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Old 02-11-2020, 11:38 AM   #1
rfitzpatrick
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Default Wobble On Braking

When I take my '31 PicUp out for a drive, first one of the day, and I lightly press the brakes - I get the front end wobble. Have new tires, brakes all around, F-150 Ford Steering Box, new king-pins/bushings and the rest of steering is tight. Have already adjusted F-100 Steering Box per instructions. What I've noticed: It happens after setting over-nite. It happens ONLY when I lightly use the brakes. It happen ONLY with the brakes are in use, however, if I brake aggressively -- it doesn't happen. After I've driven for a few miles, the wobble seems to go away when I lightly brake -- it's as if after the brakes have heated, it's normal. What am I missing?
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Old 02-11-2020, 11:40 AM   #2
Ruth
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Default Re: Wobble On Braking

What kind of tires do you have? Maybe your getting flat spots from sitting?
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Old 02-11-2020, 11:52 AM   #3
rfitzpatrick
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Default Re: Wobble On Braking

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Originally Posted by Ruth View Post
What kind of tires do you have? Maybe your getting flat spots from sitting?



One year old Firestones, front end alliment last week, when (front) brake shoes were changed out again
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Old 02-11-2020, 12:04 PM   #4
Purdy Swoft
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Default Re: Wobble On Braking

Check the toe in . The toe in should be adjusted at 1/16th
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Old 02-11-2020, 12:49 PM   #5
5lugnuts
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Default Re: Wobble On Braking

When cold, the drums are acting as if they are warped. When hot, the drums are acting as if they are not warped. Could one drum be bent or slightly warped.

I had the reverse, wobbled when hot and brakes applied. Shoes were dragging causing drums to warp and wobble.
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Old 02-11-2020, 12:49 PM   #6
katy
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Default Re: Wobble On Braking

Check wheel bearing adjustment.
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Old 02-11-2020, 01:05 PM   #7
rfitzpatrick
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Default Re: Wobble On Braking

Toe-End done when front end alliment done, wheel bearings adjusted/inspected at brake (front) change done.



Warped Drums is item never thought about, nor looked into, Interesting. How do I check this?


This wobble only happens when my right foot is pressing the brakes

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Old 02-11-2020, 01:29 PM   #8
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Default Re: Wobble On Braking

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This wobble only happens when my right foot is pressing the brakes
Have you tried using your left foot?
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Old 02-11-2020, 01:49 PM   #9
rfitzpatrick
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Default Re: Wobble On Braking

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Have you tried using your left foot?



YES!! Same problem !!
This is a tough web-site

Last edited by rfitzpatrick; 02-11-2020 at 03:57 PM.
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Old 02-11-2020, 01:49 PM   #10
Fhane
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Default Re: Wobble On Braking

Grabbing or wobbling is sometimes experienced when a vehicle has been standing overnight. Linings tend to absorb moisture from the atmosphere, which causes slight swelling and an increase in diameter. It also increases the coefficient of friction. This phenomenon is often termed 'early morning sharpness'. These conditions may cause the brake to sprag leaving the shoes locked on when the parking brake is released. They can be released by moving the vehicle in the opposite direction. I can sprag latter if desired.
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Old 02-11-2020, 01:56 PM   #11
GPierce
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Default Re: Wobble On Braking

Quote:
Originally Posted by Purdy Swoft View Post
Check the toe in . The toe in should be adjusted at 1/16th
I had the same problem. New tires, new cast iron drums, F100 steering, new every thing in the front end.
First time I braked after sitting I got a wobble. Noticed I was scrubbing the front tires. Checked the toe-in, it was 7/16. Reset to 1/16, no more wobble.
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Old 02-11-2020, 02:00 PM   #12
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Default Re: Wobble On Braking

I can sprag latter if desired.[/QUOTE]




Plz do! I'm getting some very interesting/helpfull information. Taken a direction I've never considered

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Old 02-11-2020, 02:25 PM   #13
Fhane
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Default Re: Wobble On Braking

GRABBING AND SPRAGGING

A brake is said to grab when it has an unusually high shoe factor, making fine control difficult or even impossible. A spragging brake locks solid as soon as it is applied, i.e. it then has an infinite shoe factor. Obviously a spragging drum brake on a road vehicle would be disastrous, since wheel locking would follow even with the slightest application of the brakes. Fortunately, owing to the position of the resultant force, it is almost impossible to design a conventional drum brake, which will sprag under normal conditions.


Irregular lining wear or unbedded linings are the usual cause of grabbing. They result in tip (leading edge) contact, which brings the resultant force nearer to the pivot or abutment.
Irregular lining wear often results from repeated high deceleration stops. The high temperatures accelerate shoe wear and expand the drum so that the lining wears to a larger radius profile. Lining materials have a low coefficient of thermal conductivity, which prevents the shoes from reaching drum temperature and so, on cooling, the lining is left with a larger diameter than the drum. Tip contact is then inevitable.

IN SHORT. Riveted or bonded linings must be tight to the shoe to which it is att attached. Sprag effect is increased by loose rivets on the ends of the shoe and contemplated by not grinding the lining taper back far enough.
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Old 02-11-2020, 03:43 PM   #14
David R.
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Default Re: Wobble On Braking

Where I am, the humidity is always high. Sometimes we get a light film of flash rust on brake drums and rotors overnight. After fist application of brakes it is gone.
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Old 02-12-2020, 05:34 AM   #15
AustModelA
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Default Re: Wobble On Braking

I had a similar problem finally found a loose brake backing plate was causing my issue.

Last edited by AustModelA; 02-13-2020 at 05:45 AM.
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Old 02-12-2020, 07:57 AM   #16
Bruce of MN
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Default Re: Wobble On Braking

My car wobbled and the cause was a rotted rubber ball on the front wishbone. I went back to stock and that fixed it.
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Old 02-12-2020, 01:11 PM   #17
1931 flamingo
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Default Re: Wobble On Braking

see post #15.
Paul in CT
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Old 02-15-2020, 01:04 PM   #18
DHZIEMAN
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Default Re: Wobble On Braking

Several things in my case, Warped drums, extreme toe in worn steering parts!
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