Simple fixture to bleed and measure Clutch Slave Cylinder stroke

[Lous69]

This thread is simply to help others because I found it frustrating when I could not easily find out the stroke range or stack heights of common clutch slave cylinders in published literature. I'm guessing that is because there is so much variation that can occur in every particular combination of parts.

According to the chassis dyno results, my engine was overpowering the GM CTS-V spec dual disk clutch that was installed in my car. I decided to replace it with a Centerforce DYAD dual disk clutch. My set up is not a factory issued combination of parts so I couldn't just order parts and throw them in without first assuring they all SHOULD work together.

My set up is in my 69 Camaro named Lou's Change. I have an LSA crate engine and a GM spec T56 Magnum transmission. My car has the Detroit Speed firewall mount for the clutch master cylinder, an LS1 Camaro master cylinder and an LS1 Camaro slave cylinder. It has a 2012 CTS-V bellhousing.

Since I am NOT a clutch expert by any means I first began by learning the differences between the GM clutch and the DYAD clutch. Upon delivery of the new DYAD clutch designed to replace the clutch I had (2012 CTS-V spec), I realized that the stack height (location of the clutch fingers) is significantly different between the two clutches. I also learned that the fingers of the GM clutch generally stay in the same location as the clutch wears but the clutch fingers on a lot of aftermarket clutches including the DYAD clutch move outward from the clutch housing as the clutch discs wear. Centerforce sends you the maximum amount the fingers can move with wear on a spec sheet they send with each DYAD clutch.

As I read all the forums and recommendations it became clear to me that not everyone realizes these differences. That makes it even more difficult for them when they try to figure out what everyone is recommending as far as clearances and set up dimensions are concerned.

For me, it quickly led to my realization that I didn't want to just trust others' recommendations and Rules of Thumb without measuring and understanding how they apply to my particular set up.

To figure out exactly how much stroke my slave cylinder would provide when the clutch pedal is depressed, I built this VERY simple and CHEAP fixture using scraps of metal I had laying around. It provided a good way to both bleed the slave cylinder before installation and to measure its stroke.





https://www.youtube.com/watch?v=IhyRkwl1mu8

https://www.youtube.com/watch?v=4VqQLFEkmnM

While the dial indicator is very accurate, I was also able to get good measurements using just a ruler as you can see in this video.

https://www.youtube.com/watch?v=VrolRKAJ7M0

Bottom line, my clutch pedal causes the GM LS1 slave cylinder to stroke a total of .380" when pushed to the floor.

Now I know that I must assure that my slave cylinder is initially depressed at least that far before the clutch pedal is actuated so I don't have to worry about over stroking the slave cylinder.

I am going to set things up so the slave bearing is .500" compressed at rest. (In these newer hydraulic clutch systems, the light spring on the slave cylinder keeps the throwout bearing against the clutch fingers at all times vs. older systems where the throw out bearing sits just off the fingers when the clutch pedal is at rest.)

That way my throwout bearing will never be closer than .120" from its maximum extended position. (.500 minus the .380 measured stroke of my particular set up)

[Lous69]

Another measurement I had to check to assure my DYAD clutch would work in my application was the clutch finger position in the overall assembly along the transmission input shaft.

The spec sheet that came with my clutch gives a very accurate measurement from the crankshaft surface on which the flywheel mounts to the fingers.



It was necessary to add the distance that the flywheel mounting surface protrudes from the engine block surface that the bell housing attaches to.

If the engine was out of the car that would be a very easy dimension to get.

With the engine in the car I could not get a caliper or ruler in position to get a good measurement.

I ended up just using various size drill bits as "feeler gauges" to determine the size of the gap between the bell housing mounting surface and a bar held flat on the flywheel mounting surface as shown in the pictures.

People are more likely to have drill sets with lots of letter and number sizes than a set of plug gauges.

It's really easy to measure the actual drill shank diameters with a set of calipers once you find out which drill was barely too big and which one was slightly too small to fill the gap. I feel confident that I got a measurement that is accurate within about .005", which is plenty accurate enough for this particular task.







Just trying to share simple, low cost ways to get good measurements for people who do not have shops full of high tech equipment or a lot of extra hands available to help all the time.

