700R4 oscillates between 3rd and 4th gear
Thread Starter
Junior Member
Joined: Jun 2023
Posts: 23
Likes: 2
From: Ottawa ON
Car: 1986 Trans Am
Engine: 305
Transmission: 4-AT
700R4 oscillates between 3rd and 4th gear
Hi, Have a 1986 TA all stock,
This issue started just recently and quickly getting worse:,
Under light throttle at steady speed above 45Mph the transmission switches between 4th and 3rd gear for no reason.
If I lock the transmission in 3rd, all is working fine but in 4th it oscillates.
It does down shift no problem when required, and does shift smoothly into 4th.
at a higher speed (say 75Mph), it seems to stay in 4th just fine but will downshift to 3rd with a very minimal additional throttle.
This issue started just recently and quickly getting worse:,
Under light throttle at steady speed above 45Mph the transmission switches between 4th and 3rd gear for no reason.
If I lock the transmission in 3rd, all is working fine but in 4th it oscillates.
It does down shift no problem when required, and does shift smoothly into 4th.
at a higher speed (say 75Mph), it seems to stay in 4th just fine but will downshift to 3rd with a very minimal additional throttle.
Member
Joined: Aug 2004
Posts: 228
Likes: 12
From: Ottawa
Car: 86 IROC
Engine: Twin turbo L31 HSR
Transmission: 4L80E in progress
Axle/Gears: 9 bolt 4.11
Re: 700R4 oscillates between 3rd and 4th gear
Torque Converter Clutch (TCC) might be the problem. Unplug it from the side of the transmission and take the car for a drive. See what happens.
Joined: Sep 2002
Posts: 1,099
Likes: 21
From: Melbourne Australia but from South Carolina
Car: 1991 Trans Am convertible
Engine: 305 TPI
Transmission: Auto
Re: 700R4 oscillates between 3rd and 4th gear
mine did that years ago. Try around town and whenever possible use third gear only. I did that for about a month and it corrected itself. Worth a try. Even use the gears manually for awhile. That would possbily help
Thread Starter
Junior Member
Joined: Jun 2023
Posts: 23
Likes: 2
From: Ottawa ON
Car: 1986 Trans Am
Engine: 305
Transmission: 4-AT
Re: 700R4 oscillates between 3rd and 4th gear
Once I unplugged the wires that are going from the switch to the TTC the problem went away, now without the TTC lock, the motor spins about 200-300rpm higher in 4th gear.
My TA is a Canadian model, so no computer at all, everything is vacuum controlled (distributer, TTC, etc).
I must have a vacuum leak somewhere.
Junior Member
Joined: Jul 2024
Posts: 1
Likes: 0
Re: 700R4 oscillates between 3rd and 4th gear
Hi, Have a 1986 TA all stock,
This issue started just recently and quickly getting worse:,
Under light throttle at steady speed above 45Mph the transmission switches between 4th and 3rd gear for no reason.
If I lock the transmission in 3rd, all is working fine but in 4th it oscillates.
It does down shift no problem when required, and does shift smoothly into 4th.
at a higher speed (say 75Mph), it seems to stay in 4th just fine but will downshift to 3rd with a very minimal additional throttle.
This issue started just recently and quickly getting worse:,
Under light throttle at steady speed above 45Mph the transmission switches between 4th and 3rd gear for no reason.
If I lock the transmission in 3rd, all is working fine but in 4th it oscillates.
It does down shift no problem when required, and does shift smoothly into 4th.
Spoiler
Edit: Thanks for the update.
Last edited by RandalSloan; Aug 20, 2024 at 06:45 AM.
Thread Starter
Junior Member
Joined: Jun 2023
Posts: 23
Likes: 2
From: Ottawa ON
Car: 1986 Trans Am
Engine: 305
Transmission: 4-AT
Re: 700R4 oscillates between 3rd and 4th gear
The problem is not with the vacuum switch or the vacuum, the vacuum is holding well, and the switch is fine, I bypassed the switch and added a manual switch I operate while driving and the problem persists.
So it has to be something inside the transmission, either the solenoid or a switch.
For now I'm driving with the TCC disconnected.
So it has to be something inside the transmission, either the solenoid or a switch.
For now I'm driving with the TCC disconnected.
Thread
Thread Starter
Forum
Replies
Last Post
Donald Croes
Transmissions and Drivetrain
5
May 19, 2019 09:43 AM