GTO 3/2-BBL - Vacuum Actuated
 

A closer look at a unique and rare unit.

The 1964 GTO Tri-Power was designed and fitted with the full “Vacuum” operated 3/2’s unit from the factory on both the manual shift and automatic cars.

The 1965 and 1966 GTO with 3/2’s changed.
The manual trans equipped cars were built with the user friendly “mechanical” linkage.
However both the ‘65 and ‘66 automatic cars (engine code “YR”) were still built with the “Vacuum” units.
‘65 YR - 1456 built
‘66 YR - 1759 built

The vast majority of ‘64 thru ‘66 Vacuum units were changed out to the mechanical version, either at the dealerships or by the owners of these cars.

Suicide Linkage became the name for the Vacuum set-ups. I understand why.

The old 60’s magazine test articles are priceless with their text, but especially the photos showing just how the cars looked fresh from the factory.

This magazine below, “Speed and Supercar” has a little day-two with the crooked dark blue competition stripes.

This ‘66 GTO test car features that complicated Vacuum Tri-Power.
The view of the engine they show and the view of my “YR” are very close except my car was assembled at the Fremont plant which used a “Bundy Tube” fuel lines opposed to the other plants using aluminum fuel lines.

As it turns out, both the test car and my car were built with Power Brakes, Power Steering and Underhood Light.

Intricate, yes, with no less than 12 major components.

Left side.

The “Trigger” of the system.

The center carburetor “vacuum switch” has a slide mechanism built in that allows vacuum to enter a steel line that goes up and over the carbs to activate the two end Rochesters.

The flat lever on the side of carb has three arms, two of which open and close the vacuum source.
Once you put your foot into it an arm moves the slide switch and allows vacuum to open the end carbs. This is when the Howling starts.
This is shown on a spare carb.

So, once you take your foot off the loud pedal there is still a residual vacuum in the lines holding those end carbs wide open, hence “Suicide Linkage” !!!

You are freaking out at this point thinking something is stuck and your going to die. Just at that moment, the vacuum releases the carbs and your safe.

My first time in that situation I sh*t. Now I know how to feather that vacuum switch just right.

I’ve heard stories of customers with these vacuum cars back in the late 60’s being scared and demanding the dealer do something about it.
Bring her in mam and we will throw the vacuum stuff in the garbage and installed this user friendly mechanical linkage.

This adjustable trigger switch is made by Trico.

Shortly after I bought this car in 1991 I was able to locate the Original Owner, John Kennedy in San Jose, Ca. and quizzed him on his experience with this car.
He loved it, but his wife would not drive it. I understand.

Very cool. Thank you for posting that.

Interesting there is no hose going to the hollow carb mounting stud on the pass side front of the rear carb.Just has a rubber cap on it?Tom

----I'm curious weather big body Pontiacs followed the same path with the vacuum linkage on automatic cars? I remember a member here and friend, Chris P, had a gorgeous resto done on a 64 GTO convert with AC (triple black) and sourced all the vacuum stuff of the internet......Bill S

Man - I don't know about that racing stripe installation at the front...

K

I learned the hard way when I was a kid that on a Mopar Six Pack the carb linkage is to CLOSE the outer carbs.....

Me too! I had the throttle return spring break on my 440+6 Cuda coming out of a toll booth on I-95 in Connecticut back in the day. Throttles opened and stayed open with all 6 barrels at WOT. Still in first gear at 7000 rpm, all I had time to do was click the igntion key off to kill the spark. The resulting backfire blew out the mufflers and the window(s) in the toll booth. The cops found me on the side of the road about a half mile away. Shaker was already off and I was scratching my head at what the heck went wrong. The Trooper was a car guy and handed me a couple rubber bands to rig it up so I could get home. No tickets!

Great stuff, Chris!! I never would have guessed Trico made anything other than wiper parts.

tjs44,

The test car and my car have the flat top cap on the hollow stud as these cars do not have air condition.

Air condition cars with Tri-Power pulled their vacuum source from that hollow stud on either the rear carb or center carb as shown in the illustrations.

Thanks, Chris.

Hi Bill,

Yes, the Big cars used pretty much the same Vacuum linkage/components as the A body.

Although the Bigs did not use a throttle cable.
Instead they used link arms and couplings.

Thanks, Chris

Right Side.

Where would we be without Vacuum.

Brass fittings, steel pipe, crush clamps are what comes off the front carb throttle plate and provides Vacuum for the Power Brake booster, Automatic transmission module and the Vacuum reserve tank.

After this busy intersection comes a check valve leading down to a cast T fitting clamped in place.
One long hose goes to the Vacuum reserve tank mounted up front of the fender skirt.

The other, shorter hose goes to the thermostatic Vacuum control assy.
The purpose of this unit was to disable secondary throttle activation until the engine reached operating temperature (165 degrees).

Right side secondary arm operation.

End carbs were activated by a Vacuum Control diaphragm.

This “Control” mounted to the two RH rear carb studs and provided the pulling power to open the front and rear Rochester’s.

The two end carbs each had a small throttle return spring that clipped into the base plates to assist with deceleration.

The “Automatic” return springs #7013783 were twice the size of a “Manual Shift” spring #7029689 which (helped) on this Suicide Linkage.

I’ve seen many Original Vacuum Tri-Powers converted over to the Mechanical version and these springs were never changed out, because most are unaware.

Thanks for posting thread. Hey 60sstuff, I'm in SF Bay Area as well, curious if I know you? I have a 64 Black GTO w Tri Power. Was thinking of putting the vacuum secondaries back on my car but almost forgot how much I enjoy the ease of having mechanical, which I installed in 89'. My car was built in Fremont as well, First week of February 64'. Anyways thanks for post a great thread that will help future owners if they decide to go this route, very educational and spot on. Dave

Follow-up on tjs44 above question.

This 1966 GTO sold through Hemmings about 9 months ago and offers a good photo of the air condition vacuum hose coming off the hollow carb mounting stud.
You can still see the end of hose marked with dark blue paint just as the shop manual illustration shows.

The knowledge base here never ceases to amaze me. Great summary - thank you.