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Discussion Starter · #1 ·
Hi guys, first post, but couldn't find anything similar. My smart has 51,000 miles, the engine seems to be in great shape but lately, in the summer heat, the clutch sometimes slips really badly between 2nd, 3rd, and 4th gears mostly. I notice it mostly when the AC is on full blast, recirculate, and it's really hot outside.

I'm not gunning it wherever I go, so it seems odd to me but it feels like the torque is overcoming the friction of the clutch plate. It'll slip all throughout 2nd, then shift, and halfway through 3rd it'll start slipping again, and then through the end of 4th gear it'll slip a little more until I shift to 5th. It doesn't happen all the time, but it's worrying when it does happen.

I tried adjusting the clutch actuator one notch away from the clutch, and spraying white lithium grease in the actuator housing, but neither of these seemed to help.

When I turn off the AC, I feel a ton of power returning to the engine, and it stops slipping completely.

Has anyone noticed this before?
 

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The actuator largely isn't going to control slipping in most case, that would be the clutch itself typically. Is it actually slipping or are you just noticing a loss of power? I'm no expert, but my limited experience has been that a clutch slips when it's worn, but that load on the engine doesn't seem to have much effect in that way. If anything, I would expect an engine under load to cause the clutch to slip a little less.
It sounds to me like perhaps your cooling system is causing extra load or perhaps the engine itself is not performing as it should, thus causing poor performance when the AC is running.
 

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Discussion Starter · #3 ·
Thanks for the reply!
It's definitely reduced performance, it's super bogged down when the AC has a heavy load, but this feels like it's losing grip, and then lurching again just a fraction of a second later. It only does it when it's ridiculously hot with AC on though. As soon as I turn off the AC (even with the blower still running) it returns to normal
 

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Discussion Starter · #4 ·
Not throwing any codes, and no lights on the dash even for a second, but it feels like it's related to the transmission for sure
 

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When this slipping occurs, are the revs rising much faster than the car is accelerating? I had a motorcycle with a slipping clutch and when the slipping happened it would race to redline.

If so, it would sound like your clutch is slipping. It's very rare for these cars to eat their clutches (lots of these cars are surpassing 200k on their original clutches) but it can happen. I'd also definitely make sure your transmission fluid is good.

The air conditioner in my 2012 absolutely robs the engine of power and it also has a slipping belt. Combined, they do kinda feel like a slipping clutch, especially when the belt finally grabs and the car lurches.
 

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Discussion Starter · #7 ·
The RPMs are still very much under control, and when I turn off the AC it doesn't slip no matter how hard I push the car, so it would actually explain a lot if the AC belt was slipping! I got the car from the previous owner at 45,000 miles and he hadn't done a ton of maintenance on the car aside from oil changes. So I suspect it still has the original serpentine belt, as the tires, spark plugs, and cabin air filter were all original.
Thank you for your reply!
 

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Interesting thread. I’ve noticed that when I turn on the AC, I see an almost immediate increase of engine load of about 10% using my UltraGuage. This corresponds to a decrease in my instantaneous fuel economy.

I suppose that the variations in engine load caused by a slipping and grabbing AC clutch belt could be interpreted as a slipping transmission .
 

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Discussion Starter · #10 ·
See, it feels like much more of a change in performance than just 10% though; my smart feels like it is going to stall under AC load sometimes. Is there any sort of failure that could cause AC to require tons more power without losing any functionality?
 

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See, it feels like much more of a change in performance than just 10% though; my smart feels like it is going to stall under AC load sometimes. Is there any sort of failure that could cause AC to require tons more power without losing any functionality?
There sure is. If the bearings are going bad, the compressor can cause some serious drag. I would expect that you would see lots of belt slipping and maybe hear it and the belt would be glazed if this were happening.

Also, if the AC system has too much coolant, the compressor can bind. I’ve seen systems that were overcharged so much they were on the verge of triggering the AC overpressure blowoff valve cause the car to stall when the AC clutch pulls in because of the added drag on the system. Too much AC coolant is bad.

Another thought... if the AC system is seriously overcharged, your AC won’t be as cold as it should be because the system can’t compress, and condense the R134A efficiency. It’s not a good idea to arbitrarily add coolant without knowing what the system pressure is.
 
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