wes8398

iTrader: (2)

So I've had my "PMC" sitting on my workbench for a few months now, procrastinating on having it installed because this will be the 3rd time I'll have to pay my mechanic to drop the trans for LS7 clutch-related reasons. The first time was to install the LS7. Then I has serious issues with proper disengagement and clutch drag. So trans drop #2 was to have him measure and install the appropriate slave spacer from Tick. That solved the clutch drag issues and made shifting much better. A couple weeks later, Philistine released his new Tilton-based master cylinder for us. Even though the tick spacer seems to be doing the job, I felt like the PMC would help overcome some of the notchy-ness and occasional downshift to 2nd that takes more work than it should; so I bought one.

I would just install the PMC myself but I'm afraid of installing it along with the 0.113 slave spacer because I don't want the new MC to drive the slave's piston too far and ruin my new clutch. Know what I mean?

Basically, do you guys think it'd be necessary to uninstall the slave spacer before installing the PMC? Or do you think the PMC would work with the slave spacer installed? Really, I'd rather not take any stupid risks so I'm probably just going to bite the bullet and have my guy remove the slave spacer and just install the PMC for me while he's in there. But if I can safely save paying for a 3rd trans drop, I'll entertain that too. I would have loved to do the clutch myself and do all these trans drops in my own garage, but I just don't have the time and I don't want my garage tied up for as long as it would take for me to complete the task. Plus, it's getting damn cold and my (attached) garage isn't insulated, so laying on that floor for hours really isn't very appealing. My guy is only $50 an hour and he's very knowledgeable, so having him do this stuff is a reasonable thing for me right now. Doing just the MC is something I'd tackle myself, but another trans drop isn't.

Goosecaddy05

my slave went out twice on me because when i got my clutch put in by Vengeance racing they did not measure it and just put something in they thought would work(who knows if that's really true though because i'm going off what a different shop told me, and that's impossible to verify) so after the 2nd one failed after 6000 miles i had the new shop measure the spacer they put in bc i felt somthing must be off if 2 failed at only 5-6000 miles of use each... sure enough the spacer Vengeance put in was too big(supposedly)... so on the 3rd slave i bought the pmc master and had the spacer cut to the right size by the new shop i go to in town that has been much more thorough although much more expensive but i feel either does quality work if paid for it...(Injected Engineering) and also did my motor swap and wired everything extremely pretty... I'm not sure if it really matters about your slave though in regards to the new master... from my understanding if its the right size for your current clutch it should be the right size for the new master as well...

itsdaveonline

Where can i get this MC at? I think i need one if you read my thread. It could probably help me out. Do most ls7 clutch guys report improved shifting and feel after install this?

wes8398

iTrader: (2)

Type "philistine master cylinder" into the search bar and you'll come across the thread with ordering info. I can't speak to what results people are having; I suggest you just read around and see what people are saying.



Goosecaddy - Thanks for the input. Maybe I'm not fully understanding what you're saying, but I'll explain my concern a little more. After MUCH consultation with some folks from around here over this summer, this is how I understand it:

The reason some of us needed a slave spacer was because our OEM hydraulics didn't push the LS7 slave rod through enough of it's travel to completely disengage the clutch. So, the spacer physically moves the slave rod closer to the clutch fingers in order to compensate for the rod not traveling far enough. To my knowledge, a spacer moves the slave so much closer to the clutch fingers that the rod actually "pre-loads" the clutch fingers; meaning the UNextended rod puts a small amount of pressure on the clutch fingers before you've even depressed the clutch pedal. This may reduce some of the clutch's clamping capacity, but for those of us who aren't significantly modded, it's insignificant. Regardless...

With Philistine's MC, the hydraulics now allow the slave's rod to extend significantly more, thus eliminating the need for the spacer. Trouble is, if you have a spacer installed along WITH Philistine's MC, you now have the extra travel of the slave rod ADDED TO the spacer. My concern is with this, because I don't know if the extra rod travel plus the spacer will cause the rod to travel TOO far, possibly damaging the clultch fingers or other clutch parts.

