Shudder between gears 3 and 4 (OD)

[trinacriabob]

I know there are a lot of smart people on the board so I am enlisting your help.

My Regal, 1992, with the above transaxle (no electronic control ... that came the following year). Under a cruise type of throttle, it will exhibit a shudder between 3rd gear and overdrive at a speed of about 50 mph....when it tends to hunt betwen 3rd and 4th anyway.

OK, the car does have 222,000 original miles. The trans has been serviced every 20,000 miles and it is mostly freeway driving. Shifts from 1 to 2 and 2 to 3 are virtually flawless and so are most 3-4 shifts when under moderate acceleration.

When it does do this little act (it's been going on for a couple of months), pressing down on the accelerator a little more deliberately clears it.

Questions:

Do you know what it might be? Are there solenoids that help determine the shift points on the non-electronic transmissions? Your input is appreciated.

[76ChevyTrucker]

Bob, on that one, no soleniods to control the shift, but there is a Transmission Vacuum Modulator that's on the tranny. It should be located on the driver's side, with a vacuum line going to it. I know that on the older trannies (THM350 and 400), the modulator controlled shift points using engine vacuum pressure, if I remember right, yours does too, and it might not be getting proper vacuum to ensure a positive and firm shift, so I'd try seeing what kind of vacuum you're getting from the little hose and if that doesn't show funky, change the modulator, it might be clogged.

[trinacriabob]

Bob, on that one, no soleniods to control the shift, but there is a Transmission Vacuum Modulator that's on the tranny.  It should be located on the driver's side, with a vacuum line going to it.  I know that on the older trannies (THM350 and 400), the modulator controlled shift points using engine vacuum pressure, if I remember right, yours does too, and it might not be getting proper vacuum to ensure a positive and firm shift, so I'd try seeing what kind of vacuum you're getting from the little hose and if that doesn't show funky, change the modulator, it might be clogged.

Thanks. Didn't realize there were still modulators. I'll look for the vacuum hose and then the modulator to see if I can plop one on. I did look into this topic via search engine and also found that there is such a thing as torque converter shudder.

It is so intermittent that it's freaky. The fluid was just changed for the 11th time....at about 220,000 miles and it is a beautifully transparent light pink, as it has always been. I will look into your suggestions as we are working from cheaper options first. Thanks again.

[76ChevyTrucker]

no problem at all, like I said on here before (at least I think I've said it) I'm a parts guy and I like to diagnose and help out anyway I can when it comes to parts and problems.