What good is a 4T60e transmission modulator?

[TopNotch]

The other day I found and fixed a vacuum leak on the 3800 engine in my white car. It was a little T connector on the throttle body, with one branch going to the fuel pressure regulator, and the other branch going to the transmission modulator. I couldn't find that T connector anywhere, so I jury rigged up a fix.
Yesterday on the trial run, my transmission wasn't shifting correctly, and at a gas stop, I noticed that exhaust heat had softened the new plastic vacuum line going to the transmission modulator, and it had flattened.
Today I replaced that vacuum line, but the transmission still didn't shift right. So I tried disconnecting it, and plugging it so that there was no vacuum leak. I went on a test drive, and the transmission shifted perfectly.  So what good is the transmission modulator anyway? I'm just going to leave it disconnected for now.
I ordered an "adjustable transmission modulator" from Rock Auto, and I'll see what that does when it gets here.

Edit: A minor problem noticed with the modulator disconnected is that the torque converter lock-up happens at a very low RPM. it seems like it should be a little higher. I'll see if I can fix that with the adjustable modulator.

[TopNotch]

I think I found a modulator that works good in my car. There seem to be several choices of these things available, each with different specs, and I have no idea what the specs mean, but the one I have now seems to work good. If anyone is interested, it's a Rostra model no. 51-0069.
Back to the original thread for further adventures with the car.

[Raydar]

My 4.9 came with a 4T60E. I ended up replacing my modulator, before I gave the trans away and swapped in a 5 speed. (The Cadillac 4T60E does nothing quickly. It's designed to be seamless and unobtrusive in a Cadillac DeVille. Not exactly desirable in a Fiero application. Didn't help that the overalll FDR was 2.97.)
My replacement modulator had a screw that you could crank inward, theoretically to firm up the shifts. I never found it to be firm enough for my liking.

[Wreck It Ralph]

Every transmission can be “reprogrammed” to how ever you want it. I used to get any valve body and then tune it to the customers requirements. A 4t60e is a 4T60e no matter what car it’s in. The guts are identical but the servo, accumulator, and valve body springs make most of the difference. Caddy’s have double soft springs in some locations so you didn’t get that snap from gear to gear. If I still had the $50,000 worth of tools at my disposal I could tune your transmission any way you like. Had a guy want a hard 1-2 and smooth everything else up to lockup. To each their own.

[Raydar]

That's good to know, for the next time. And really not surprising, all things considered.
But mine was "un-inspiring" all the way around. Aside from its non-existent shift firmness, it also had the 2.97 overall FDR. (Yeah, I know about chains and sprockets, but it just wasn't worth it, to go through all that.)
It was like driving a Cadillac. A very light, very quick Cadillac. But a Cadillac, nonetheless.
Even though the 5 speed gearing is far from ideal, it's still a lot more fun to drive than the previous iteration.