Steptronic jerk

On putting the transmission into D or R, a couple of seconds later the
car jerks slightly. The handbook says to wait for it before moving and
I assumed it was it going into gear. However I discovered the other day
that the car will move forward (or back) almost instantaneously D or R
is selected, but you still get that jerk 1-2 secs later even after the
car is moving.

So I was curious about that anyway, but more seriously I had it in P or
N (forget which) at a slow traffic light and was a bit late noticing it
change, so I hurried into D and pressed the go pedal moderately, which
if you've driven a 540 you will know is something like being shoved
quite gently by a large elephant. The car took off but 1-2 seconds
later there was a massive jerk, and a sound almost like a bang.

It seems likely this is the same thing as the slight jerk when the car
is at rest or creeping, but magnified by speed/acceleration. The
question is, what is it? Is it right? Fair enough if you are supposed
to wait for the 'jerk' before moving off, and I should have left it in D
anyway, but surely the Steptronic is supposed to protect the
transmission from damage.

1998 E39 540iA. I had the ATF changed last week although I'm still
concerned about only being able to change half of it because of the
torque converter.

In article >,
Dan Buchan > wrote:
> On putting the transmission into D or R, a couple of seconds later the
> car jerks slightly. The handbook says to wait for it before moving and
> I assumed it was it going into gear. However I discovered the other day
> that the car will move forward (or back) almost instantaneously D or R
> is selected, but you still get that jerk 1-2 secs later even after the
> car is moving.

First thing to check is the switch on the brake pedal. On mine, if you
move off with the brakes still slightly applied it (sometimes) appears to
confuses the transmission and you get a slight thump as it actually starts
in third then changes to first when you release the brake. If you left
foot brake you might be unconsciously be doing this. I dunno how obvious
this starting off in a higher gear would be on a V-8, though.

However:-

IIRC, on a ZF HP5 there are 7 clutches of various types. When you select a
gear from neutral more than one has to change state. The timing of this
sequence is I think still controlled by hydraulics. So could be a valve or
clutch sticking.

> So I was curious about that anyway, but more seriously I had it in P or
> N (forget which) at a slow traffic light and was a bit late noticing it
> change, so I hurried into D and pressed the go pedal moderately, which
> if you've driven a 540 you will know is something like being shoved
> quite gently by a large elephant. The car took off but 1-2 seconds
> later there was a massive jerk, and a sound almost like a bang.

> It seems likely this is the same thing as the slight jerk when the car
> is at rest or creeping, but magnified by speed/acceleration. The
> question is, what is it? Is it right? Fair enough if you are supposed
> to wait for the 'jerk' before moving off, and I should have left it in D
> anyway, but surely the Steptronic is supposed to protect the
> transmission from damage.

There's really little difference between Steptronic and drive in this
respect. The timing of the various clutch sequences doesn't alter. Could
be your transmission is actually partially engaging two gears at once -
known as tie up.

> 1998 E39 540iA. I had the ATF changed last week although I'm still
> concerned about only being able to change half of it because of the
> torque converter.

It's a difficult one. Most transmission specialists simply do a full
re-con on a box due to the labour cost in removal and stripping down which
is far greater than any likely parts cost. It's possible the valve tray
can be easily removed with the transmission in situ and cleaned/checked.
Not so with a clutch.

--
*I just got lost in thought. It was unfamiliar territory*

Dave Plowman London SW
To e-mail, change noise into sound.

"Dan Buchan" > wrote in message
...
> On putting the transmission into D or R, a couple of seconds later the car
> jerks slightly. The handbook says to wait for it before moving and I
> assumed it was it going into gear. However I discovered the other day
> that the car will move forward (or back) almost instantaneously D or R is
> selected, but you still get that jerk 1-2 secs later even after the car is
> moving.
>
> So I was curious about that anyway, but more seriously I had it in P or N
> (forget which) at a slow traffic light and was a bit late noticing it
> change, so I hurried into D and pressed the go pedal moderately, which if
> you've driven a 540 you will know is something like being shoved quite
> gently by a large elephant. The car took off but 1-2 seconds later there
> was a massive jerk, and a sound almost like a bang.
>
> It seems likely this is the same thing as the slight jerk when the car is
> at rest or creeping, but magnified by speed/acceleration. The question
> is, what is it? Is it right? Fair enough if you are supposed to wait for
> the 'jerk' before moving off, and I should have left it in D anyway, but
> surely the Steptronic is supposed to protect the transmission from damage.
>
> 1998 E39 540iA. I had the ATF changed last week although I'm still
> concerned about only being able to change half of it because of the torque
> converter.

It probably moved off in direct drive (third or fourth, but it would depend
on the box) before the correct bands engaged for first or second. As you
had far number revs on there would be a quite a lot of inertia in the sun
and planet arrangement and this would give your jerk.

If you jump from reverse to drive at say 3,000rpm (as I did once when
distracted by a burglar trying to decapitate me with a machete) then there
will be a huge jerk and you will break the gearbox!

R. Mark Clayton wrote:
>
> If you jump from reverse to drive at say 3,000rpm (as I did once when
> distracted by a burglar trying to decapitate me with a machete) then there
> will be a huge jerk and you will break the gearbox!

I once thought I was in manual mode but wasn't and shifted up (to
neutral) at about 5000rpm and I felt like a huge jerk.

