Transmission hard shifts

[cc7891]

Maybe you guys can help. My 2012 bmw has a ZF 8 speed automatic with a torque converter. It's been having hard shifts since almost two years.

The initial symptom - very hard shifts from 1st to 2nd gear, especially when cold, but also when warm, sometimes - like being hit from behind.Other shifts noticeable.

I serviced the transmission one year ago (fluid drain & pan change) - fluid was not burnt and had no debris, used ZF Lifeguard 8 - a little better 1-2 shifts when cold, went better as it got warmer.

Then I added 1/4 gallon more fluid - apparently didn't have enough fluid, now it seems to be right level.

Currently: The shifts are harder in the morning - I can feel 1-2 gearshifts both at very slow and harder acceleration.
The sensation of the gear shift is a clutch is disengaging and the car picks a bit more speed (feels loose) and then it hits something which is slowing it down.

After around 10 miles of driving (with many shifts) and way after the transmission/engine have reached their operating temps, the 1-2 shift will get perfect under hard acceleration. It remains slightly perceptible under very slow acceleration (a gentle push from behind).

There is also a vibration/bump when braking almost to a complete stop - like the transmission is grappling onto something which slows down the car more than I'm braking, then lets go.

The haven't been any error codes from the transmission, never and no other problems.

What I find very surprising is that it seems to shift better if I stop the car for around 30 minutes and also if I drove a lot in the morning (to the point of shifting good) and I park it 8 hours (50deg F outside) it will still shift good although the fluids must be cold again. But if I leave the car overnight the bad shifts return.

What do you guys think?

 

[RooflessVW]

Sounds like a sticky shift solenoid.

 

[cc7891]

Originally Posted by rooflessVW
Sounds like a sticky shift solenoid.


what does this mean?

 

[demarpaint]

How many miles was it driven a quart low on ATF?

Here's what a shift solenoid does:

"A shift solenoid opens and closes the valves that allow hydraulic fluid to flow in and out of a transmission. It is computer-controlled and electronically activated. Its purpose is to allow the vehicle's transmission system to function efficiently." "Every time a gear change is required, the car's computer activates a transmission solenoid, which directs transmission fluid into the valve body to engage the correct gear."

You might have a bad/sticky solenoid as rooflessVW stated.

 

[cc7891]

Well, I know what the solenoids do... I didn't think they can be sticky. It had been driven for around 20k miles with low fluid (1/4 gallon less, probably), most of the driving was done in the city. It behaved very well at high speed though, but because of the 1-2 gearshift, it made city driving unpleasant. Even now, after 10 miles of driving when most of the symptoms are gone there is a gentle push from behind at very light acceleration when shifting 1st to 2nd.

Btw, manually shifting 1-2 as well as auto shifting in sport mode will always result in jerks, even though the shifting is smooth in normal (comfort) mode.

I've been told it's a valve body issue - it cannot be fixed, the valve body has to be replaced (expensive part). Is this true?

 

[Egg_Head]

I am not familiar with common problems with the ZF 8, do you have a trusted mechanic you can take it to? If not it's back to the BMW service center. I think you are beyond curing your ills with another fluid change but you can always try. Welcome to 2 pedal BMW ownership.

 

[Vern_in_IL]

I thought hard shifts are a good thing.

 

[cc7891]

Well, the trusted mechanic could only add more fluid following the recommendations from the manufacturer. It appears to be full. The BMW service only replaces the entire transmission (omg). The valve body from other transmission shops is around 3k - they don't do repairs on them they say. I was wondering if someone had faced this issues before.

As a curiosity, when the car moves forward in Drive (without applying gas at all) and I manually shift from 1st to 2nd there are multiple quick jerks (around 3 in half a second), similar from 2nd to 1st. How should this shift feel?

 

[demarpaint]

I hate to say it but driving about a quart low for 20K miles might have contributed to your problem too.

 

[StevieC]

Have you had it scanned for stored codes? I would start here first.

 

[Overfill]

If its the shift solenoid being sticky, you might want to try and mitigate it. If what's causing it can be solubilized, then Maxlife synthetic ATF or Lubegard might work.

 

[dave1251]

With my ZF-8 Valvoline Maxlife worked better than ZF-8. Search the web for reputable transmission shops in your area. Sure someone has experance with ZF transmissions but it is fairly rare.

 

[cc7891]

I have scanned the car for codes multiple times (with a laptop connected to the car). None.
I've also reset the adaption multiple times (the pressures in mbars are always negative, e.g. -200mbar).
I also added Lubegard - made no difference, then I added almost 1/5 gallons more atf fluid (that's all I could get in, following the procedure - there's no dipstick) - the 1-2 gearshift is not so brutal anymore (previously was very strong on very light acceleration).

What more should I do?

 

[StevieC]

Modern transmissions are really fussy on fluid types and fluid levels being precise. Driving it a quart low could have caused damage. That it's not storing codes and that you have double checked it is full I would say you will have to live with it until it gets worse because if you take it anywhere you are going to get the "It needs a rebuild".

 

[SubieRubyRoo]

What is the capacity of the trans? Lubegard Red is to be dosed at 1oz per qt... it looks like its about 10qts to change all the fluid, so you should add around 12oz of Lubegard Red. It usually takes 300-500 miles for the Lubegard to really free everything up. I also second the choice of using Maxlife ATF, it's good stuff.

 

[benjy]

typical tranny fluid changes get about a third or a bit more, so multiple changes or a full machine replacement is best, good luck!!! great cars but $$$$ to keep on the road when issues arise

 

[RooflessVW]

Do not put junk in your transmission. It needs to, at this point, go to a workshop to be properly diagnosed.

Where in Europe do you live? I would visit a ZF workshop.

 

[MolaKule]

Originally Posted by cristiancc
Well, I know what the solenoids do... I didn't think they can be sticky...


1) You won't know how much debris is in your fluid unless you have an analysis done which includes a check on particulate matter.

2) Solenoid coils can fail and the valves they are connected to can varnish up or the movements be interfered with by particulate matter.

3) How does the person you spoke to know you need a valve-body replacement?

4) Have the motor mounts and transmission mounts been inspected for cracks and separations?

5) Make sure you have the proper level of fluid when hot.

As a last resort, try another drain and fill with a bottle of LubeGard Red which might clean the valving.

 

[BMWTurboDzl]

Originally Posted by MolaKule
Originally Posted by cristiancc
Well, I know what the solenoids do... I didn't think they can be sticky...


1) You won't know how much debris is in your fluid unless you have an analysis done which includes a check on particulate matter.

2) Solenoid coils can fail and the valves they are connected to can varnish up or the movements be interfered with by particulate matter.

3) How does the person you spoke to know you need a valve-body replacement?

4) Have the motor mounts and transmission mounts been inspected for cracks and separations?

5) Make sure you have the proper level of fluid when hot.

As a last resort, try another drain and fill with a bottle of LubeGard Red which might clean the valving.


I like this suggestion. It's not like the OP can break it more.

 

[Carbuff]

Don't overlook the possibility that its NOT the transmission.

I've had rough shifts on Chrysler transmissions be caused by engine programming. IE, the ECU provides too lean a mixture when shifting. Caused chugging on shifts. Just as you describe in post 4924799.

On our Dodge, I replaced the spark plugs and the issue went away!