Money72

Greetings all,
Just purchased a 69 cutlass with 350/th350. While driving it will not shift to 2nd gear. It stays in first revving to bout 3,000 before I let of the gas. I changed the governor and hooked up vacuum modulator, adjusted kick down cable, still won't shift. Thanks in advance for all responses.

Vintage Chief

All good you hooked up the vacuum modulator. Did you actually 'test' the vacuum line to determine you have vacuum to the modulator?

Money72

No, but as I was reading past threads I see a few suggestions I need to try. I have vac modulator hooked to carb not manifold. So I will check for vaccum and change port location tomorrow. Anything else I might be missing.
Thank's again

droldsmorland

Is fluid level ok?
What recent service has been performed?
Did this problem just start or has it been progressively getting worse?
Is the modulator a stock part and where did you plug it in?
What governor did you use?
Did you inspect the governor drive gear?
Try going a bit beyond 3K say 3500. Does it shift?
If you are running the OEM metal line check it for obstructions. Verify there is a vacuum signal down at the modulator.

EDIT> hook it up to direct intake manifold vacuum. This is likely the problem.

Vintage Chief

Yes, hookup to manifold not carburetor. Measure the vacuum w/ a gauge.

Money72

Thanks for all the suggestions. I will get at it again tomorrow.

matt69olds

Remove the govenor from the case, make sure the gear isn’t chewed up. The weights are few to move, and the bore it rotates in isn’t chewed up.

oldcutlass

Your modulator needs to be connected to manifold vacuum. It does not matter whether its at the carb or a manifold port.

Money72

Thanks for all the advice guys.The car drove like this when I received it off the trailer when I bought it Nov 26th. Here's what I did this far. Fluid level is ok and looks clean I checked gear on governor when removed and it was not chewed up. Weights moved freely. Piston inside governor moved up and down as I moved weights, and springs looked ok. Vacuum modulator is not stock (adjustable). When I check vacuum what #'s am I looking for?

Vintage Chief

~16"Hg-18"Hg

matt69olds

Make sure the vacuum gauge responds immediately to changes in engine speed. In other words, if you snap the throttle open, the gauge should immediately drop, and then come back up. If it’s slow to rise, make sure the vacuum nipple isnt plugged up with carbon.

matt69olds

Even if the vacuum is low, it should shift, only at a higher engine speed. If the modulator is unhooked, the trans should still shift at whatever it normally would upshift at WOT. If it refuses to shift, either the shift valve won’t move, or the valve isn’t getting enough govenor pressure to overcome the shift valve spring.

The shift valves are normally held in the downshift position by spring pressure. Govenor pressure (vehicle speed) and modulator pressure (engine load) work to move the valves depending on engine load or speed. It’s a balancing act to get the trans to shift as needed.

Fun71

And my experience has been if you let off the throttle, it will upshift and you can coast along (if it didn't upshift engine braking would occur), but giving any throttle at all will cause it to downshift again.

droldsmorland

If you have a good vacuum signal down to the modulator nipple then the modulator would be the next suspect. It can be pulled out and tested with a vacuum source to see if the piston moves. (tip...jack the passenger side of the car way up to reduce fluid loss).
If it's a TM50 adjustable modulator someone may have over adjusted it. This will cause a high 1-2 shift point
The adjuster can be drawn in too far which will cause the adjuster to separate from the diaphragm. I don't remember if simply backing it all the way out will reset the adjuster.
Google TM50. You will see a pic or two showing what it looks like and I do see at least one pic showing the adjuster in the nipple(flat blade screwdriver slot). Stupid work firewall won't allow pic uploads GAH!

oldcutlass

If someone turned the adjusting screw too far inward (don't ask me how I know) it cannot be rethreaded back into the body. The adjustment moves the shift point about 5-7 MPH one way or the other. The intended purpose of the adjustable modulator is to adjust shift firmness and the shift timing is an indirect result.

matt69olds

You won’t have engine braking unless the shifter is in 2 or 1. With no vacuum, if you accelerate to say 20-25 mph and let off the throttle, the trans will freewheel. That’s because the low roller clutch (holds in any forward gear, “freewheels” or overuns in reverse) isn’t overdriving the input shaft due to the band not holding the direct drum.


Think of it like this, with no engine vacuum, as far as the valve body is concerned, the engine is at full throttle. No vacuum=high engine load. If you accelerate fast enough, govenor pressure will go high enough to overcome both modulator pressure and the shift valve spring. Like I mentioned earlier, spring pressure tends to hold the shift valves in the downshift position, as does modulator oil. When gov pressure rises high enough to overcome both of those pressures, the trans up shifts.

Money72

Thank's everyone for the valuable information. I finally got around to changing modulator. Went for test drive and transmission shifted like normal. One hurdle overcome now on to the next.

Vintage Chief

Good deal.

droldsmorland

Cool tx 4 following up here.

oldcutlass

Glad you got it fixed.

EdwardB

If I may add a question to this thread. Will the use of a high-rise aftermarket intake manifold necessitate the modulator to be tweaked?

matt69olds

If that’s the only change, probably not. If you swap in a cam that’s pretty aggressive, The resulting lower vacuum may require a little adjustment.

Dave26

Just an F.Y.I......if you experience hard shifts due to low vacuum, one of these may be helpful. The one on the left is for low vacuum, on the right is adjustable for different vacuums.

Fun71

I installed a Performer RPM and it did not affect the modulator, but I did have to adjust the secondary air valve tension spring on the QuadraJet.