Replacing rear brake line - abs(?) unit under m/c fitting removal

[tom-rad]

Having some trouble with the fitting under the master cylinder, it's the rear line into what I assume is the abs unit (rear only), or proportioning valve. Mine's quite rusty, and I can't tell if the steel unscrews from the aluminum or not. Looks like 7/16 fits, just doesn't look like I can get a backup wrench on the other piece, or maybe it's just that rusty? A close up picture of a non rusty one would help (no luck on Google so far). It's a 1999 F150 with rear drums (10-98 build). Thanks.

[mkosu04]

what do you mean by "backup wrench on the other piece"???

Sounds like maybe you are talking about a proportioning valve?

Post a picture of what you have and perhaps I can help more

[tom-rad]

Thanks.
The piece I mentioned (if this were plumbing), resembles what could be called a threaded nipple. That's what it appears to be, something like that anyway. In other words, there seems to be a bit of steel tubing attached to the aluminum proportioning valve, and I can't tell if it unthreads along with the brake tubing or is permanently attached to it. The brake line fitting does not thread in directly to the aluminum proportioning valve, there is maybe 1" of steel tube extension, slightly bigger diameter than the brake tubing, coming out of it. `There are no 'flats' on it that I can see, no hex for a wrench to fit on it (that's what I meant by 'backup wrench'). There is, of course, a fitting on the end of the brake tubing, 7/16" fits it perfectly. What I need to know is, can I just stick a 7/16" tubing wrench on the brake line fitting and try to turn it? Will the piece in the proportioning valve stay put, twist off, or unthread out?
Sorry if it's a little unclear, you see, the whole mess is rusty and pitted.
I'll try to get a picture posted, but have never posted pictures here before (hope it's easy!)