C-6: Strange Kickdowns
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Senior User
Joined: Aug 2000
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C-6: Strange Kickdowns
Hey guys, just recently my truck has been acting a little wierd. heres the problem: if im driving along at say, 15-30mph, (with barely any pressure on the gas) it will sometimes drop out of third into second. when it does that, it will stay in second unless i give it more gas, in which case it will usually go back into third at around 2500 rpm's. the wierdest thing is that it only does it sometimes, and theres no specific time that it happens... its totally random. its nothing horrible but it gets really annoying and i worry it might be the start to a bigger problem. would i be wrong in assuming that this could be a vacuum leak? its all thats coming to mind right now and it would make sense too. is there anything else that could cause this? well, thats about it, thanks in advance for any help.
Fleet Owner
Joined: Jun 1999
Posts: 24,552
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From: Creedmoor, North Carolina
C-6: Strange Kickdowns
Bob, your question would be real easy to check out. There is a rubber hose that goes from the engine to the modulater on the tranny. I believe it is on the passinger side facing rearward. Your modulater valve could be going bad as well.
John
jowilker
66 F100s
In the still cool hours of the night,
you can hear chevys rusting away.
John
jowilker
66 F100s
In the still cool hours of the night,
you can hear chevys rusting away.
Senior User
Joined: Jul 1999
Posts: 472
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From: USA
C-6: Strange Kickdowns
79supercab4x4,
I don't think lack of vacuum at the modulator would cause an incorrect/erratic downshift, but it's easy to verify correct vacuum on a gauge while wiggling the hoses and steel line. I suggest checking the kickdown lever next, and verify that it is "loose" and free to move - and also pushes the transmission lever down against its internal spring when the carb is "to the boards". The other possibility I can think of is an internal leak in the governor pressure circuit. There's always the contaminated valvebody too.
Good luck troubleshooting,
Art
I don't think lack of vacuum at the modulator would cause an incorrect/erratic downshift, but it's easy to verify correct vacuum on a gauge while wiggling the hoses and steel line. I suggest checking the kickdown lever next, and verify that it is "loose" and free to move - and also pushes the transmission lever down against its internal spring when the carb is "to the boards". The other possibility I can think of is an internal leak in the governor pressure circuit. There's always the contaminated valvebody too.
Good luck troubleshooting,
Art
