| Tranny modulator vac line [message #133127] |
Sat, 02 July 2011 18:53  |
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JShot
Messages: 485
Registered: October 2006
Location: NW Ohio
Karma: 0
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Is there any reason the vacuum line from the transmission modulator can't be replaced with standard vac hose. Is there a reason it is a steel line?
John
John Shotwell
Ridgeville Corners, OH
78 Royale Center Kitchen
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| Re: [GMCnet] Tranny modulator vac line [message #133131 is a reply to message #133127] |
Sat, 02 July 2011 19:02  |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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John,
The upward loop on the steel line has a significance I've forgotten.
It's also got an intentional crimp in it to dampen the reaction of the
modulator to vacuum changes. So it's probably not a good idea to
eliminate it. But you do need to be sure it's not plugged -- the
small orifice left by the crimp, with all the oil that can potentially
get in there, right beside the hot exhaust crossover, can easily clog
up.
Ken H.
On Sat, Jul 2, 2011 at 7:53 PM, John Shotwell <jshot@rtecexpress.net> wrote:
>
> Is there any reason the vacuum line from the transmission modulator can't be replaced with standard vac hose. Is there a reason it is a steel line?
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] Tranny modulator vac line [message #133135 is a reply to message #133132] |
Sat, 02 July 2011 19:33 |
Larry
Messages: 2875
Registered: January 2004
Location: Menomonie, WI
Karma: 10
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| JShot wrote on Sat, 02 July 2011 19:13 |
Probably best to remove it and make sure it's not clogged. And maybe the loop is a trap of some type. I installed a new vacuum tree on the manifold and the steel line now attaches at an odd angle - I may have to put in a 90* elbow to connect it.
Thanks for the replies!
John
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It is indeed a water trap. Intended to trap water/moisture so that it does not get down to the modulator. In the north country where temps go well below freezing, if water gets into the modulator (just gravity will take it down there) and it freezes, it freezes the action of the modulator. When it does that, trans pressures run wild. So you start the car on a cold morning, (Modulator is frozen in place) put it in reverse to back out of driveway, and it blows out the reverse servo. The first Cad Eldo that I bought did not have reverse. When I pulled the pan, I found a the reverse servo and the iron chunk of the valve body laying in the bottom of the pan. I asked a tranny guy that I know well and teaches Auto transmissions at the local tech school, how that happened....
JFWIW
Larry 
78 Royale w/500 Caddy
Menomonie, WI.
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| Re: Tranny modulator vac line [message #133206 is a reply to message #133167] |
Sun, 03 July 2011 14:48 |
midlf
Messages: 2212
Registered: July 2007
Location: SE Wisc. (Palmyra)
Karma: 1
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| mcolie wrote on Sun, 03 July 2011 06:00 |
I asked this question years ago at one of the OE design groups and was told that the line was steel because A - that would be difficult to mis-connect or mis-route during assembly, B - it did not require multiple tie points to keep it out of danger, C - the steel line provided a restriction feature to slow the response of the modulator, D - the steel was a good enough heat sink to cause the fuel vapors to collect and run back into the intake instead of down to the modulator where they could collect. Once the fuel fills the line to the restriction, the modulator stops responding at all.
Matt
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So my question is: If it is necessary to replace the steel line due to deterioration, what size orfice is needed to duplicate the factory crimped orfice? I would do this by bending a steel line to match the original and soldering the engine end of the line closed and drilling the orfice.
Steve Southworth
1974 Glacier TZE064V100150 (for workin on)
1975 Transmode TZE365V100394 (parts & spares)
Palmyra WI
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| Re: Tranny modulator vac line [message #133209 is a reply to message #133127] |
Sun, 03 July 2011 15:03 |
g.winger
Messages: 792
Registered: February 2008
Location: Warrenton,Missouri
Karma: 0
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I ran a new line on the Caddy install for the Edelbrock aluminum manifold. Cut a short piece of TIG rod,,,,measured the restiction with a drill bit. Turned the rod down in the lathe. You could use a drill and sand paper. Pressed into the line.JWID,,,,,,,PL
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| Re: Tranny modulator vac line [message #133210 is a reply to message #133206] |
Sun, 03 July 2011 16:27 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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That was my thought also. Just measure the existing one with very small number drill bits. Something like you would use to drill jets in a carb.
The other thing you could do is cut the crimped portion off of the existing tube and is reuse it.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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