TH 400 Issue....
Thread Starter
Burning Brakes
Joined: Mar 2010
Posts: 803
Likes: 4
From: Christchurch, New Zealand
TH 400 Issue....
Why would my TH400 shift down while going around sweeping bends at around 35MPH? Happens going both left and right. We're not talking sharp bends here either!
Thread Starter
Burning Brakes
Joined: Mar 2010
Posts: 803
Likes: 4
From: Christchurch, New Zealand
Thanks. I'm sure the fluid level is good. I've been meaning to do the filter for a few weeks now. I've had one sitting around for ages. It's a good excuse to get off my butt!
Burning Brakes
Joined: Nov 2006
Posts: 893
Likes: 7
From: Orange Park Florida
If you are going to pull the pan, go ahead and replace the detente relay/solonoid. This relay controls the kickdown action in the tranny (shifting down to second gear). The relay could be weak and the rocking of the car could be causing it to open or close.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,114
From: Crossville TN
The vacuum modulator could have a leak in the diaphragm and occurs more under load during turning. If oil gets into that vacuum tube, then the vacuum signal may not function properly. Or, there could be some mechanical malfunction in that modulator. In any event, I think the modulator is the problem.
Thread Starter
Burning Brakes
Joined: Mar 2010
Posts: 803
Likes: 4
From: Christchurch, New Zealand
Sure Jim.
First thing I've noticed after reading the AIM, is that I'm missing the hard line from the trans to the intake. Bubba has rigged up a length of hose. Could that be a cause?
First thing I've noticed after reading the AIM, is that I'm missing the hard line from the trans to the intake. Bubba has rigged up a length of hose. Could that be a cause?
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)
Joe Kucinski
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Top 10 C9 Corvette MUST-HAVES to Fix These C8 Generation Flaws!
Michael S. Palmer
10 Revolutionary 'Corvette Firsts' Most People Don't Know
Joe Kucinski
5 Reasons to Upgrade to an LS6-Powered Corvette; 5 Reasons to Stay LT2
Michael S. Palmer
2027 Corvette vs The World: Every C8 vs Its Closest Competitor
Joe Kucinski
10 Most Common Corvette Problems of the Last 20 Years!
Joe Kucinski
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,114
From: Crossville TN
If the hose is collapsing when you let off the throttle in the turn, then no vacuum would pass to the modulator. Once throttle picks up again, it should shift OK. Yes, I think that might be your problem. If you want to Gerry-rig it to test for that problem, just get a length of inexpensive aluminum tubing and stick some hose on each end to make the intake & modulator connections. Duct tape it in place, if you have to, just for testing. Try it out and see.