Mechanical vac regulator
Thread Starter
Racer
Joined: Jun 2015
Posts: 315
Likes: 20
From: Vasteras, Sweden
Mechanical vac regulator
Hey Guys!
Since i have put in a wilder cam my vac has decreesed.
I need i mech reg for my TH400 that has just been rebuilt, thing is were can i get it? Summit is a no go.
I am in Sweden so its a bit tricky..
Chip in please!
Since i have put in a wilder cam my vac has decreesed.
I need i mech reg for my TH400 that has just been rebuilt, thing is were can i get it? Summit is a no go.
I am in Sweden so its a bit tricky..
Chip in please!
Race Director
Joined: May 2006
Posts: 18,734
Likes: 2,582
they are called vacuum modulators and I see Summit having 5 different ones all of them adjustable
https://www.summitracing.com/search/...ibanner=SREPD4
https://www.summitracing.com/search/...ibanner=SREPD4
Last edited by MelWff; Apr 1, 2017 at 11:33 AM.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
A regular vacuum modulator isn't going to help him; he doesn't have enough vacuum to operate it...or vacuum is so low that it doesn't work properly. Low vacuum would make the clutches shift harder and later.
I'm not aware of a mechanical device that can substitute for the vacuum mod on a THM-400. Do some searching on the web to see what you can find. You might need to go with a more modern transmission which has a TV cable instead of a vacuum modulator.
I'm not aware of a mechanical device that can substitute for the vacuum mod on a THM-400. Do some searching on the web to see what you can find. You might need to go with a more modern transmission which has a TV cable instead of a vacuum modulator.
Melting Slicks
Joined: May 2002
Posts: 2,717
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From: Sulphur LA
St. Jude Donor '05-'06,'11,'13-'14,'16,'18,'19,'24, '25
The Summit brand modulator is adjustable and will allow for shift point adjustments (low vacuum). It doesn't give a chart of how much adjustment it allows so it's hard to say if it will have enough adjustment for your car.
Neal
Neal
Tech Contributor
Joined: Aug 1999
Posts: 14,380
Likes: 6,390
From: At my Bar drinking and wrenching in Lafayette Colorado
On the TH400, even the stock modulators are adjustable. Have you tried adjusting the one you have...? Just pull the hose off, and the adjustment screw is right inside. It has significant adjustment range.
This picture is not a TH400, but shows the technique. Some TH400's have a forward-facing vacuum nipple with the adjustment screw right on the top of the "dome" on the modulator:
Typical TH400. You can see the adjustment screw in the middle of the dome:
This is a TH400 with the vacuum nipple facing outwards. On this one, you pull the hose off, and the adjustment is right inside the nipple as shown in the first photo:
This picture is not a TH400, but shows the technique. Some TH400's have a forward-facing vacuum nipple with the adjustment screw right on the top of the "dome" on the modulator:
Typical TH400. You can see the adjustment screw in the middle of the dome:
This is a TH400 with the vacuum nipple facing outwards. On this one, you pull the hose off, and the adjustment is right inside the nipple as shown in the first photo:
Last edited by lars; Apr 1, 2017 at 11:23 AM.
Thread Starter
Racer
Joined: Jun 2015
Posts: 315
Likes: 20
From: Vasteras, Sweden
I have adjusted the modulator all the way out and its not enough...
It shifts but to late.
I have heard there is mec modulators with cable adjustment, but were to get it...?
My vac is 12 Hg.
It shifts but to late.
I have heard there is mec modulators with cable adjustment, but were to get it...?
My vac is 12 Hg.
Last edited by clwi; Apr 1, 2017 at 03:50 PM.
Tech Contributor
Joined: Aug 1999
Posts: 14,380
Likes: 6,390
From: At my Bar drinking and wrenching in Lafayette Colorado
12 inches of vacuum is in a very normal number for a modest performance engine - the stock modulator should not have any problems dealing with that vacuum range. There is no special modulator required to handle that. I would suspect either a defective stock modulator or that you have issues not related to the modulator at all. Replace the modulator with a stock replacement unit. If that doesn't fix your issue, look at other areas of concern.
