Yet another GEARBOX problem topic...

[Dan Alex]

Hi,

Can't seem to get rid of the my gearbox rough shifting problem. Box is the GM model 5L40E, no errors, good oil changed properly, no debris in the box, clean magnets, etc...STILL, the problem is constantly related to the II-III rd shift when it does so roughly, with a jerky feel to it.

Mornings, low temps, it jerks when driving off softly. If going at it with a little more oomph, it shifts smoothly. It will continue to shift roughly (IIIrd only) until reaching operating temperature, and then, everything ok.

Have done a remapping of the box, it's gotten worse, in the sense that sometimes, the 5th has a rough shift, whilst before remapping etc the 5th was the smoothest.

Any ideas? No errors, no NOthing! nobody can find anything wrong with the box. Feels like i'm looking for the needle in the haystack. Frustrating!

Anyone seen this symptom without any apparent cause????

[X5-D-Sport]

If the change up/down is very abrupt and causes a clonk the goes thru the whole vehicle... but only when cold...
Im sure I know exactly what this is !!!!

In the mechatronic unit that lives in the belly of the gearbox, there are a bunch of little pistons about 15mm long x 8mm wide, they each have a rubberised teat/tip on on end to act as a damper when they move in the guides when diverting oil from one place to another....

These rubber tips harden with age or compress flat when cold.
As the oil warms up, the tips soften and regain their original shape.

I get the clonk changing up from 1st to 2nd... so nowadays I manually select 2nd gear and pull off gently with that, then pop into auto mode when rolling.

The strip and rebuild of the Mechatronic unit isnt too complicated, and the rebuild will usually replace the rubber tipped pistons witha spring tipped piston instead.
The job will likely cost you approx £500 from an indie... but make sure thay have done lots of these before, as it is easy to totally knacker the Mechatronic unit with a amature rebuild !!!

If youre lucky enough to have a decent drive way, you can possibly run the vehicle for 10 minutes to warm the gearbox oil before you set out... and this will often warm the box oil enough to stop the mechanical shock until you get the Mech unit rebuilt.
Regards
Grant B

[Dan Alex]

[quote="X5-D-Sport Salisbury"]
If the change up/down is very abrupt and causes a clonk the goes thru the whole vehicle... but only when cold...
Im sure I know exactly what this is !!!!

In the mechatronic unit that lives in the belly of the gearbox, there are a bunch of little pistons about 15mm long x 8mm wide, they each have a rubberised teat/tip on on end to act as a damper when they move in the guides when diverting oil from one place to another....

These rubber tips harden with age or compress flat when cold.
As the oil warms up, the tips soften and regain their original shape.

I get the clonk changing up from 1st to 2nd... so nowadays I manually select 2nd gear and pull off gently with that, then pop into auto mode when rolling.

The strip and rebuild of the Mechatronic unit isnt too complicated, and the rebuild will usually replace the rubber tipped pistons witha spring tipped piston instead.
The job will likely cost you approx £500 from an indie... but make sure thay have done lots of these before, as it is easy to totally knacker the Mechatronic unit with a amature rebuild !!!

If youre lucky enough to have a decent drive way, you can possibly run the vehicle for 10 minutes to warm the gearbox oil before you set out... and this will often warm the box oil enough to stop the mechanical shock until you get the Mech unit rebuilt.
Regards
Grant B
[/quote]


THanks,

I GET THE CLONK AS WELL, first time after firing the engine and driving off, always wondered what that was....i assumed it was normal. It feels just when setting it into P, when the gearbox break is applied and one can hear the clicking noise. Interestingly enough, when the oil warms up it doesn't make the clonk noise anymore. You are probably right, the tips warm up a little bit. I usually drive off quite enthusiastically in order not the hear that noise...

