K2500 wheel cylinder/ bleeder screw

2000 k25 350 JB7
So, I bought some bleeder screws awhile back-AC Delco 18K2339 M8-1.25 listed for 13 inch drums.
I pulled my wheel cylinders due to weeping and “brake mud” and noticed the bleeders are M7x1.0. I can’t find any reference to that bleeder screw size for a JB7 wheel cylinder. I replaced wheel cylinders with the specked Raybestos ones(WC37290)they don’t look identical but the bore is listed as the same. Seemed strange overall and didn’t want to add unnecessary problems. Anyone have a similar experience or insight?

Are you sure the bleeder screw is metric? Kinda thinking 1/4-28, maybe.

A proper thread gauge--or even an assortment of various size nuts--would tell that tale.

Your doing your own work. These days with SAE and Metric. Get a good set of thread gauges, in both types. Some metric are very close to American SAE. The factory size is M8x1.25 as shown. GM # 19244561. The correct reacement should be that.

Yeah those show M8x1.25 as well. Interesting that the GM part number on the Delco I bought shows front caliper. An M8 either way is too larger to fit the bore of the wheel cylinder/bleeder I took off. Is there a set of thread gauges y’all like? I definitely get a set.

What’s odd is still I can’t find a bleeder listed for M7-1.0 or 1/4-28 for JB7. I did find some OEM wheel cylinders on the ACDELCO Amazon site, they were like $50, thought about it-then saw the country of origin was China???? Seriously OEM in 2000 was China?

These are the bleeders I bought. Same dimensions. There shouldn’t be any difference between a front and rear bleeder when the specked size it the same, correct?

The manufacture of the original part was probably done in North America.

The "official" replacement may come from some hell-hole. Aftermarket replacements may have the same mounting arrangement, and the right bore size, but the rest could be different, including the bleeder screw.

I first ran into that when I bought a Genuine GM driver's side mirror for my '92 Lumina. Original part came from Canada with the rest of the car. GM Replacement in a sealed GM box, made in China. Piece-of-crap went six months before the paint was dull grey instead of shiny black. Total junk.



Given that your wheel cylinders may not be original, the original bleeder screws may or may not be the right size. You need whatever size bleeder screw was spec'ed by whoever made that wheel cylinder.

For the record...what's wrong with the bleeder screws on your new wheel cylinders?

Nothing at all. I just like to compare what comes off versus what goes on. Mine plan is to rebuild the leaking wheel cylinders to have in the future if needed. When I was comparing parts I liked the length of the original wheel cylinders. Noticed the bleeders didn’t exchange and kinda had me perplexed. I started looking and just thought it really odd that every….every resource listed M8x1.25. The PO obviously was not as serious about maintenance as myself, I’ve never had brake fluid/mud like that in mine…..until I bought it. Yeah, I guess they could be “poor” replacements. I’ll check the treasure yard next time I go. Thank y’all for your expertise.

Well it was M7, weird stuff