70 coupe th400 issue?
Thread Starter
Melting Slicks
Joined: Oct 2012
Posts: 2,156
Likes: 273
From: Dunedin NZ.
70 coupe th400 issue?
On a dead flat very twisty road with a lot of low speed corners posted at 20 - 35 mph. I find the transmission will continually hunt between third and second gears if I am taking it slowly with barely any gas. If I lock it into second I typically find I'm doing 2500 rpm, the engine feels like it would be happy enough pulling top gear but the trans wont let it unless locked down.
Is this an annoying characteristic I will have to put up with or would adjusting the modulator on the transmission help? Not having had a car with this trans before I'm not sure what to expect.
Is this an annoying characteristic I will have to put up with or would adjusting the modulator on the transmission help? Not having had a car with this trans before I'm not sure what to expect.
Race Director
Joined: May 2006
Posts: 18,620
Likes: 2,553
do you know the maintenance history regarding the transmission? If not try replacing the filter and fluid. After that you can try playing with the modulator, make sure there is no vacuum leak on the line running to the trani.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,113
From: Crossville TN
If those turns tend to slow you down just a bit, that could be just enough for the trans to 'think' it needs to downshift.
BTW, it's a Corvette....why would you ever go slower than 30 thru a turn???
BTW, it's a Corvette....why would you ever go slower than 30 thru a turn???
Thread Starter
Melting Slicks
Joined: Oct 2012
Posts: 2,156
Likes: 273
From: Dunedin NZ.
Oil line to the trans is steel with short rubber link to inlet manifold and to modulator. These seem to be in good condition.
Thread Starter
Melting Slicks
Joined: Oct 2012
Posts: 2,156
Likes: 273
From: Dunedin NZ.
I will change the fluid and filter, then have a look at the modulator, does anyone know which is the correct unit for a 70 vette? I can't see any stripes on the one fitted.
Also, I read somewhere that you can change all of the trans fluid by first draining the pan and refilling, then disconnecting the feed line to the oil cooler and running the engine for a few seconds to pump the old fluid out of the torque converter. Has anyone tried this?
Also, I read somewhere that you can change all of the trans fluid by first draining the pan and refilling, then disconnecting the feed line to the oil cooler and running the engine for a few seconds to pump the old fluid out of the torque converter. Has anyone tried this?
Thread Starter
Melting Slicks
Joined: Oct 2012
Posts: 2,156
Likes: 273
From: Dunedin NZ.
Update: I adjusted the modulator adjustment screw by turning in two turns, this cured the problem but was probably a little too far as it is holding top gear a little too long so I will back the screw out half a turn and see how it goes.
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