Turbo 400 experts please step in....
 

69 Chevelle , 496.
3.42 gears.
2 things:
The 1-2 shift is waaay too early. I want to delay that. I don't think I'm going to get there with just modulator adjustment. How about reducing or limiting the vac. source?
Secondly , is it essential that the electric solenoid switch be connected..........because it currently isn't.

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There are several companies that sell governor weights and springs to move the shift points around . You are correct that playing with the modulator won't get it done . The kick down solenoid basically bypasses the modulator circuit at WOT only .

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I knew that if you saw the original post, you would have the answer, Russ. From what Pustelny tells me, there are very few people who know GM automatic transmissions as well as you.

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https://www.hotrod.com/articles/hppp...ing-turbo-400/

Had someone use this to adjust RPM

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What is the modulators job? If it has little to no effect on shift timing , then why are they offered as "adjustable"? I've already played around with the weights , 2-3 shift at WOT is about 5800-6000....which is fine. Presumably , under WOT the 1-2 may be similar.
This post is about shift timing at part throttle around town driving though.It shifts almost immediately into second , part throttle casual driving.
Does the kick down have to be connected to increase lne pressure?

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How much vacuum do you have at the modulator? -Al

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Check the modulator vacuum like Alan said. Some factory metal vacuum lines had a restriction at the modulator end. If so drill it out. The governor has more influance on the 1-2 shift, the modulator has more effect on the 2-3.

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NOT AN XPERT -- but I was always taught to believe the modulator determined to an extent the "firmness" of the shift that is "hard or soft" --where as the governor determines at what rpm the shift is made--FED 387

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The idle vac is 10"
From experience I know if the mod isnt connected , it wont shift.
That being said I would think low vac would make it MORE reluctant to shift.
No one has addressed the kick down solenoid? IF I dont care about kickdown , then its not required to be connected.....somewhere I read where the solnoid increases line pressure in kick down mode?

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Some how I thought your post was to set the shift points at WOT . It is harder to set the part throttle shift points . The modulator system basically makes a pressure to tell the transmission what load is on the engine . This is based on manifold vacuum . The lower the vacuum the higher this modulator pressure would be . So if you have an engine with high vacuum at idle , and you lightly drive away from a stop , you get a very low modulator pressure and therefore a early shift point . A hot rod engine might have a fairly low idle vacuum and if you did that light throttle drive away , you might get a delayed shift . So most hot rodders put a high stall converter in place of the stock tight converter , and what happens is the manifold vacuum is much higher than it would normally be , creating a low modulator pressure and an early shift . Most of the newer transmissions that are built now have electronically controlled shift patterns . They don't shift based on manifold vacuum . Before electronics there were cable controlled transmissions , like the 200 THM or 700-R4 . There were many different modulators to deal with different engines , with different manifold vacuums , but not anymore . The adjustable modulators are really not for you to adjust , but to set the modulator to a factor specification . There is not much you can do with your current vacuum modulator system . One thing you might try is a B&M Modulink , which basically converts the vacuum modulator to a throttle cable controlled modulator . I worked on a similar system for the Hummer , which was a diesel , so no manifold vacuum .

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Check the vacuum at the intake as well. It’s been a while , but from my training during GM tech school, govenor pressure overcomes modulator pressure to make the shift. Someone correct me if I’m wrong, but I don’t think disconnecting the downshift solenoid will have any effect on shift timing.

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X2, I agree.

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Thanks , your friend was correct., you know your stuff..........yes this is about "part throttle" shifts.

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Sorry for the confusion. The reference to the solenoid was about whether I can leave it disconnected and if that has any consequence . No connection to upshift timing.

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The solenoid will delay the upshifts past the 0 vacuum shift point. You can leave it disconnected as the line pressure is controlled by the modulator only but you will get early full throttle upshifts and no kickdown.

Jim Mantle

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Joe, It's hooked to a n/o switch that only passes 12v at WOT, so ,about 99 % of the time, it's not doing anything anyway. So yes , you can leave it unhooked.

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OK , thanks everyone for your contributions.

