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Clutch slave rebuild kit or replacement
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CAVEHEAD
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Joined: April 07, 2022
Posts: 20
Location: GEORGIA
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PostPosted: Wed Oct 05, 2022 7:31 am    Post subject: Where to get parts for your 411 and 412... Reply with quote

Looking for a clutch slave rebuild kit or (NOS or suitable sub replacement) for 411 manual trans.
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raygreenwood
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Joined: November 24, 2008
Posts: 20203
Location: Oklahoma City
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PostPosted: Wed Oct 05, 2022 11:56 am    Post subject: Re: Clutch slave rebuild kit or replacement Reply with quote

CAVEHEAD wrote:
Looking for a clutch slave rebuild kit or (NOS or suitable sub replacement) for 411 manual trans.


Which one? Early or late?

And.....you need to please move this to the main body of this forum. This is NOT just a simple ....."hey anyone got a spare seal".....issue. These are officially "unobtanium". Wink

Either you can ask Everett to move this post or I can.

Early 411 was ~22.5mm and late was 44.5mm diameter.

I have not seen a new or NOS kit in decades. Fixing this availability issue has been one of my pet projects for a LONG time.

Really I have two potential work around for this problem.

Method # 1. In one respect, the late model clutch slave is simple enough and low pressure enough (compared to the brake and clutch master cylinders) that it responds well to a fairly normal type "U-cup" if you can find one in the right size and rubber type.

Back in the late1990s when there were few to no seals available period.....I went to a seal house and got whatever would fit. It turned out to be a 1.75" OD "U-cup" with flared inner and outer lips (which is different from stock which has a straight inner wall)...that can be used either for sealing a hydraulic rod or piston.

It was not exactly the right width/thickness for the piston groove so they gave me a flat EPDM backing ring to make up space. This actually worked quite well! Good pressure and no leaks!........until it flat out failed about ~10 to 15,000 miles later!!
At my current miles that was roughly 4 months of lifespan. I can find out for sure by checking my log book.

See.....the problem was....and I knew this but it was the only seal I could get.....the U-cup was made of URETHANE....and not EPDM. Brake fluid kills any rubber except EPDM.

I found that the lifespan was TIME related and not miles related. So.....I bought about 8 seals from this place and just rebuilt two slaves. I would drive for about 10 weeks until I started to feel that the clutch was getting soft (air bypass) ....and would stop, jack up car, remove left rear wheel and pull two nuts and the fluid hose to remove the slave, stick in the other slave, bleed for five minutes and go on for another 2-3 months and rebuild the one I took out and put it in the trunk.

As long as you do not let it fully fail and bypass fluid onto your clutch.....this works. Not ideal. If you let it fully bypass or fail....you get brake fluid on the clutch.

BUT.....it proved that you do NOT need to have the exact seal "configuration".....meaning that if it's set up correctly you do not need the compound "double lipped", shaft seal or " "squeeze type" seal cross section that came from the factory.

The original type of seal.....is also very low elasticity because of its thick double lipped cross section. It's VERY hard to stretch onto the piston.....and if it is NOS....and it will be....and has "shelf" years in it....there is a high chance of breaking it while installing it. This is what happened to the last two.....expensive....NOS seals I bought and tried back in about 2001.

So, two years ago I found a shop up in Ontario that stocks a standard EPDM u-cup seal that will fit the OD, but is a little thin....and that means it is basically the same configuration as the urethane seal I described above.
It is a little thin but will work with a backing ring.
I have not been able to buy and try one because of Covid so this went to the back burner. I will try to do so this week.

So the internal seal can be worked around....but that still leaves the outer boot. I have one pristine one that I can and will make a mold from and cast these from high temp silicone. I have been waiting to gauge interest.....including mine.....because.....

The other problem with these slave cylinders is the cylinder and piston itself. You will note that at one point in time there were slaves available with two seals. The second outward facing seal was not for "sealing". It is not functional in that respect. It served two purposes:

A. It helped push debris and clutch dust out of the way of the main seal path.

B. It helped centralize the piston. The stock piston is a poor design. It's long....and the main and only seal is at the very rear 10-15% of the piston. This causes the piston to cock very slightly in the bore from back pressure on the puston rod. This causes elliptical wear to the seal and some wear to the piston.....which is never supposed to contact the bore wall.

The cylinders that had the second seal....the seal acted more like a packing ring to keep the piston straight in the bore which increases the life of the seal.

