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Old February 14th 18, 10:33 PM posted to alt.home.repair,rec.autos.tech,ca.driving
Clare Snyder
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Posts: 72
Default Vibration at 50 to 60 mph coasting in neutral after rear brake shoes

On Wed, 14 Feb 2018 11:37:48 -0800, ultred ragnusen
> wrote:

> wrote:
>
>> For years I've done it by trial and error - adjust the shoes to what
>> I think is right, then dry-fit the drum - too loose, pull it off and
>> adjust up. Don't fit? back it off and try again. Usually only a few
>> minutes. Then fine adjust with the brake spoon. ALWAYS check the
>> ebrake cables - and REPLACE if they are sticky - or you'll just end up
>> doing the job again. Also make sure you have the wheel brake
>> adjustment right BEFORE applying the e-brake -particularly if there is
>> any chance it has a self adjusting e-brake linkage. Do it on a Ford
>> Aerostar and you'll find out why REAL fast!! You'll spend half an hour
>> backing off the cable adjuster - - - -

>
>I am very glad you explained the error which I agree with you that it was a
>big make for me to ass-u-me that since the daily automatic adjustment keeps
>the shoes adjusted, that a manual adjustment would do the same.
>
>I also agree with you that there seem to be three major methods of
>determining the /initial/ adjustment, all of which use the manual star
>adjuster (and each of which has a flaw for noobs like I am).
>
>1. As you said, one method is to repeatedly dry fit the drum from far too
>loose to just a teeny bit too tight, and then, as a final step, back off
>the star adjuster a bit.
>
>2. A similar method is to put the drum on the vehicle once, and adjust the
>star adjuster until it just begins to feel friction.
>
>3. The third method is to measure the width of the drum and the shoes to be
>about 1/2 mm (20 thousandths of an inch) difference.
>
>Each method works, but all three have noob flaws:
>1. You have to know what to feel for.
>2. Again, you have to know what to feel for.
>3. You have to have the tools to measure drum width to reasonable accuracy.
>
>I thank you for helping me understand what caused the vibration at speed,
>which, as you said, I think it was that the shoes were too loose and the
>brake cable too tight. I don't understand exactly how but that combination
>caused a floating which caused the leading shoe to grab at speed which
>caused the wobble.
>
>It's a good thing this was found on a short test run, and not after long
>term damage might have been incurred.
>
>Thank you for your comprehensive explanation, where I apologize that I just
>don't understand everything you said about why the shoes were floating but
>that's my problem in comprehension and not yours in explanation.

When I was teaching the trade I would have had a brake unit in front
of me, and you face to face - which would make the "understanding" a
whole lot easier.

Next time you have a drum off, pull the emergency on part way and
then lookat what has happened to the position of the shoes. Check
closely before and after. then picture what would happen if the front
shoe was "picked up" by the drum and consider the e-brake cable to be
a spring. You'll get the picture.
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