The fact that you apparently have the PMC installed but also still have some sort of slave spacer installed is interesting to me, but I'd have to hear some more details to be sure of what you have going on. I'd be curious to talk to your shop... or you, if you're the nosey type and you know exactly what your shop was doing with your car.

'99REDTA

iTrader: (1)

From my understanding the master is not used to make up for any needed stroke in the slave, it simply moves a little more fluid (I believe 10%) to ensure full stroke of the slave even under high rpm and high tempurature situations. Notchy shifts or blocked gears in the previously mentioned circumstances are common amungst GM vehicles, and most platforms have a Tick performance replacement available, we do not and this is the solution. That said, I have a spec 2 and aftermarket flywheel, wich requires my slave be shimmed which it is and it all works well with my PMC, it shifted before but Iwas getting blocked out of high RPM shifts.
Sorry for the book hope this helps

wes8398

iTrader: (2)

My chats with Philistine lead me to believe that his MC does indeed move more fluid (yes, in the ~10% range) which in turn makes the stroke of an LS7 slave longer. IIRC, reading a number of his write-ups and PMing with him, he learned through his testing that our OEM hydraulics were moving an LS7 slave's rod only a fraction of what it's full stroke was. IE if an LS7 slave's stroke was 2 inches, our hydraulics were only pushing it 1/4 inch (just an example, not real numbers here). That's why he made this PMC move more fluid. More fluid moving equals a larger stroke. So if that's the case, I don't wan to add MORE stroke with a slave spacer unless I know there's still room for more without over-doing it and breaking a clutch finger or something. No?

'99REDTA

iTrader: (1)

I didn't realise that it was meant to move the slave further, I thought that was where a lot of the math came into play to ensure that it did not push the slave too far to blow any seals. Maybe he will jump in and answer question

wes8398

iTrader: (2)

A quote from FuzzyLog!c (before he got banned from here):

...I know your reaction is going to be somewhere along the lines of "WTF?", so briefly, the issue here is that the stock CTS-V master cylinder is not capable of producing enough fluid volume to drive the slave through its full 0.700" (18mm) travel. In fact, based on my testing this weekend (had the transmission out) and a couple of technical discussions with McLeod engineers, I strongly suspect that we're getting less than half of that travel... When Philistine finishes his Tilton 76-875 project, it'll be a game-changer because we'll finally be able to set our slaves correctly with the recommended gap and get better performance than we have now...

'99REDTA

iTrader: (1)

My car still has CTS V slave in it as well as the shim it had when I bought the car so the only thing that should be different is the master, with that other than gettin high speed shifts without blocking the only difference I've notice is my engagement point is a little higher than it used to be. Before it started to catch dirrectly off the floor, I would imagine if the fingers were bottoming out on the clutch I would hear or feel something but it all seems ok, I guess only time will tell with mine but I am pretty confident all is as it should be. I didn't think this setup was meant to affect measurements down on the transmission side

Becker

iTrader: (4)

I would imagine if clutch pedal stroke stayed the same and volume increased to the slave then throw would increase.

Is my thoughts wrong?

wes8398

iTrader: (2)

We're not comparing apples to apples here. If you have an LS2/6 slave, then you don't have a shim, you have a spacer... no? Not trying to play semantics here, but in terms of products there is a major difference between a slave spacer (like Katech's) and a slave shim (like Tick's).

Two things here. One is that the OEM LS2/6 slave doesn't have the same throw/stroke as the LS7 slave does. So we're not talking about the same thing here. Everything I've said about the PMC is relating to an LS7 slave. Second, if you did have an LS7 slave, you wouldn't necessarily "feel" any difference with the added stroke from the PMC. You'd feel the effects of it, in that your shifts should be smoother and you shouldn't get blocked out anymore. But you wouldn't have any direct "feel" differences due to the increased slave stroke.


I doesn't thinks your thoughts is wrong.

fitz98ta

iTrader: (29)

the only way to physically extend the slave too far is if you aren't using a slave cylinder spacer and use an adjustable master cylinder (of any brand) to make up the short stroke. In that case you can adjust a master to push further than the slave can physically move and push the seal out. The slave cylinder is only going to move so far before it fully presses the pressure plate fingers down and it will stop. So if your clutch is good now you won't have to worry about overextending, that's what the adjustable master is for. Now you can adjust your master to match your already setup clutch/slave system that is already working.

