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Clutch slave cylinder gasket?
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Lars S
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PostPosted: Thu Oct 30, 2014 10:50 am    Post subject: Clutch slave cylinder gasket? Reply with quote

Bought this from a friend of mine dealing with old VW parts , the box says it is a clutch slave cylinder gasket kit for 411/412 from 1970 and on, diameter is 40mm.
I thought theese were not available anymore can anyone confirm?


/Lars S

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raygreenwood
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PostPosted: Thu Oct 30, 2014 11:17 am    Post subject: Reply with quote

They are nit except in NOS form.

That is the seal for the 42mm slave cylinder on the late 411 and all 412.
I can get individual seals made via CNC at will.....but up until recently the companies able to do this could not make them of the correct material (EPDM). They worked well bad had to be replaced at 1 year....religiously.

The 42mm slave had several design flaws that made life short....about 30k miles in a constantly driven vehicle....especially in hot and humid climates.

1. The skirt on the piston near the spring is the exact same diameter as the rest of the piston. This means that fluid must squeeze through about a .002" gap to simultaneously lubricate and inflate the sealing cup. It leads to fast lip wear in hot weather and fluid leakage before warm up in very cold weather.

2. The seal is located on the piston down near the 1/3 mark. That means the longer heavier front section of the piston is unsupported. The allows the pistkn to drag the cylinder and it cocks about 1° in the bore.....causing seal wear and bore wear. The later design had two seals.....the 2nd seal never seeing fluid.....but simply acted as a piston guide.

I have a bucket of cors cylinders. In January I am honing them to one alight kversize and then having the lot chrome plated on the inside. I have had good results from cutting 6 small grooves in the skirt to allow fluid to instanyly reach the cup.

I have contacted one of the CNC seal companies I use and they can now so an EPDM seal for this.
previously they could only machine rubber materials that were 75 durometer and higher. Now they can chill materials in process to cut softer rubber like EPDM accurately.

The cost would be aomething like a minimum or 25 seals for about $250. I will let everuone know when this gets closer.

For piston support I can have the pistons, chucked into a, lathe and have a forward groove ground and snap in a teflon strip that supports the piston in the bore.....pennies.

The recast of the dustboot in high temp silicone is 3rd on my list after a few more items.

Ray
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camperco
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PostPosted: Mon Mar 13, 2017 5:22 am    Post subject: Re: Clutch slave cylinder gasket? Reply with quote

Hello Ray from England. We might have come to the party a little late so I hope you see this. We are rebuilding a '74 car.

Its got a sad looking 44mm dia. slave cylinder with a single grove piston. Can you sell us any parts or steer us towards a source please?

Thanks,

Angus
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raygreenwood
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PostPosted: Mon Mar 13, 2017 7:38 am    Post subject: Re: Clutch slave cylinder gasket? Reply with quote

camperco wrote:
Hello Ray from England. We might have come to the party a little late so I hope you see this. We are rebuilding a '74 car.

Its got a sad looking 44mm dia. slave cylinder with a single grove piston. Can you sell us any parts or steer us towards a source please?

Thanks,

Angus


I have no parts to sell you or I would.

You have several options to look into. If you carefully remove the seal from the piston....even if it breaks in one spot......there are numerous places here and should be in the UK as well.....that do the type of work I listed in my first post in this thread a few years ago.

The name of that original technology where I used to have seals made is "Seal-Jet". It is CNC cutting of elastomers for seals and round o-rings.

They sold this off into franchises. I found one in the UK.

http://www.cdkseals.com

You will be able to find more of these companies.....usning search keywords of CNC seals and SealJet.

These are not cheap.....but are reasonable for what you get. The issue is that unless you can do your own CAD work....they will do that for you. It will probabpy cost about $100-150 for the cad work....maybe less if they already have a similar seal profile in their system that they can scale up and down.
After the CAD (computer aided design) work is done.....they will usually cut the parts in quantities of just a handful and up....getting cheaper as they get more numerous.

The other cost related problem is that its a relatively large seal. Even though they can make seals up to 1000mm in diameter......from my experience in the past.....small rods of starting material are cheap...but more expensive as they get larger. So the raw material will have a charge as well. It has been my experience that something like a quantity of 10 seals will cost about $35 each.
Great price for a seal actually.....but someone has to put money out front. I would have gotten around to this sooner or later....but if you do this I may be able to buy about 2 of them.

But......lets talk about the slave cylinder itself. It has problems in design. I REALLY would like to keep using these cylinders because they are original.

But that is the only reason. The problems with these cylinders.....and I will post pictures later today:

1. Even if you get seals made.....you do not have a usable boot. You have to cast or replace that part. Without the outer boot the lifespan of this part is very short due to abrasive clutch dust.

2. The piston sizing is too large. You NEVER see a piston this large in any automotive slave cylinder. Only in trucks. It makes for not only an overly light clutch feel......it makes for a low pressure cylinder that has issues with keeping the seal cup inflated as it ages and hardens up.

3. The piston form is defective in design. You will notice in the books that at one time.....a piston was manufactured that had two seals. The outer seal served the dual purpose of keeping the piston centered in the bore so it does not cock and wear the piston and main seal......and it,served as a scraper ring to keep dust and debris away from the main seal.

