Modulator vacuum line

Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.

Old60Driver

1983 K20 Silverado
Joined
May 17, 2020
Posts
229
Reaction score
270
Location
Houston
First Name
Michael
Truck Year
1983
Truck Model
K20 Silverado
Engine Size
350
Is it possible to swap out the long metal modulator line going from the intake to the modulator with a regular vacuum line? The existing line is pretty gnarly looking (bent to he**), and is a pain in the rear to work around.

I'm a bit worried about heat softening it up over that long of a distance.

Thoughts?
 

squaredeal91

Full Access Member
Joined
Mar 10, 2023
Posts
2,001
Reaction score
3,496
Location
Cave junction Oregon
First Name
Greg bush
Truck Year
1991 SB
Truck Model
K30
Engine Size
5.9 Cummins 12 valve
On my truck I'm using a rubber fuel hose for temporary. The previous rubber hose got so soft that it wouldn't stay on the nipple anymore. I'm planning to run some brake line out of the way and use rubber at each end Like it should be.
 

Ricko1966

Full Access Member
Joined
Apr 11, 2017
Posts
4,426
Reaction score
6,570
Location
kansas
First Name
Rick
Truck Year
1975
Truck Model
c20
Engine Size
350
You shouldn't use rubber as the modulator line it can suck shut in the middle of the run,trapping vacuum and giving false signal to the modulator. You can get a piece of 3=16 ths steel line from the parts store for about 15 bucks and bend up a new one.
 

CheemsK1500

Full Access Member
Joined
Jun 3, 2022
Posts
782
Reaction score
1,363
Location
Texas
First Name
Paul
Truck Year
1984
Truck Model
K1500
Engine Size
305
I’ve had a hard enough time keeping the little rubber boot at the end of the hard line attached to the modulator. I am not even going to entertain the idea of making the whole line out of rubber. Get a cheap harbor freight tubing bender and some new metal line and just do it correctly now to save yourself misery later.
 

Matt69olds

Full Access Member
Joined
Jan 8, 2018
Posts
2,392
Reaction score
3,699
Location
Central Indiana
First Name
Matt
Truck Year
81
Truck Model
GMC 1/2 ton
Engine Size
455 Olds
Steel line with a couple inches of rubber hose on the ends for the connection.

Todays useless bit of tech: ever wonder why GM put that loop in the modulator line? It’s to prevent condensation from collecting in the modulator. Let me explain.

Imagine a bunch of short trips in cold damp weather. The engine never runs long enough to boil off the condensation that naturally collects in a line. No imagine that water pooling in the modulator, and then freezing. That will lock the modulator valve solid in the case.

Next morning, the driver starts the car. Naturally, the choke is set and the engine is on fast idle. Cold thick trans fluid, fast idle, and a transmission that can no long control line pressure due to the locked valve. You put the transmission in reverse, normal line pressure of 250-300 is now 2 or 3 times that amount. Something has to give. If you’re lucky, it just breaks the piston. If your unlucky, it will break the case.

The little loop is designed to catch condensation before it gets to the modulator. As much as we like to bitch and complain about engineers, there is usually a reason why something is designed the way it is.
 

squaredeal91

Full Access Member
Joined
Mar 10, 2023
Posts
2,001
Reaction score
3,496
Location
Cave junction Oregon
First Name
Greg bush
Truck Year
1991 SB
Truck Model
K30
Engine Size
5.9 Cummins 12 valve
Was at the Napa again and scored this fir $9.29
There phasing out all there evercraft.
 

Attachments

  • 20240611_140413.jpg
    20240611_140413.jpg
    133.4 KB · Views: 14

Latest posts

Forum statistics

Threads
42,669
Posts
920,279
Members
34,202
Latest member
Diggs816
Top