1980 vette lock up problem??

1

1980corvette

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Sep 3, 2009
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I have a 1980 vette california edition wid a 305 THM350c and the rpms are higher than normal I believe it has something to do with the lockup but I don't know anything about it like where it is and how I can fix it, the car has only 39k miles and I hate seeing it in this condition. wherever tranny shop I've taken it they all say this is how they run, and I always get dissapointed because I know that's not how it runs so please if u have an idea I'd much appreciate it
 
1980 is unique. I believe a MAP sensor regulates lock up, but Doug knows. He has one. He will be along later.
 
When the lockup does not engage the trans should operate as a normal turbo 350 with same RPM as normal 350. If I recall the lockup drops it maybe 300 to 500 RPM.

The 80 model 305 still isn't computer controlled if I recall correctly so the lockup is governed by the vaccum switch on the firewall next to the distributor (drivers side) which only allows it to engage when high vaccum level (cruise), the brake light switch which disengages it when pressed and the govenor on the trans will only let it engage when trans is in 3rd gear.

My 80 L82 had the lockup but I took the solenoid out of the trans so it operated as a turbo 350 not 350C. I have since put in a 5 speed.

Do you have stock rear gears? What RPM at 55?
 
You can easily test to see if the lockup is working as follows:

Cruise down the highways at 55-65 mph and note the rpm. Without moving your foot off the gas pedal, use your left foot and very lightly touch the brake pedal (to the point that the brake lights come on). The lockup will unlock when you do this, so you should see about a 300 rpm increase. If you see no increase in rpm, your lockup is not working.

Keep in mind that your tranny does not have overdrive like the later 700R4, so the cruise rpm will be within a few hundred rpm of a regular TH350. The difference between the car running in 3rd gear and 3rd gear with lockup would not be noticable in terms of performance and drivability, so if you feel that the car isn't running right, chances are you have problems other than the lockup.

Lars
 
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daveL82 said:
When the lockup does not engage the trans should operate as a normal turbo 350 with same RPM as normal 350. If I recall the lockup drops it maybe 300 to 500 RPM.

The 80 model 305 still isn't computer controlled if I recall correctly so the lockup is governed by the vaccum switch on the firewall next to the distributor (drivers side) which only allows it to engage when high vaccum level (cruise), the brake light switch which disengages it when pressed and the govenor on the trans will only let it engage when trans is in 3rd gear.

My 80 L82 had the lockup but I took the solenoid out of the trans so it operated as a turbo 350 not 350C. I have since put in a 5 speed.

Do you have stock rear gears? What RPM at 55?
Click to expand...

lars said:
You can easily test to see if the lockup is working as follows:

Cruise down the highways at 55-65 mph and note the rpm. Without moving your foot off the gas pedal, use your left foot and very lightly touch the brake pedal (to the point that the brake lights come on). The lockup will unlock when you do this, so you should see about a 300 rpm increase. If you see no increase in rpm, your lockup is not working.

Keep in mind that your tranny does not have overdrive like the later 700R4, so the cruise rpm will be within a few hundred rpm of a regular TH350. The difference between the car running in 3rd gear and 3rd gear with lockup would not be noticable in terms of performance and drivability, so if you feel that the car isn't running right, chances are you have problems other than the lockup.

Lars
Click to expand...

Both posts are correct and also the car has to be going over 40 MPH for the lock up to engage. First thing I would check is for a vaccum leak to the switch on the firewall next to the distributor (drivers side) and check that the plug from the electrical harness didn't fall off. There could be many reasons why...Have you owned the car since new?...and it just stopped working? Reason I ask is is because the TH350C lock up was a unpopular setup and many people disconnected or gutted(removed) the the whole vacuum setup.
You haven't filled out your location so I don't know if your in the Socal area,if you are your welcome to stop by and I'll take a look at it for you.
 
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yea around 65 the car is doing 3500rpm i feel bad even driving it on the road its doing about 2200 rpm at 40
 
That sounds completely normal for a 3-speed car depending on rear end ratio. Whether or not the lockup is functioning won't change that by any more than a few hundred rpm. I assume you have verified that the tranny is going into 3rd..? If it's in 3rd, your rpm is normal for the rear end ratio you are running.

Lars
 
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