Alternative Clutch master cyl. Diameters?

[STARION]

Does anyone happen to know of any larger diameter clutch master cylinders which might be worth trying to make fit a DSM? The bolt pattern being different isn't really too much of an issue, I'm using a 90 FWD turbo drivetrain in a tube-chassis car I'm building, and having to fabricate a new mount is easy, but it would be nice if maybe there was a slightly larger one which was also in the mitsu family (3kgt maybe?? ) which would fit, I'm just looking to make the pedal a bit more easy on the leg in the shitty D.C. traffic.

Thanks

[Defiant]

You'll run into travel issues if you change diameters. If it'd be enough to matter, I don't know.

[pneumo]

Did I read that right? You're building a tube framed car to drive in crowded city traffic? Holy Overkill, Batman!

BTW, a larger diameter Master cylinder will decrease the pedal travel and increase the pedal pressure.

If you want to lighten the pedal effort, why not look into custom building a stiffer clutch pedal helper spring?

[Morphius]

DSM's, 3kGT's, Conquest/starions all share a common 5/8 dia. bore master cylinder. The differences between systems is in the slave. Pedal effort will acutally decrease as you make the ratio between the master and slave larger.

Diameters as follows:

N/T DSM 3/4
Turbo DSM 13/16

N/T 3KGT 13/16
AWD 3KGT 11/16

I'd suggest trying the AWD 3KGT slave. Be careful, you will increase your output at the slave and could over-stroke the clutch if the pedal is fully depressed.

[STARION]

Did I read that right? You're building a tube framed car to drive in crowded city traffic? Holy Overkill, Batman!

Yeah, well, the car is being built as a daily driver, weekend racer (well see if that actually happens), but I'm sure at some point I'd be stuck in traffic.

DSM's, 3kGT's, Conquest/starions all share a common 5/8 dia. bore master cylinder. The differences between systems is in the slave. Pedal effort will acutally decrease as you make the ratio between the master and slave larger.

Diameters as follows:

N/T DSM 3/4
Turbo DSM 13/16

N/T 3KGT 13/16
AWD 3KGT 11/16

I'd suggest trying the AWD 3KGT slave. Be careful, you will increase your output at the slave and could over-stroke the clutch if the pedal is fully depressed.

Hey, that's excellent info, thanks. I think I'll have a look at the 3kgt VR-4 slave and likely give it a try, I think then I can just adjust it, then see where it disengages, and weld in an adjustable stop, to make sure that I don't over-stroke it.

[pneumo]

Originally Posted by Morphius

Pedal effort will acutally decrease as you make the ratio between the master and slave larger.

Diameters as follows:

N/T DSM 3/4
Turbo DSM 13/16

N/T 3KGT 13/16
AWD 3KGT 11/16

I'd suggest trying the AWD 3KGT slave.

If you want to make the difference between the master and the slave bigger, then why recomend the slave that's closest in size to the master? Wouldn't the smallest slave cylinder make the pedal effort harder? I would think a bigger slave would make the effort lighter.

[pneumo]

I just had another thought, since you're going to build a custom master cylinder mount anyway, why not move the point where the master rod attaches to the clutch pedal? Just drill another hole in the clutch pedal arm and move it up closer to the pedal arms pivot. Then just move the master up a little so the rod coming out of the master isn't at an angle. That should change the leverage so you have less pedal pressure. Theoretically that should do the trick, but I haven't looked under the dash yet to see if the pedal arm has room for another hole.

[Morphius]

Originally Posted by pneumo

If you want to make the difference between the master and the slave bigger, then why recomend the slave that's closest in size to the master? Wouldn't the smallest slave cylinder make the pedal effort harder? I would think a bigger slave would make the effort lighter.

You are right in your thought the bigger slave would make the effort lighter. Here is my reason for recommending the smaller slave: I'm speculating that Starion will be running a high clamp load clutch. We all know how the pedal effort is with say a 2600. There is also the issue with the clutch pedal and pedal assy. It needs welded and yet it still has some flex issues. People start adding the longer pushrod or modifiying other parts to help with the disengagement. That only preloads the throw-out bearing and will cause excessive wear. (If you don't believe me, I've got pics. I've got over 50K on a 2600 on my 90 and it's got some interesting wear on the pressure plate fingers. )

With the 2600 overstressing the pedal assy, most of you will find you use the entire range of the pedal, just to make it work. As you push the pedal through it's throw, you are changing the effective pedal ratio. As you stroke the pedal forward the ratio decreases. Thus, as you hit the end of the pedal swing, it's ratio is at it's smallest point. This just further increases your pedal effort.

