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Old 09-28-2007, 10:24 PM   #1
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Default 4L60E Shifts hard from N to Drive

Recently built 4L60E with vacuum modulator shifts great while driving but slams hard into gear from park to drive. Any ideas what can be causing this? Does vacuum control how hard the transmission shifts into drive? Could a vacuum leak cause this problem?
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Old 09-28-2007, 10:31 PM   #2
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Low vacume caused by a large am or a vacume leak will cause the mod to make the line presure high and this can result in a hard neutral drive or park to drive hit during engagment.
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Old 09-29-2007, 07:24 AM   #3
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To solve this you will need to put a .187" checkball in the forward abuse spring in the valve body. TransGo you to supply this checkball years ago, why they stopped I do not know, but that is how to soften the Neutral to Drive situation when using a camshaft with low vacuum numbers.
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Old 09-30-2007, 09:04 PM   #4
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I think this is more of a sensor problem because it is sort of intermittent. What sensors are related to shift firmness that could possibly cause this? The car is having several problems that come and go and they may all be related. Sometimes the idle seems to stick really high(around 1500rpm) and sometimes drops low enough for the engine to die, but most of the time the car runs great. Geoff at Thunder tuned on it for quite a while and worked out most of the issues but he was using his MAF because mine was modified. When I brought the car home, I put an old stock one off of a 98 TA on the car. Could this be related?
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Old 09-30-2007, 09:33 PM   #5
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Actually since you went vacc mod the pcm nor any of the sensors have any effect on the shift firmness, Now you could be on to something with the idle being to high if thats the only time it happens.
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Old 09-30-2007, 09:44 PM   #6
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Geoff probably changed you MAF because there is an issue with it that he did not like for your application. Higher idle will create less vacuum and in return higher transmission line pressure. I would leave the car the way Geoff set it up for you. Why did you change your MAF?
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Old 09-30-2007, 10:54 PM   #7
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The one on the car had been modified so he tuned it with a stock one he had at the shop. I drove it home with my modified one but put an old stock maf on that I had laying around because Geoff said I needed a stock one. I'm just wondering if the idle issues could be caused by the maf and lead to the shift issue?
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Old 09-30-2007, 10:59 PM   #8
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Yes the MAF can affect idle
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