Shifting back and fourth between 4th and 5th gear.

4255 Views 11 Replies 6 Participants Last post by giorgos123, Sep 10, 2021

TheFadingTheory

Discussion Starter · Mar 22, 2017 (Edited)

Good morning all.

I have searched and read info on this site about a few of you that for one reason, or another had this problem. I never found a clear diagnosis, or remedy that was used for those that had the issue.

My issue:
My 08 Passion Coupe with 190k always shifted smoothly, however I needed to replace my from wheel berrings and all motor mounts a month, or so ago. The day I picked up my car from the mentioned repairs it was shifting back and fourth from 5th down to 4th and back up to 5th repeatedly. Car is in 4th for 30 secs, shifts up to 5th for 10 secs then goes back to 4th. This happens with constant pressure on the throttle on level ground. I understand if going up a hill, or increasing my speed, etc. the car will shift to get to the proper gear for the speed at that moment. When in manual mode there are no issues with shifting. Again, before motor mounts and berrings my car shifted fine and all other gears and shifting was normal. This issue only happens with 4th and 5th gear.

Wheels bearings are good to go and the wheels spin freely without drag. I plan(today) to put a little more air in the tires as some have suggested in other threads, although I don't see what difference that would make if the tires are at factory specs. I also don't understand why no other gears are effected. The mechanic said the throttle wire may be out of whack because of the new mounts, and may need to be adjusted. (I think that's what he said, trying to remember) Any ideas on what this issue can be???

Thanks in advance.

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TheFadingTheory

Discussion Starter · #3 · Mar 22, 2017

Ok, thanks for the info, I will pass it to the shop. It's a small Shop that has worked on several of my Mercedes vehicles over the years. I am picking the car up in a few hours,(new e-brake cable install) so I will speak with them about the drive by wire.

My issue could be something simple that I have not thought of yet. I thought it could be my new wheels causing the issue, but I remembered that I still had my old spoke wheels on when this problem started. Maybe some folks on here will know.

Johannesl said:
Sorry, wish I could be more help, but no idea what is causing your issues.

But I can debunk what the mechanic said about the throttle wire. The smart uses a drive by wire system and replacing the motor mounts should have nothing to do with it as the wires only send a signal to the throttle body. The only way it could is if he accidentally loosened the connectors, but then I think it would happen to more gears/speeds.

It's not like a car that uses an actual cable connected to the gas pedal to operate the butterfly in the throttle body (meaning that it could kink or bind because of different angles after moving/stiffening up the engine).

Sent from my iPad using Tapatalk

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TheFadingTheory

Discussion Starter · #5 · Mar 22, 2017 (Edited)

When I am driving it back home in an hour I will confirm, but if I had to guess it is around 40, 45mph. Just cruising, but if I go much faster (60,65,70,etc.) its drive fine and stays in 5th gear. When the issue happens it's like the car doesn't know which of the two gears it wants to stay in.

Update: when driving the Smart home the back and fourth shifting happens anywhere from 45ish to 55ish. The shop said maybe it's the sensor in the throttle, or something. I will continue to research this. Besides why is it doing this, my questions are.

Why does this not happen in other gears like between 1st and 2nd, 2nd and 3rd, or 3rd and 4th? Is there a throttle position sensor that could need adjustments?

Rustedwrench said:
The salient question is: At what speed does this happen? All speeds? Or just around 45 mph, give or take a little?

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TheFadingTheory

Discussion Starter · #7 · Mar 22, 2017

I am cunfused with your statement.
Why would this type of shifting NEVER have happened before? Manual driving is not an issue, never was. I do drive faster to avoid this situation, but at times on some roads it is not possible to go any faster because of traffic. I can't imagine that this rapid back and fourth is normal, especially since the car has never done it before. If it's normal it should have been doing it all the time since I drive the same roads home daily. I'll post a vid shortly.

Thanks.

Rustedwrench said:
The shop does not know what it is talking about. I asked about the speed for a specific reason. In fifth gear at 45-50 mph any addition load on the engine will cause a down-shift to fourth gear. That is normal because there is not enough torque being produced by the engine at that speed in fifth to accelerate. The trans is programmed to up-shift at as low a engine speed as possible and the speed will depend on the load on the engine. In summary, there is not likely anything wrong with it.

Solution: Drive at that speed in fourth manually or drive faster. :burnout:

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TheFadingTheory

Discussion Starter · #10 · Mar 23, 2017

All good points. I'm getting an oil change this weekend and Also an air filter. Although I did have the AC on yesterday the issue happens no matter if act is on, or off. I'll keep an eye out after I do the oil change.

jimvw57 said:
There are lots of variables that can account for the difference, like weather, gas quality, air temperature, Phase of the moon... Ok maybe not the last one.. these cars are programmed to get into 5th gear as soon as possible and at lower speeds, there isn't much torque, so they downshift when it is needed. a minute bit of pressure on the gas pedal can make it shift at times. Maybe the defrosters were on (which uses the A/C)

I was caught in a traffic nightmare where there was a bunch of construction. went about 7 miles in 1 hour. creeping along, the transmission was going crazy until I dropped it in manual 1st gear. An hour later I went back int auto and things were fine once speeds were faster. Found out they were replacing a bridge over the highway. Unfortunately there was no other route around it.

I still think the transmission 'learns' set patterns and gets confused when they change.

Ok. Tire air pressure was good, but I put a little more are in yesterday per another thread. I'll try the battery thing too. Oil change happening this weekend. Stay tuned. Thank you

mattwithcats said:
First, tilt the computer.
There may be a fuse to pull that removes power to the SAM,
but I usually just remove the positive cable from the battery for 20 minutes...

Second, air up the tires, and last, use a half to a full quart of Castrol Edge 0W-30, black bottle.
Hard to find, but it's MB 229.5 rated, same add package as the 0W-40, just a little thinner...

Long oil filter, Fram 7317 or Purolator 14610, may help too.

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TheFadingTheory

Discussion Starter · #11 · Mar 24, 2017 (Edited)

mattwithcats,

As I type this I am giving the disconnect the battery for 20 min thing a try. In 5 more minutes I am reconnecting the battery, so maybe I will get lucky and it will correct the issue.

On a side note, I confirmed this morning that the shifting issue occurs even at higher speeds. (65,70ish) The higher speeds made no difference, because although going faster with steady throttle the car continued to switch back and fourth between 4th and 5th. This was tested on the highway this morning, so that debunks the idea that going faster will fix the issue. Switching to manual seems to be the only way to resolve, but I'll also try the oil change/air filter update.

Thanks.

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