Carb variants: auto vs manual

[Jesse Jaymes]

In searching for a "new" Quadrajet carb, I've educated myself, along with the assistance from members here. I've found many on Ebay that seem worthy. I've found a few from the years I need. But the codes state that they may be from manual transmission vehicles. This is for an auto 350/350 Blazer.

If I need to rebuild the carb, and am hopefully going to become a Quadrajet Pro, will this matter ? Meaning, can I buy the manual carb if it appears to be in better shape, or is there more to it than that ?

 

[dyeager535]

They seem to work ok no matter the intended transmission.

I'd almost bet the only difference is simply in how they come calibrated...primary metering rods, power piston spring, primary jets, secondary rods, hangars, secondary air valve tension, etc.

There are a fair number of casting differences (mainly choke or vacuum ports) in the q-jets over the years, but that doesn't account for the HUGE list of ID numbers. The differences are obviously very minute.

 

[Hogback Fabrication]

I don't think there is any difference between q-jets for a manual or auto.

The rebuild instructions do recommend setting the fast idle higher on auto equipped trucks.

 

[dyeager535]

Reason to use stamping numbers if there weren't differences in calibration? Since manual and auto is one of the numbers in the stamping number, it had to be somewhat significant.

Don't misunderstand what I'm saying, I don't believe the differences are typically anything to worry about, however since GM had to have each drivetrain combo certified, each carb would be part of that certification and would have been tailored to the engine, etc.

 

[77crewcab]

The throttle linkage is different between the two from my experience. But you could always swap throttle shafts or base plates.

 

[Chevy911]

Yep, the arm on the throttle shaft is different between manual and auto carbs, the auto ones have a place to clip the kickdown cable onto. Although a T400 truck will or can use a manual carb, since there is no cable.