clutch bites slow?

juld0zer

Here's a simple test: press the clutch pedal all the way down then suddenly pull your foot back quickly, as if you were doing a clutch kick. Does the pedal almost chase the sole of your shoe or does it lag behind and slowly reunite with your sole?

The Z has a restriction orifice in the clutch fluid circuit. There is at least one that i know of but there might be a second, in the master cyl but i've never inspected our masters to be sure. google clutch delay valves and you will find heaps of disgruntled owners of other sports or non sports oriented cars. Pretty much the same problem.

Simple braided replacement lines wont fix or eliminate it. To get rid of it you need to remove the restrictor which is in the left fender well and get a custom 4mm braided line made up. Most braided lines for our cars are only -3AN. You'll understand the need for -4 inner diameter hose when you take out the restrictor piece and have a look at the hard line that goes INTO the restrictor. It will make you wonder whyyyyyyyyy Nissan, whyyy? Get the line made long enough to reach the slave cylinder port directly and terminate it with a union fitting rather than a banjo because the inlet to the banjo will probably be 3mm or 2.5mm.

Downside is a slightly heavier feel in the pedal but oh man, it makes a massive difference with quick shifts. Slow shifts will take a tad more concentration

JARblue

I bought a replacement restrictor a few years ago but never bothered to located the stock one to replace lol. Will have to look into this again

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RadioFlyer

Can you confirm the size of the union fitting? I think I read somewhere that it is a M10x1.25 bubble flair union, but when I went to look it up, I couldn't find it. What size do you have?

JARblue

I found one at my local AutoZone based on the post below. But as you can tell, it doesn't open it up that much (from 2mm to 3mm).

And thanks for the photos - I'll definitely be sending a rep your way

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RadioFlyer

Thank you sir!

Forgot to add, the whole thing took maybe an hour. Add a few minutes for bleeding the clutch lines. Oh, and last thing to remember is to have brake fluid on hand to be able to refill and bleed the system when it's all back together.

Ryan @ RJM

Just thought I'd add my 2cents to this discussion since I've done a lot of research and development on this topic lately with the HD master cylinder project. I just wanted to clear up a few things that I've noted reading thru this thread to maybe help out others.

First off near the top the recommendation of using -4AN lines because the -3AN lines aren't adequate is not correct. The AN system was developed by the US Army/Navy and has absolutely nothing to do with the metric system so saying -3AN is 3mm is inaccurate. The Dash Number is multiplied by 1/16ths of an inch to get the inside size of the flow tubing so -3AN is .1875" (3/16) or 4.8mm in metric INSIDE the tube for flow. -4 is huge at 0.25" Inside or 6.35mm

The factory hard lines that run from the master cylinder to the brass block and from the brass block to the transmission flex line point are all 3mm or 1/8" Inside diameter. The -3AN braided SS lines are 3/16" or 4.8mm inside and flows 50% more fluid than stock so no need to go huge with -4 lines.

Next since the factory hard lines on either side of the brass block in discussion here are only 3mm internally the largest size you need to drill this block to is 1/8" (3mm) and it will act like it's not even there. Going bigger like shown above is likely to destroy your brass block as you can see in the photo that almost all of the Inverted Flare sealing surface has been obliterated by drilling it to 5/32" and you're now relying on the treads to hold back fluid pressure instead of the invert flare union. RadioFlyer you may have gotten away with this, it may be slowly weeping fluid past the threads at both sides of the block already or may begin weeping down the road... only time will tell.

My recommendation is to drill this to 3mm MAX as it won't remove as much of the inverted flare sealing area.

Final note which I've not seen discussed or noted is that while everyone is fussing with this brass union block no-one has stopped to question the orifice size at the outlet of the factory master cylinder. The factory master cylinders outlet is only 2mm and exactly the same size as the brass block. So without eliminating the restriction at the MC you could add a sewer pipe connecting the MC to the slave but it won't get you any faster clutch release with this 2nd restrictor still in play.

Hope that adds to the discussion, helps save a few people destroying the brass block and clears up the miss-information early on in this thread.

Best Regards
Ryan@RJM

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JARblue

Great info, Ryan

I've given up on this mod since I've ordered your heavy duty clutch master cylinder kit that will take care of it

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RadioFlyer

Excellent input, Ryan@RJM! Thanks!

Yes, that was the unknown - that drilling out the brass block was in fact, the actual bottleneck in the line. I did notice a difference by just drilling out the block, but it was a minimal difference. I have not experienced a leak at the brass block, so I'm all clear there. Car has been off the road for a few weeks because of an unrelated problem so I'll be able to get back into the car with a fresh feel for the clutch. I also upgraded the clutch/master/slave to HD units, so maybe that helped my car show a difference? I'll also look into drilling out the MC outlet!

2010Nismo370z

Has anyone else done this anymore reviews how safe is it any issues?

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