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.

[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]

Originally Posted by 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???

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]

Originally Posted by 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]

Originally Posted by mil

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
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 CSL owners on here.
Thanks for sharing your info.

[mil]

Originally Posted by mattCSLnut

Interesting read and discovery
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 CSL owners on here.
Thanks for sharing your info.

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