[Sonar Chief]

Nice info here, question .... do you have a stop attached to the floor so that you don't over extend the slave cylinder?
I haven't done this yet and find this very interesting, thanks,
Michael

[Lous69]

I think I understand your question. It is a good one.

The spring I used is stronger than the spring on the slave cylinder so by threading the nut down the shaft I was able to preload the slave cylinder similar to how the clutch fingers will preload it when it is installed. I was careful to thread the nut down enough that the slave cylinder was just shy of it's maximum compressed position before I bled the system and ran the test for slave stroke length. Adding something to the fixture to absolutely prevent over stroking the slave cylinder would be an improvement.

Also, I used a spacer under the slave cylinder that supports the back end of the slave cylinder exactly as the transmission does. That could be very important for slave cylinders that are constructed in a way that would allow them to blowing themselves apart without proper mounting base support. I believe that is why to be safe, some people advise you never should compress a slave cylinder until it is mounted.

[Lous69]

Assuming it's ok to hijack my own thread, there are a couple of other things that I feel compelled to share in hopes of saving someone from potential headaches.

When someone who has never removed a pilot bearing/bushing googles it for suggestions, they will find a lot of posts showing both conventional ways with the proper pulling tools and some unique and creative ways that do not require a special tool. While I am all for finding ways to do things well using common tools if I can, sometimes it just isn't a smart option.

Many of the more modern crankshafts, like mine for instance, have a sort of freeze plug in the end of them. My guess is that the crank has oil passages machined in it from the end and the plug seals them.

Therefore the cavity that accepts the pilot bearing /bushing is not a blind hole that deadheads into solid metal.

One of the methods that would work fine in blind hole, solid end crank is to fill the cavity with grease, then insert an alignment tool or spare input shaft and then hammer on it to force the bearing out via hydrostatic pressure.

I'm pretty sure that would NOT be a good method to use on cranks like mine because it probably would not be a good thing to inadvertently dislodge or move that "freeze plug".

Hope this picture helps you see what I'm talking about:

[Lous69]

One other thing that some people may not realize the first time they remove and replace flywheel bolts:

Many modern cranks, like mine for instance, do not use blind holes for the flywheel bolts.

They have through holes that poke into the crankcase.

I hope you can see what I'm talking about in these pics:





As usual, I have found numerous posts with all kinds of conflicting opinions about this. Some say they have never used any sealant on the bolts and never had any problems. Others claim they have had their clutches ruined by the oil that seeped out around the crank bolt threads.

I called Centerforce and asked for their recommendation. They recommended I use any locktight (red or blue) to seal the threaded holes in applications like mine. I went with their recommendation.

I'm not suggesting everyone should agree. I just want to encourage people to think about it before they decide what they do, especially those who might not have realized some cranks have through holes.

[Centerforce]

Great information! This thread should be stickied for others to read.

We'd also love to hear what you think about your DYAD so far.

[Lous69]

To help anyone who is trying to figure this stuff out for the first time I am posting the sketch I made while figuring out the dimensions of my set up. I included the list of the parts used. Almost everyone will have specific variations in their set ups but this may help people figuring this stuff out for the first time.



The driveshaft in my car was almost 1" shorter than what is recommended by Modern Driveline. I'm pretty sure that was the reason I had a vibration at certain speeds under light load. Therefore I ordered a new 4 inch aluminum driveshaft from Modern of the proper length. It just came in so I haven't yet road tested the DYAD but it feels good on the lift so far. I'll follow up with my impressions once I get a few miles on it.

[Lous69]

Now that I have put a few miles on the car I have to say I am very impressed with the DYAD clutch I installed. So far with 100 easy miles mine is super smooth and totally silent at all times. I think the pedal pressure is actually less than it was with the stock CTS V dual disk clutch. I know clutches are like anything else and everyone has their valid opinions but so far I'm impressed with this one.

The 1" longer drive shaft also cured my pesky vibration issue.

[Centerforce]

Originally Posted by Lous69

Now that I have put a few miles on the car I have to say I am very impressed with the DYAD clutch I installed. So far with 100 easy miles mine is super smooth and totally silent at all times. I think the pedal pressure is actually less than it was with the stock CTS V dual disk clutch. I know clutches are like anything else and everyone has their valid opinions but so far I'm impressed with this one.

The 1" longer drive shaft also cured my pesky vibration issue.

Thank you for the feedback! We're very happy to hear you're liking the new DYAD!