'92 Chevy P.U. won't shift into high gear.

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Old 01-17-11, 02:49 PM
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'92 Chevy P.U. won't shift into high gear.

I got the truck with a 4L80E recently and it won't upshift into 4th. Shifts fine otherwise, fluid level and condition seems ok too. Any ideas where to start on finding the problem?
 
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Old 01-18-11, 06:03 AM
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Same tranny in my wrecker. First thing to do is to read codes to see if there is a clue. Pretty easy on the older GM stuff; just jumper the test connector and count the flashes of the check engine light. The tranny codes are mostly in the 70s & 80s and don't unsually turn on the CEL even though the codes will be there. I'm thinking a shift solenoid, maybe. I'll try to ask my tranny guru today if I get a chance.

Here's more on reading the CEL:

Troublcodes.net Trouble Codes OBD & OBD2 Trouble Codes and Technical info & Tool Store. By BAT Auto Technical

I'll also browse the tranny section of my factory manual to see if there's any help.

You didn't mention engine; 5.7L with throttle body?
 
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Old 01-18-11, 06:10 AM
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And a late thought; are you sure you have 1, 2, & 3? I know that sounds like a silly question, but it's just another piece of the puzzle.
 
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Old 01-18-11, 06:32 AM
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Okay, here's the full list from the service manual:

NO FOURTH GEAR

(Fourth clutch components)

Seals Nicked or cut
Cup plug Missing
Bolt Loose, broken, or missing
Piston Jammed
Spring assembly Jammed
Snap ring Not seated
Friction plates Worn or burned
Reaction plates Splines worn
Housing Damaged or cracked

(Overrun clutch components)

Housing Broken
Reaction plates Splines worn
Sun gear Worn
2-3 solenoid Stuck "off"
Pinched wire
O-ring failure
No voltage to solenoid
2-3 shift valve Stuck
PCM No signal to solenoid
QDM Failed

-----------------------------------------------------------------
Possible DTCs:

21 Throttle position sensor high
22 Throttle position sensor low
28 ATF pressure switch assembly
68 Overdrive ration
75 System voltage low
81 QDM and 2-3 solenoid
 
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Old 01-18-11, 06:43 AM
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I've got an AutoXray 6000 scanner that should be able to read the codes. It's a 6.5TD in a rollback. And yes I have 1,2,3.
 
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Old 02-04-11, 04:30 PM
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Is the engine getting up to it's proper temperature? You may have a thermostat that isn't getting the job done and the sensors think the engine is "cold" and will not let the tranny get into high gear.
 
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Old 02-05-11, 05:54 AM
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Coincidentally, towed a Chevy p/u to the tranny guy yesterday morning with what sounded like similar symptoms. Tranny guy mentioned 3/4 clutches to the customer, but would reserve diagnosis for further investigation. Rebel has a good point, too. I don't recall how restrictive the temp sensor may be, I always have high gear even on the coldest mornings (which, of course, aren't quite as cold as DC).
 
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