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1G Clutch drag fix

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donniekak

DSM Wiseman
5,713
1,061
Mar 23, 2008
Surprise, Arizona
After battling the 1g clutch setup for years I finally found a fix for poor disengagement.

Running everything up to an act 2600, I didn't have much of an issue just swapping around oem clutch parts. In particular the 3000gt slave cylinder with its smaller diameter bore added enough throw for every clutch I've used. Until I installed an act 2900.


No matter how I setup the 2900, I couldn't get it shift good at high rpms. Doing a clutch drag test the car wouldn't move in 1st gear on the limiter, but the engagement right off the floor was saying otherwise coupled with the slow high rpm shifting.

I pulled the pedal assembly, installed brass bushings, and welded the arm onto the end of the shaft. Nothing different here.

The fix is what I did to the arm. I welded solid the factory hole where the Clevis pin goes. I then drilled another hole about 1/4"-3/8" further down the arm. The effect of this is to get maximum travel of the slave due to changing the ratio of pedal movement to slave movement, while still allowing the master to be in self adjusting range.

The car now shifts great.

I believe it's very important to make sure every part of the clutch system is working properly, and the clutch is bled before thinking you need this mod. Like I said above, for every clutch I've ever used, act 2100, act 2600, oem, xtd, competition, spec, southbend, a 3000gt slave was all I ever needed. The different geometry of the heavier act plates require more throw to work properly.

It's imperative to use metal bushings, and weld the assembly as well with this mod due to the added pedal effort.
 
Great, now I have to remove my pedal assembly...:). I also have not heard of 3000gt mod. I'm all for anything that helps the clutch/drivetrain.
 
The 3000gt slave has to be mounted with bolts and nuts, the holes have to be enlarged, and the flanges have to be ground flat. All these mods are due to it having a slightly different bolt center, and usually being mounted on the other side of the ears. Make sure to get the later years vr4 slave, it's the one with the smaller bore.

I'm not sure on how much stiffer it is. I'm 6' 225 and it doesn't really matter as long as I can shift.
 
Great, now I have to remove my pedal assembly...:). I also have not heard of 3000gt mod. I'm all for anything that helps the clutch/drivetrain.
Use an impact with an extension and one of those u joint swivel things. Got mine out in 45min :D

The 3000gt slave has to be mounted with bolts and nuts, the holes have to be enlarged, and the flanges have to be ground flat. All these mods are due to it having a slightly different bolt center, and usually being mounted on the other side of the ears. Make sure to get the later years vr4 slave, it's the one with the smaller bore.

I'm not sure on how much stiffer it is. I'm 6' 225 and it doesn't really matter as long as I can shift.
Have you measured fork travel?
 
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Just to update, I have a new engine/turbo setup on the car. So far in tuning the power is still climbing at 8700 rpms and the clutch mod is working great. I was thinking I may need a twin disk, but I'm going to keep bumping the limiter up until power starts to fall, or I can't shift.
 
thisw is really a great idea to get the needed extra travel, I think one thing that plagues many people is getting the FWD or N/T slave which has a larger bore and therefor doesn't travel as far with the same amount of fluid moved.

I recently swapped my 1g master push rod for a 2g rod, which at first touch felt great but was really too long and caused pump up unless it was threaded in so far that the rods threads were grinding into the clevis at the pedal.

I found the perfect length to cut or make your own rod to is exactly 85mm total length. this mod worked so well for me I actually made a few extra custom 85mm push rods for future use or for any friends that had a 1g and were having the same issue.;.. just like when I made my brass BISS screw, worked so well I machined a few extra right off the bat LOL

I think i'll do what you've outlined here, next time I take my pedal assembly out (hopefully no time soon since I just rebuilt the whole thing and welded the arm solid)
 
Anyone else try this mod with success? I have my pedal assembly out at the moment and I am awaiting brass bushings.
@donniekak do you happen to have pictures of this method?

Make sure I get this correct before I start drilling. Hole on the right is the stock hole. Where the clevis is currently placed, I drill here and install my new brass bushing?
 

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Not to take anything away from donnie, it's a good idea, but think about what you are doing, and the downstream effects. It's not a one size fits all deal. Anything you do to increase the force needed to compress the master results in more deflection of the pedal assembly.

I'll tell you about an eye opener I had. I have a significantly modified pedal assembly(longer travels, needle roller bearings instead of bushings), I use a wilwood .7" master. I had a 2600 and a stock slave .75" in the car, it shifted pretty good. but the clutch was a little touchy. I swapped in a .875" isuzu slave, and now it put the fingers into the disc. I had raise my pedal stop like an inch. .75^2/.875^2 is .734. I should have only had 73% of the initial throw out bearing travel, but instead I had more..... DEFLECTION. The pedal shaft twists, the master cylinder seals swell, the clutch line swells, the slave swells, the pedal assembly/firewall flexes. It's called clutch release system efficiency, some sae papers on it out in the interwebz. It's why I run needle rollers instead of the bushings. Every little bit helps. .
 
Not to take anything away from donnie, it's a good idea, but think about what you are doing, and the downstream effects. It's not a one size fits all deal. Anything you do to increase the force needed to compress the master results in more deflection of the pedal assembly.

I'll tell you about an eye opener I had. I have a significantly modified pedal assembly(longer travels, needle roller bearings instead of bushings), I use a wilwood .7" master. I had a 2600 and a stock slave .75" in the car, it shifted pretty good. but the clutch was a little touchy. I swapped in a .875" isuzu slave, and now it put the fingers into the disc. I had raise my pedal stop like an inch. .75^2/.875^2 is .734. I should have only had 73% of the initial throw out bearing travel, but instead I had more..... DEFLECTION. The pedal shaft twists, the master cylinder seals swell, the clutch line swells, the slave swells, the pedal assembly/firewall flexes. It's called clutch release system efficiency, some sae papers on it out in the interwebz. It's why I run needle rollers instead of the bushings. Every little bit helps. .
I ended up ordering a set of brass bushings from a buddy that makes them as well as an OEM master from Nate and John at performance partout. I have an aftermarket, non OEM and heard of these causing trouble that I am experiencing. Maybe the new bushings, the pedal assembly welded, and an OEM master cylinder in place Will solve my disengagement problem. I figured “while I was in there” I’ll give everything a shot. Including drilling a hole and changing the geometry like Donnie did. Thanks for the advice
 
New OEM slave, master, good pedal assembly, correct step height, good ball, good fork, SS clutch line, good TO bearing, and bled properly and there is no reason ANY DSMer should have clutch disengagement issues. I have ran a 2900 for a long time and never had any problems at 9K shifts.

Keep it Simple.
 
New OEM slave, master, good pedal assembly, correct step height, good ball, good fork, SS clutch line, good TO bearing, and bled properly and there is no reason ANY DSMer should have clutch disengagement issues. I have ran a 2900 for a long time and never had any problems at 9K shifts.

Keep it Simple.
2900s add a lot of stress. One thing I’ve seen is the actual firewall flex while pumping the clutch. If one little thing moves in each spot, clutch won’t work right.
 
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