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[GMCnet] Sensitized Master Cylinder [message #109043]

Sun, 19 December 2010 19:52

Charles Aulgur

Messages: 78
Registered: March 2006

Karma: 0

Member

Rob stated:

Braking performance improved but still left something to be desired.

Before our tour this summer while at the COOP I installed one of Jim B's
sensitized boosters. After installation Jim told me to head out on to
Anno
Drive, get up to about 30 and hit the brakes. I followed his
instructions
and the difference was UNBELIEVABLE. With a modicum of foot pressure
Double
Trouble came to a VERY quick stop. On our tour this summer I was no
longer
worried about not being able to come to a quick stop.

Rob, all the experts have said that a sensitized MC does not increase
the pressure that a MC can develop-it just requires less pedal
pressure to develop the maximum. What are your thoughts?

Chuck
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Re: [GMCnet] Sensitized Master Cylinder [message #109048 is a reply to message #109043]

Sun, 19 December 2010 20:21

WD0AFQ

Messages: 7111
Registered: November 2004
Location: Dexter, Mo.

Karma: 207

Senior Member

Chuck, You are exactly right. That is what I get from mine. Makes the pedal easy to push with one foot, does not increase braking pressure. But, it feels like you have better braking because of the ease.
Dan

3 In Stainless Exhaust Headers One Ton All Discs/Reaction Arm 355 FD/Quad Bag/Alum Radiator Manny Tran/New eng. Holley EFI/10 Tire Air Monitoring System Solarized Coach/Upgraded Windows Satelite TV/On Demand Hot Water/3Way Refer

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Re: [GMCnet] Sensitized Master Cylinder [message #109079 is a reply to message #109043]

Sun, 19 December 2010 23:44

USAussie

Messages: 15912
Registered: July 2007
Location: Sydney, Australia

Karma: 6

Senior Member

Chuck,

Thanks for the compliment of putting me up there with the "experts!" ;-)

The amount of force that a standard brake booster or a sensitized brake
booster can apply to the master cylinder is the same. Of course that is
assuming they both have the same number of internal diaphragms of the same
diameter. Rather than go into a lengthy explanation of how the booster works
click on the following link:

http://www.autoshop101.com/forms/brake05.pdf

The GMC booster has two diaphragms (Parts Book 78Z / Page 4-8 / Key 10 &
11).

Note: I have listed all the documents below relating to brakes on this
website as I found them to be extremely easy to read and understand. There
are a number of other articles that I have bookmarked for future reference
as well!

As noted in my previous message I had replaced every component in the brake
system on Double Trouble EXCEPT the brake booster yet it did not stop easily
no matter how much force I put on the pedal. I'm a pretty big guy and have
pretty strong legs/feet and can put one hell of a lot of pressure on the
brake pedal. While I never experienced anything as bad as Steve's incident I
did have to "stand on the brakes" a couple of times to get Double Trouble to
stop.

There was a dramatic improvement in braking after installing Jim B's
sensitized booster. I found that the pedal force decreased markedly and the
stopping power increased markedly. I attribute the decreased pedal force to
the sensitized booster. Since a sensitized booster cannot apply any more
pressure to the master cylinder than a standard booster I believe the
booster I removed was not operating properly. I noted that "1993" was
engraved in the body of the booster so it was 17 years old. Unfortunately I
did not tear the old booster down and have a look to see what I could find.
I was too busy getting Double Trouble ready for Helen's arrival!

Regards,
Rob M.
USAussie - Downunder

PS - I did a search and found a website called Autoshop 101.

http://www.autoshop101.com

On that website I found the following information:

Technical Articles - Brakes

Fundamental Principles
http://www.autoshop101.com/forms/brake01.pdf

Master Cylinder
http://www.autoshop101.com/forms/brake02.pdf

Drum Brakes
http://www.autoshop101.com/forms/brake03.pdf

Disk Brakes
http://www.autoshop101.com/forms/brake04.pdf

Brake Booster
http://www.autoshop101.com/forms/brake05.pdf

Parking Brake
http://www.autoshop101.com/forms/brake06.pdf

Brake Diagnosis
http://www.autoshop101.com/forms/brake07.pdf

Hydraulic Control
http://www.autoshop101.com/forms/brake08.pdf

Anti-Lock Brakes
http://www.autoshop101.com/forms/brake09.pdf

ABS Diagnosis
http://www.autoshop101.com/forms/brake10.pdf

Other ABS Actuators
http://www.autoshop101.com/forms/brake11.pdf

Traction Control System (TRAC)
http://www.autoshop101.com/forms/brake12.pdf

Appendix
http://www.autoshop101.com/forms/brake13.pdf

-----Original Message-----
From: Charles Aulgur

Rob, all the experts have said that a sensitized MC does not increase
the pressure that a MC can develop-it just requires less pedal pressure to
develop the maximum. What are your thoughts?

Chuck

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Regards, Rob M. (USAussie) The Pedantic Mechanic Sydney, Australia '75 Avion - AUS - The Blue Streak TZE365V100428 '75 Avion - USA - Double Trouble TZE365V100426

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Re: [GMCnet] Sensitized Master Cylinder [message #109080 is a reply to message #109079]

Mon, 20 December 2010 01:17

Ken Burton

Messages: 10030
Registered: January 2004
Location: Hebron, Indiana

Karma: 10

Senior Member

I also installed the sensitized brake booster. I do not think the old one was broken since it never leaked down when parked. I also have tried to drive a GMC with no vacuum applied to the booster. It was impossible to stop.

With the new booster it takes only light pressure on the pedal to stop it. My wife can now easily drive it where before she refused to drive because she was afraid of the brakes. It may be true that the booster can not apply more maximum pressure than an OEM one, but it sure will take less pedal pressure to reach maximum braking.

I can not answer what it takes to reach maximum brake line pressure since I drive slower than most and leave extra distance between me and the vehicle in front of me.

Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana

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