The other problem, the jerky shift feels like the body valve is changing the gear very very fast. It feels somewhat like a SMG box is an M3, very fast, unlike the others gear shifts in mine, which are smooth and you can feel that they take a second or so, this is blistering fast and accompanied by an oomph. It doesn't feel like a kick in the behind as some describe it, i mean it doesn't push the car forward or anything, so i reckon there is no pressure building up in the gearbox and when it engages it propels you forward, it just shifts very very quickly and there's that jolt or something...trying my best to describe it...like going over a speed bump, that's the noise it makes, but without reverberating throughout the car.

[Steamyrotter]

Sorry to pee on this....

The GM box doesn't have rubber bits on the end of the shuttles......
coupled to that there are only 3 shift solenoids which are operated in specific sequence to select the gears.

I think the potential point of your issue is one of the 4 accumulators within the valve block.
They each have a spring in them to ensure the pressure transient is damped suitably.
Chances are one of them has snapped and is not damping correctly.
It is a common fault in the 1st to 2nd accumulator as that one doesn't have a full size locating lug on the casting, whereas the other 3 do.

Could be a pressure regulating solenoid issue but you will need to have access to live data and a pressure gauge / transducer to see what its doing..

[Dan Alex]

You mean a live diagnosis of the thing? Absolutely no errors were found on the gearbox so everyone's puzzled. I've taken the systematic approach, first oil change and filter, resetting the adaptations, afterwards remap, now i'm contemplating changing the solenoids, after that, the body valve entirely, the computer of the gearbox, and, in the end, the shitbox, i mean gear box

Any chances that changing the solenoids will solve this? (2-3rd is acting up) but they come as a set.

Solenoid equals electrovalve or are they different things?

[Steamyrotter]

Did they monitor the gearbox fluid pressure against regulator drive current??
I have posted the details of the rebuild manual on here previously which has a chart of pressures / Drive current so you can tell if that bit is working right.
As your managing to drive i would say the pump is OK though.

Still sounds like an accumulator fault to me...

I would be tempted, and this is my view and experience, to remove the bottom cover of the box, take out the valve body (all can be done with box in situ) and send it off for overhaul...

I sent my valve body to Robbs Garage (www.Robbsgarage.com) phone 0151 638 1384 and had it refurbed.
They found a few minor faults in it and rectified it, Mainly a shuttle was worn and passing fluid.  They fitted a sonax kit to it and repaired it better than new, then then fully bench tested the block up to full operating pressures and temperatures and warranted it for 12months. Cost less than £250 delivered back, and was away for less than a week.
I would whole heartedly recommend them. (Even if i cant spell it!!)

[Dan Alex]

[quote="Steamyrotter"]
Did they monitor the gearbox fluid pressure against regulator drive current??
I have posted the details of the rebuild manual on here previously which has a chart of pressures / Drive current so you can tell if that bit is working right.
As your managing to drive i would say the pump is OK though.

Still sounds like an accumulator fault to me...

I would be tempted, and this is my view and experience, to remove the bottom cover of the box, take out the valve body (all can be done with box in situ) and send it off for overhaul...

I sent my valve body to Robbs Garage (www.Robbsgarage.com) phone 0151 638 1384 and had it refurbed.
They found a few minor faults in it and rectified it, Mainly a shuttle was worn and passing fluid.  They fitted a sonax kit to it and repaired it better than new, then then fully bench tested the block up to full operating pressures and temperatures and warranted it for 12months. Cost less than £250 delivered back, and was away for less than a week.
I would whole heartedly recommend them. (Even if i cant spell it!!)
[/quote]

Sounds great price wise. In RO, they charge about 500 Eur for this...and you'd be better off placing the 500 eur on either red or black in a casino )

However, TODAY, for the first time i got that jerky shift on the 4th. Then, gone, as if nothing had ever happened. I'm thinking (wishfully, that is) that it's a software problem. Otherwise, why would this symptom move from gear to gear?  but mainly it's the 2nd to 3rd when cold, when it gets up to temp everything ok

will changing the solenoids solve anything?

[Steamyrotter]

Changing the solenoids may help, and is an easy thing to try,
From recollection they are not that expensive in the scheme of things.

If the valves are iffy they won't make any difference though..