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#1 |
Registered User
Join Date: Aug 2006
Location: Redmond, WA
Posts: 6,332
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What the heck is this brass fitting for?
While Jim Pontius has been helping me sort out the various braces that mount the 72 3/4 ton disc setup, I found a reference photo that shows a brass fitting on the master cylinder that I have NOT installed yet. Actually, I have the fitting but didn't know where it went until all the digging.
It's marked as K/H (D) 78497 Googled that many ways to no avail. Male port goes into MC, line from combo valve into female port, and an unused-in-the-picture small (3/16" ?) port on top. Remember that on the 3/4 ton the front is the rear brakes and vice versa, so this would be on the rear brake side of the system. It's not a residual pressure valve, as you can see straight through it. So, anyone know what the heck this T is for? Heaven hope they never made a hydraulic trailer brake setup that took pressure from the master cylinder of the tow vehicle!
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1970 GMC Sierra Grande Custom Camper - Built, not Bought 1969 Pontiac 2+2 427/390 4-speed Coupe 1969 Pontiac 2+2 427/390 4-speed Convertible |
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#2 |
Registered User
Join Date: Oct 2008
Location: Indianola, Iowa
Posts: 11
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Re: What the heck is this brass fitting for?
The old style trailer brake controllers T'd into the line like that.
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#3 |
70+ ( Old Skool Club )
![]() Join Date: Nov 2003
Location: Saskatoon, Saskatchewan ,Canada
Posts: 9,119
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Re: What the heck is this brass fitting for?
Back in the day before trucks had lots of electronics when you wanted to hook up a trailer brake to had to physically cut into a brake line and run a hard line to the brake in the cab of the truck so I'm pretty sure that is what the t-fitting is for.
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#4 | |
Senior Member
![]() Join Date: May 2010
Location: Wisconsin & Arizona
Posts: 4,844
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Re: What the heck is this brass fitting for?
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#5 |
Registered User
Join Date: Aug 2006
Location: Redmond, WA
Posts: 6,332
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Re: What the heck is this brass fitting for?
Crazy. Guess it worked though! Given the complexity of things like cruise control and air conditioning I'm surprised they couldn't come up with an inertial controller by that point. They made it to the moon using inertial guidance, so you should be able to stop a trailer :-)
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1970 GMC Sierra Grande Custom Camper - Built, not Bought 1969 Pontiac 2+2 427/390 4-speed Coupe 1969 Pontiac 2+2 427/390 4-speed Convertible |
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#6 |
Registered User
Join Date: Aug 2010
Location: Edwards, CA
Posts: 7,503
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Re: What the heck is this brass fitting for?
Yep, An added tee to allow routing brake fluid to a controller that in turn sent an electrical current to the trailer brakes. Easy to install and easy to use. Funny how many trucks still have them with the controller pulled off and even after a M/C change. If you look through truck handbooks from the 70s you will see warnings about not using trailer brake systems that tap fluid from the master cylinder or more than "x" amout of fluid. Just changing technology.
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#7 |
Senior Member
![]() Join Date: May 2010
Location: Wisconsin & Arizona
Posts: 4,844
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Re: What the heck is this brass fitting for?
Yup, a change in technology that was, in part, prompted by the advent of anti-lock brakes. Interesting to note is that new GM and Ram trucks with the integrated brake controllers utilize an inertia system. I've heard that Ford relies on a brake system pressure reading. Frankly, I'd have more confidence in the Ford system.
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#8 | |
Account Suspended
Join Date: Jan 2007
Location: Tucson
Posts: 2,183
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Re: What the heck is this brass fitting for?
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#9 |
Registered User
Join Date: Mar 2012
Location: Boulder, CO
Posts: 350
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Re: What the heck is this brass fitting for?
Most of the trucks I run across have a trailer brake set-up like that. If there's not a little box with a lever on it under the dash between the parking brake handle and the steering column, there'll be a line from the tee fitting to it. I've got a collection of them in my storage area in the shop AKA 'house of horrors'.
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If 'that which does not kill me, makes me stronger', then I should be Superman by now! |
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#10 | ||
"I ain't nobody, dork."
Join Date: Sep 2007
Location: Whidbey Island, Washington
Posts: 8,940
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Re: What the heck is this brass fitting for?
My '72 GMC was the only truck of this vintage I have owned that did not have a brass T-fitting in the brake line for a trailer brake controller. The '67, '69 and my Dad's '70 all have that fitting installed for a brake controller. I have installed a few of those myself in the past.
Gary
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