By using the smaller slave, you will be increaseing the output of the system. The release lever will travel through it's motion quicker than before. Moving back to the pedal, this means you will disengage sooner.

The inital pedal force might be greater with the 13/16 slave, but the pedal force at the end of stroke or disengagement point should be less, due to the pedal ratio at that point.

And you get to stear away from the longer pushrod type remedies and premature pressure plate wear.

[Morphius]

Originally Posted by pneumo

I just had another thought, since you're going to build a custom master cylinder mount anyway, why not move the point where the master rod attaches to the clutch pedal? Just drill another hole in the clutch pedal arm and move it up closer to the pedal arms pivot. Then just move the master up a little so the rod coming out of the master isn't at an angle. That should change the leverage so you have less pedal pressure. Theoretically that should do the trick, but I haven't looked under the dash yet to see if the pedal arm has room for another hole.

That might be viable. The smaller 11/16 slave would need to be used to ensure there is enough output at the release lever.

[STARION]

I just had another thought, since you're going to build a custom master cylinder mount anyway, why not move the point where the master rod attaches to the clutch pedal? Just drill another hole in the clutch pedal arm and move it up closer to the pedal arms pivot.

Well, you actually kind of brought up the reason that I posted this... (BTW, the clutch I'm using is a clutchmasters stage 4), See, with the space I'm going to have in the footwell, I will actually have to cut a few inches out of the clutch, brake, and gas pedals to make them fit, and I'm obviously going to lose some leverage, having to do more work on the brakes and gas isn't much of a big deal, but losing some leverege on the clutch is major, especially with the already high-effort needed. So, more or less, I'm hoping for the pedal effort I had when it was in a DSM, so I was hoping that I could find another slave or master which could give me that.

[bigfoot]

This thread has good timing. After sitting during the winter my 2600 clutch went south after only 800 miles of easy use, it barely goes into 1st and reverse. The release fork is in the perfect position and not even close to the stop when the pedal is down. I've replaced the master and the slave and it's bled very well. I've either got a leak in the SS line, a bad clutch spring, or the pedal assembly needs to come out and get welded, although it doesn't look like it has much play. The problem is I can't weld the pedal or drop the tranny for a few of weeks so I'm looking for alternatives. Untill I saw this thread I'd thought about boring my old master to 3/4" and using a different rebuild kit, still could. I like the smaller slave idea.

I looked up the 3000gt slave and this guy said the 92- AWD slave has a larger piston then the 91 AWD-FWD. http://www.team3s.com/digests/v01n431.htm Can anybody double check the piston diameters?


Here is a comparison pic of the two, the 91-FWD is shorter. Towards the bottom, http://www.3sxperformance.com/clutch.asp I can't tell from these pics if it bolts up, anyone?

When I weld the pedal lever I'm going to drill another c-bracket hole lower. All of these mods will give me more slave rod travel and increase the pedal effort, but they can all be easily switched back to stock too.

[cbassgsx]

okie so which would be better a larger master or smaller slave?
i have a 2600 welded pedals and still barely get enough travel to engage. I dont want to preload so whats the better alternative.
cbass

[PieEyedPiper]

Truly an interesting thread.
From what I gathered, the AWD 3kgt Slave is going to give a stock system more throw? If someone can please clarify that I interpreted the thread correctly that would be great.

I was going to buy a new (stock) slave today so any response could influence my purchase.
Thanks!

[cbassgsx]

I can say it is smaller 11/16" on 90-91 awd and 92-99 fwd 3s cars. I'm trying to acquire one used to test this out. If your shopping goto here http://www.3sx.com/store/comersus_vi...dProduct=24254
It's the blue one the gray one is the same size as a dsm. Ill keep you posted when i get one. It should have a bit heavier pedal but possibly a better throw for heavy (ie 2600) clutches.

[PieEyedPiper]

Originally Posted by cbassgsx

I can say it is smaller 11/16" on 90-91 awd and 92-99 fwd 3s cars. I'm trying to acquire one used to test this out. If your shopping goto here http://www.3sx.com/store/comersus_vi...dProduct=24254
It's the blue one the gray one is the same size as a dsm. Ill keep you posted when i get one. It should have a bit heavier pedal but possibly a better throw for heavy (ie 2600) clutches.