I wouldn't pull any shim out if it is setup good and it sounds like you are ready to install the master, get it adjusted and enjoy the smoother shifting the added line pressure is going to give you!

When I replace a clutch I make sure that engagement/disengagement is setup in the middle and will add/remove shim until I am happy with the point the clutch starts to react. I mainly dealt with Spec clutches with my old TA and almost everyone required a different amount of shim. If you want to be real accurate there is a way to measure setup depth to make sure it only takes one try.


-Jason

ls1247

iTrader: (2)

Bottom line....

You can take the trans out and remove shim now not really knowing if you still need it or not.

Or, put master in, drive it and see what happens. If it doesn't feel right take it out put the stock one back in.

The first way, you're definitely paying to take the trans out with unknown results.

Option 2...you don't know if you'll need to r&r trans at all as chances are good IMHO that it will be fine.

I vote install and try versus paying to remove shim for unknown results to fix a problem you may not have in the first place.

wes8398

iTrader: (2)

Is that the bottom line though? I'd already determined that these were options, but I just don't want to damage anything and I certainly don't want to wind up costing myself even more money. If the clutch fingers will stop a slave rod at a given point of pressure, that's great. But if it's possible that the rod could travel too far and actually damage the clutch fingers, then I need to be damn careful with what I try here, no?

One thing is for sure. The slave shim would become redundant, because the PMC basically does what the shim does, just by a different method. If I can be really confident that I'm not going to hurt anything by installing the PMC with the .113" shim remaining, then I'll give it a shot and save myself the money from having the trans dropped again.

Goosecaddy05

When Injected Engineering put my slave and MC in they measured for the correct size the spacer needed to be to make the slave not over or under extend and make my mantic clutch, which is basically just a really fancy pants ls7 clutch work properly, if you have any aftermarket clutch you need a spacer because of the deletion of the huge dual mass flywheel from my understanding... they then installed the master to match up to that... that way the slave is getting its full operation and the master is adjusted to suit... if your slave to clutch geometry is correct you should have no worries with the MC as long as its installed properly as well... i love mine btw, totally worth it... no more high rpm lockout

Goosecaddy05

but if you have your slave spacer so big that its forcing your slave to push more than it should stock to make up for the stock hydraulics not pushing it out fully then you will be over extending it with the new MC like i was with the slave spacer Vengeance racing put in and will have to replace the slave very soon... i was over extending it on a stock mc btw the Vengeance spacer was so big... that cost me 2 new slaves and the labor to pull the trans apart, not happy at all about that(but that is also just what i was told from one shop Injected engineering after they "measured") If the slave goes out again I'll start thinking Injected can't put in a clutch(since the ones that went out were both at their shop or after they worked on the car) or the mantic is killing my slaves

ls1247

iTrader: (2)

Honestly, I don't think we know what the bottom line is with the PMC and clutch slave shimming. I have yet to hear anyone say...

"Installing my PMC solved my clutch shimming issues"

I installed a PMC on my LS7 clutched V1 and while I like the way the pedal feels, like the fact that it is adjustable and appreciate that I will need this for sure if I ever go to a stouter clutch combo, I can't say that I feel an appreciable difference in how my car shifts after installing it. I've bleed it 3 times so I don't think it has air in it either.

Based on my personal experience, I don't think you'll notice any huge difference in the clutch performance of an LS7 clutched V1 with the PMC which leads me to conclude that it will be just fine with the shim you already have...

philistine

iTrader: (2)

A lot of discussion here and for the most part, everyone is correct regarding the PMC and clutch hydraulics - I'll splain...

Clutch Disengagement:
Clutch pedal to the floor, the clutch is disengaged. The master cylinder is completely stroked. The hydraulic reaction is that the slave cylinder extends, like a bottle jack. Neglecting friction losses, the only opposing force is the pressure plate. There must be sufficient force to extend the slave cylinder against the pressure plate to disengage the clutch.