"adder1969" > wrote in message
ups.com...
>
> R. Mark Clayton wrote:
>>
>> If you jump from reverse to drive at say 3,000rpm (as I did once when
>> distracted by a burglar trying to decapitate me with a machete) then
>> there
>> will be a huge jerk and you will break the gearbox!
>
> I once thought I was in manual mode but wasn't and shifted up (to
> neutral) at about 5000rpm and I felt like a huge jerk.
>

In the old days this would have done for the engine (as did shifting down at
too higher speed), but you were probably saved by a rev' limiter.

In article >,
R. Mark Clayton > wrote:
> > I once thought I was in manual mode but wasn't and shifted up (to
> > neutral) at about 5000rpm and I felt like a huge jerk.
> >

> In the old days this would have done for the engine (as did shifting
> down at too higher speed), but you were probably saved by a rev'
> limiter.

The rev limit on older engines was generally set by valve float if
mechanical tappets or pump up if hydraulic. This wouldn't protect an
engine from being over speeded by changing into too low a gear, though.

--
*If you can read this, thank a teecher

Dave Plowman London SW
To e-mail, change noise into sound.

"Dave Plowman (News)" > wrote in message
...
> In article >,
> R. Mark Clayton > wrote:
>> > I once thought I was in manual mode but wasn't and shifted up (to
>> > neutral) at about 5000rpm and I felt like a huge jerk.
>> >
>
>> In the old days this would have done for the engine (as did shifting
>> down at too higher speed), but you were probably saved by a rev'
>> limiter.
>
> The rev limit on older engines was generally set by valve float if
> mechanical tappets or pump up if hydraulic. This wouldn't protect an
> engine from being over speeded by changing into too low a gear, though.
>

Actually, some of the US automatics had downshift protection as early as the
1950's. IIRC, my dad's push-button shift Torqueflite '57 Desoto would
downshift to 2nd at speeds over 35 when the "1" button was engaged. And if
the Reverse button was pushed in at speed on our '60 Rambler
("Flashomatic"?), the transmission shifted into "Low" range - initially 2nd
gear and then 1st. When the car finally came to a stop, it would shift into
reverse.

Of course, there was no such protection for similar stick shift stupidity.

Tom K.

adder1969 wrote:
> I once thought I was in manual mode but wasn't and shifted up (to
> neutral) at about 5000rpm and I felt like a huge jerk.

I once shifted from first to second in a Jaguar XKR. Except I didn't,
it was an automatic box, and it went into Park at 30 miles an hour.
Well it did look awfully like a manual gear stick.

At least the BMW is fool proof enough to mostly prevent that kind of thing.

Hi Dave, thanks for the reply.

Dave Plowman (News) wrote:
> First thing to check is the switch on the brake pedal. On mine, if you
> move off with the brakes still slightly applied it (sometimes) appears to
> confuses the transmission and you get a slight thump as it actually starts
> in third then changes to first when you release the brake. If you left
> foot brake you might be unconsciously be doing this. I dunno how obvious
> this starting off in a higher gear would be on a V-8, though.

Is that the same switch for the brake lights?

It seems to start in second when it's raining. Don't ask me how it
knows. Or perhaps it decides you are not in a hurry. You can only
really tell by flooring it, and then it changes down into first in an
amusing way.

> IIRC, on a ZF HP5 there are 7 clutches of various types. When you select a
> gear from neutral more than one has to change state. The timing of this
> sequence is I think still controlled by hydraulics. So could be a valve or
> clutch sticking.

I phoned a local BMW specialist and he reckoned it was all normal. He
said the car can move forward/backward the instant you engage D/R
because it's engaged mechanically by the lever. He said what happens a
second or two later, the slight jerk (when stationary or creeping) or
nasty thump (when accelerating), was the solenoids kicking in. I asked
what this meant, what the solenoids did, and he said something about the
fluid. I wish I knew more about how these worked.

> There's really little difference between Steptronic and drive in this
> respect. The timing of the various clutch sequences doesn't alter. Could
> be your transmission is actually partially engaging two gears at once -
> known as tie up.

Sorry I meant Steptronic as in the system in general. I wasn't using
the manual mode. I just thought with all those electronics it would
prevent you from damaging it. It's true the manual does say to wait for
the jerk before moving off, but still.

> It's a difficult one. Most transmission specialists simply do a full
> re-con on a box due to the labour cost in removal and stripping down which
> is far greater than any likely parts cost. It's possible the valve tray
> can be easily removed with the transmission in situ and cleaned/checked.
> Not so with a clutch.

Seems OK apart from this one thing, and I'm still not sure if it's a
fault or user error.

R. Mark Clayton wrote:
> It probably moved off in direct drive (third or fourth, but it would depend
> on the box) before the correct bands engaged for first or second. As you
> had far number revs on there would be a quite a lot of inertia in the sun
> and planet arrangement and this would give your jerk.

It seemed to pull away too quickly for third or fourth. When it went
bang it was almost like something locked up. It didn't feel good at
all, but even with my paranoia I can't detect any damage from the way it
drives.

> If you jump from reverse to drive at say 3,000rpm (as I did once when
> distracted by a burglar trying to decapitate me with a machete) then there
> will be a huge jerk and you will break the gearbox!

Sounds like fun. Did you manage to kill him?