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Brake noise; sudden loud 'BANG' and then normal
Topic Started: Jan 16 2013, 10:31 AM (502 Views)
Goose
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Driving my 3b yesterday as I approached a changing light, I hit my brakes pretty hard (not quite panic braking) and a loud bang and simultanious knock came from under the frame. I'd compare it to a good whalop with a 3lb hammer against a frame rail. I almost expected to have the pedal go to the floor and was even reaching for the E brake, but then it stopped normal. All I can figure is since my jeep had sat for a week, while it's been raining here, and the red light was my first stop from the driveway, maybe something was rusted open and slammed shut with the shoes against the drums. What do you guys think?
1963 CJ3B
Roaming the woods of WNC
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Lawrence
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Lawrence
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Maybe you left that 3 lb hammer laying under the hood and the heavy braking dissloged it.
Seriously look for anything loose like tools under hood.

Lawrence
1955 CJ3B
Family Tradition
Decatur, AL
~~"Seen it all, done it all, can't remember most of it"~~
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jeeper50
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ol' skool jeeper jeff
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Leaf spring bushings worn out?
In the land of the blind... the one eyed man is king
Texan at heart, Georgian by paycheck

'53 CJ3B, F134, 12v alternator, lockrights, Hot-Spark electronic module,11"self energizing brakes, Belleview winch, Beachwood summertop, OD color, built to honor all Veterans of this great country


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Goose
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No tools left behind and leaf spring bushings all new last year. I just took her back out after a visual inspection and it happened again, this time to a much lesser degree.
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Rus Curtis
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Goose,
You say it’s associated with applying the brakes. Do you fill any "kick back" or "pulse" in the peddle when you hear the knock?

Do you hear anything similar when accelerating from a dead stop? (I'm thinking something shifting back and forth here).

You said it sounded like a hammer on the frame rail. Have you crawled under and taken said 3lb hammer and tapped on various objects to try and replicate the sound? Each component will sound a bit different i.e. Engine block, frame, crossmember or exhaust.

You may also want to pull your wheels and inspect the brakes. As goofy as it sounds, something there may be loose and is moving like the wheel cylinder or anchor point.

Look closely at nuts and bolts. If anything has shifted you may see a tell-tale area adjacent to the backing washer or lock washer indicating a shift (that may not move when you wiggle it).

Inspect pedal shafts the same way - any signs of wear or shifting: Joints, pivots, fasteners, etc.

Read a story on the 2A Forum about an old time mechanic who tried to identify a knock. He crawled under and just sat there and looked. He touched and moved things but eventually found it.

You may need to lay under (or start with engine compartment) and look at everything and visualize what could move. Even if it sounds ridiculous, like engine mounts, battery hold down, loose jack rolling around in the tool box under the seat, stuck spring shackle, bad shock (bounce test on each corner for the last two), slack in the stay cable, (sorry but the list just keeps going), etc.

This is one of those puzzles. I'm interested to see what you find.
Rus Curtis
Alabama
'54 CJ-3B "Green Gruntt"
Bantam T3-C
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oldtime
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Noise occuring when brakes are applied does not = brake noise.
Could just as easily be associated with something in the drive train.
Such as a loose tapered axle shaft key, ring + pinion, or even the universal joints.
Visually inspect the leaf springs while your at it.
Then try to locate more exactly where the sound is coming from.
Currently building my final F-134 powered 3B .
Rock Crawler using factory parts from the Willys Motors era (1953-1963)

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Goose
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Thanks guys. Any way to visually inspect the axle shaft key? I'm not even sure what that is. I did have a guy rebuild my tranny last month, maybe he left something loose.
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Rus Curtis
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Goose,Jan 17 2013
07:34 AM
Any way to visually inspect the axle shaft key? I'm not even sure what that is. I did have a guy rebuild my tranny last month, maybe he left something loose.

key:
Pull the hub cap off, take the nut off and pull the washer off. The key is wedged in a slot on the tapered axle against the hub.

Also suggested is bad u joints. Usually, you hear these make noise when starting off from a dead stop or at speed when it knocks around. Still worth a look. Check all drive train security:

With brake full on (right foot brake pedal - not just the hand brake) and a bit of speed (you can use the throttle knob), let the clutch grab in 1st gear. Repeat with trans in reverse. You're looking for movement either in drive shaft, crossmember mount under transmission or engine mounts up front. You need to keep the vehicle from rolling when doing this and observe from OUTSIDE the wheel tracks! not from under the vehicle. Locking the wheels with the brakes will allow the different components to bind and hopefully show any worn or loose part. Moving from forward to reverse and allowing the clutch to begin to grab should magnify anything loose.
Rus Curtis
Alabama
'54 CJ-3B "Green Gruntt"
Bantam T3-C
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jeeper50
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ol' skool jeeper jeff
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Check the backing plate mounting bolts also. might have worked loose.
In the land of the blind... the one eyed man is king
Texan at heart, Georgian by paycheck

'53 CJ3B, F134, 12v alternator, lockrights, Hot-Spark electronic module,11"self energizing brakes, Belleview winch, Beachwood summertop, OD color, built to honor all Veterans of this great country


Kayaks- Hobie Revo 13, Hobie Outback 12' both ready for the salt...
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