SMG Gearboxes

[The Gorilla]

Hi,

Its worth noting that on the SMG Box
the rod selector is not spring loaded for
obvious reasons.

In a manual box it is and the detent is set to neutural

Hence when the SMG actuator selects a new
gear, any wear or misalingment on
selection will cause hesitant selctions as
the ECU will detect a] resistance, and b]
greater pressure.

As the selector fork then starts to engage and slide
in to the correct position the pressure is reduced
back to normal, and the resistance point has been
passed, so the gear is then slected.

Hesitant selection is another factor of clutch slur.

Small particules of metal will be evident in the
Gearbox oil due to the misalingment rubbing.

This also explains in part why there is no Gearbox
slur upon a Manual Car, which has almost the same
Gearbox and clutch arrangement.

Regards,

The Gorilla.

[TANKSLAPPER]

I agreed with "The Gorilla"

Mine was missing 4th gear over a 6 month period when I was putting the car under load and did nothing about it until the loose actuator broke off completely.

Replaced the broken actuator and worked ever since perfectly.

I even got a specialist gearbox engineer to check it over and they reported that they never seen a box with so little wear for 50,000 miles. :thumbs:

[Thorney]

Good research form members, here well done.

Just to add some positive comment, my old race car (CSL) has been running with SMG for last two seasons without any issues, however we do inspect the gearbox each season. We've had to replace two manual boxes over the same period so if SMG works well it does protect the gb under hard use.

[The Gorilla]

Hi,

Any Gearbox is under its greatest load when the
Clutch is in, not out.

Hence why flat shifting on a sequential gearbox
causes less load into the box than when using the clutch.

This is why SMG gearboxes in regard of the gearsets will
show very little wear as opposed to a Manual box.

The SMG idea is very sound, but it was a work in progess,
that has since moved on to dual clutch engagement etc, and
a whole new set of issues.

Its like all component intense design, usually fantastic
when it all works as it should, and a right pain when
it don't.

Regards,

The Gorilla.

[manos///3]

I have a serious problem in my smg.
On the road everything is ok.
But on track after two laps , when the whole system (engine,gearbox) reaches high temps ,smg starts to shift 3rd to 4th , or 4th to 6th by its self.

I' ve checked everything on GT1 with no results .

I also changed clutch disk ,pressure plate and the smg relay recently. But the problem still remains.

Yesterday I went to my local BMW service dealer and the mechanic saw liquid under the hydlaulic unit.He cleaned the area under the unit and today there is liquid again at the same point. Is this an issue for upshifts?

Any help???

[shane@mbtech]

I have a serious problem in my smg.
On the road everything is ok.
But on track after two laps , when the whole system (engine,gearbox) reaches high temps ,smg starts to shift 3rd to 4th , or 4th to 6th by its self.

I' ve checked everything on GT1 with no results .

I also changed clutch disk ,pressure plate and the smg relay recently. But the problem still remains.

Yesterday I went to my local BMW service dealer and the mechanic saw liquid under the hydlaulic unit.He cleaned the area under the unit and today there is liquid again at the same point. Is this an issue for upshifts?

Any help???

If you are losing fluid it means it's losing hydraulic pressure, which yes will cause problems.

[grumps]

When you say rod selector are you talking about the shaft that the hydraulic actuator connects to ?

[mil]

Hi Flow,

Thanks for the input. Anything is possible in this case I think. Please let us know if that will help with your car.

Since my previous post my car has got:
- gear identification switch (strange call as this should be included in the complete gearbox swap earlier)
- rear differential
- output shafts (left and right)
- rear wheel bearings and hubs (a separate problem there, but changed anyway)
- clutch bleeding several times
- all possible reset/adaptations several times

No solution. Next on the line is clutch output cylinder and then.. you guessed it: the smg hydraulic unit.

Update: my car seems to be finally fixed.

After the previous post I have got new hydraulic unit (pump), another new clutch and new gearbox (warranty replacement). 2nd replacement gearbox changed behavior a little, shifting failures happened only when hot (basically in track conditions), but did not solve it for good.

Per my own request they then changed engine rubber mountings and gearbox mountings (rubber also). After the work mechanic told me that the engine got positioned 10mm higher and surprisingly everything now works. Mountings were not broken in anyway. This is not an expensive job, just two hours and parts needed are cheap also.

So I'm thinking that track driving, especially Nordschleife, affects those mounting rubbers (like any other rubber in suspension) and when it goes over certain threshold, SMG does not function properly and system cannot be calibrated to work properly even with brand new gearbox. You may still need to replace gearbox if situation has gone bad as this grinding noise comes from synchros, but this is my speculation only. If new gearbox does not help, change for the engine mountings before anything else. If you need to pay gearbox change yourself, you may even try mountings before gearbox especially if the car has been driven hard.

