Author Topic: TH400, no 2nd gear anything easy to check?  (Read 2589 times)

Online zieg85

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    • 73-87 GM squarebody extended cab and conversions up to 91 R/V series
TH400, no 2nd gear anything easy to check?
« on: December 02, 2012, 12:41:42 PM »
I just got my latest truck which is a 1984 C30 with what I assume is a TH400.  It had a bad tire which blew on the way home so I took it real easy anyway.  With a spare I actually was able to drive it normally and with all the rattles I noticed something didn't feel quite right.  I manually shifted through the gears and found that second was not there.  First is fine, shift to 2 which trans stays in 1st.  Shift to drive it goes into 3rd.  Is there any common areas that would cause this that could be easily fixed by dropping the pan or am I looking at a rebuild?  Any help would be greatly appreciated.  Thanks in advance.
1985 C30 Custom Deluxe Ext. cab 5.7L TH400 3.21 
1985 C20 Scottsdale 7.4L 4 speed 3.21
1986 C10 under construction

Offline werewolfx13

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Re: TH400, no 2nd gear anything easy to check?
« Reply #1 on: December 03, 2012, 01:22:32 AM »
IIRC, at least on a th350, there are pins that act like valves in a portion of the valve body. If one is missing or stuck, the truck will not have the corresponding gear. I remember cutting a 6 or 8 penny nail to length for a shadetree rebuild to replace just such a pin that came up missing from the first transmission I had a hand in rebuilding.
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'76 Chevy k20 LWB 6.5'x8' Flatbed
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Online bd

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Re: TH400, no 2nd gear anything easy to check?
« Reply #2 on: December 03, 2012, 10:53:00 AM »
Possibly, you lost the 2nd gear sprag clutch (a known weak component in the TH400) and maybe the intermediate band.  Sprag failure will foil 2nd gear application; the band usually fails when the transmission is shifted manually to compensate.
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