Resolved Extend master clutch rod or shim pivot ball

[AWD-Tony]

I’ve been searching but I can’t find it. Does anyone have a part number or link for the smaller diameter oem slave cylinder?

 

[EVLGSX]

As a test, you could reach in through the fork window with a modded 14mm wrench and back the pivot ball out maybe 2-3mm

then feel the pedal and see if its what your looking for. dont drive it this way , but then at least you will know what you need to do.

 

[AWD-Tony]

As a test, you could reach in through the fork window with a modded 14mm wrench and back the pivot ball out maybe 2-3mm

then feel the pedal and see if its what your looking for. dont drive it this way , but then at least you will know what you need to do.

How do you mod the 14mm? If it’s simply grinding down the tip, that I can do.

I was able to back out the pivot ball about 2-3mm. Drag test and engagement point are good. Slave also goes back in by hand. Now the question is can I shim the pivot ball with the trans in the car. We shall see.

Again, thanks all for the input!!!

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[EVLGSX]

word!

 

[1990TSIAWDTALON]

Can you cut a washer just enuf to go under the pivot and slide it in like a front end alignment shim?

 

[AWD-Tony]

Fml. I started another thread.

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[AWD-Tony]

Can you cut a washer just enuf to go under the pivot and slide it in like a front end alignment shim?

I might try that. Cut it and twist it enough to sneak over the threads. Definitely can’t do it with in the car

 

[1990TSIAWDTALON]

You can get to the ball enuf to loosen it but don't think you can sneek a washer in....magnet or hemostats? I use those curved ones in places like that but was just trying to save you sone work.
So what do you think the change was from, step height, master, slave....?

 

[AWD-Tony]

We’re out. Just need to lower it but shimming is the least of my worries right now

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[GST with PSI]

I'm curious about this. If the hydraulics are free to self adjust then it is not physically possible to gain travel by moving a piston. For all those reading consider this. How about an air bubble at the slave?Would it react differently if it were in the slave vs in the small line?
This reply isn't meant to dispute what you are seeing. It's meant to understand why. Everything I know about hydraulics and physics says what you're seeing isn't possible. There needs to be something else to help explain. Would you agree?

This is exactly right.

Yeah I agree. I can't explain it.

I'll try my best.

You're not actually increasing travel in a physical sense with an extended slave rod, extended clutch master rod (in stock form), or by adjusting the clutch master rod, to include adjusting it to the end of its travel. You can only change the point at which those those components begin working together (in this case specifically, passing hydraulic fluid between one another). By making the appropriate adjustments to optimize the way these components all work together, the end result is getting the most (or the appropriate amount) of travel at the clutch fork. So, perception may be you're getting more travel, which may be true. In reality, you're just adjusting the system to get it to work at full capacity (which is also when it will move the clutch fork greatest distance). That's why extended slave rods and master rods have always been considered "band aid" fixes. Loosely demonstrated in math terms, say your clutch hydraulic system moved the clutch fork 10 inches when it's moving 100% of the fluid its supposed to. If you're system is only moving 70% of that fluid, you're now getting 7 inches of travel. You can either fix the issue, or find ways to make up for the 30% loss in capacity. Either that, or physically change components that net you more travel, e.g. different sized clutch masters and slaves.

The clutch master is limited to how much fluid it can move only by its bore size, and piston travel in that bore. Piston travel translates to pedal travel in the car, which is why there is a mechanical adjustment that can physically be made to the pedal. The pedal adjustment equates to the total amount of bore stroke allowed at the clutch master, or put simply, how far the master cylinder piston is allowed to travel in the bore. The more stroke allowed, the more fluid is moved to the slave, which translates to physical movement of the clutch fork, which disengages the clutch. In summary, increasing the clutch master rod length increases piston stroke, which translates to the amount of fluid moved to the slave. Longer stroke = more fluid moved = more travel at the slave cylinder.

Regarding the extended slave rod, the same principals apply. However, since the slave only receives fluid from the clutch master, there's no way to increase travel by increasing input to the cylinder (meaning unlike the clutch master, there's no pedal travel variable allowing you to control fluid movement).

In theory, just increasing the slave rod length shouldn't increase overall clutch fork travel. However, in practice it does in most cases. I believe the reason is because you change the resting position of the piston inside the clutch slave. For whatever reason, when you move the slave piston farther into the slave bore, you get more travel. If I had to guess, it's probably something screwy with how the relief ports are configured for the slave. That's also the reason you need to compress the slave completely when bleeding, to ensure air doesn't get trapped between the piston and relief. Again, on paper, an extended slave rod shouldn't increase travel, but it simply does.

