Z4 M 1st to 2nd gear shifts

[funkle]

I'm still in the early stages of getting used to the shifting on my Z4M. Every now and then, when trying to shift quickly between 1-2, I get the horrible metal to metal grind (embarrassing & painful). It seems to occur when I try to shift a bit too quickly. Is this because of the technique I use, or is it a result of the CDV slowing the clutch actuation? (maybe the clutch hasn't fully disengaged when I hit 2nd).

[angelr]

I think it's a combination of things. Mounts allowing deflection, cdv slowing clutch movement and shifter slop. Not to mention synchros that don't like to be rushed. If you slow yourself down a little and be deliberate you won't miss as many shifts but I admit that if you're really hustling the shifter the 1-2 shift is hard to hit. Mine is much better now that I've done away with the cdv and replaced the motor/trans mounts and diff bushings. Hoping it will improve a bit more when I do a shifter and new bushings. But I've mostly just changed the way I drive it, treat it more like and old school sports car with a gated shifter...a bit slower with the shifts but enjoying the mechanical feedback and feeling for gear engagement.

[GuidoK]

CDV only slows clutch engage, so that can't be it (when the clutch pedal is pressed, clutch is always disengaged).

Grinding teeth can only mean 2 things: inproper clutching (drivers error), or slow synchro's (aka wanting to shift too fast and forcing the shift)
If you're sure the pedal is pushed down to the full extend when you shift and stil hear grinding, you're shifting too fast (or too sturdy).
Motor mounts, tranny mounts or ssk linkeage won't change that.
SSK or new linkeage might only give more control/feedback on the shifter so one would feel better if the synchro's have properly engaged to shift.
You have to 'feel' the teeth of the synchro's grabbing, aka feel the gear fall into place when shifting. Not forcing the synchro's into gear.

Grinding gears will result in irreparable damage to the synchro teeth, so be careful with that. (the more you grind, the more the synchro's will grind in the future as the indexing teeth on the synchro's get blunt.)

What might help when the synchro's work way slower than usual (the clutchcones of the synchro's that speed match the indexing teeth) is replace the gearbox oil. But that only helps if there's a problem with that .
Otherwise it's replacing the $ynchro's


To put it into images:

This is how it's NOT done 1:55

That 1-2 shift might be really fast, but when you listen closely, you can hear the synchrogrind, and that box probably has sustained permanent damage from that one shift.
You can see the drivers muscles flexing when he wants to shift.... Clearly not his own car
(professional driver who wants to 'set a time' (at what cost....))
The 1-2 shift is the most critical shift from a technical view, as that is the shift with the most torque (by far)

[gas-can]

Guido, that was painful to watch. That poor gearbox!

Isn't this also a common complain with you M guys? IIRC, that gearbox was never designed for the s54 level of power- the engineers used it b/c the actual M gearbox mated to that engine in the standard M3s wouldn't fit on the Z. This is just what I recall, so it may be complete conjecture!

Not to mention, even in my 3.0, the gearbox doesn't like to be rushed. It confused me in the beginning cause I wasn't used to it, but once you get used to it, it's very satisfying - I love the feedback as the gears slide in. Like a very fine and oiled rifle bolt.

Anways Funkle, the only cure is to give the car to me. I shall ensure that it is given a good home and shifted gently.

[GuidoK]

I have no problem with shifting the 3.0i
The z4m box is almost the same (probably only other bell housing for the clutch and mounting holes. Also the torque requirements for the z4m and 3.0i are about the same (I currently run at 465Nm; about 100Nm more than the stock s54).
But that is all of ample influence on the synchro's doing their rev matching.

The only difference is that the s54 revs high. And high revs (fast gearspeed) has a lot of influence on the kinetic energy of the gears themselves:
1/2mv²
So double the revs, quadrouple the energy that has to be (partly) dissipated by the synchro's
So the higher revs from the s54 make it more difficult (and slower) for the synchro's to do their job of revmatching both gears. (even when the following gear obviously also spins faster; the gear ratio difference scales linear; the kinetic energy in high revs scales exponentionally)

The high revs make it that shifting should be slower and more careful (more feel) than the 3.0i.
That is of course when shifting in higher (+7000rpm) rev ranges than the 3.0i/m54

At least, that's my view on it.

