Tranny Swap gone bad, maybe - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 06-30-2005, 08:39 AM   #1
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Default Tranny Swap gone bad, maybe

Swapped a junk yard tranny into my 93 SE (What learning experience). Two problems now, one major one minor.
Minor first - The shift indicator does not read correctly now. How this got change I have no clue but should be a easy adjustment on the column
Major - When it shifts into 2 and 3 it shifts hard, bang right now. No noise just bang there it is. Like someone installed a shift kit? Shifting into 4th and OD is hard but not as but not like 1st & 2nd. It shifts very hard, harsh, solid. Fluid is at the correct level.

What could be causing this????

Any and all help welcome.

Thanks
Steve.
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Old 06-30-2005, 08:44 AM   #2
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Sorry to hear that Steve. Working with a mechanic buddy of mine over the years I have seen bad tranny'* come from the junkyard. When they start and try them or get them in after asking the person if it runs...."yeah it runs" is the answer they got.

Assumption is that it runs and drives good, but they never really check it. Talk to the junkyard, they should at the least supply you with another one.
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Old 06-30-2005, 10:13 AM   #3
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Are you sure the vac line to the modulator isn't cracked or the rubber connectors aren't dry rotted/leaking?
Try pulling the vac line off the modulator and if it shifts the same, you might want to try and swap the vac modulator on the front of the trans.
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Old 06-30-2005, 12:11 PM   #4
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Quote:
Originally Posted by 95naSTA
Are you sure the vac line to the modulator isn't cracked or the rubber connectors aren't dry rotted/leaking?
Try pulling the vac line off the modulator and if it shifts the same, you might want to try and swap the vac modulator on the front of the trans.
I agree with this... The shift quality is mainly controled by the Vacume Modulator... Check it and or swap it out and let us know what if any changes there are

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Old 06-30-2005, 08:20 PM   #5
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Quote:
Originally Posted by jr's3800
Quote:
Originally Posted by 95naSTA
Are you sure the vac line to the modulator isn't cracked or the rubber connectors aren't dry rotted/leaking?
Try pulling the vac line off the modulator and if it shifts the same, you might want to try and swap the vac modulator on the front of the trans.
I agree with this... The shift quality is mainly controled by the Vacume Modulator... Check it and or swap it out and let us know what if any changes there are
Check the spectrum diodes too...i mock that which i dont understand :(
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Old 07-01-2005, 01:05 AM   #6
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Quote:
Originally Posted by ShatteredEagle
Check the spectrum diodes too...i mock that which i dont understand :(
Theres a hollow line that'* attached to the throttlebody. Vacuum is applied to the line from air moving past the one end of the line in the throttlebody. The vac pressure is pretty much constant through the line till it reaches the other end at a part of the transmission.
This part of the transmission (vac modulator) uses the intensity of the vacuum pressure to determine the line pressure in the trans (how hard it shifts). When the velocity of the air in the throttlebody changes, the line pressure changes accordingly. Unless it'* leaking, not connected, broke, or something i can't think of yet.
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