Google "Clutch delay valve", and you'll find a lot of posts for other high performance cars (a lot of BMW posts) that complain about the clutch system not letting the clutch release quickly. They say this is to protect the transmission during high rpm shifts- it hits the next gear softly. I found it pretty annoying to run a gear up to redline, snap off a quick shift, and feel the car shift like it's an automatic. So I looked into it.

Our cars have a restrictor block in the clutch line between the clutch master cylinder and the clutch slave cylinder. Other high performance cars have a valve on either the clutch master or slave for this purpose, but on ours it's a block that the clutch line threads into and out of. If you can find a union fitting that is M10x1.25 Bubble Flair, then you can just bypass the block. I ended up drilling it out because I couldn't find the union fitting locally. Here are my pics:

This is where it is located. You have to remove the rear half of the fender liner in the front left (front, driver's side) wheel well. Once you remove that, you will see this. The restrictor block is in the right side of the shot, in the bottom rear of the wheel well:



This is what the actual restrictor block looks like:



Close up of the restrictor block:



Once you remove the clutch lines and the mounting bolt in the center, you can pull it off the car. Here is a shot of the restriction:



I drilled it out with a 5/32" (4mm) drill bit. There isn't much to have to drill through. Basically, as soon as the bit started cutting, it fell through. Here is a shot of it drilled out:



Then everything gets bolted back together the same way as it came out of the car. Pretty simple.

After refilling and bleeding the clutch, I went out for a quick test drive, and I gotta say, it made a difference! It's hard to tell how much quicker it shifts since it's 40 degrees out, so I don't have any grip from my tires. On high rpm shifts, it either wheelspins, or traction control comes in and softens the shift. But the clutch feel improved, and I do think that helped remove the clutch delay. I'm excited to test this when it's warmer out.

 

Excellent find. I'll be doing this soon. I hate how soft the clutch feels between high rpm shifts.

 

Wow nice I will definitely do this soon.

 

Awesome post man. I'll probably research a bit more into this then give it a shot.

 

Thanks. Will add this to my to do list

 

Update: It's warmer out, and I've been driving with this mod for a few days now.

First off, I'll say that yes, it makes a noticeable difference on very quick shifts. If you were trying to shift faster than the restriction block allowed you to, then you WILL notice it. (Duh.) Otherwise, it drives like stock, but with slightly more consistency on the friction point. No downsides that I've found. And when you're really running a gear out and snapping off quick shifts, it's far more satisfying. And for drag racers on a prepped track, I'd estimate that this is worth a tenth or so, after the 3 shifts in a 1/4 mi.

I'd love to hear your impressions when you guys do it. And I'll try to remember to give periodic updates as time passes, or if anything comes up related to this mod. But so far, I'd say it's worth doing. Even if you forget about it in a daily driving setting, you remember when you run a gear out, and then you love that you did it! That's how most of these, "Car should have come this way" mods are.

 

This is very intriguing, as I run the car out a lot. I notice a stutter as it goes into the next gear, for sure. If this fixes that, I'm all in.
Do you have any links to BMW guys doing this? I would like to research more.

 

I don't know if it will fix a stutter. You might be engaging the trac control due to wheelspin. The behavior I was trying to address is when you run a gear out to redline and hit the next gear with a really quick shift, the clutch slips when you release it, making the shift slow, and feel like an upshift in an automatic. This mod eliminates that.

Here are some links for some other cars:

https://en.wikipedia.org/wiki/Clutch_delay_valve

https://www.bmwcca.org/forum/index.p...ay-valve.6643/

https://www.zeckhausen.com/catalog/index.php?cPath=6562

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