TH400 Modulator Vacuum Line
Thread Starter
Racer
Joined: May 2007
Posts: 391
Likes: 2
From: NC
TH400 Modulator Vacuum Line
Wow. The ultimate oopsie in forgetting to install the steel modulator vacuum line before dropping the body...and installing too many items to retro-fit that line in the proper place.
It appears as if that vacuum line is reduced at one end, probably as a vacuum regulator? Can I cut the steel line about half way up and continue with a rubber hose to a vacuum source?
It's not the first or last dumb move I'll discover along this trek.
It appears as if that vacuum line is reduced at one end, probably as a vacuum regulator? Can I cut the steel line about half way up and continue with a rubber hose to a vacuum source?
It's not the first or last dumb move I'll discover along this trek.
Burning Brakes
Joined: Jan 2010
Posts: 884
Likes: 84
From: New Boston, NH
Wow. The ultimate oopsie in forgetting to install the steel modulator vacuum line before dropping the body...and installing too many items to retro-fit that line in the proper place.
It appears as if that vacuum line is reduced at one end, probably as a vacuum regulator? Can I cut the steel line about half way up and continue with a rubber hose to a vacuum source?
It's not the first or last dumb move I'll discover along this trek.
It appears as if that vacuum line is reduced at one end, probably as a vacuum regulator? Can I cut the steel line about half way up and continue with a rubber hose to a vacuum source?
It's not the first or last dumb move I'll discover along this trek.
Good luck,
Bryan
Thread Starter
Racer
Joined: May 2007
Posts: 391
Likes: 2
From: NC
Is that reduced tip an actual regulator of sorts?
Le Mans Master
Joined: Dec 2007
Posts: 6,422
Likes: 591
From: McHenry Illinois
The reduced diameter on the end of the line is just so it can insert into the vacuum fitting and then that connection is covered by a short vacuum hose. Not a regulator function to it. Just keeps the connection from flexing as much.
Team Owner
Joined: Aug 1999
Posts: 30,995
Likes: 98
From: Ontario
Safety Car
Joined: Mar 2007
Posts: 3,652
Likes: 49
From: Bridgewater nj
Fishing it up from the bottom shouldn't be that hard. You may want to pull the distributor if you really need the room. Don't be afraid to bend it a little to help. If you are not a show car with everything original, just run a vac line and keep it away from the exhaust
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What they said.
Melting Slicks
Joined: May 2002
Posts: 2,431
Likes: 52
From: Florida
The reduced diameter proceeds a pinch restrictor, we often cut them off as they over time, fill/clog with carbon and present a delayed or no upshift condition. GM used the restrictor to inhibit strong vacuum signal from creating early upshifts. They later came out with an adjustable diaphragm in the modulator itself. Use the black stripe modulator for firmer/later upshifts and adjust according to your preference.
Melting Slicks
Joined: May 2002
Posts: 2,431
Likes: 52
From: Florida
POST #11 & 12
https://www.corvetteforum.com/forums...ns-vacuum.html
POST #2
http://forums.off-road.com/jeepster-...-question.html
TO OP: If you can drop the tail of trans down and or remove dipstick tube, you should be able to fish that hard line back in there. I'd use fresh rubber hose not made in china on each end if it was mine. Long sections of rubber tend to collapse under vacuum after being subjected to oil fumes and over time, you may experience that using the method you proposed IMO.
Good luck ... Jim
Last edited by jimvette999; Mar 16, 2017 at 01:15 PM.
Thread Starter
Racer
Joined: May 2007
Posts: 391
Likes: 2
From: NC
If you're asking me...yes it worked. We cut them off because clearing the blockage with a pin/small probe would result in them re-clogging later and then the transmission would come back under warranty, I'm not saying all trans. vacuum lines on all cars have the pinch restrictors or that yours does, I just know we encountered them on many GM products among others. Here's further evidence for you FWIW.
POST #11 & 12
https://www.corvetteforum.com/forums...ns-vacuum.html
POST #2
http://forums.off-road.com/jeepster-...-question.html
TO OP: If you can drop the tail of trans down and or remove dipstick tube, you should be able to fish that hard line back in there. I'd use fresh rubber hose not made in china on each end if it was mine. Long sections of rubber tend to collapse under vacuum after being subjected to oil fumes and over time, you may experience that using the method you proposed IMO.
Good luck ... Jim
POST #11 & 12
https://www.corvetteforum.com/forums...ns-vacuum.html
POST #2
http://forums.off-road.com/jeepster-...-question.html
TO OP: If you can drop the tail of trans down and or remove dipstick tube, you should be able to fish that hard line back in there. I'd use fresh rubber hose not made in china on each end if it was mine. Long sections of rubber tend to collapse under vacuum after being subjected to oil fumes and over time, you may experience that using the method you proposed IMO.
Good luck ... Jim
Burning Brakes
Joined: Nov 2006
Posts: 893
Likes: 7
From: Orange Park Florida
Where is the best vacuum source for the modulator, manifold or carburetor base; or is there any difference?
I have a mild cam on my 72 stingray so my vacuum readings are a little low. Brake booster issues(minor) but within tolerance. Was just wondering if one source is better than another.
I have a mild cam on my 72 stingray so my vacuum readings are a little low. Brake booster issues(minor) but within tolerance. Was just wondering if one source is better than another.