Cruise wanders
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From: Jacksonville Florida BWO Dayton, Cincinnati, Bloomsbury NJ, Cincinnati
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Based on the OPs description I don't see anything wrong with his transmission. He is noticing the engine rpm varying as he drives with the cruise control set, he hasn't mentioned anything about shuddering.
The A8 transmission (actually any slushomatic) will declutch the Torque Converter Clutch when more resistance (such as when going from level ground to an uphill stretch) is encountered or when the engine switches from 8 to 4 cylinder operation or from 4 to 8 operation. When the TCC declutches due to increased load you will see engine rpm vary and if the load is high enough the transmission may downshift.
If you have a manual transmission the rpm won't change the same way since the clutch stays engaged. An increased load will slow the engine until the cruise control can react. If you have a cruise set while driving in 7th gear you will see more of a drop and a longer time to recover, but if you have the transmission in 4th gear there will be a slight drop followed almost instantaneously by a surge to recover lost speed.
Bill
The A8 transmission (actually any slushomatic) will declutch the Torque Converter Clutch when more resistance (such as when going from level ground to an uphill stretch) is encountered or when the engine switches from 8 to 4 cylinder operation or from 4 to 8 operation. When the TCC declutches due to increased load you will see engine rpm vary and if the load is high enough the transmission may downshift.
If you have a manual transmission the rpm won't change the same way since the clutch stays engaged. An increased load will slow the engine until the cruise control can react. If you have a cruise set while driving in 7th gear you will see more of a drop and a longer time to recover, but if you have the transmission in 4th gear there will be a slight drop followed almost instantaneously by a surge to recover lost speed.
Bill
Post #5 he mentions shudder.
Elmer
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Cruising
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From: St Augustine, fl
I believe The “shudder” I feel is related to the change in RPMs, it’s not much, but I can feel it when the RPMs change. This is fairly constantly and occurs at speeds from 60 mph up. And I mean it occurs constantly like at least once per minute. I do notice that if I try to maintain a constant RPM without using the cruise, my speed will gradually either increase or decrease, mostly increase. I guess I’m so used to the cruise control on my diesel pickup that this is very noticeable.
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The suggestion to slip it into "M" when the problem is happening is very valid. If the RPM surge and shudder stop, then you need another flush or it might be the torque convertor in trouble.
Elmer
Elmer
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I may be alone in this, but every car I have ever owned with cruise has an RPM change. NOT a speed change, but RPM. It is effected by other traffic (behind a truck vs a car or no one) wind, air drag, road surface. I have never been concerned. SPEED change is a different story.
Burning Brakes
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From: MSP
I may be alone in this, but every car I have ever owned with cruise has an RPM change. NOT a speed change, but RPM. It is effected by other traffic (behind a truck vs a car or no one) wind, air drag, road surface. I have never been concerned. SPEED change is a different story.
Thread Starter
Cruising
Joined: Dec 2022
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From: St Augustine, fl
Okay, I had a chance to take it out today and try it on manual. It doesn’t wander on manual, the RPMs stay constant. In automatic mode, the RPMs vary pretty constantly about 100 rpm. Does that mean I need the triple flush? The car has about 27000 miles on it, and since I just bought it, I have no idea if it’s ever been done.
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Okay, I had a chance to take it out today and try it on manual. It doesn’t wander on manual, the RPMs stay constant. In automatic mode, the RPMs vary pretty constantly about 100 rpm. Does that mean I need the triple flush? The car has about 27000 miles on it, and since I just bought it, I have no idea if it’s ever been done.
Elmer
Burning Brakes
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From: MSP
Yep, the shudder you're feeling is absolutely attributed to the V4 mode then. Most people seem to just opt out of using the V4 mode (either disable it with an addon device, or use manual mode all the time). Lots of information about that (and how it's damaging to the automatic) on the forum, give a quick search. General discussion has a stickied thread about the 8AT failures.
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