KustomJeff

Sorry if this has been discussed before, I tried to do a search but didn't find anything except one thread about an 81 model. My car runs and drives good EXCEPT when I put it in Drive or stop at a light/sign. The transmission isn't letting the car idle. In neutral it idles around 800-1000, in Drive it drops to 500 and pulls pretty hard. What should I be looking at on this. I've always believed transmissions were voodoo created by witch doctors at the factory anyway :-P Thanks for any help. By the way it is a 1978 L-48 with a TH350 trans.

TimAT

Normal idle speed should be around 650 in Drive.
And you are correct Automatic Transmissions are witch doctor created voodoo. I figured that out after I went to GM's Tech school on the 700-R4 and started repairing them at the dealer. Just plain magic.

KustomJeff

Glad to see I was correct about the voodoo part. Basically the car is still trying to pull at a stop, I can give it gas to keep it running, but I have to hold the brakes tight because it wants to go.

MelWff

hook up a hand held tachometer and with the wheels chocked and in drive adjust the idle speed screw and the mixture screws

HeadsU.P.

Accident waiting to happen. Put somebody behind the wheel, foot on brake.
This procedure really isn't neccesary anyway. I know someone who was pinned against a wall, crippled for life. If it will idle in park, it should idle in gear.

OldCarBum

Did you just purchase this car?
Did you make any recent modifications?
Is this something new it has started doing or has it always done this?

MelWff

Placing your foot on the brake changes the idle characteristics and if you read the tune up specs on the emissions label for automatics it states to make these adjustments in Drive with the wheels chocked and the parking brake on. If the OP is experiencing such a drastic change in RPM between neutral/park and drive the first thing to do is determine if the carburetor is correctly adjusted.

derekderek

I have a feeling the torque converter is going or gone bad. There is a set of fins that push on the tranny fluid. The fluid then pushes another set of fins that then spin the Trans input shaft. At idle, it doesnt have enough force to spin input and drive the car-usually. Sounds like it is locking up and is becoming direct drive instead of fluid drive. For the time being, pop into neutral as you stop. Drive when light turns green.

KustomJeff

I've had it a couple of months and it has done it the whole time. I recently started driving it more is why I want to address it now. All I have done under the hood is clean the carb with carb cleaner and change the air filter. My earlier work was new rubber in the rear suspension, now I'm headed toward the front of the car. I am also about to start working on the vacuum system for the lights.

OldCarBum

Do the easy stuff first. Make sure the idle is set right and the carb is properly adjusted. Next check your timing, then all your vacuum lines. If all these things are correct then, as stated above, I would look at your torque converter.

derekderek

if you put it in gear without your foot on the brake, what does the car do?