speedometer sending unit question

[PhoneGUy]

Setup
MK4 Complete Kit with vintage gauges and T5Z transmission.

I am using the supplied speedometer sending unit and I notice that there are 2 connections. 1 connects directly to the RF harness and the other appears to be for a mechanical type of speedo cable. That being said, do I need to purchase a plug for the empty/unused mechanical hole in the sending unit? My concern is that fluid will leak out this unused hole.

Thanks in advance for your help.

[edwardb]

I've seen/read where guys have tried to plug the speedo cable connection. Personally, I wouldn't. The right part is not that expensive. There are two different types of sensors, one with and one without the speedo cable connection. I would strongly suggest getting the right one. Ask for Standard Motor Products SC37, or equivalent. Breeze has them: http://www.breezeautomotive.com/details.php?prod_id=670. Also available at Forte's, NAPA, etc. Pretty common.

[Brian Z]

You should not have to cap the sending unit that comes with the kit. If it does leak from there you have a problem inside your transmission.

Best regards,

[ram_g]

You should not have to cap the sending unit that comes with the kit. If it does leak from there you have a problem inside your transmission.

Best regards,

Not sure what comes with the Mk 4 kit, but relative to my Mk 3.1 Complete Kit, this response is incorrect. The sending unit that I received is a mechanical speedo sending unit (that also has the electrical connector, exactly as described by the OP) and it can and does leak if the mechanical output is not plugged (nothing needs to be wrong with the transmission for this to happen). It is possible to silicon plug the mechanical output and use this sender, but the better solution is to get an electronic-only sender that already has the mechanical output disabled/plugged, exactly as outlined by Edward in the second post.

(Since Edward's post nailed it I wasn't planning on responding, but I'm doing so because it appears that the "official" response seems incorrect.)

[Brian Z]

We don't plug them on our cars here. Mk4 in the showroom and Jim's spec racer from 04 don't have the sending unit plugged. Guess what?.... No leaks!

It is possible it might leak a very in very small amounts, but it is highly unlikely. We haven't had any problems with leaving it open.

[AC Bill]

I would still be wanting to get an electric only style VSS, or plug the one you have with some RTV, as that opening directly into the tranny might not only allow fluid to leak out, but also allow contaminants to get in. Water, dust, etc. I also wonder if when parked (upward) on a steep hill, it may allow tranny fluid to seep out.

I am actually a little surprised at FFR's reply, as I have read in the past of builders having leaking issues, and having to plug or replace the old style VSS?