GM LS9,GM LS7, McLeod, Mantic, Monster clutches etc. do not all share the same pressure plate spring force. Remember...that is the opposing force that the slave must overcome to disengage the clutch.

A little history:
The factory OEM hydraulics are not robust, they are weak and insufficient - it is a symptom with many GM cars, e.g. GTOs, Camaros, Vettes etc. Part of the reason is that if you have a kick-*** hydraulic system, it usually results in a stiffer clutch pedal. The GM engineers decided to incorporate a spring assist on the clutch pedal and a small diameter master cylinder with an average stroke of ~1.1 [in].

The result from the GM engineers has not been too good. There are numerous notchy shifting, blocked gears, worn synchros, dead clutch pedals with high rpm shifts, clutch drag (poor disengagement), and the list goes on.
It has made things difficult for aftermarket clutch vendors because they cannot design a pressure plate for a platform that has unreliable clutch hydraulics and still have a gripping force that can handle 500-800 HP at the flywheel.

Philistine (Tilton) Master Cylinder (PMC):
The Tilton master cylinder has a larger cross section and equal stroke compared to the factory. The increase in the surface area is directly related to the stiffness of the clutch pedal but it is NOT an equal function of hydraulic force. The hydraulic force is actually increased by ~17% while the pedal stiffness will increase by ~10%.

Now that you have more volume and pressure (hydraulic force per area) that will result with extending the slave cylinder. Remember the pressure plate (opposing force)? If that opposing force was zero then the slave cylinder would extend to the maximum stroke whether there is a Tilton or factory master cylinder pushing it. However, the opposing force are those finger springs from the pressure plate. The slave cylinder must overcome the opposing force and extend sufficiently to disengage (let go) of the flywheel. That is where the Tilton master cylinder comes in. It has sufficient hydraulic force to overcome the pressure plate finger springs and release the clutch disc for full disengagement.

Clutch drag - this is when the clutch disc does not disengage from the flywheel. Minor clutch drag results in notchy shifting. If not corrected, it leads to blocked gears. Severe cases will result in grinding gears, warped disc and warped pressure plate. I point my finger to the root cause of the factory hydraulics with a poor performing clutch master cylinder.

Now that clutch drag has been defined along with disengagement, what about clutch engagement? Ideally, we want clutch engagement to be quick and it is controlled by how fast our foot can let off the clutch pedal. If too slow during power shifting then it results in "riding the clutch". If you ride the clutch too often then it will result in premature wear on the clutch disc and eventually start slipping. Fast engagement will result in a "jerk" or "jolt" which is kind of the point when accelerating fast or clutch dumps.

Since the PMC provides the proper clutch disengagement already fully explained above, we now have to avoid slow engagement to prevent clutch slippage or "riding the clutch". To assist, the Tilton has a built-in return spring to avoid dwelling or relying on the pressure plate springs to force the slave cylinder to retract. So it's actually very gentle on the pressure plate and independent of the springs unlike the factory MC.

To answer the OP and other's reading this...set your clutch according the manufacturer's instructions including the air gap. The engineers of those aftermarket clutches did not and will not take into account a poor performing hydraulic system. They are looking at the ideal displacement of the slave cylinder. The PMC will do the rest and it is adjustable.

The detailed instructions provided in every kit explains how to adjust the disengagement to the comfort of the driver and safely for the health of the clutch. I have designed the adjustability with mechanical limitations to avoid damaging any components and to retain the safety functions during start-up with the clutch pedal position sensor (that devil). It is a turnkey kit and provides every installation part to integrate into the factory hydraulic system. It does not require any drilling or disassembly of the clutch pedal and some have installed in 2hrs including bleeding the clutch.

I hope that helps and thanks!

ls1247

iTrader: (2)

So if I'm reading and interpreting this correctly, the PMC will allow a properly shimmed clutch slave assemble to fully disengage the clutch because the factory master just doesn't have enough *** to do it but the PMC won't compensate for a slave cylinder that isn't shimmed correctly?

Becker

iTrader: (4)

Sounds like it.