3 speed Auto stuck in low - Pontiac GTO Forum
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post #1 of 3 (permalink) Old 05-13-2019, 11:20 AM Thread Starter
 
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3 speed Auto stuck in low

Apologize for being off subject ??, but about 10 years ago, my son bought a 67 Firebird with a hacked up chevy 350 + a 3 speed automatic (probably chevy TH350??). Shortly afterwards we replaced the engine with a new chevy crate motor keeping the same transmission. It does not get driven that much but when it is it just performs great, lots of power etc. Last week he attempted to take it for a drive and it would not shift out of low gear. Neutral and reverse are "normal" with some problems. You better have you foot on the brake when you shift it into reverse as it seems to be a hard shift. Manually shifting thru the gears does not bring it out of low. Fluid is clean and full, no smell, linkage is tight etc.

Questions before we either pull it or have it towed for service. I know this is skimpy info, but looking for some guesses as to what it might be.

1. Modulator valve (if it has one)?
2. Gummed up, need a drain/flush
3. TC, valve body or plugged filter if it has one

Tx Mike
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post #2 of 3 (permalink) Old 05-13-2019, 11:54 PM
 
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I would check the vacuum line going to the modulator...
it should have a couple inches of rubber tubing on both ends
make sure they are tight fitting... even cut 1/2 inch off ALL ens of the tubing and reinstall

make sure its vacuum rubber tubing ,,,I have seen wiper hose on rigs before
and it collapses under vacuum

https://www.google.com/search?q=turb...w=1067&bih=690

it should be steel tubing in the middle so it doesnt lay on the exhaust

IF you still have the steel line the tranny end hose is preformed.... I recommend
buying one IF you have the steel line in the middle ... as sometimes the hose gets hot
and it bends and flattens out and pinches itself off of vacuum

start with checking the rubber hoses and the vacuum modulator

pull on the kickdown cable a couple times on the drivers side of the carb

is it stuck or sticky?

any body else ??

Scott T
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post #3 of 3 (permalink) Old 05-14-2019, 11:04 AM Thread Starter
 
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Thanks Scott, will have a look this weekend? and see if anything is ok..
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  Pontiac GTO Forum > The 1964-1974 Pontiac Tempest, Lemans & GTO > 1964-1974 Tempest, Lemans & GTO Undercarriage, Frame, Transmission and Differential Discussions.

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