I hope that makes sense

[Nate4641]

Doing the CDV delete or swapping with a modified one has helped a number of Z4M owners. I installed a Zeckhausen one last year and didn't have any more 1-2 grinding issues.

[Beedub]

mines never grinded....ever , pre or post motor mounts or CDV....

and i actually love the shifting feel/action in the z4m, I'm on bone stock shifter mech and shift knob.....

the motor mounts made the largest difference to the feel of the drive train however.

[Shipkiller]

[funkle]

Originally Posted by Nate4641

Doing the CDV delete or swapping with a modified one has helped a number of Z4M owners. I installed a Zeckhausen one last year and didn't have any more 1-2 grinding issues.

How does the Zeckhausen Modified CDV compare with CDV delete?

[Nate4641]

doing the delete takes the part out of the car. The Zeckhausen maintains a similar part in place, but the internals are different so that it doesn't have the CDV effect. If you just delete the CDV you end up stretching the hose a little bit moreto cover the space the valve takes up.

[funkle]

Originally Posted by Nate4641

doing the delete takes the part out of the car. The Zeckhausen maintains a similar part in place, but the internals are different so that it doesn't have the CDV effect. If you just delete the CDV you end up stretching the hose a little bit moreto cover the space the valve takes up.

Is it just a way to make it look stock so as to not raise flags with the dealer, or does it behave differently?

[chickdr]

Originally Posted by funkle

How does the Zeckhausen Modified CDV compare with CDV delete?

It is the same thing. No reason to go with the Zeck since the car isn't under warranty. It was mainly used to make it appear the CDV was still in place.

[Nate4641]

Originally Posted by funkle

Is it just a way to make it look stock so as to not raise flags with the dealer, or does it behave differently?

thats one function, but also not stretching the hose is a plus. Internally it doesn't have the valve mechanism.

[funkle]

Thanks a lot for the replies. I plan to get the CDV delete, but will try to be a little more mindful and develop the habit - sounds like timing & the correct force are key - gentle but assertive, just like dealing with kids . I just received the ZHP knob as well - we'll see if that helps.

[elerner61]

When I took out my CDV there was no stretching the hose, none at all.

My gearbox has never grinded, but I never "Chuck Norris'd" any gear changes either. It doesn't want to shift fast, you can feel that it needs a pause. Like a previous post, be deliberate and you'll get the most out of it.

[Shipkiller]

Use the 'heartbeat method'.... wait one heartbeat and shift...

[GuidoK]

The hose is long enough to compensate for the 1/2" lenght (or so) of the cdv.

[Nate4641]

http://m3.madrussian.net/diy_cdv.shtml Here are some instructions.

I made the mistake of trying to be gentle with clamping the hose and it bit me in the ass and spilled all of the fluid out of the hose. Clamp the hell out of it to make sure you don't drain the hose.

[Shipkiller]

Use something 'flat jawed', not serrated so as not to damage the hose.

[TennesseeZ4]

When we used to drag race, we speed shifted a lot, and bought some trannys as a result (old Corvettes; Hemi powered Lancer). When I moved to road racing, my crew chief acknowledged that 'brakes are cheaper than transmissions', so I did the heart beat shifts, and if the gear was not ready, I didn't force it, sometimes double clutching. Over a decade or so in road racing, I never lost a transmission. Most of the Z's transmission work is done with a road course in focus, so a speed shift is not really that important imo. It's the feel that makes a sports car a unique animal, and one that is able to move in the fashion that addresses the demands of the road. Sorry to be so philosophical, but there is a zen to shifting and driving.

[Finnegan]

^ Good points.

[funkle]

So what is the most syncro friendly way to shift; pull the lever quickly out of 1st to where you feel it stop initially, let it rest there a moment before easing it into gear. Or a slow consistently smooth movement from 1st to 2nd?