<VV>Brakez

[Tony Underwood]

At 05:32 AM 11/9/2006, Padgett wrote:

>>Yeah wet drums take longer to dry out than wet disks
>
>So soon they forget. The idea is to ride the brakes lightly *when 
>going through the puddle* and they will stay dry. If it comes up too 
>soon, ride a little afterwards and they will dry off quickly.
>
>A good set of drum brakes will stop just as fast as disks, they just 
>need occasional adjustment to keep working properly. In general, 
>disks do not need adjustment, dissipate heat more quickly, and are 
>more resistant to wet conditions. They are also considerably easier to work on.
>
>But the main advantage to drum brakes is that they are 
>self-energising and usually require much less pedal pressure than a 
>disk brake. Power brakes were "optional equipment" on most cars 
>untill disks became popular and back in the day, the master cylinder 
>for manual brakes had smaller diameter cylinders than ones for power 
>brakes to reduce the effort. A lot of the pedal effort can be 
>reduced with the right master cylinder at the expense of a bit more travel.



Many people still assume that disc brakes require power assist or the 
pedal pressure to make them work would be unacceptably high.   This 
is not the case.


What has happened is that people seem to have become accustomed to a 
feather-light (relatively) brake pedal.    I never much liked it; the 
power brakes on some cars back in the day were so ambitious that if 
you had been used to manual brakes and you sit down in something like 
a big Chrysler Imperial or the like, you lock 'em up at the first 
intersection.    Power brakes were simply overkill back 
then.    Today it's much better, and there's more road feel to 
today's power brakes than the stand-u-on-yer-nose power brakes of yesterday.

Now:   I know from experience that with those earlier power brakes, 
you could remove the master cylinder booster and hang the MC back in 
place with no power assist and the brakes would still stop you just 
fine, with no horrendous pedal pressure... it simply didn't stop you 
with as little pressure as the weight of a shoe on the pedal.    Use 
a manual brake MC with discs and they stop you pretty much like 
manual drums, with perhaps a "little" more pedal pressure, depending 
on the design of the calipers and the size of the bores.  You *will* 
get more pressure on the pads against the rotor since the pistons in 
disc brake calipers are much larger than the pistons in drum brakes, 
thus brake fluid pressure against the disc brake piston is greater, 
thus more pressure on the pads against the rotors.     In the case of 
a particular '66 intermediate I'm familiar with, it had the optional 
4-piston Budd disc brakes (and a power booster which wouldn't allow 
you to remove the driver side valve cover if need be without removing 
the booster) along with a SINGLE BOWL master cylinder (remember, this 
was a '66 vehicle).   When the power booster (and it's "erector set" 
lever and fulcrum offset mechanism to move the power booster up and 
away from the valve cover) finally failed and started sucking wind, 
it was learnt that there ain't none available unless you special 
order the damned thing, and it was expensive (anything for a 426 
Mopar was expensive) along with not being all that great to begin with.

Removed the booster, mount the MC in place sans power assist, and 
those disc brakes worked pretty much the same as any other manual 
brakes and that's how the car remained until it was sold and went to 
Jersey, nobody being the wiser because the brakes worked 
OK...  except for the leaks in the calipers which were an ongoing 
issue, still so to this day with some of those 4-piston Budds.

The point was that if you have respectable size piston bores in the 
calipers and it's set up right, you *Can* get respectable performance 
from discs without a power booster.

One more note:    The V-8 powered later model AMC Gremlin-X with disc 
brakes did NOT have power assist from the factory.   Again, there was 
so little room under the hood, and the power booster would not have 
fit because of the engine being in the way.

The Gremlin stopped just fine, thanks, with NO booster to power its 
discs.      There seems to be an acceptance that if you run disc 
brakes they must have power assist.  This is simply NOT the 
case.   ...also had a Fiat  1500 Cabrio sports car with discs and no 
power assist, stopped like a champ.



tony..