C4 Tranny Help Please

[modifiedmustang]

When I set the idle on my car at 500 rpms and put the tranny in gear, the idle on the car slows to where it will barely run, and I have to stand on the brake to keep it from moving.

It seems that the tranny is trying to fully engage at this slow of an RPM. I understand that the stall speed is determined by the torque converter, so could that be bad, or could other factors such as fluid type, fluid level, or other problems be causing this?

I don't know this tranny's history as it came from a non-running car when I got it. The fluid seemed fine and filter was clean when I changed it. I replaced the fluid with Pennziol Dextron/Mercon III, but understand most run Type F. Could that cause the early engagement?

I had the dipstick tube out of the tranny. If it weren't calibrated right or seated, and I had a false oil level reading and had too much oil, would that cause the early engagement?

I have another torque converter I can try, but before I yank the tranny, is there any other factors I can try before I go through the trouble of installing the second converter?

Thanks,
Glenn

 

[65fastback2+2]

park idle should be about 1000 rpms for an auto tranny, check your fuel mixture.

 

[modifiedmustang]

I'm certain my car is running pretty rich. The idle screws are about 1.5 turns out on my holley 600 cfm vacuum secondary electric choke holley. To lean it up I would need to screw them in right? Or would I need to mess with the main jets to correct this? I'm new to this whole carb tuning thing.

So the engine's fuel/air mixture does have a direct correlation to the stall speed of the tranny? I'd like to understand the logic!

My engine does have a lope to it, as if it had a beefy cam in it. I don't know the specs of the cam, as it was a freebie from a friend who yanked it from his car. He didn't recall it being that lopey though. Would the rich fuel mixture contribute this rough idle?

Thanks,
Glenn

 

[modifiedmustang]

More Info on my dilemma...

It also seems that when the car is driven a while and gets nice and hot it gets worse, because the engine labors more as the tranny engages and pulls even harder.

More specs to help solve this tranny dilemma:

Lower half pretty much a stock '97 crate motor.
Stock 1970 heads unworked
Edelbrock performer 289 intake
Hooker comp headers
Unknown cam specs (RV cam)
Holley 600 cfm vacuum secondary electric choke
Stock (new) vacuum adv. single point distributor 10deg advance timing
Flowmaster 2.5 2 chamber exhaust

Thanks in advance for the help,
Glenn

 

[modifiedmustang]

Yep....Tranny line is plugged in! I tried both with it plugged in and with it unplugged (plugging the outlet on carb when line not connected of course), and yeilded the same results either way.

When the line is plugged in, the tranny will shift almost immediately into second (running 4:11 gears), and then will shift into third accordingly. All seems fine there.

 

[65fastback2+2]

how about a vacuum leak? do you have the tranny vacuum line plugged in?

 

[modifiedmustang]

Mini spool until I can afford to upgrade to a 9" locker....

 

[65fastback2+2]

Yep....Tranny line is plugged in! I tried both with it plugged in and with it unplugged (plugging the outlet on carb when line not connected of course), and yeilded the same results either way.

When the line is plugged in, the tranny will shift almost immediately into second (running 4:11 gears), and then will shift into third accordingly. All seems fine there.

what kinda setup is the 4.11??? posi, spool, locker??

 

[65fastback2+2]

Mini spool until I can afford to upgrade to a 9" locker....

theres your problem. mine had a 4.11 spool in it and would clunk hard into gear, had to push the brake pretty hard, then i switched to a 3.00 open and it all went away. The torque multiplicity makes a ton of difference on how the tranny acts.

 

[modifiedmustang]

Wow, never thought of that! It does make sense that the car has enough torque to really pull in idle.

So my problem is a double edge sword....

The torqe from the low gear ratio is why i have so much pull when at a stop. So to compensate, I had the idle way down thinking it was early engagement on the part of the converter. Now, to get the idle set right, I will even have more of a problem with the pulling at a stop.

To solve it, I should probably get a higher stall on the converter then right? There again, I would probably bark tires every time I left a stop though..... decisions, decisions..... what to do....

Thanks for the input!

 

[Max Power]

Actually, 500rpm idle in nuetral is way to low. Should be 800-900.

 

[WORTH]

Is this a manual brake car by any chance?

 

[Ozsum2]

Park idle is closer to 700 rpms and around 550 in gear with an auto of course.

 

[Ozsum2]

Actually, 500rpm idle in nuetral is way to low. Should be 800-900.

Sorry Max, didn't see your post. We are ballpark.