Question on TH400 modulator hard line
 

Did the factory vacuum modulator line have an orifice at carb
side connection.

And if so what was purpose?

Thanks
Gerry

Not that i have seen, If iam not mistaken its a closed system so a restriction like that would just slow down the modulators action either way in changes of vacuum a tad bit

so like when you stab the throttle it wont downshift as fast and when you let up off the throttle it will upshift a touch slower vrs an open line

Did the vehicle ever have a power adder? You do typically see some sort of check valve on the vacuum modulator when a blower or supercharger is used.

Other than that I couldn't really think of a reason to have that type of orifice on the line.

modulator line
 

this was on a stock drivetrain. friend bought a drivetrain from a parts car.
appears clean original 400 block with TH400 trans. Modulator line appeared
original and this a grocery getter wagon!!!

Gerry

Could that be a imperfection of the tube building process?

like how a tube cutter closes the tube ID. as the cutting wheel is forced down on it

imagine a tube that spins to much in relation the cutting wheel being forced down on it

or it was time for the tube manufacture to change the cutting wheel, it was worn out / dull edge

or the mandrel that forms the rib close to the tube end had issues

i would drill it out to .120- .187 ish whatever is appropriate spray carb cleaner and shop air through it

The factory line was pinched at 1-end for some sort of cal. I preferred the TH400 had instant awareness of the engine POWER increase so it would respond with appropriate Line Pressure. You will thank me later.

That's something they could of did before going to a plastic restrictor in the rubber hose. I have the plastic one.