Replacing brake lines - plug size for master cylinder?


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As I've mentioned in other threads, my Sierra suffers from the well-known brake line rot.

Mine are intact, at least, but the one that crosses over in the front (on the crossmember underneath the radiator) is especially scary looking.

Picked up a complete stainless kit from Dorman - about $80 shipped, IIRC. Everything is pre-sized / pre-bent / flared / labeled (!) Now it's time to put it in.

I know I'm going to lose a bunch of brake fluid (and it's new, besides, but oh, well - at least it's fairly cheap.)

If I can find the right size plug to put in the master cylinder outlets while I have the lines out, then I won't have to bleed the master -- which scares me enough to have a shop put the lines in --which would be a shame, as this is easy, otherwise. (Yes, I know there's a thread on the site that discusses bleeding the MC.) I do have a Tech2, so I can bleed the ABS module when I'm done - that's cake.

I don't plan on touching the pedal, but I'm thinking the fluid will still leak out of the reservoir, unless I cap the outlets.

Does anyone know what that threaded size would be for the cap / plug? Not having much luck tracking it down (I'll find it, I'm sure - but if anyone knows offhand, feel free to chime in). I suppose I could rig up something with the old line connections, in a pinch. Or find some generic plug at the hardware store, with some o-rings to fit.

Places I've found online that offer the threaded plugs don't list the sizing (and they want $15 to ship an item they price at 0.79, which is patently ridiculous.)

The retail stores don't list just the plugs for sale on their website (and the replacement MCs look to just have plastic 'dust' caps; nothing that would keep fluid from leaking, from what I see.)
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I would cut the old line and pinch it with vice-grips. If you bend it upwards higher than the fluid level in the MC, it should not leak out.


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Yep - I had planned on taking a sawzall to the old lines anyway (no sense fishing them out, right?)

Even if the pinch doesn't result in "100% leak-free", I can tolerate a very slow drip - just recycle fluid from the (clean) drip pan as needed. Because I'll probably be putzing around on this for

Appreciate the suggestion!

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