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Old 06-18-2019, 05:58 PM
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Slave Cylinder Internal Spring

The question that will arise out of this post is will a clutch slave cylinder work OK if the internal spring is removed?

As per the pictures below, please note the external return spring in the top picture and the internal one in the picture below that.



The purpose of the external spring is to keep the slave fully retracted so there is clearance between the pressure plate fingers and the throw-out bearing.

The purpose of the internal slave cylinder spring is unknown to me other than for clutches where the throw-out bearing is allowed to continually rotate with the pressure plate due to constant contact.

The problem is that the external spring must over-power the internal spring to get throw-out bearing free-play. This isnít always so easy as in my case the internal spring is quite strong and is cylindrical, and not a cone shaped weak one.

This means I need a very strong external spring. This makes it difficult to install and adds force (although fairly minimal) to the clutch pedal. To make matters worse, the external spring has minimal tension when the clutch is released, where the internal spring reaches maximum force at the same point.

I have read the internal spring helps keep the slave piston from jamming sideways due to push-rod side loads, but I doubt that as the piston is quite long compared to the bore.

SoÖ. Any ideas on whether I can remove the internal spring, or what will happen if I do?

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Old 06-18-2019, 08:15 PM
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Right off I see a problem with the piston & seal not returning. why are you trying to reinvent the wheel ?
Pep
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Old 06-18-2019, 09:28 PM
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Do like hot rodders have been doing for a hundred years, remove the spring and drive it. See what happens.
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Old 06-19-2019, 03:50 AM
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Oh my. Not quite the answers I was hoping for, but I appreciate your replies none the less.

First of all Pep, the slave cylinder internal spring is always in compression so it tries to push the piston/seal forward. It has no function in returning the piston seal. That is done by the external spring.

Second, Iím not trying to reinvent the wheel, Iím trying to reinvent the spring. This is a non-standard car with non-standard parts so I canít just go to a Dealer and ask for a clutch return spring.

When I first built up this car, I had to find a spring that was close and modify itís length for proper operation. After a lot of fiddling, it worked fine for a long time until this clutch change. The new P-P is a diaphragm while the old one was a Long style. The unloaded finger heights are different and the new one requires a longer throw for disengagement. My old external spring no longer had sufficient tension to over ride the internal spring so I needed a new one.

Have you ever tried to change the length of a spring? Itís very tough to make a bend. So you wind up heating it and it bends easily. First time you use it, the metal, soft from annealing, bends more and stays bent or stretched if some coils got hot. So you try again, but this time you try quenching it after heating to restore the temper. But it gets quenched while too hot and becomes brittle. No stronger than a piece of uncooked spaghetti and breaks under the mildest test.

If you make it too long, thereís insufficient tension to overcome the internal springís compression. If you make it too short, once extended it can stretch and stay stretched.

Now if the internal spring wasnít there, then almost any old spring would serve as an external spring.

I think the answer is to replace the internal spring with a weaker one as it dawned on me that without any internal spring, the piston could migrate back (although unlikely as it would need to move fluid back up through the master cylinder vent hole and into the reservoir) and then youíd have to pump the clutch pedal to make up the unwanted travel.

Now TechInspector, you are correct, and this is what Iíve been doing over this long and tedious clutch change. First there was trying to identify why the old clutch system failed and while waiting for the new parts, there was flywheel cleaning, bell housing alignment and a new throw-out bearing to check out due to spring clips which in my mind werenít located quite right.

Once I had everything installed, I found I had to adjust the pedal forward to get the clutch to disengage. Then I noticed the pedal throw was now much longer and was uncomfortable. So I had to modify the clutch shaft bell crank. This caused the Master Cylinder rod to not be aligned quite right and everything would bind up. I had to tilt the M-C a bit. As a temporary measure, I merely installed a washer under one side of the M-C and then everything worked fine. I'll sort out a more elegant solution later.

Now with the longer throw, I was using up more travel in the Slave and discovered the piston would stick and stay down while I was adjusting the free-play where you need to bottom out the piston to measure the clutch fork free-play.

So I took the Slave apart to confirm this, and then used my old Slave housing with my new piston/seal and that fixed it. That was an opportunity to leave the internal spring out, but I find itís best to only change one thing at a time when experimenting.

Have I mentioned about jacking up the car for access? Thereís only 5Ē of clearance under there. To do it properly takes about 2 hours, and Iím familiar with doing it. Once the clutch was installed, I now donít bother with all that for adjustments. I just jack up the front to the max extension of the jack and use axle stands. Doesnít take long. I just barely fit under the car and it doesnít give much room to work.

Basically, after countless trips under the car, and continuously raising and lowering the car for testing, Iím getting tired of all this, so before I go and remove the Slave Cylinder internal spring, and then quite possibly find I have to put it back, I thought Iíd ask here.

Did I mention that I donít like getting brake fluid in my eyes, and crawling under the car 50 times a day isnít as easy as it used to be. Iím getting old.
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Old 06-19-2019, 04:07 AM
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The purpose of the external spring is to keep the linkage engaged at all times. The purpose of the internal spring is to cushion the piston from hitting the internal stop when you release the clutch quickly. It also prevents the piston from getting stuck if there is sludge or rust in the cylinder.
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Old 06-19-2019, 06:17 AM
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I swapped the slave and master cylinder when answering, not paying attention.


I'll be the one that's standing over in the corner .......
Pep
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Old 06-19-2019, 06:24 AM
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Quote:
Originally Posted by rip-tide View Post
I swapped the slave and master cylinder answering, not paying attention.

Pep
LOL. I did that writing my original post, but managed to spot it before hitting "submit".

Joe: Thanks for your info. I guess the internal spring should stay. So it really looks like I have to modify another external spring like I did a long time ago. Oh well, I suppose it's only a drop in the bucket compared to the whole job.

At least I get to most of the work on the bench modifying the spring, and only squeeze under the car to install and test it.
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