Re: IML: a brake answer or two

[Kenyon Wills <imperialist1960@xxxxxxxxx>]

--- Joe <joestill1@xxxxxxxxxxx> wrote:


> 
> 1)  After the rebuild, I have a very firm brake
> pedal, which is good.  However, I don't have much
> stopping power without pumping the pedal.  I suspect
> I didn't get the brakes bled correctly because if I
> am reading the stuff on the site correctly and based
> on past experience, this is classic "air in the
> lines."  Correct?  Missing something here?
> 

Air in lines = squishy pedal
Pump pedal = better response = air in lines being
compressed so that it progressively responds better. 

Solution:  Bleed brakes more and get the last drops. 
You've likely forced them out to the end of the lines
by usage, so should be comparatively easy.



Poor stopping response = not as much friction as
needed/expected.

Could be poor pressure and/or could be that your brake
shoes need to "bed" into the drums.  This happens with
use.  In the old days they had machines that would
"arc" a shoe so that it's curvature matched the drum
as closely as possible before installation.  This
meant that the shoe was already about the right shape
and got maximum surface area contact quickly - stopped
to its best ability soonest.

Your shoes were not arc'd, I'll presume?  If so, then
you have a smaller portion of the shoe touching the
drum.  Use them, wear the shoe down so that it matches
the shape of the drum face, and you get more surface
area.  Shoe can be a smaller circumferance and have a
spot in the middle that needs to wear down or can be a
larger circumferance and have the outside edges
hitting, with a "low" spot in the center.  

Either way, you'll have to wear down the high spots
till everything matches.  Regular use will do it, or
you can be aggressive and drag the brakes or whatever.
   DO NOT PUT THE CAR AWAY WITH ULTRA-HOT SHOES - they
will transfer their heat into the drum and yeild
hard-spots that effectively ruin your drums - this
goes for any time that the brakes are used hard - let
them cool BEFORE parking the car!  Always.

Betcha it's a combo of air and shoes that need to bed.
 


> 2)  Sort of not related to the master cylinder
> replacement:  When I pedal the brakes, especially
> stopped at a light, engine idle gets more rough. 
> Again, if I am reading the "stuff" on the site
> correctly, there is a vacuum leak somewhere, likely
> at the brake booster, possibly at the check valve,
> also possibly somewhere else in the vacuum system. 
> Vacuum leak causes poor engine idle, correct? 
> Missing something here?
> 

Your booster is actuated by vacuum from the manifold
using that big, black hose connecting both, right? 
Imagine poking a hole in the tube so that it sucked
air - it would instantly drop air straight into the
manifold, diluting the air/fuel mixture, and causing a
change in how the engine was being fed.

Betcha there's a leak.  Take your booster hose off. 
Plug it.  Run the car and press the brake.  No change
means it's the booster.  Change present from the
get-go means that it could be a bad hose or a bad
plug?  

-Kenyon
 

Kenyon Wills
 
 






















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