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10-22-2018, 06:50 AM | #1 |
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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. |
10-22-2018, 11:00 AM | #2 |
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Re: Turbo 400 experts please step in....
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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10-22-2018, 12:22 PM | #3 | |
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Re: Turbo 400 experts please step in....
Quote:
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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10-22-2018, 01:40 PM | #4 |
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Re: Turbo 400 experts please step in....
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10-22-2018, 01:42 PM | #5 |
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Re: Turbo 400 experts please step in....
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10-22-2018, 03:44 PM | #6 | |
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Re: Turbo 400 experts please step in....
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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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10-22-2018, 06:04 PM | #7 |
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Re: Turbo 400 experts please step in....
How much vacuum do you have at the modulator? -Al
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"That'll never work....." |
10-22-2018, 06:29 PM | #8 |
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Re: Turbo 400 experts please step in....
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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10-22-2018, 06:45 PM | #9 |
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Re: Turbo 400 experts please step in....
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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10-22-2018, 07:16 PM | #10 |
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Re: Turbo 400 experts please step in....
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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