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Old 08-31-2010, 06:31 AM
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Th-350 vacuum modulator

Hello guys i'm going to try out Holley dominator carb for one race, and at races I shift manually 1-2-3 So since the Dominator carb doesn't have any vacuum ports would it be all right to run the trans without this vacuum line and keep the kickdown cable stuck like it was at full throttle ?

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Old 08-31-2010, 09:36 AM
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Don't you have a vacuum port on the intake? That's where it's supposed to go anyway, not the carb. The only port's you need on the carb would be for PCV valve or distributor vacuum advance.
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Old 08-31-2010, 10:43 AM
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I agree with sqzbox find you a spot on the intake. But for only (one race) i am sure it will be ok, I have run like that a few times did ok, Like you said your going to be manual shift anyway.


Cole
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Old 08-31-2010, 11:01 AM
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Unless your Trans is setup for a Manual Valvebody I don't think that's going to work. With the Detent cable locked In downshift position it wont shift at all without feedback from the vacuum Modulator. Or I may be wrong.
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Old 08-31-2010, 11:07 AM
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All you have to do is leave the cable un-hooked and run that way, Shift it manual like you are going to do anyway. it will be fine especially for one race or so. JMO


Cole
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Old 08-31-2010, 02:12 PM
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Thanks guys, By running the kickdown unhooked do you mean that I should have it loose and just slack or loose and stuck like it was down shifting ?

Does the Vacuum modulator only have influence when in drive ?

Monzter.
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Old 08-31-2010, 03:23 PM
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Quote:
Originally Posted by monzter
Thanks guys, By running the kickdown unhooked do you mean that I should have it loose and just slack or loose and stuck like it was down shifting ?

Does the Vacuum modulator only have influence when in drive ?

Monzter.
You need to leave the kickdown cable slack . The vacuum modulator isn't going to mean anything with the kickdown cable unhooked . The transmission will upshift to the next speed when you manually select no matter what the throttle position or manifold vacuum . If I'm wrong , somebody please correct me .
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Old 08-31-2010, 04:32 PM
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Here's what you can do, unhook the cable all together. Hook the vacuum modulator to manifold vacuum port, and go for it. the down shift cable is not needed on the track when shifting manually.
Without the vacuum modulator hooked up, you'll be running the full length of the return road back to the pit's in 1st. gear because it won't shift.
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Old 08-31-2010, 05:17 PM
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Quote:
Originally Posted by sqzbox
Here's what you can do, unhook the cable all together. Hook the vacuum modulator to manifold vacuum port, and go for it. the down shift cable is not needed on the track when shifting manually.
Without the vacuum modulator hooked up, you'll be running the full length of the return road back to the pit's in 1st. gear because it won't shift.
it will shift with no vacuum. it will be late and firm, but it will shift. unlike if a governor gear breaks or "apple cores", then it wont shift at all.
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Old 08-31-2010, 05:41 PM
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Well I'm only going to run 300 foot sand drags
So it ok if it shifts late and firm on the way back in 3/D gear
The main thing i asked this question was because i was wondering if I could get it to shift normally (quickly) when shifting manually with these things unhooked ! /modulator and kickdown...

Thanks guys

I'l just keep the vacuum modulator unhooked and run the kickdown cable slack, Will let you know how this is going to work out.

Monzter.
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Old 08-31-2010, 08:36 PM
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You will be fine i run without the cable at all, I removed it plugged the hole in the trans. I do have a modulator valve though but sometimes it comes un-hooked and all i do is manual shift it and it does fine ex-specially in the 1/8 or 1/4 mile strip. If it's just a play toy for what you are saying 300 ft at a time it should be fine .IMHO Heck your coming off the line WOT right.


Cole
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Old 09-01-2010, 01:33 AM
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I don't run a kick down at all on my Willys. I do run a vacuum mod for the street. You can run with the vac line blocked but it will up shift harsh and late. Unless you have a shift kit in it it will up shift automatically no matter what.

I start mine in 2nd and let it upshift automatically 1st to 2nd then manually shift 3rd. The Lokar shifter is not easy to shift quickly when you are really digging.
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Old 09-01-2010, 11:48 AM
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Ever Had A Broken Modulator Spring ?

I was working on a C4 that had a severe shifting problem that about drove me buggy . As I recall, the trans shifted like the throttle was closed no matter how much throttle you gave it . Finally removed the shift modulator and went to an independent shop / parts store with the modulator and pin . Comared to a new modulator and determined that the spring inside the modulator was partly colapsed and not pushing the pin out all the way . The guy that owned the shop is 11 yrs my senior and had never seen that before . Anyone else ever seen that ? BTW . After I installed the new modulator the trans' shifted perfectly .
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