The other problem with these slaves is that with age they get rust spots and pots on the bore. So this can be lapped lightly (do not "hone" them oversized)....but then you start getting into the same issues as master cylinders.....oversized bore to piston tolerances which along with the cocking of the piston in the bore....causes short seal life.

So.....you can fix that oversized/undersized issue by either having the piston hard anodized which will bring the piston tolerance up by as much as 0.003" .....or by having the bore platec (something I am working on).....or having the bore sleeved.....which is pretty common.

Method #2:

I may go this way myself. It really is the easiest if you have cylinder wear or piston issues but will take some testing.

So, Go down any flaps and buy a clutch slave cylinder for any mk4, mk5 or mk6 VW with q 2.5L five cylinder and manual trans. They are all the same cylinder. They come in all plastic or metal cylinder with plastic piston....all are equal.

You can see it here:
https://www.fcpeuro.com/products/audi-volkswagen-v...GeEALw_wcB


They are a two bolt pattern which is a little narrower than the late type 4....and they have a longer stroke and are 19mm bore diameter. This means that your clutch pedal feel on the type 4 that uses the 44.5mm slqve and pedal pressure will be 59% higher....which in my opinion will be a benefit. The late type 4 clutch is too soft.

To fit this you will make an aluminum or steel plate with a hole in the center, two holes for the existing studs on your transmission to go through and two threaded bolt holes to mount the cylinder to the plate with bolts.

You will either use shims under the bolts to adjust the stroke to the correct length or use a thicker or thinner mounting plate.

Since this cylinder uses modern push-lock for either a metal or nylon fluid line.....you can simply buy two barb-to-push-lock adapters and a length of tube....about $25 all told...........and you can install a readily available modern slave cylinder for about 2 hours of work and maybe $100 all told.

Back to the seals and cylinder. .....I have a "how to" I have been working up for years to address the same availability issues with the brake master cylinders and it's seals.

I am almost ready to post that.....and it has a section at the tail end about the clutch slave and master cylinders.

If you have the earlier 411 slave cylinder with the 22.25mm slave......a similar set of methods can be used......rework the cylinder bore....source a 7/8" U-cup and epdm backing washer.....or source an aftermarket slave and make a mounting plate.

More to come. Ray
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CAVEHEAD
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Location: GEORGIA
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PostPosted: Thu Oct 06, 2022 5:33 am    Post subject: Re: Clutch slave rebuild kit or replacement Reply with quote

Thank you Ray, Please relocate my post to the correct location when time permits, sorry about that. Please download your entire brain of knowledge concerning 411/412 to a book Smile Haha You a great value to all of us. Regards Dk
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heimlich Premium Member
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Posts: 5249
Location: Houston, Texas
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PostPosted: Thu Oct 06, 2022 10:11 am    Post subject: Re: Clutch slave rebuild kit or replacement Reply with quote

I have lots of people asking me about this. It would be very useful if I could provide them with a link to the information.
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raygreenwood
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Joined: November 24, 2008
Posts: 20203
Location: Oklahoma City
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PostPosted: Thu Oct 06, 2022 11:55 am    Post subject: Re: Clutch slave rebuild kit or replacement Reply with quote

heimlich wrote:
I have lots of people asking me about this. It would be very useful if I could provide them with a link to the information.


It's coming not far off. NOS slaves are great because the bore should be good and the outer boots are usually good. The outer boot is Viton. Bit if you ever get an internal seal leak....it's starts deteriorating because brake fluid kills viton.

It's the single inner seal of NOS slave cylinders ...just like NOS master cylinders....that goes bad with age.

But....unlike the brake and clutch Mc's where we call steal seals from any 19.05mm master cylinder kit.....these damn slave cylinders have pretty unique seal sizes.

That being said.....the upcoming "how to" for brake master cylinders....with a section for clutch.....is all about sourcing alternate seals.....something I know YOU have also been working hard on.in..


From what I have been finding out from the seal manufacturers....we do not have to source the EXACT seal for brake MCs, clutch MC and slave.

As long as it is the correct material (EPDM).....made for the pressure range (our brakes and clutch are low to medium pressure with a top end on brakes of 900-1000 psi and about 700 nominal).....and the seals we use follow some basic rules for lip shape and gland size......which can be corrected for with backing rings and other common hydraulic seal methods.....we can use a wide range of seals with perfect safety.

All of this will be gone over in the thread I will post in a few days. Ray
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