Brakes

[gary j zingle]

Date: 2 May 2000 00:26:15 -0000

"Boy! =

First there is no correlation between pedal travel and
pressure to the rotor. None what ever. Pedal travel in
its simplest form determines how FAST the caliper
can apply force to the rotor."

To sorry to have to disagree:

1) - The smaller diameter of the master cylinder the
more pedal travel and the less leg pressure required
to create the same amount of hydralic pressure.

2) - The larger the diameter of the wheel cylinder or
caliper the more pressure will be applied to the friction
material for the same amount of hydralic pressure.

In conclusion you can reduce the leg effort/increase
the braking by either reducing the size of the master
cylinder (theory only, I am not recommending this) or by
increasing the diameter at the wheel (within the limitations
of volume etc.)

Regards

Gary Zingle
1973 GMC 26 foot

FORCE to the rotor is a function of:

1. Contact area between the pad and the rotor =

2. Coefficent of friction between the two materials

3. PRESSURE in pounds per square inch delivered to the caliper piston

4. Area of the caliper piston

Secondly the vacuum booster reduced the amount of force necessary to appl=
y
pressure to the master cy linger. Nothing more or nothing less.

Arch thats my opinion for tonight.

 

[gary j zingle]

"The whole point of my original question was to try and find out why =

people were going to an 80 mm caliper. By doing so they will increase the=
=

pressure to the front pads, but at the expense of pedal travel and the
ratio =

of pressures between the front and rear brakes allocated by the
proportioning =

valve. Having no experience with this conversion, and VERY interested in
safe =

brakes, I want to hear what everyone's experiences are."

Oh so you want the whole story do you?

When I went to the larger calipers on the front (about 30% larger surface=

area)
I also went to the larger rear wheel cylinders (1 1/16 as compared to the=

stock
15/16 for an equal increase in surface area)

Intended result was a 30% reduction in pedal pressure (prior to the chang=
e
I couldn't skid the wheels even though I have a strong leg).

The 30% increase in pedal travel was acceptable to me.

Although I would like even more brakes or even less pedal pressure
the results have been in the right direction.

Seems to be working for me

Regards

Gary Zingle
1973 GMC 26 foot

 

[david l greenberg]

> I did the 80 MM front and the 1 1/16 front bogie. It was ok but no
> home run. The sensitized booster and combi valve made a big difference.
I
> dont think it was the combi valve since I still cant lockup the front
> brakes.
>
> Take Care
> Arch

I really hesitate about getting into a technical discourse on things like
how braking systems are supposed to work, but caution to the wind!

Is the objective to see if the brakes lock up as a test to see if they
are functioning at full potential?

It would seem from my primitive logic, that locking up the brakes is
really the last thing one wants to do when faced with the need for panic
action. Once the brakes are locked up the coach will simply slide along
the ground. Is this reasoning faulty?

I am not challenging those whose experience and knowlege may be different
from mine but ................?

David Lee Greenberg
GMC Motorhome Registry
Dedicated To The Preservation Of The GMC Classic!
www.gmcss.com/registry.htm

 

[dave1]

>It would seem from my primitive logic, that locking up the brakes is
>really the last thing one wants to do when faced with the need for panic
>action. Once the brakes are locked up the coach will simply slide along
>the ground. Is this reasoning faulty?

You are correct. But maximum braking occurs at the point just before the=20
wheels lock up. So the goal is to be able to reach that point without being=
=20
superman standing on the peddle. Its also a good idea to have the fronts=20
lock up just a bit sooner than the rears. The idea being that you will feel=
=20
the skid in the front and lighten up on the brakes just before the rears=20
let loose of the ground and you fishtail.

The center of mass wants to be in front of the center of deceleration. If=20
the front wheels are holding and the rears are skidding the center of mass=
=20
will change places with the center of deceleration. Not a good thing...

Dave
Ann Arbor, MI.
73 Sequoia (26'/455/HEI/TBI/160=B0/3.42)

 

[blank]

Interesting logic, but counter to my understanding of the physics involved.
Once a tire starts to slide on pavement, you've lost control of that contact
patch. If the rears lock first, you still have steering control. If the
fronts lock first, you've got an E-ticket ride coming.

To my knowledge, all current production cars proportion the brakes to apply
the rears first and bias the system so the rears lock first. Racers usually
try to get simultaneous lockup of all four in the attempt to get maximum
braking on all four corners before any tire starts to slide.

Not saying I can't be wrong on this, but I've never seen it recommended in
print before now to have the fronts lock first.

Patrick

>
> Its also a good idea to have the fronts lock up just a
> bit sooner than the rears. The idea being that you will
> feel the skid in the front and lighten up on the brakes
> just before the rears let loose of the ground and you
> fishtail.
>
> The center of mass wants to be in front of the center of
> deceleration. If the front wheels are holding and the
> rears are skidding the center of mass will change places
> with the center of deceleration. Not a good thing...

 

[bob mclaughlin]

David,
The idea is to have maximum braking capabilities. To test this easily, one
should be able to lock up the brakes at some speed. Then when needed one
must act as a human anti-skid system which will give maximum braking for
conditions.
Bob McLaughlin

- -----Original Message-----
From: owner-gmcmotorhome
[mailtowner-gmcmotorhome]On Behalf Of
davegreenberg1
Sent: Wednesday, May 03, 2000 6:27 AM
To: gmcmotorhome
Subject: GMC: Brakes

> I did the 80 MM front and the 1 1/16 front bogie. It was ok but no
> home run. The sensitized booster and combi valve made a big difference.
I
> dont think it was the combi valve since I still cant lockup the front
> brakes.
>
> Take Care
> Arch

I really hesitate about getting into a technical discourse on things like
how braking systems are supposed to work, but caution to the wind!

Is the objective to see if the brakes lock up as a test to see if they
are functioning at full potential?

It would seem from my primitive logic, that locking up the brakes is
really the last thing one wants to do when faced with the need for panic
action. Once the brakes are locked up the coach will simply slide along
the ground. Is this reasoning faulty?

I am not challenging those whose experience and knowlege may be different
from mine but ................?

David Lee Greenberg
GMC Motorhome Registry
Dedicated To The Preservation Of The GMC Classic!
www.gmcss.com/registry.htm

 

[gary j zingle]

"I did the 80 MM front and the 1 1/16 front bogie. It was ok but no home
run. The sensitized booster and combi valve made a big difference. I dont=

think it was the combi valve since I still cant lockup the front brakes."=


Ya I did the combi valve too. Just couldn't see leaving the old one in wi=
th
all the other new parts.

Home runs are rare. Howevr nothing wrong with a good solid hit as long
as it is well placed.


Regards

Gary Zingle
1973 GMC 26 foot

 

[bob mclaughlin]

Gary,
Can you lock up your front brakes now?
bob McL

- -----Original Message-----
From: owner-gmcmotorhome
[mailtowner-gmcmotorhome]On Behalf Of Gary Zingle
Sent: Wednesday, May 03, 2000 10:32 AM
To: GMC Mail Server
Subject: GMC: Brakes

"I did the 80 MM front and the 1 1/16 front bogie. It was ok but no home
run. The sensitized booster and combi valve made a big difference. I dont
think it was the combi valve since I still cant lockup the front brakes."

Ya I did the combi valve too. Just couldn't see leaving the old one in with
all the other new parts.

Home runs are rare. Howevr nothing wrong with a good solid hit as long
as it is well placed.

Regards

Gary Zingle
1973 GMC 26 foot