Making smooth shifts... Finally figured it out!

[mackeroni]

Like many 135i manual shift owners, I have struggled with making smooth shifts. I have driven stick all my life and the fact that I could not shift correctly was killing me!

I read all the posts about the pros and cons of removing, replacing and punching out the CDV (Clutch Delay Valve), however, I was reluctant to do anything that would possibly void any part of my warranty. So... I dedicated myself to figuring out how I could shift smoothly without fussing with the CDV.

Here is what I discovered: The clutch engages and disengages at different points in the travel of the clutch pedal. When depressing the clutch to perform a shift, it disengages when the pedal is about three-fourths of the way to the floor. However, after a shift is made and the clutch pedal is released to engage the new gear, the engagement takes place about two-thirds of the way back to the top. This is different from any car I have ever driven! My lifetime of experience has been with clutches that engaged and disengaged at roughly the same point in the travel of the pedal. It turns out that this phenomenon is the sole reason why I have been unable to shift smoothly.

Once I figured this out, I began to drive differently. I did not release the accelerator pedal until the clutch was nearly to the floor and I did not slow the clutch for re-engagement after a shift until it was much nearer the top of its travel. It has taken several weeks of practice, but using this technique, I am now able to drive my 135i without any of the previous jerkiness I experienced in the lower gears.

Try it!

1. Keep your foot on the gas until the clutch pedal is very near the bottom of its travel.

2. Then, do not slow the clutch pedal for reengagement until it is near the top of its travel.

Hope this works as well for you as it does for me.

[3lusive]

Interesting phenomenon, I will try it out tomorrow morning!

[daMau]

Sounds to me the shift points are delayed because of some restricted clutch valve I've heard about.

[gordongekko]

I've driven a mix of manuals and autos in my life and haven't had a problem with the 135i. I must just be awesome I guess.

[MPFit]

Just a note, this Clutch engagement zone you are talking about is commonly called the "friction zone" of the clutch.

[romak47]

smooth shifts on this car is hard in general.. more torque down low just makes it that way.. its the way this car is and i embrace it like a tender baby...

never had issues with the clutch myself. and i drove 2 years w/ delay valve.. and a few months with cdv mod.. Honestly, i think shifting w/ cdv mod is a bit harder to adjust to but its more predictable at the same time.

However, if you plan to track your car and / or drag it, the cdv mod is a must..

[Sylon]

Interesting concept. Now I have a question, did you figure this all out with your AC on or off? I've noticed that my driving is different when the AC is on, my shift timing is completely different than when my AC is off.

My guess is because the AC unit is sapping power, thus messing with my timing.

[daMau]

Originally Posted by Sylon

Interesting concept. Now I have a question, did you figure this all out with your AC on or off? I've noticed that my driving is different when the AC is on, my shift timing is completely different than when my AC is off.

My guess is because the AC unit is sapping power, thus messing with my timing.

I actually think it's easier to shift quickly and smoothly with the AC on because the RPMs don't hang for so long. They just drop after I let off the gas and fall right into the next gear. With it off I can't shift as fast because they hang there after I let off the gas.

[Dackelone]

The way you make smooth shifts is to get rid of that damm CDV!

Go to the "CDV delete DIY" to learn more on what all is involved.

[Light_Em_Up]

Good observation. I also have been driving strictly manuals for the past 45 years and though haven't had a problem with clutch op. in my 128, have noted that it is different. Your explanation is right on and does explain why the odd time (spirited driving around a corner and upshift 1 - 2) I seem to slip the clutch on re-engagement. The CDV is the probable cause (as opposed to my age) as it is slowing the return of the hydraulic fluid from the clutch slave cylinder to the reservoir and thus delaying clutch engagement. Jack

[Sylon]

Wow, I just went for a drive and realized that my normal shifting is just like the OP explained. I guess I've been doing it right all this time, lol.


Now, I was driving with the AC off. I still find my timing off when the AC is on.

[JimD]

Every vehicle requires a little different timing. I can shift my 128 as smoothly as any of my other 5 manual transmission vehicles (1 I rotate nearly daily with the bimmer). I have a bigger problem with the fact that my SUV is a 5 speed. When I am not thinking I want to move the shift lever from 4th to what would be sixth in the bimmer. Not at all a good thing to attempt.

Anything that helps you get the timing right is OK by me. For me, it is just a matter of moving the clutch smoothly and moving the shift lever at the right point. On downshifts, I taught myself to blip the throttle too. Now if I can do it right my next autocross..... I can do it routinely at low speeds but the magnitude of the blip is different up near redline.

Jim

[mackeroni]

Originally Posted by Dackelone

The way you make smooth shifts is to get rid of that damm CDV!

Go to the "CDV delete DIY" to learn more on what all is involved.

Thanks for your suggestion. I hear ya... and have heard others say the same thing. What bothers me is that the guys who put the CDV there in the first place are undoubtably way smarter than me. The fact that it has been put in place to presumeably remove stress from the clutch mechanism makes me reluctant to remove it.

Believe me, I have a rich history of removing thingys from my cars and motorcycles that did not appear to improve speed, control or reliability, only to learn later that the removed thingy was performing an important function or protecting an expensive component.

I think I will continue to hone my smooth shifting skills with the CDV thingy intact.

Thanks again.

[fatbaldandhappy]

Good point about the CDV. In the limited post readings I've done it is mentioned frequently, including many who have done the COBB ECU. Anyone have some tech detail on what its purpose is and any downside to removing it? Is mackeroni right in thinking it's there to remove stress from the clutch and removing it could shorten the clutch life?

[Sylon]

Originally Posted by fatbaldandhappy

Good point about the CDV. In the limited post readings I've done it is mentioned frequently, including many who have done the COBB ECU. Anyone have some tech detail on what its purpose is and any downside to removing it? Is mackeroni right in thinking it's there to remove stress from the clutch and removing it could shorten the clutch life?

Well one of the downsides to removing the CDV would be voiding the drivetrain warranty if your dealership found out. Thats kind of a biggie, lol.