Rough Automatic 2-1 Downhift Upon Stop

General information about the first-generation Nissan Maxima in the US. What was the Datsun 810 became the luxury leader Maxima in the US in 1981.

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Carimbo
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Rough Automatic 2-1 Downhift Upon Stop

#1

Post by Carimbo » 14 years ago

The last few days I have been noticing a rough 2-1 downshift (auto trans in D) when coming to a stop, say off a freeway offramp. Definite kick/thump. Not all the time, but mostly when slowing to a stop from higher speeds, yet nowhere near a panic stop. Mostly I drive pretty easy, in fact. I do give it the Italian tuneup when I get the chance, to burn out the carbons but since the brakes seem somewhat marginal in this model, and given the heavy forward weight bias, I try not to stand on them too much. Almost never manually downshift to use engine braking.

Time to change the tranny fluid? Still a light pinkish color, gives off a slight chemical odor. Any way to do a tranny fluid flush at home?

1982 Diesel, 3-spd AT, no OD.

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asavage
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#2

Post by asavage » 14 years ago

How's the upshift?

My first thought is that the trans is doing a part-throttle downshift, where it thinks you are actually on the accel while the vehicle speed is decreasing. Harsh 2-1 downshift in a gasser is often a too-high idle. Since the vacuum system is the weak point on these old cars, that's where I'd look first. Low vacuum to the trans' vacuum modulator would do this, but it'd also affect upshifts, delaying them.
Regards,
Al S.

1982 Maxima diesel wagon, 2nd & 4th owner, 165k miles, rusty & burgundy/grey. Purchased 1996, SOLD 16Feb10
1983 Maxima diesel wagon, 199k miles, rusty, light yellow/light brown. SOLD 14Jul07
1981 720 SD22 (scrapped 04Sep07)
1983 Sentra CD17, 255k, bought 06Jul08, gave it away 22Jun10.

Carimbo
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#3

Post by Carimbo » 14 years ago

asavage wrote:Since the vacuum system is the weak point on these old cars, that's where I'd look first.
Good advice, I looked and did find a cracked vacuum hose, one of those skinny ones, the short one that connects directly to the vacuum pump, connecting to the tee that feeds the cruise control and air conditioner fast idle
solenoid. Replaced that and seems better now.
asavage wrote:How's the upshift?
A little mushy and way too early for my tastes but I guess that's the way it was designed. For an automatic, seems like work to get it to downshift for power. I find myself often mashing down on the accelerator (trip the switch) to force a downshift when in town. Seems like the engineers wanted us to putter along in 3rd all the time.

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asavage
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#4

Post by asavage » 14 years ago

Referring to the vacuum control schematic in '83 FSM, pg AT-12 . . . maybe the variable valve on the IP is allowing too much system vacuum to the modulator on the trans. It's supposed to route more vacuum to the trans at idle, and less at higher accel levels. I've often suspected that my '82 Wagon has this problem, because it nearly always upshifts at what I think is too low road speed. The '83 Wagon upshifts higher, I've noticed.

Inadequate system vacuum could give you harsh downshifts, and a failed vacuum valve on the IP could explain the early upshifts. All guesses of course.
Regards,
Al S.

1982 Maxima diesel wagon, 2nd & 4th owner, 165k miles, rusty & burgundy/grey. Purchased 1996, SOLD 16Feb10
1983 Maxima diesel wagon, 199k miles, rusty, light yellow/light brown. SOLD 14Jul07
1981 720 SD22 (scrapped 04Sep07)
1983 Sentra CD17, 255k, bought 06Jul08, gave it away 22Jun10.

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kassim503
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#5

Post by kassim503 » 14 years ago

If you try to flush the transmission its a bad idea to cut a cooler line and run the engine while adding fluid. This method would make a giant mess that the EPA would flip out over.

You could try changing the fluid twice, pick up a trans fliter kit and change the fluid, and only replace the filter. Run it through the gears and then change it again, and this time replace the gasket. This is what i did and it worked really well and the fluid was the original and had the consitency of gear oil.
'83 maxima sedan, l24e, a/t, black

227K SOLD 6/7/2012

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