You can test all this by installing everything, then leave the slave rod boot and clutch fork boot off. Have a buddy push in the pedal, and put a mark on the trans case where the clutch fork stops in the window. Repeat that process with various length clutch slave rods, and while adjusting the pedal stroke on the clutch master. You'll find changing each variable will yield different amounts of travel. At that point, you just need to figure out how much travel you need, and what combination of parts and adjustments will get you there.

Of note, the hydraulics have to be completely blead to do any meaningful work on the system. That process is outlined nicely here: https://www.dsmtuners.com/threads/how-to-properly-bleed-your-hydraulic-clutch.213503/

Lastly, if using an extended slave rod, you need to ensure the internal fluid return port isn't blocked by the piston being too deep in the bore. An easy test for that is to take your fingers, and compress the slave all the way in by hand. If the slave returns on it's own, you're good. If it doesn't, the master piston is blocking the fluid return port, and bad things are coming your way if you run the car like that.

 

[m_0ney_pit]

I know the original poster solved the issue but to elaborate a bit on shimming with the trans still in the car...

I have given this a lot of thought after dropping a 14mm headbolt washer ground into c into the trans that had been coated with gorilla glue . One could simply use some springy 2-3mm diameter wire (316L?) formed around a 14mm bolt with a torch into a circle then that would go around the base of the ball and slide it down onto the pivot ball threads.

 

[silvreclips]

@GST with PSI you have it mostly correct. What happens when you change over to an extended slave rod is you bottom the slave piston out in the bore and that rod actually pushed a little on the cover giving you a head start on releasing the clutch. This causes premature wear on the pressure plate, TOB, and you lose some clamping force on the disc.

You can't get the slave to travel more without pushing more fluid or using a slave with a smaller bore.

 

[GST with PSI]

@GST with PSI you have it mostly correct. What happens when you change over to an extended slave rod is you bottom the slave piston out in the bore and that rod actually pushed a little on the cover giving you a head start on releasing the clutch. This causes premature wear on the pressure plate, TOB, and you lose some clamping force on the disc.

You can't get the slave to travel more without pushing more fluid or using a slave with a smaller bore.

Using an extended slave rod will not bottom out the slave piston in most cases. It will, however, change where the piston normally rests in the slave bore, which seems to affect travel. Again, you can test this by doing a back-to-back comparison between two different slave rods, everything else being equal. You'll get slightly more travel with a longer rod.

 

[silvreclips]

It's simply not possible to get more slave travel from changing the rod. The master pushes X amount of fluid, it does know or care what is on the other side of the slave piston. The slave can be bottomed out in the bore, and still function. The master cylinder is the one that can block the return ports if your not careful.

 

[GST with PSI]

It's simply not possible to get more slave travel from changing the rod. The master pushes X amount of fluid, it does know or care what is on the other side of the slave piston.

It is possible, and I can demonstrate on my car if you'd like. I literally just swapped in a new slave and went through this whole thing myself, trying to get some more travel at the fork. From my own personal experience at least, I can say it absolutely changes things. As I said above, I understand on paper, it shouldn't work, but it does (at least on my Galant).

https://www.dsmtuners.com/threads/gstwithpsi-galant-vr4-1837-of-2000.482807/page-17#post-153750177

The slave can be bottomed out in the bore, and still function. The master cylinder is the one that can block the return ports if your not careful.

You're right. I edited my posts above, which were misleading.

 

[Mello]

Any info on part number or other about this 3/4" slave cylinder? I've read thru the entire thread & followed the links as well without finding enough info to try & get one for myself. I noticed the 95-96 (MD742158) slave p/n is different that the 97+ (MD749823). Would it be one of these that's the 3/4" slave?

 

[GST with PSI]

Any info on part number or other about this 3/4" slave cylinder? I've read thru the entire thread & followed the links as well without finding enough info to try & get one for myself. I noticed the 95-96 (MD742158) slave p/n is different that the 97+ (MD749823). Would it be one of these that's the 3/4" slave?

Shamelessly stolen:

Mitsu Part Number: MD733623 (1G Turbo AWD)
Mitsu Part Number: MD733620 (1G Turbo FWD)
Mitsu Part Number: MD733228 (1G Non-Turbo)
Mitsu Part Number: MD742158/MD749823 (2G Turbo AWD/FWD)
Mitsu Part Number: MD749823 (2G Turbo AWD/FWD) [Build 9607.1]

DSM:
1G turbo = 3/4"
2G turbo = 13/16"

Galant:
1991 turbo models = 13/16"
1992 - 1993 turbo = 3/4"

I can confirm MD733623 is an OEM type AISIN with a 3/4" bore. This slave should bolt up to a 2G, but the bleeder location may give you trouble.

