gwf545

I was in DS today creeping up to a stop sign and BANG! It felt like I got rear-ended by a truck, but there was nobody behind me. My wife was sure we had been hit. It was very unnsettling. I have had a recent S/W upodate due to CCC replacement and I think it is CIP 20.x I thought this slam problem was supposed to be eliminated with CIP 17.02. Has anyyone else had this happen recently? Did BMW regress the S/W or just never fix the original problem? BMW NA, are you out there?

mixterk

My dealer took my car to 20.01 to try and fix the shift lag from pulling away to the gear being input (it would snatch as the revs increased). Instead of an improvement it has become worse and more frequent. It seems 20.01 is a backward step :thumbsdown:

gomac

This unfortunate event has happened to my car recently as well. If memory serves me correctly the "slam" has happened under CIP 15, 19, and now 20. You would think they could fix it. This particular time I was looking down since the car did not start as I pressed the gas pedal. The RPMs went up to about 700 before the kick in the rear. I am not sure if it made it to 750 or 800 since the jolt was so violent. I just wonder if a class action suit like what happened with the Audi's is possible. I guess in their case they had a wrecked car and insured people to show what happened. Unless this happens with a BMW rep it is just our word

spareone3

Mine's in for this again today.. Talking to the dealer they tell me that the process of purely updating the software is not enough (info from BMW) and the adaptive box requires "re-training". To do this they need to run the car in top gear (above 70mph) and do a series of slow downs and slow accelerations, 10-15 cycles. This apparently then teaches the box to be more sensitive...! To be honest if correct this sounds like why people often experience an initial improvement after s/w upgrade. Then due to various driving styles the fault manifests itself again after time. All sounds like a real band-aid fix rather than getting to the root-cause.
As said, this is what he told me BMW Germany had instructed all dealers to do when upgrading software for transmission slam! Anybody else heard this..?

Saudi_545i

It happened to me before. I was making a U-turn and I also thought I was rear ended. I?m not sure if I was on the DS mode. It was scary, but not as scary as the faulty puncture message I got on i-drive when I was doing 130 miles/hour

KAF

This follows this thread
http://forums.e60.net/index.php?showtopic=20994

But I may as well post here instead.

This morning I took my car out with an engineer from ZF (who make the transmission) heis seconded to BMW UK to troubleshoot transmission issues.

He connected up a diagnostic kit to the plug in the drivers footwell to monitor the tranny whilst I drove.

We were able to reproduce the 'slam' to order by slowing to about 3 mph gradually and then just before coming to a halt, accelerating fairly briskly.

Almost every time the revs went up and after a delay the car picked up the drive and shot forward.

We could also reproduce another behaviour. When going down a steep hill, causing acceleration due to gravity with foot off throttle, touch and release the brakes. The car downshifts 2 gears, giving high revs, then accelerate again and you get quite harsh upshifts.

His explanation of the 'slam' was as follows.
The transmission is working 'normally'. The shift point is set up with a stop/go system so that as you drive in traffic the car does not drop below 2nd gear. This enables a smooth progress without unnessecary shifts into 1st. The normal pick up with gentle acceleration is easily achieved in 2nd.

The consequence of this set up is that if you suddenly ask the car for high acceleration levels it detects that it cannot achieve this in 2nd and selects 1st with a consequent delay. This has been measured by ZF as about 0.75 seconds, though he accepted it often feels a lot longer.
I pointed out that when pulling out into traffic which is travelling at 50mph, on oncoming car travels at 75 feet per second, so 0.75 of a second delay is not good news.

The only solution to the issue is to reset the shift points so that the car always selects 1st when the speed drops, this however would mean a huge number of 1>2 > 1 shifts in stop start traffic giving a poor ride and the risk of harsh low speed shifts.

The problem is exacerbated in larger diesel engines due to the high torque and the slight turbo delay.

The same process is present in petrol engines but is felt much less due to the faster response of the engine to the throttle and the lower torque at lower revs. hence it is often viewed as a diesel only problem. The greater the torque the more noticeable the behaviour. This explains why the 530D and 545i and up raise complaints whilst the 520i and 525D seem less prone.

The only way to mitigate the issue is to select DS which forces selection of 1st at low speeds, but be aware that you will feel harsher 2>1 shifts in traffic.

Every 5 series 'suffers' as do Jaguars, Audi's and others but due to different driving styles and road environments, some drivers will notice it more than others. It is especially noticeable if you are a frequent user of roundabouts where you often approach at a very slow speed the accelerate without coming to a full halt.

The downhill behaviour is due to the software detecting acceleration whilst also detecting a braking signal. It interprets this as brake failure and, as a safety system, initiates downshifts to provide engine braking.

The bottom line is that currently there is no 'solution' to the 'slam' issue, there is no software update beyond 17.10 that will have any direct effect on the tranny behaviour, though he does not rule out that at some time in the future there may be changes. There is nothing currently on the radar.

I have made my point that I am very unhappy that a ?40,000 car does not have a better matching of transmission with engine and that this will probably be my first and last BMW if that is the quality I get for this kind of money.

I will now hit every car review website I can find to ensure that potential buyers of BMW's are made aware of this problem and are prepared to live with it.

spareone3

That's by far best and most plausable explaination I've heard to date...Far from satisfactory as you rightly point out but I'd say it was accurate and certainly "hits the nail on ethe head" as far as I'm concerned!
Many thanks for the detail....

pedrollo

Thanks for the report Keith. Unfortunately it makes sense, but if BMW know it can't be fixed, why are they sending a ZF engineer to investigate reports?

It strikes me that with a diesel the 2>1 downshift is actually costing more lost time directly than just accelerating in second. I found with my E39 530D that the extra torque from a tuning box resulted in noticeably less downshifts and that had less power than a current 530d.

Can the downshift to first be eliminated unless the vehicle is stationary (i.e no kickdown from 2>1)?

Interesting that some people report not having the problem at all, can it be only the way they drive and not related to a change of spec.?

KAF

Only way of eliminating the downshift is to be more gentle with the right foot and bring on the gas in a more gradual manner, then the box will be happy to stay on 2nd, it is the sudden request for power that triggers the downshift.

Alternatively if you come to a junction with crossing traffic and think you might need to get out quick, slip it into DS, which I started to do some time ago.

pedrollo

Thinking about this again:

This is where the problem is, they don't seem to have allowed for the high torque engines which CAN achieve this but are slow to rev. Or perhaps they are doing it to protect their gearbox from this amount of torque.