freakyhead94

Hey an greetings from Germany, this is my first post except for my little introduction and I hope that someone knows the answer to my problem. I bought my first american classic car, an 89 Caprice LS Brougham, 305TBI with the TH200-4R.

The car is basically running great, except for one problem. Sometimes the transmission doesn't want to downshift/deactivate the torque converter clutch, i'm not sure what it is.
I can recreate the problem in the following way. Drive on the highway/autobahn, 60/70mph for 30 minutes or more. When getting off the highway, braking to 20 or 30mph for example and then stepping on the gas, the engine vibrates and the car wont accelerate. It feels like the trans is not shifting down, or the tcc keeps engaged.
Same problem when there is alot traffic and the speed drops to 40 or 50mph, driving up a hill the car vibrates because of the low rpm. It feels the same as in a manual car when the selected gear is too high.

When I am driving through town after the highway, 1 or 2 minutes later the problem is gone and the car shifts perfect. Same effect when there is a traffic jam. 1 minute of slow driving or standing still solves the problem and it comes back after a few minutes of fast driving.
If I get off the highway with the car not downshifting, stopping at a red light and directly taking off after that, I can feel the trans engaging the tcc directly after the shift from first to second gear, which as far as I know should not be the case. There is the little rpm drop with the shift and then the tcc kicks in. The car then shifts through the gears up to 4th with the rpm rising and dropping exactly like in a manual transmission, not like it normally is with a torque converter.
But the engine does not stall when coming to a stop, so if it is the tcc, it at least has to disengage at a complete stop.

What was done to the trans in march by the pre-owner: Fluid and filter change. The problems existed when I bought the car.
What was done by my mechanic this month: Again fluid (dexron 2D) and filter change, new tcc solenoid, adjust tv-cable and repair broken wire inside the transmission pan (not actually broken but the insulation was broken).

The problem still exists.

Maybe someone of you had that problem and can help me find the solution for that.

Have a nice weekend everyone!

freakyhead94

Few months later, the problem got worse to a point where the car is almost impossible to drive uphill slowly.

We found the problem, the new torque converter clutch solenoid was bad out of the box. The old one was propably dead, the new one worked a bit and then died too, it was always active. In first gear, the converter clutch does not get any oil pressure from the transmission itself, so the engine did not stall. But directly with shifting into 2nd gear, the converter stayed locked in every gear.
Got a new solenoid installed, transmission is now shifting perfectly.

Problem solved.