90-96 VD clutch slave o-rings

[Rick Kirchner]

I thought it might be a good idea to document these sizes for posterity if I can figure them out.

I have two cylinders - the std VD unit and one made by Tab McBlaine a looooong time ago (nice piece!). Tab had the part numbers for two of the three sizes, but not the 3rd. I've been trying to figure that out, so if someone has info it would be greatly appreciated.

There are 6 o-rings in the re-build kit.

Two thin ones go between the cylinder and the bore in the bell. Those are 2-032 size.
There's one that goes on the outside of the middle barrel - that's a 2-222

From what I've heard, VD got some dimensions wrong with either the glands on the outer and middle barrel or the dia of the inner barrel. There are three rings that go around the outside of the inner barrel. One is at the back of the outer barrel, and the other two are on the inside of the middle barrel. Evidently the Taylor kit has custom sizes to solve this. Tab tried to make his parts so this wouldn't be necessary, and he kept the inner barrel the same. The problem is that I only had one set of Tab's parts and of course trying to measure them after they'e been installed for years is a lesson in futility. I'm guessing that Tab was building parts that would use the original VD kits but not leak.

So I've been looking at Tab's drawings, and trying to determine o-ring sizes from groove sizes using the parker catalog, and I really can't figure it out, I can only get close. Measuring the rings out of the two kits I have using the parker cone gauge is pretty inconclusive. So maybe those are custom parts.

Gland sizes are 1.590 dia x .157 wide, the inner barrel is 1.414. I've narrowed it down to a potential of 5 sizes: 2-126, 2-127, 2-219, 4x32 or 5x30. Anybody know what the size actually is?

[Rick Iverson]

Rick;

May I presume McBlaine is no longer in business?

I recall a thread on this subject, and I am supremely confident I saved it somewhere (I will look through my archives tomorrow, in the middle of cocktail hour(s)). IIRC, the issue was US O-rings size vs UK O-rings size.

I once sent a badly damaged bell housing to a known fabricator with the notion of enlarging the bell bore, installing a recessed cup to accommodate a Saab slave. However, the unknowns were the minimum and maximum measurements of the throw out bearing relative to clutch engagement and release.

Recently, during my semi-annual half day chat with Doug Learned Sr., he mentioned he has developed the technology to build pumps with tolerances sooooooo close, o-rings are not necessary. Thoughts?

There are options we should explore. And I am definitely not alone about splitting the the ass-end because of a poorly designed slave system. Thoughts?

[Rick Kirchner]

I checked UK sizes and they appear to be the same, just different terminology. I could be wrong.

as far as seals sans o-rings, I've seen some machining videos where mating parts were made as part of an insert in a block. When inserted they drop incredibly slowly as the air has to find a way out, and once fully inserted, you can barely see the parting lines.

so I guess it all gets down to delta-P, surface finish, and viscosity.

[mark elder]

Rick

Success here depends on
1. O rings that tolerate brake fluid for a long time (most don't)
2. Smooth surfaces for O rings to slide on
3. The nasty oblique hole that brings the brake fluid to the unit needs to have smooth edges otherwise it cuts the O rings on installation. As always, lube helps.
4. The correct size; this means O rings that have the right amount of crush to seal but can still move. The crush also depends on how much wear various bits have. In the end, I have metric O rings as I could get (from memory) 8 thou crush whereas the imperial ones gave about 2-4 thou crush. Don't be scared of these metric beasts (you can always measure them in imperial and pretend). The unit should be able to slide when you push with 2 thumbs.

[DaveW]

Be careful where and what you buy. Many EPDM o-rings are cured wrong. They have to be Peroxide-cured to have resistance to set at the high temperatures they see, and a lot of EPDM's are not.

Post with link to possible source:
https://www.apexspeed.com/forums/sho...l=1#post556807

[Rick Kirchner]

I've always trusted Parker....

Dave, did you. get small quantities from them?

[DaveW]

I've always trusted Parker....

Dave, did you. get small quantities from them?

Yes, I did. The whole order in 2014 was $534 for enough o-rings and x-rings (same as quad-rings) for my SAAB slave to last the rest of my racing career. Order below:

mm ID $ ea Quantiity sub-total
O-rings
36x3 3.70 15 55.44
39x3 3.74 15 56.16
51x3 3.98 30 119.52
sub-total $ 231
X-rings
36x3 9.96 15 149.40
39x3 10.20 15 153.00
sub-total $ 302
Total $ 534

[Rick Iverson]

Rick;

There is safety in numbers to buy in quantity. Once the o-ring sizing issue has been resolved, I am in for a few sets. And presumably there other midyear owners out there willing to contribute to eliminate (or at least forestall) the regular routine of o-ring changes. Thoughts?

I've always trusted Parker....

Dave, did you. get small quantities from them?

[Rick Kirchner]

Last time I bought o-rings from McMaster they came in a Parker bag - and I got the wrong size.

The reason I'm asking all these questions is that a lot of sizes are 50 minimum, so yeah, one guy could buy the o-rings and parcel out tons of kits.

to give you guys an indication of the difference, when I put a standard set of o-rings (whatever is sold in the kit) in it takes me a while to assemble. After putting the outer and middle together I usually have to heat those and freeze the inner to get it to go together.

With the Taylor kit, its not as hard.

Tab's pieces go together as smooth as silk.

[DaveW]

Last time I bought o-rings from McMaster they came in a Parker bag - and I got the wrong size.

The reason I'm asking all these questions is that a lot of sizes are 50 minimum, so yeah, one guy could buy the o-rings and parcel out tons of kits.

to give you guys an indication of the difference, when I put a standard set of o-rings (whatever is sold in the kit) in it takes me a while to assemble. After putting the outer and middle together I usually have to heat those and freeze the inner to get it to go together.

With the Taylor kit, its not as hard.

Tab's pieces go together as smooth as silk.

What you said makes sense, but going together easily (too easily?) may be an indication of not enough squeeze on the o-rings, meaning they might be more prone to leakage after they take a set.

[Rick Kirchner]

Tab's stuff is rock solid, but I ran out of the rings that came with it. The stock VD stuff, not so much. The Taylor kit is pretty good.

Honestly, I've not changed them out in a veeeery long time. I began taking the approach "if it ain't broke, don't fix it" after installing a set and having them leak right off the bat.

I've learned not to hit the clutch until there's some heat in the oil to give the rings a little elasticity, so I know I need to change them out sometime in the near future.

I also built a test fixture so I can pressurize it before going to all the trouble to put the rear clip back on.