Lars
Lars
Thread Starter
Racer
Joined: Jun 2015
Posts: 315
Likes: 20
From: Vasteras, Sweden
12 inches of vacuum is in a very normal number for a modest performance engine - the stock modulator should not have any problems dealing with that vacuum range. There is no special modulator required to handle that. I would suspect either a defective stock modulator or that you have issues not related to the modulator at all. Replace the modulator with a stock replacement unit. If that doesn't fix your issue, look at other areas of concern.
Lars
Lars
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Safety Car
Joined: Oct 2004
Posts: 3,926
Likes: 739
From: Youngstown Ohio
How wild of a cam did you install? I've had as low as 9° vacuum and had no trans shifting problems. A new modulator may only change shift a couple hundred RPMs but that's all. The governor controls shiftpoint more. I'd look for a vac leak or blockage somewhere.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
I'm wondering if your vacuum modulator is damaged and/or you have blockage or trans fluid in the downpipe to the modulator. If vacuum isn't getting to the modulator (even though it looks to be connected) it will give you harsh shifts just the same.
Thread Starter
Racer
Joined: Jun 2015
Posts: 315
Likes: 20
From: Vasteras, Sweden
My cam is: Dur. 288/300, Lift .580/.620, LSA 109.
No fluid in downpipe and no vac leaks.
Maybe i need heavier weights or/and lighter springs in the govenor (26gram and red springs now)
Its a PITA to change weights/springs, have to remove exhaust and lower the trans...
At light throttle 1:st and 2:nd is ok, but 3:rd comes at over 40mph, thats to late IMO, but i might be wrong?
At WOT it shifts very nice, but at light throttle very harsh.
No fluid in downpipe and no vac leaks.
Maybe i need heavier weights or/and lighter springs in the govenor (26gram and red springs now)
Its a PITA to change weights/springs, have to remove exhaust and lower the trans...
At light throttle 1:st and 2:nd is ok, but 3:rd comes at over 40mph, thats to late IMO, but i might be wrong?
At WOT it shifts very nice, but at light throttle very harsh.
Last edited by clwi; Apr 4, 2017 at 11:29 AM.
Safety Car
Joined: Oct 2004
Posts: 3,926
Likes: 739
From: Youngstown Ohio
My cam is: Dur. 288/300, Lift .580/.620, LSA 109.
No fluid in downpipe and no vac leaks.
Maybe i need heavier weights or/and lighter springs in the govenor (26gram and red springs now)
Its a PITA to change weights/springs, have to remove exhaust and lower the trans...
At light throttle 1:st and 2:nd is ok, but 3:rd comes at over 40mph, thats to late IMO, but i might be wrong?
At WOT it shifts very nice, but at light throttle very harsh.
No fluid in downpipe and no vac leaks.
Maybe i need heavier weights or/and lighter springs in the govenor (26gram and red springs now)
Its a PITA to change weights/springs, have to remove exhaust and lower the trans...
At light throttle 1:st and 2:nd is ok, but 3:rd comes at over 40mph, thats to late IMO, but i might be wrong?
At WOT it shifts very nice, but at light throttle very harsh.
You can change the shift points via governor by trial and error, or by a knowledgeable trans mechanic who knows by experience which weight/spring combo to use.
Thread Starter
Racer
Joined: Jun 2015
Posts: 315
Likes: 20
From: Vasteras, Sweden
Not a modulator problem, or it would not shift "nice" at WOT. Sounds like a "shift kit" was installed (harsh at light throttle) or line pressure is a little high, which is sometimes done for high perf. applications.
You can change the shift points via governor by trial and error, or by a knowledgeable trans mechanic who knows by experience which weight/spring combo to use.
You can change the shift points via governor by trial and error, or by a knowledgeable trans mechanic who knows by experience which weight/spring combo to use.
Burning Brakes
Joined: Nov 2011
Posts: 1,170
Likes: 201
From: Willoughby Ohio
Not a modulator problem, or it would not shift "nice" at WOT. Sounds like a "shift kit" was installed (harsh at light throttle) or line pressure is a little high, which is sometimes done for high perf. applications.
You can change the shift points via governor by trial and error, or by a knowledgeable trans mechanic who knows by experience which weight/spring combo to use.
You can change the shift points via governor by trial and error, or by a knowledgeable trans mechanic who knows by experience which weight/spring combo to use.
Get a kit if you want to try it yourself or take back to the builder and have him do it.