I can't confirm the actual bore size on any of the other slaves, since most of the old ones I have are aftermarket. My suggestion would be to reach out to whoever you're buying the slave from, and see if you can confirm the bore size. Alternatively, if you're shopping for one at your local parts store, they would probably have no issues unboxing it and letting you measure the piston.

Parhaps @twicks69 can chime in. Pretty sure he stocks all the OEM slaves. Hell, he might know this info off the top of his head.

 

[Mello]

@GST with PSI Thanks a bunch for the complete info. Very helpful!

 

[Mauispyder]

Late to the party, sorry. Plus I’m no pro rebuilder. Just some thoughts though for others with clutch replacement drag at high rpm problems. The first clutch, PP, flywheel I replaced had all the specs checked and the clutch worked and felt great. I was never able to eliminate all the drag above about 6500 rpm however without degrading the rest of the clutch performance. All new mc slave lines fluid bled, Jacks video etc. My second clutch job, same thing (although now if I’m within a third of a turn of the adjustment bolt to blocking the return, the car makes a horrible rubbing clacking noise when the clutch is depressed hard and fully to the floor). I read everything I could about drag testing the clutch adjustment. One of the things mentioned by Jack and others is that the minuscule space between the clutch and the flywheel only “closes” and causes drag at high rpms is because of distortion or wobbling if you will by the engine/flywheel at high rpms. In some cases the clutch can be adjusted correctly and there will still be drag. Could be a bad harmonic balancer or could be a tired engine. Just something else to consider.
My car rarely sees over 5000 rpms, so I’m satisfied for now as I don’t have the time or resources for a major refresh of the drivetrain.

 

[ErikTande]

@GST with PSI you have it mostly correct. What happens when you change over to an extended slave rod is you bottom the slave piston out in the bore and that rod actually pushed a little on the cover giving you a head start on releasing the clutch. This causes premature wear on the pressure plate, TOB, and you lose some clamping force on the disc.

You can't get the slave to travel more without pushing more fluid or using a slave with a smaller bore.

But an extended master rod won't cause those issues? Is that correct?

I have the exact same problem as tk106. I'm going to try back the pivot ball out first. If that doesn't work I want to try the longer master rod.

 

[AWD-Tony]

I don't think it will as long as you don't block the relief valve. But these guys would know best.

I didn’t like how my master rod was on its last few threads. The 2g master rod is 17mm longer

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[ErikTande]

Thanks for the pic!!! I pulled a 2g rod out of the junkyard yesterday, I'm going to put it in the car tonight and see if it fixes my issue.

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[AWD-Tony]

Thanks for the pic!!! I pulled a 2g rod out of the junkyard yesterday, I'm going to put it in the car tonight and see if it fixes my issue.

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I just finished installing mine. If you have a die, put a few more threads on it, about the width of the locking nut. It blocked the relief port even when it’s screwed all the way in.

Also, after you adjust the rod so the relief port isn’t blocked, use a sharpy and mark the rod. The rod will turn when you tighten the lock nut. This took me a few times.

 

[ErikTande]

thanks for the tips!!!

I just finished installing mine. If you have a die, put a few more threads on it, about the width of the locking nut. It blocked the relief port even when it’s screwed all the way in.

Also, after you adjust the rod so the relief port isn’t blocked, use a sharpy and mark the rod. The rod will turn when you tighten the lock nut. This took me a few times.

So once I block the relief valve, then back it out 1/2 turn or full turn (whatevever it takes to unblock the relief port), then I test for clutch drag again.

If it is still dragging, or still engaging right off the floor, then just back it out a little more and test again, right?

 

[AWD-Tony]

So once I block the relief valve, then back it out 1/2 turn or full turn (whatevever it takes to unblock the relief port), then I test for clutch drag again.

If it is still dragging, or still engaging right off the floor, then just back it out a little more and test again, right?

Once you set the rod and you’re not blocking the port, that’s all the adjustment you can make as there’s no more room. You can do 1/4 or 1/8 turns.

If yours is engaging off the floor, I think you need to shim the pivot ball. That CAN be done with the trans in the car. I did it yesterday.

Here’s my update:
I shimmed the pivot ball 4.2mm with two washers since I felt like I backed out the pivot ball about 3mm. Put the trans back in and installed the 2g master rod. Adjusted the rod, relief port is good and even bleed the slave. Engagement point is good but it still drags. So I cut a 1mm washer and was able to add this shim with a magnet and a long screwdriver. It fell once but no big deal fishing it out with the magnet. IT STILL DRAGS and idk why. So I’m going to pull the extra shim out and most likely order an oem slave with the smaller bore and possibly an oem master while I’m at it.