4. The piston skirt....the portion of the piston below the seal on the spring side.....is the same diameter as the piston head.....and this is a very tight tolerance piston. The fluid does not readily flow past the skirt to inflate the seal cup. This causes leakage over time.
It can be fixed by three grooves in the skirt with a file....maybe .010" deep that connect the fluid side to seal groove.

So.....I have been looking for other slave cylinders that could be substituted. It looks like a slave from a 2012 Golf will fit close enough that a mounting plate can be easily fabbed.

It has a smaller diameter....more similar to the earlier slave from pre 1971 411. You would have to either space it out to adjust the stroke or something similar. I will post part #s later.

EDIT:

OK first a couple things.

The part # for this unit is 411 721 261 F

I found this online in Houston Texas..NOS..which means seal life will be short.

http://www.2040-parts.com/411-721-261-f-volkswagen...r-i722093/

The really Odd...Odd..Odd..freaking Odd thing is...that the very part from a late model Golf that I think can be made to work......is the very first thing to come up on Google when you search for our part # as our cylinder..... Shocked Shocked Shocked Very Happy

http://www.ebay.com/itm/like/132052856163?lpid=82&chn=ps&ul_noapp=true

This is part # 1K0721261F...for probably 2010 and on VW Golf/Jetta with five speed. Look at the bolt pattern and think of the possibilities...These are about $65 new. Even if the bolt spacing is slightly larger or smaller..and adapter plate could be made easily...then its just up to setting the pushrod/stroke length.

Image may have been reduced in size. Click image to view fullscreen.


Here is the bolt spacing of our current cylinder.

The original slave cylinder and seal issues:

Image may have been reduced in size. Click image to view fullscreen.


The piston diameter is advertised as 44.45mm which = 1.75". Find them to be slightly undersized 44.37mm...which is about 1.746.

The cylinder bores I measured..yes have been honed slightly by were found to be about 1.754" which is about 44.54mm...which is about .008"...which by most standards is large.

I measured more than one bore...and they are all at or over .006"...which is a little big and part of why these pistins cock in the bore and wear...and the seal is poor sealing over time.

Also noted that the back of the piston is the same diameter as the front.

Image may have been reduced in size. Click image to view fullscreen.


I got much better sealing when I added three of these grooves at 120* apart.

Image may have been reduced in size. Click image to view fullscreen.


You can see above the wear to the anodizing on the piston from grit in the bore after the boot wore out and the piston cocking in the bore because of the long unsupported piston nose.

Image may have been reduced in size. Click image to view fullscreen.


This is the approximate seal cross section needed. It must have the foot or flange on the bottom. This is equivalent to what they call a shaft seal. The flange prevents fluid from bypassing on the inside diameter of the piston.

this particular seal was made by seal jet. You can tell by the hard sharp top edge. It is made of Buna-N and failed in 6 months. This is the incorrect material.

The correct material is EPDM for automotive brake fluid. In a Pinch you can get away with EPR rubber. It will last 2-3 years maximum if made of EPR.

I will measure the center to center bolt pattern later today or tomorrow...on my 2012 Golf.

By the way...the complete piston and seal assembly from a late Vanagon clutch master cylinder can be used in the FAG clutch master cylinder.


Ray
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JVOI
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Joined: September 06, 2023
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PostPosted: Wed Sep 06, 2023 2:24 am    Post subject: Re: Clutch slave cylinder gasket? Reply with quote

Good morning,

my cylinder needed a new thread and had to be opened.
The bucket jumped out. possibly more. (?)
Is there a spring in the piston too?

On the drawings, the cylinder with spring is also constructed differently.

Image may have been reduced in size. Click image to view fullscreen.


Image may have been reduced in size. Click image to view fullscreen.


PS
an new Clutch for the slave cylinder anywhere avable ?
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raygreenwood
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PostPosted: Thu Sep 07, 2023 12:47 pm    Post subject: Re: Clutch slave cylinder gasket? Reply with quote

JVOI wrote:
Good morning,

my cylinder needed a new thread and had to be opened.
The bucket jumped out. possibly more. (?)
Is there a spring in the piston too?

On the drawings, the cylinder with spring is also constructed differently.

Image may have been reduced in size. Click image to view fullscreen.


Image may have been reduced in size. Click image to view fullscreen.


PS
an new Clutch for the slave cylinder anywhere avable ?


Sorry for the delay in answering.

There is a spring inside of that assembly right behind the piston in your pictures (what you are calling the bucket).

There may be some old stock slaves available but they are suspect due to age.

If you look around in germany you may be able to find a repair kit for the 44.5mm slave you have. It should include a single new seals and a new outer boot.

I have an answer/method to be able to refurbish the slave with the parts of another type but it requires a little machine work to make an adapter part and will require some limiting device inside the master cylinder but is very cheap and makes new seals and boots readily available.

I will not be able to get back to that project for about a month.

If you can find a simple U-cup seal of 1.75" OD or 44.5mm OD and an ID of 1.259" or 32mm and a thickness of 0.365" or 9mm you can use that fairly well. It may seep a little at times but should not leak.

The problem is finding seals made of EPDM rubber. If you can find one made of urethane you can use it for a period of time before it melts. It may be a year...it may be 3 months.

I am right now looking at some U-cups on line that are EPDM. They are a little different but may work and are cheap. Let me order two and see how they work and I will let you know.

Your boot can be reused, the cylinder can be lapped (do not hone it) with 600-800 grit abrasive paper. I can also recast the boot.

Ray
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