Transmission moan becomes a sigh
05-15-2008, 01:20 AM
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Transmission moan becomes a sigh
A week or so ago, you’ll recall, I wrote that the automatic transmission in my 1980 Porsche 928 was given to moaning during upshifts. One wag on the Forum asked whether my 928 wanted a cigarette afterward, and another suggested the transmission was moaning, “Oooooh, I wish I were a 5-speed.”
But seriously, folks, here’s an update.
I discovered that the moaning stopped entirely when I capped off the vacuum line to the tranmission’s modulator. Without vacuum, though, upshifts became unacceptably harsh. The absence of the moans led me to believe that the modulator might be at fault. So I ordered a new one ($43 at a local transmission repair shop).
I duly installed the new modulator, along with a fresh neoprene O-ring in the snap-on cap. I then took the car out for a spin and, to my dismay, the moaning continued. There was absolutely no difference.
In the process of installing the new modulator, however, I did discover that it’s adjustable. In fact, the new modulator came with a tiny T-shaped wrench for just that purpose. So I began adjusting. There’s a hollow, threaded, plastic sleeve at the mouth of the modulator that screws in or out with this wrench, although a flat-bladed screwdriver would work almost as well.
Long story short, by turning the sleeve in (clockwise) one turn at a time, the moan diminished but the shifts became progressively harsher. The trick, I discovered, was to reach a compromised balance: minimal moan during upshifts with an acceptable degree of shifting smoothness. It took about eight adjusting sessions...up on the lift, adjust, down, road test, come back, up on the lift again, adjust...pure trial and error.
The moan isn’t gone entirely, but it’s now more like a sigh, and a short sigh at that. Much better, in my opinion but, as I say, still not 100%. I might give it another go over the weekend, and if there’s any improvement, I’ll let you know. Meanwhile, if anyone has any further suggestions – or clever remarks – please pass them along.
-Michael Lamm, Stockton, California
1980 Porsche 928
But seriously, folks, here’s an update.
I discovered that the moaning stopped entirely when I capped off the vacuum line to the tranmission’s modulator. Without vacuum, though, upshifts became unacceptably harsh. The absence of the moans led me to believe that the modulator might be at fault. So I ordered a new one ($43 at a local transmission repair shop).
I duly installed the new modulator, along with a fresh neoprene O-ring in the snap-on cap. I then took the car out for a spin and, to my dismay, the moaning continued. There was absolutely no difference.
In the process of installing the new modulator, however, I did discover that it’s adjustable. In fact, the new modulator came with a tiny T-shaped wrench for just that purpose. So I began adjusting. There’s a hollow, threaded, plastic sleeve at the mouth of the modulator that screws in or out with this wrench, although a flat-bladed screwdriver would work almost as well.
Long story short, by turning the sleeve in (clockwise) one turn at a time, the moan diminished but the shifts became progressively harsher. The trick, I discovered, was to reach a compromised balance: minimal moan during upshifts with an acceptable degree of shifting smoothness. It took about eight adjusting sessions...up on the lift, adjust, down, road test, come back, up on the lift again, adjust...pure trial and error.
The moan isn’t gone entirely, but it’s now more like a sigh, and a short sigh at that. Much better, in my opinion but, as I say, still not 100%. I might give it another go over the weekend, and if there’s any improvement, I’ll let you know. Meanwhile, if anyone has any further suggestions – or clever remarks – please pass them along.
-Michael Lamm, Stockton, California
1980 Porsche 928
05-15-2008, 01:25 AM
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The Lady's Man
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I was told the smoother the shifts the wear on the internal clutches...just have to find a compromise but it shouldn't moan, groan or howl. Might be a temporary adjustment that speeds up the inevitable demise of the tranny. Hope not...best of luck to you.
05-15-2008, 06:53 AM
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A week or so ago, you’ll recall, I wrote that the automatic transmission in my 1980 Porsche 928 was given to moaning during upshifts. One wag on the Forum asked whether my 928 wanted a cigarette afterward, and another suggested the transmission was moaning, “Oooooh, I wish I were a 5-speed.”
But seriously, folks, here’s an update.
I discovered that the moaning stopped entirely when I capped off the vacuum line to the tranmission’s modulator. Without vacuum, though, upshifts became unacceptably harsh. The absence of the moans led me to believe that the modulator might be at fault. So I ordered a new one ($43 at a local transmission repair shop).
I duly installed the new modulator, along with a fresh neoprene O-ring in the snap-on cap. I then took the car out for a spin and, to my dismay, the moaning continued. There was absolutely no difference.
In the process of installing the new modulator, however, I did discover that it’s adjustable. In fact, the new modulator came with a tiny T-shaped wrench for just that purpose. So I began adjusting. There’s a hollow, threaded, plastic sleeve at the mouth of the modulator that screws in or out with this wrench, although a flat-bladed screwdriver would work almost as well.
Long story short, by turning the sleeve in (clockwise) one turn at a time, the moan diminished but the shifts became progressively harsher. The trick, I discovered, was to reach a compromised balance: minimal moan during upshifts with an acceptable degree of shifting smoothness. It took about eight adjusting sessions...up on the lift, adjust, down, road test, come back, up on the lift again, adjust...pure trial and error.
The moan isn’t gone entirely, but it’s now more like a sigh, and a short sigh at that. Much better, in my opinion but, as I say, still not 100%. I might give it another go over the weekend, and if there’s any improvement, I’ll let you know. Meanwhile, if anyone has any further suggestions – or clever remarks – please pass them along.
-Michael Lamm, Stockton, California
1980 Porsche 928
But seriously, folks, here’s an update.
I discovered that the moaning stopped entirely when I capped off the vacuum line to the tranmission’s modulator. Without vacuum, though, upshifts became unacceptably harsh. The absence of the moans led me to believe that the modulator might be at fault. So I ordered a new one ($43 at a local transmission repair shop).
I duly installed the new modulator, along with a fresh neoprene O-ring in the snap-on cap. I then took the car out for a spin and, to my dismay, the moaning continued. There was absolutely no difference.
In the process of installing the new modulator, however, I did discover that it’s adjustable. In fact, the new modulator came with a tiny T-shaped wrench for just that purpose. So I began adjusting. There’s a hollow, threaded, plastic sleeve at the mouth of the modulator that screws in or out with this wrench, although a flat-bladed screwdriver would work almost as well.
Long story short, by turning the sleeve in (clockwise) one turn at a time, the moan diminished but the shifts became progressively harsher. The trick, I discovered, was to reach a compromised balance: minimal moan during upshifts with an acceptable degree of shifting smoothness. It took about eight adjusting sessions...up on the lift, adjust, down, road test, come back, up on the lift again, adjust...pure trial and error.
The moan isn’t gone entirely, but it’s now more like a sigh, and a short sigh at that. Much better, in my opinion but, as I say, still not 100%. I might give it another go over the weekend, and if there’s any improvement, I’ll let you know. Meanwhile, if anyone has any further suggestions – or clever remarks – please pass them along.
-Michael Lamm, Stockton, California
1980 Porsche 928
