TH400 vacuum line

[ThreeQuarter]

After searching many a thread for an answer, I can't seem to get confidence around finding the correct steel vac line for a '68 327/TH400. Can anyone show me some pics, especially ones that capture the top end of the line and how/where it ends and transitions into a rubber vac hose?

I've also been shopping for a new one from an aftermarket supplier, but nobody's application guide seems to list parts for a '68ish GM pickup. Wouldn't one from a car in this era work OK? ...but they have many different part numbers for the different GM cars in these years, so maybe not? Can anyone give me a part number that will work for my pickup?

[Redneck Rydes]

Maybe check one out for a 1968 Impala/Caprice,the there is some extra room on a Impala,my old 68 was a 327/300 hp with a Turbo 400 amd i remember there was room,Try Modern Chevrolet in Winston-Salem,NC I used to buy a lot of parts from them,I just checked,Ecklers has them for Chevelles,28.00

[FirstOwner69]

I can't help with a source, but here are some pictures of my '69 with a 350 and TH400. The "clean" pictures show the original line on my GM 350 crate engine and Holley carb. The "dirty" pics are the installation with the original 350. The line runs to a "T" on the intake behind the carb along with vacuum lines for the power brakes and A/C vacuum line (if so equipped). I don't know if the 327 would be similar.

[demian5]

Yes

[RustyPile]

$28.00 + shipping for a "pre-bent piece of tubing?? Have you tried bending your own for 5 bux or less?? the line runs basically from a fitting on the intake manifold, down the bell housing area and connects to the modulator valve via rubber tubing..

[ThreeQuarter]

Thanks for the pics and the suggestions. The pics make it easier to see what the right one should look like. They also make me think I should take a stab at bending my own before I decide to pay for a pre-bent one.

How critical is it that the ends be made like the factory lines were? Is it a good alternative to slide a vac hose over a cut end and use a hose clamp?

[FirstOwner69]

Classic Industries carries the line for 69-70 but not 67-68 and 71-72. That implies the lines may differ. Note the ends of the line are unique (smaller). I don't know if there would be a reason other than properly attaching the lines at each end with the short pieces of rubber hose.
https://www.classicindustries.com/sh...0vacuum%20line

[ThreeQuarter]

Classic Industries shows this one part number fits both TH400 and TH350? Aren’t the modulators in very different places on those two transmissions?

[Steeveedee]

You can make your own, yes. What I do in this case is make a bulge in the end of the tube by making the start of an inverted flare on the end of the tube. If you have a line flaring tool kit, you can see what that looks like. The bulge, properly made, will keep the hose on the tube without an unsightly clamp.

[FirstOwner69]

The Right Stuff obviously makes what Classic Industries sells (same part number). Also says TH350 and TH400.
https://www.getdiscbrakes.com/ttv6905

[HO455]

I've got one. It is pretty crusty but doesn't seem to be mangled up. If your interested I can send it your way.

[KQQL IT]

Buy an extra elbow on the transmission side.
The new rubber doesn't hold up like it used to. And creates and vacuum leak and your trans won't shift too well.

[NGN]

The original vacuum line has a tab on it so that it can be bolted securely to trans.
Not that original, off by a tab.
NGN

[HO455]

Originally Posted by KQQL IT

Buy an extra elbow on the transmission side.
The new rubber doesn't hold up like it used to. And creates and vacuum leak and your trans won't shift too well.

????? Where does the elbow go?

[KQQL IT]

Mine has an adjustable modulator, the nipple sticks out 90° to yours.
And has a elbow in the vacuum line

[FirstOwner69]

Originally Posted by NGN

The original vacuum line has a tab on it so that it can be bolted securely to trans.
Not that original, off by a tab.
NGN

Correct. The 4th picture I posted in post 3 shows the tab on the vacuum line, as well as the tab on the dipstick tube, attached by a transmission bolt. It doesn't look like the Right Stuff line they show has the tab.

Originally Posted by KQQL IT

Mine has an adjustable modulator, the nipple sticks out 90° to yours.
And has a elbow in the vacuum line

Sounds like your modulator was replaced. I don't believe GM used an adjustable version. Do you have a picture of the transmission attachment point?

[FirstOwner69]

Originally Posted by KQQL IT

Buy an extra elbow on the transmission side.
The new rubber doesn't hold up like it used to. And creates and vacuum leak and your trans won't shift too well.

I mentioned earlier that the ends of the original line are a reduced diameter. As I recall this allows the ends of the line to fit inside the barbs on the manifold fitting and modulator. I've guessing this is to prevent the rubber hose pieces from collapsing under vacuum.

[KQQL IT]

After seeing the one posted.
I'm sure it's not stock. But both of my th400s have them. And recently had a rotten vacuum hose cause some headaches.

[C10Nick]

maybe a dumb question but I'll ask anyway...

Anybody ever tried to run the line as a rubber hose from the intake manifold all the way down to the modulator at the trans? That's what I did and now she won't shift into 3rd.

Do you guys think the rubber hose the culprit? Should I switch it out for a steel tube?

[BigBird05]

Inline tube sells the correct vac line in SS for $35.00. If you go on line you can look at it and probably make your own. #SCTT7104

[kidatheart]

Originally Posted by C10Nick

maybe a dumb question but I'll ask anyway...

Anybody ever tried to run the line as a rubber hose from the intake manifold all the way down to the modulator at the trans? That's what I did and now she won't shift into 3rd.

Do you guys think the rubber hose the culprit? Should I switch it out for a steel tube?

Try shifting your transmission manually into 3rd at about the speed you think it should shift on its own. If it shifts manually into drive then it very well could be your rubber line or bad modulator.

[Steeveedee]

Originally Posted by C10Nick

maybe a dumb question but I'll ask anyway...

Anybody ever tried to run the line as a rubber hose from the intake manifold all the way down to the modulator at the trans? That's what I did and now she won't shift into 3rd.

Do you guys think the rubber hose the culprit? Should I switch it out for a steel tube?

Depending on how old that hose is, it is possible that it is collapsing under vacuum. That's a long run for a vacuum hose, which is why GM uses a steel line.