I have now driven several thousands without any shifting errors. Of course this can be combination of several things in the end, but in my case engine and gearbox mountings seem to be the final cause.

//mil

[mattCSLnut]

Update: my car seems to be finally fixed.

After the previous post I have got new hydraulic unit (pump), another new clutch and new gearbox (warranty replacement). 2nd replacement gearbox changed behavior a little, shifting failures happened only when hot (basically in track conditions), but did not solve it for good.

Per my own request they then changed engine rubber mountings and gearbox mountings (rubber also). After the work mechanic told me that the engine got positioned 10mm higher and surprisingly everything now works. Mountings were not broken in anyway. This is not an expensive job, just two hours and parts needed are cheap also.

So I'm thinking that track driving, especially Nordschleife, affects those mounting rubbers (like any other rubber in suspension) and when it goes over certain threshold, SMG does not function properly and system cannot be calibrated to work properly even with brand new gearbox. You may still need to replace gearbox if situation has gone bad as this grinding noise comes from synchros, but this is my speculation only. If new gearbox does not help, change for the engine mountings before anything else. If you need to pay gearbox change yourself, you may even try mountings before gearbox especially if the car has been driven hard.

I have now driven several thousands without any shifting errors. Of course this can be combination of several things in the end, but in my case engine and gearbox mountings seem to be the final cause.

//mil

Interesting read and discovery :thumbs:
How & against what were these measurements of the engine positioning taken, before and after the replacement rubber mounts ? Sounds like good, preventative measures to be taken by a number of enthusiastic :whistle: CSL owners on here.
Thanks for sharing your info. :beer:

[mil]

Interesting read and discovery :thumbs:
How & against what were these measurements of the engine positioning taken, before and after the replacement rubber mounts ? Sounds like good, preventative measures to be taken by a number of enthusiastic :whistle: CSL owners on here.
Thanks for sharing your info. :beer:

Don't know exactly, I would guess that it's just an estimate by the mechanic after he dropped the engine back and not really measured figure.

I spoke about this last year already with Tom Schirmer at the Ring and I think he mentioned that somewhere after 100000km the mountings could need replacement. My problems started at 114k (incl. hundreds of Ring laps) .

//mil

[mattCSLnut]

Don't know exactly, I would guess that it's just an estimate by the mechanic after he dropped the engine back and not really measured figure.

I spoke about this last year already with Tom Schirmer at the Ring and I think he mentioned that somewhere after 100000km the mountings could need replacement. My problems started at 114k (incl. hundreds of Ring laps) .

//mil

I wonder if this engine mount wear could be measured from the engine bay strut brace to a solid part of the engine, like the cylinder head or something similar. Would be interesting to compare the figures of a 20K miles CSL to lets say a 60K+ miles (100K ish kilometres ) CSL with Track history. I don't have these SMG problems (that you've described) on my CSL (as yet) and I have BMW Warranty but I'm way past the 100,000 kilometres mark and have also driven a fair few laps :whistle: at the Ring in the past few years :smokin:
High time for some NEW engine & gear box mounts I thinks :smokin: but I bet they are NOT covered by BMW Warranty on 60K+ miles cars :bigcry: Group buy anyone ? :whistle:

[m3novo]

I am facing the same problem. Check spring and was ok.

how can I diagnose syncro or SMG? Anyone know how to use INPA for this diagnose? I noticed it has a lot of analog parameters that could be helpful.

[shane@mbtech]

I am facing the same problem. Check spring and was ok.

how can I diagnose syncro or SMG? Anyone know how to use INPA for this diagnose? I noticed it has a lot of analog parameters that could be helpful.

which spring did you check?

There are 2 separate ones on the left of the box. One behind a screw out bung, and one behind a press fit plug.

There are also 3 springs under the plastic blanking cover on right of the box.

Some don't know to remove the press fit plug.

I've got one in at the minute and the spring has snapped and wedged under the plunger, the plunger was wedged so would not hold it in gear correctly.

The faults with this were difficult getting 4th gear, and slow to get any gears, especially under hard acceleration. The clutch release bearing has also worn on this and was dragging considerably, not helping matters any at all.

Also worth noting if your car has a thud on gearchange or take up of drive, then the flywheel is probably knackered. This car has a bad thud and upon removal of box the flywheel has about an inch of free play.

[shane@mbtech]

Also worth noting that on GT1, it passed all the tests. I did however notice that whilst running through all the gears on the test it was very noisy selecting gear compared to a good box. And did feel a little slow.

But the computer was picking up no faults. Back to old school diagnosis for these type of faults.