Upshifting problems
Thread Starter
Heel & Toe
Joined: Nov 2008
Posts: 17
Likes: 0
From: Jacksonville Florida
Upshifting problems
My turbo400 won't upshift from 1st gear and I have checked the vacuum pressure from the intake manifold hose to the modulator. It is almost not perceptable. Any info on how much vacuum pressure the modulator needs would be a huge help! Also, is there a way to check if the diaphram in modulator is functioning correctly? Thanks again!
Race Director
Joined: Jan 2000
Posts: 13,011
Likes: 2,249
From: Corsicana, Tx
2020 C2 of the Year - Modified Winner
2020 Corvette of the Year (performance mods)
C2 of Year Winner (performance mods) 2019
2017 C2 of Year Finalist
Should be pretty strong vacuum. Check the fitting iteself in the intake..they sometime become clogged with carbon.
Any other vacuum leaks? How does engine run? Stock cam?
JIM
Any other vacuum leaks? How does engine run? Stock cam?
JIM
Burning Brakes
Joined: Nov 2006
Posts: 893
Likes: 7
From: Orange Park Florida
You can remove the modulator and use a vacuum source (mityvac, etc) and actually see the internal valve working.
If you are talking about kickdown, there is a kickdown solonoid in the turbo 400 that is actuated by a switch on the gas pedal (a 12volt source). Check your wiring, check for a 12volt reading at the kickdown connector on the tranny while someone floors the gas pedal. If all is there and still no shift, you have a bad solonoid. Most tranny shops and NAPA sell them (less than $20 bucks).
If you are talking about kickdown, there is a kickdown solonoid in the turbo 400 that is actuated by a switch on the gas pedal (a 12volt source). Check your wiring, check for a 12volt reading at the kickdown connector on the tranny while someone floors the gas pedal. If all is there and still no shift, you have a bad solonoid. Most tranny shops and NAPA sell them (less than $20 bucks).
Melting Slicks
Joined: Dec 2006
Posts: 2,669
Likes: 3
From: Kingston Ontario
If the diaphragm on the modulator valve is leaking, you will know it!
Once the engine is warm the burning hydraulic fluid in the exhaust system will pump smoke out the exhaust, looking like a blown head gasket.
Once the engine is warm the burning hydraulic fluid in the exhaust system will pump smoke out the exhaust, looking like a blown head gasket.
Thread Starter
Heel & Toe
Joined: Nov 2008
Posts: 17
Likes: 0
From: Jacksonville Florida
shifting problems
Other than needing to have my edelbrock carb jetted (runs a little rich) it runs fine. I've stayed with the stock cam. I'll check your suggestions..thank you!
Le Mans Master
Joined: Oct 2006
Posts: 7,123
Likes: 433
From: Gladstone MO
C3 of Year Finalist (appearance mods) 2019
Pull the hose off the modulator- if fluid runs or drips out, the modulator is dead. Chack the vacuum at the trans end as suggested. Disconnect the wire on the left side- the detent solenoid- check power as suggested- key on, see if there's 12v at the trans with no throttle.
Still no up shift at light throttle, it's a good bet the gear on the governor is "applecored" or broken. Also possible the screen in the governor feed line is plugged with trash.
Still no up shift at light throttle, it's a good bet the gear on the governor is "applecored" or broken. Also possible the screen in the governor feed line is plugged with trash.
Last edited by TimAT; Feb 1, 2010 at 11:36 PM.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
2027 Corvette vs The World: Every Model vs Closest Competitor
Joe Kucinski
10 Most Common Corvette Problems of the Last 20 Years!
Joe Kucinski
5 MOST and 5 LEAST Popular Corvette Model Years in History!
Joe Kucinski
2027 Corvette Buyer's Guide: Everything You Need to Know!
Joe Kucinski
10 Things C8 Corvette Owners Hate (But Won't Tell You)
Joe Kucinski
10 Best Corvettes Coming to Barrett-Jackson Palm Beach 2026!
Brett Foote
Every Corvette Grand Sport Explained! (C2, C4, C6, C7, & C8)
Joe Kucinski
Grand Sport & Grand Sport X Launch Alongside All-New 535hp LS6 V8!
Michael S. Palmer
5 Reasons Bad Drivers Crash & 5 Ways to Avoid a Costly Mistake!
Joe Kucinski
Thread Starter
Heel & Toe
Joined: Nov 2008
Posts: 17
Likes: 0
From: Jacksonville Florida
Upshift problems fixed!
