On the wbx flywheel seal

A fellow attempting to repair a flywheel seal leak on a recently rebuilt engine had the seal pop out of the case, and he wondered why. A helpful participant posted this:

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Are you recessing the seal on the seal bore or is it flush with the case? Also, there are two thicknesses if seals out there that carry the same part number…a 12mm thick for use with the automatics, and a 10 mm used in the manuals…

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My response:

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This is unfortunately internet myth. There is only one spec seal regardless of transaxle type, 12mm depth. There are 10mm deep seals on the market which can be used, they can be driven in flush or the extra 2mm until they bottom on the step within the seal recess. Makes no difference except sometimes by bottoming a 10mm deep seal, the lip may ride on an unworn part of the f/w or driveplate seal hub. But it’s better to use a 12mm depth seal for its shell strength (read on to learn why) and repair or replace a worn seal hub.

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The 12mm deep seal is preferred, and there are notable quality differences between the commonly available seals, which I described in a post long ago. Here’s the relevant passage, lightly edited and annotated:

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“The ones that come with the gasket sets are pretty inferior. Three obvious measurable aspects differ from the OEM seal: the depth of the shell front to back, the thickness of the tension spring around the seal lip inside, and the weight of the shell material.

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I have 4 different ones, and took measurements: a Reinz cheapo that come in the gasket set; an Elring cheapo from their set; a Reinz orange Viton that sells for $10 by itself at VC*; and the Sabo all-black one, $30 from GW, that they claim is the OEM VW seal**.

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Reinz cheapo is dark purple in color. The shell depth is 9.8mm, spring width only 1.9mm. Weight 48g.

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Elring is black, grey, and red. Depth 10.1mm, spring 2mm. But this one weighs only 40g! Very thin shell material.

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Reinz orange Viton* is 11.8mm and 2.25mm, 51g.

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Sabo black is 12.1 and 2.5mm. You can feel in your hand how much heavier this one is: 61g! **

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So the more expensive ones have a deeper and meatier shell, and stronger spring to keep pressure on the seal lip. The difference in weight between the cheap Elring and cheap Reinz is remarkable. The Sabo is even much much heavier than the Reinz Viton even though dimensionally they’re very close. The deeper shell means that when they are driven into the case until they bottom out, they present the seal to a wider part of the flywheel flange, which is flared, so there should also end up being a bit more lip tension***. There are other slight differences in the lip design. And of course they are made of different compounds.

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I think the Reinz Viton is a good value, and they work pretty well for me. But the Sabo, although expensive, is truly bomber. “

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*NLA at VC/RMW. This was promoted as Viton back then but I later learned it’s silicone, which is also a great material for this application.

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**This is in fact the OEM seal. Now sold at GW for $7.95 https://www.gowesty.com/product/mechanical/3944/flywheel-flexplate-seal-rear-main-?v=
and VC/RMW has what appears to be the same for $6.50 https://www.vancafe.com/029105245B-p/029105245b.htm
I later learned this one is Viton. They were hard to find when that was written, and GoWesty claimed to have bought all the stock and was charging $30 apiece! But, they became commonly available years ago from many places, which even GoWesty had to admit to by charging a reasonable price.

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*** This was based on casual examination, has been repeated by many, but is incorrect. Later on I made measurements that showed that although the f/w hubs flare from the f/w body, within the position range a seal could present its lip the hub is perfectly cylindrical. AT driveplates are plainly cylindrical all the way.

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If it’s not recessed (causing the dish of the flywheel to rub on it), or if you’re using the 12mm thick one, the seal won’t stand a chance and will fail quickly.

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A 12mm deep seal driven in to the step inside the bore will be less than 1mm below flush. If the seal is set at this depth or at any depth below flush, it is impossible for either f/w or driveplate to contact the outer seal face. That can only happen if the seal starts coming out from the bore, but if it does emerge only a couple mm its face will meet the spinning f/w or driveplate which will spin the seal and/or tear it up. In either instance, the problem is the seal not staying in its bore.

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Reasons for this? Well, seal shell strength provides the basis for the seal to continually exert the outward tension needed to stay in the bore, so the heavier, stronger shelled ones have an advantage in staying put. Often people drive a seal in unevenly so that parts of the outer rubber covering are torn, invisibly until removal, which results in a reduction in outward tension. And blockage of the seal cavity drain and breather channels from excessive sealant will obviously cause hydraulic pressure to build in the cavity which will drive out the seal with ease. Even if the drain hole is blocked but the breather is open, at high rpms the amount of oil escaping the f/w bearing may be able to overfill the seal cavity at a rate faster than the oil can escape out the top breather channel alone. With its large surface area, it would take very little internal pressure to drive any of the seals right out of the bore. Both those channels need to be clear!

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I’ve found that a fairly thin, stiff wire can be poked into the breather and drain channels on an assembled block to check that the channels are clear. I keep a spool of gardening twist ties (tomato ties) in the shop for many uses, it’s plastic covered and stiff enough to push thru the channel while flexible enough to make the curve, and the wideness of the plastic coating strip helps clear a bit of the sealant. Concerns about bits of sealant bead loose in the sump are overstated, things like that will in most cases lay harmlessly in the sump, and if they’re sucked up by the oil pickup the large and fairly fine pickup screen will catch them. Any bits small enough to pass the screen (extremely unlikely) will pass harmlessly thru the oil pump and be picked up in the filter. Compared to anything that small, all the engine oil passages are enormous and the idea of such things blocking them are the fever dreams of amateurs. Don’t worry about imaginary stuff, get the job done.

2 Comments

  1. Peter

    I’m replacing my clutch and associated parts this winter and while the seal was dry when I removed the flywheel, there is a small wear line on the flywheel sealing surface. I’m considering installing a “speedi-sleeve” for the new seal to ride on.
    The new seal is the same as the original and it will be installed fully seated as far as it will go. I figure that by doing so, the seal helps to hold the thrust washer in place against the case and by seating it fully, the sealing lip is square to the flywheel hub.
    For this reason, the seal lip will ride on the existing wear line on the flywheel hub. While it is not severe, I would like to start with a new surface for the seal, but worry that the increased diameter, although small may cause accelerated seal wear.

    Pete
    Hamilton, Ontario

    Reply
    • Chris

      Hi Peter,

      Thanks for visiting. I have a follow-on post that should help address your concerns.

      Reply

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