Thanks for the link and all but I decided to not feck with it and just use a stock OEM slave. I figured why gamble on it when I know this combo(stock) works fine.

[hopwoodp]

Has anyone found where to get a larger diameter master cylinder? I am guessing one that is 11/16" to 3/4". I would prefer to use the master cylinder for this than the slave cylinder, due to the overthrowing of the clutch for stuff. =)

My reason for this is because I have the ACT 2600 clutch and have some bad arthiritus in my knees. If I can find out where to get one, I will be doing this asap.

[Morphius]

Originally Posted by hopwoodp

Has anyone found where to get a larger diameter master cylinder? I am guessing one that is 11/16" to 3/4". I would prefer to use the master cylinder for this than the slave cylinder, due to the overthrowing of the clutch for stuff. =)

My reason for this is because I have the ACT 2600 clutch and have some bad arthiritus in my knees. If I can find out where to get one, I will be doing this asap.

Although I haven't tried it myself, I know there are 2-3 people on here that have used the 3000gt VR4 slave with success, after I recommended it. At least with a ACT2600 clutch. Sorry, I don't recall who. If you're running a 2600 or clutch with similar pedal load, you shouldn't have any issues. The pedal crossshaft flexes enough as it is, I don't see anyone overstroking the clutch. Install it. Set the pedal up as it should, per the manual. Pay attention to where it releases/engages. Typically, in any vehicle, the clutch is designed to release 25-35mm off the floor.

[hopwoodp]

Originally Posted by Morphius

Although I haven't tried it myself, I know there are 2-3 people on here that have used the 3000gt VR4 slave with success, after I recommended it. At least with a ACT2600 clutch. Sorry, I don't recall who. If you're running a 2600 or clutch with similar pedal load, you shouldn't have any issues. The pedal crossshaft flexes enough as it is, I don't see anyone overstroking the clutch. Install it. Set the pedal up as it should, per the manual. Pay attention to where it releases/engages. Typically, in any vehicle, the clutch is designed to release 25-35mm off the floor.

Roger that. I know some people that have certain engagement issues and some are tied to the slave cylinder and/or clutch (which would make sense). As for the clutch pedal adjustment itself, I don't think would be much of an issue.

Hopefully after doing this, I should be able to see a difference and comment about this. It does make sense that it would work and (what I learned from my uncle) that it would "lighten" up your clutch pedal. The only variable in this would be, how it is installed, adjusted and quality of the part. Other than that, I can see this as a good mod for those running heavy clutches like the 2600. Thanks Morphius

Alright, I just finished putting in a 91 awd 3000gt slave cylinder. It is 11/16" in diameter and what looks like 3/4" of an inch shorter than the stock one. It took me a little over three hours to get this thing swapped over.

Of course you will need some longer bolts w/ nuts. But, that was the easy part. I couldn't figure out why the d@mn thing would bleed out. I had put on a 10mX 1.0 speed bleeder in and figured it should work but, I left out something pretty important.

Here is what I discovered: The slave cylinder on our cars has the speed bleeder mounted on top of the cylinder and the feed from the master near the middle/bottom. On the 3000gt in is flipped the other way. I tried swapping the bleeder and the feed but, the feed inlet isn't designed to close off the bleeder when it is fully secured. What I ended up doing was I bleed the slave cylinder by pulling off the rubber boot that holds the rod and put a clamp on the slave cylinder to keep the piston from coming out. I then bled it and it worked!!!!

I checked the clutch pedal and it did increase the travel (throw/ swing) of the clutch pedal. The pressure on the pedal dropped a small bit but, that didn't bother me to much knowing that I have a longer range on my pedal to engage the clutch.

Another thing I forgot to mention was, because of the fact that the slave cylinder is around 3/4" of an inch shorter, I used a slave cylinder extension rod to compensate.

Was it worth it? I am not 100% sure but, I would suggest another means of obtaining the desired effects. I would recommend a larger bore Master cylinder. I know that they are out there somewhere floating around.

[hopwoodp]

Just another update on this. I went and looked at summitracing.com and found a few master cylinders that are made by wilwood and a few other guys that are universal. They have the larger bore that we want and seems like they would only require a little bit of modification.

I think the majority are brake master cylinders. They have no boost connections, single outlet, and look pretty much like out stock clutch master cylinder. I think one of the hard thing would be mounting it due to a 12 to 6 bolt on flange instead of the 9 to 3 o'clock on.