This is a weird problem to explain, so please bear with me. On my '82 Firebird Base v6, when I select D and attempt to move off, I have no power until midrange to high RPM. Like, so little power that the car does not move off the line at all without almost flooring it. I bought the car used and just sort of assumed this might be the sadness of the V6. I am doing all kinds of replacement stuff for worn out parts, practically everything in the engine compartment, brakes, suspension, etc. so I am not driving it around regularly while working on it. I've put a total of about 150 miles on it since buying it.

Even getting it to go up the driveway into the garage requires a good deal of throttle. Randomly, the other day, after a test run I had it in 1, and when I released the brake the car walked up the driveway itself with no throttle at all. This led me to the question of: why wouldn't it do that with D selected? Every automatic I have driven inches forward as soon as you release the brake at a full stop and then obviously moves through gears as appropriate. The way the car behaves is like when you drive a manual and start off in 2nd or even 3rd - lots of rev, tons of clutch, zero power, painfully slow movement until in the right RPM range for the gear. Is it possible that this kind of thing can happen with an A/T? Like when D is selected, the car is trying to start off in 2nd or even 3rd gear instead of starting in 1? I know 1 and 2 work if I select them manually, but obviously the car can't shift out of them when I do this.

It sounds dumb, but I can't really tell if it is shifting at all. It certainly doesn't jerk or pause at all like a shift. My car only has the idiot telltale dash so I can't see any real information about RPM. I have no exhaust after the Y pipe right now, so it is very loud and hard to hear changes in the engine RPM while driving.

What could cause something like this? Torque converter? Cabling? Solenoid? Some kind of adjustment?

There is no shuddering, slamming, or grinding. I have changed out the fluid, replaced the filter, mount, and cooling lines, which go to a brand new radiator.

Any help is appreciated!

 

It is possible to rework the valve body in the transmission to work like this for racing, but I can't imagine anyone doing this for that car. Maybe something is sticking in it? Odd, but I'd sure do the manual shift to save wear and tear on transmission.

 

Thanks for the reply. I also can't imagine anyone doing this intentionally to the car, although they did crazy things like replace the carb with one from an S10.

How might I check to see if something happened that might have the same effect as the modification you are talking about? Also any suggestions on what to check for sticking?

Thank you!

 

If you shift it manually 1,2,3 and 3,2,1 as you drive does it work? But when in D it stays in 3?

 

Forward 1, 2, 3(D) manually works. Right after I noticed this problem it went back on jackstands for more work, so I didn't test the other way.

I should be able to do a road test within the next couple days, will report back.

Thank you!

 

Check the line pressure, if too high , will get high gear starts.

Also, check that the TV cable isn't broken. that too can cause high line pressure.

RBob.

 

For simplicity...
Also since very few Members on the Forum actually have a THM200C Transmission...

This Transmission behaves in many ways like the THM700-R4 Transmission in regard to TV (Throttle-Valve) Circuit Pressures being out of Spec.
High Gear Start, difficult to achieve Down-Shifts (Detent or otherwise)...

And even the OP's description of the Vehicle rolling back/ forward... when starting from a complete stop.
The Torque-Converter will not be able to provide that same feeling of Torque Multiplication, with the Transmission in 3rd-Gear to start moving.

The TransGo THM200-4R (or even the TransGo THM700-R4, if you know what you are doing) Valve-Body Products for the TV Valve-Train will work with the THM200C Transmission.
This could be the majority of the solution...
Obviously I have no way to actually tell via this Thread.