heygibb

Drive train hiccup...does AT need work?

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My 90 coupe is still running fairly well, other than a no start condition I had a few weeks back. I'll address that in another post. But I've noticed a hiccup while underway that concerns me.

At 51-53mph, my Reatta seems to skip and chug in the power train. I’m not sure I can clearly describe the symptom but it is more a feel than a noise. It’s like the transmission is between gears and it feels like it’s free from any power influence. If I give it a little gas, it reacts in a staccato fashion, not smooth, before it accelerates normally again.

I found a very informative video on how the inner components of an AT interact, perform and fail.

https://www.youtube.com/watch?v=szu-0IqMygA

At around 4:20, he explains a common failure in ATs that involve the clutch pack and friction rings controlling higher gear engagement. There is a stack of thin clutches that react to transmission oil pressure to engage particular gears. The hesitation I am experiencing seems to relate to having degraded friction plates. Maybe they don't grab on a constant basis anymore. Am I on the right track here?

If so, is it a condition I can live with for awhile or should I anticipate total failure, at some point?

Thanks

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Here is a problem similar to what you describe and the fix: When you  reach about 50 mph under light acceleration the transmission is in 4th gear and the torque converter locks up. If you try to accelerate a little more and the engine hesitates the problem is likely to be caused by a misfire due to a weak ignition system. It is often mistaken as a transmission problem. To see if this is your problem, the next time it does it keep your foot constant on the accelerator while it is hesitating and then lightly put your left foot on the brake pedal. Not enough to apply the brakes but just enough to activate the brake light switch. That will unlock the torque converter. If the cars seems to smooth out and run better you like likely have the ignition problem I described above.

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Awesome. I hope your diagnosis is correct. I will try it next time out.

I replaced ICM, coils, crank position sensor and cam position sensor in Dec/2015. ..all new.

I replaced wires and plugs ~60k miles ago.

I'll check back after a trial run.

Thanks

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It looks like it's the ignition system. While depressing brake slightly at the trouble point and steady gas pedal, it cleared.

I'll do a plug change first. So gap at .060 w/ Rapid fire #14 plugs? I have Bosch now, I believe. 

I have three separate coils, not the old Magnavox all in one design.

 

Asa, I didn't get the drop in rpms on deceleration.

Is this the modulator you speak of?20180711_212036.thumb.jpg.52ca15be2fa55e1a7948b2ea96f607bc.jpg

 

I've never changed it, ever. What brand/design is best suited for replacement? There seems to be two designs. One is like the old and one isn't.

Looking at the business end, it looks like it plugs into position. Is that correct? If so, I guess I pry it out?

 

modulator.jpg.3a4e5d940372b0f515ee67af537cdcdb.jpg        delco.jpg.bc2e660072c4dda582b225c84884eca2.jpg

 

 

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look carefully as there is a 10mm bolt that holds a forked bracket. this set up that holds the modulator in place. The smaller one is adjustable and after market. The bigger one is like the original one.

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Has anyone tried the Iridium plugs? If this graph is accurate, they seem to outperform other designs in every way.

sparkPlugChart.jpg.9782c1daa8e03d1346ecd17980956555.jpg

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I would stick with the Rapid Fire plugs and save the extra money for a new set of spark plug wires. Old spark plug wires breaking down are the most common parts that causes a low speed misfire from my experience. Most any modern, name brand, spark plug is good for about 100,000 miles. I don't see any of the things on that chart being too relevant when you're installing the spark plugs in a low RPM, low horsepower, engine like the 3800. Just my 2 cents....

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10 hours ago, heygibb said:

What brand/design is best suited for replacement?

 

Either design will work. The small one is adjustable by sticking a small screwdriver inside the hole where the hose goes on. I guess that could be an advantage or a disadvantage depending on who's doing the adjusting. :) In my experience the larger factory modulator valve is more reliable and lasts longer but it's also more expensive. Usually the modulator fails by the diaphragm inside breaking. You can check for that by removing the hose and inspecting it for transmission fluid inside. If the diaphragm breaks it can cause really hard shifts.

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1 hour ago, Ronnie said:

I would stick with the Rapid Fire plugs and save the extra money for a new set of spark plug wires. Old spark plug wires breaking down are the most common parts that causes a low speed misfire from my experience. Most any modern, name brand, spark plug is good for about 100,000 miles. I don't see any of the things on that chart being too relevant when you're installing the spark plugs in a low RPM, low horsepower, engine like the 3800. Just my 2 cents....

Good to know. I'll do the Rapidfire and change modulator, then check results. Wires may be next.

Here is link to rebate for plugs I found at RockAuto in case anyone else is in the market.

https://www.rockauto.com/lang/en/promoCat.html#acdelco

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All I can say is 'wow'. You Reatta wizards know this car. After plug change, the hesitation/chug disappeared. This is only after one test drive with the Rapidfire brand.

My new modulator should get here by Wednesday. Should I change it out? I still have OEM mod installed. I see no ATF in hose or at port...completely dry.

I'm all for preventive maintenance but also believe in the 'if it ain't broke, don't fix it' credo.

 

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I would leave the modulator alone if the car is now working to your satisfaction. One change at a time and then verify the fix for a while. You can always change it later. If the plugs alone cured the problem, how did the ones removed look? 

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All were clean. They were the Bosch Platinum with the funky electrode design. This is what they all looked like w/ 60k miles of use. One test drive isn't necessarily all conclusive. I'll drive the car a bit more and see how she goes w/out the mod change. Suits me if I can shelve it for awhile.

Bosch.thumb.jpg.2e339af4b8bd5bf9c98d168b1e153f72.jpg

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10 hours ago, heygibb said:

All were clean. They were the Bosch Platinum with the funky electrode design. This is what they all looked like w/ 60k miles of use. One test drive isn't necessarily all conclusive. I'll drive the car a bit more and see how she goes w/out the mod change. Suits me if I can shelve it for awhile.

Bosch.thumb.jpg.2e339af4b8bd5bf9c98d168b1e153f72.jpg

Well there's your problem, the spark was confused:)

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