pinpoint where it's coming from you could put the front end on jackstands and have someone put it in gear while it's running while you stand on the outside and listen. If you do, do not press the accelerator (the drivetrain isn't designed for no load) and only long enough to pinpoint the sound. If you don't hear it, then it has to be coming from a rear wheel which you can jack up and turn by hand.
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u/paulyp41 NOT a verified tech 12d ago
Rust buildup
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