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Thinking about this a bit more . The kits you can buy just modify the secondary weights and springs of the governor . Your problem is at slower speeds that may be affected by the Primary governor weights , this is the heavier weight . I would look for a different governor that has a Lighter primary weight . Suggest you find one with a big hole drilled through the primary weight and swap it on to your existing governor . Reuse the secondary weights and springs you already have but swap on a pair of the lighter primary weights . See what the effect is to that change is . Some trans shops have used governors you may be able to purchase cheap , and maybe even the pins . We had many , many different governor weights designed , both primary and secondary . Good luck ! BTW when you adjusted the modulator , did you see any effect ?

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Also , you can use some T350 governor parts .Weights, springs. The top is different and the plastic gear turns the opposite way.

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I took it out for a test drive after running the screw in a little further.no change , at least nothing noticeable . I'll spend time with the governor as you suggest , however I don't want to change the way it acts under full throttle , now. I can see this is going to require a fair amount of trial and error.........in other words a PITA. But , I'll do it none the less.
Perhaps I should just consider a 4L80E and be done with it.

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OK , thanks........

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One thing I'm surprised no one has mentioned is that most OE vacuum modulator feed lines have a restriction ,usually a crimped area in the tube to help regulate the speed in which the modulator responds to throttle changes .
Also , if you are using the short , small 2" diameter modulator , There are many different spring calibrations for different applications identified by the color stripes ,usually black ,white ,red , red-red ,red-black are common identifiers .
Each one has a different spring rating ,the external adjustment only addresses the range of that particular spring.

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Seems that the factory had its work cut out for itself fine tuning this trans to fit all the various engine combinations it found itself behind. The basic three speed planetary gearset came behind 250 horse 327's up to 400 horse plus big blocks, plus Pontiac,Buick, Olds and Cadillac, all high torque motors with various characteristics. Vacuum modulators, modulator steel line sizes, and all kinds of valve body springs all went together to make this trans work for everybody. A certain amount of trial and error is to be expected in order to fine tune it to suit a particular user. Of course, most drag cars have a manual valve body so modulators and other spring applications turn into a moot point . The age old axiom is correct here when we find that the best dyno is the drag strip. Sounds like an assortment of modulators and springs and a trip to the track for a test and tune session would be your ultimate best bet. Just don't change anything on the engine's state of tune while you are working on the transmission. Good luck on your project,thanks for introducing a subject that resulted in quite a bit of intelligent discourse.

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Exactly , and I have the single red stripe , dual red stripe , black stripe and on and on and on , and I have no way of knowing what's doing what ......in other words , apparently I have to try everything and then MAYBE.......LOL

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Recall , this thread is only about part throttle early shift 1-2. But good points.......

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The basic differences between the modulators is a spring force , and the size of the diaphragm . It works by vacuum acting on the diaphragm area to back off the load on the spring . If no vacuum (WOT) then just the full load of the spring acts against the modulator valve which regulates a pressure that makes line pressure and also works on the shift valvetrains . This is max modulator pressure . When you have high vacuum (closed throttle) ,then the diaphragm works against the spring , reducing it to zero . This means zero modulator pressure which gets you minimum line pressure , usually 60 psi , and minimum shift points . So all these different modulators are just combinations of spring loads , and Diaphragm areas . The problem in this thread is sounding like the diaphragm area is too big so under medium engine load it backs off the modulator pressure and gives an early shift . It would be nice to have a chart of different modulator part numbers with spring load , diaphragm area , and ID stripes . Also note that the adjustment screw is usually adjusted at the factory to get a certain load at a certain vacuum , back when these were more common there was not a screw , but the adjustment was done by dimpling the top of the housing .

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OK guys , thanks again........
I'll conclude with this:
I have the "hard" line that has a "necked down" area at each end , but I'm having a hard time understanding how that would effect the 1-2 shift?
I'll replace the full length rubber hose it has now BUT , it seems to me those reduced areas joining at modulator or nipple on manifold top of runner , the only point of that feature was to locate the tube securely on the production line ( slipping inside the mating device ) and the short rubber hose at each end just kept it all together ?

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You are partly correct. The tube was necked down to locate it to the fittings. This allowed for just a straight short piece of rubber vacuum line to seal the connection. If you look closely into the opening of the tube, you will most likely see a restriction on the end by the modulator. I would open up the ends of the metal line with a drill of appropriate size.It’s possible you may have to change the 1-2 shift valve spring in the valve body to get the trans to shift where you want it to.

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Thanks.