[83GMCK2500]

Originally Posted by Tom

I've replaced the master cylinder with a stock and now a NBS version, all 4 brake calipers [disk rears] along with wheel cylinders back when the rear was drum, and all the hoses with steel braided lines. I've never needed a special tool. I've never cycled the ABS pump either. Master cylinders do go bad on occasion remember.

Originally Posted by speedygonzales

Same here and I have a Solus Pro and never needed to use it.

It is possible that when you've done your brake repairs/upgrades that you did not have any air get trapped in the abs modulator. OP didn't say how long he had the system open for, but if he did get air trapped in there it could be why he is experiencing the reduced flow and continued bubbling. Yes, a bad MC can also do that, not discounting your suggestion. I know on my '96 when I upgraded the front to GMT800 brakes it stopped better but it still wasn't "amazing" like other reviews were. I made an appointment at dealer, had them bleed the brakes, and then about choked myself with my seatbelt when I tested their bleed job. Same with a '97 K1500, all new cal/pad/rot, cyl/shoe/drm and they were better but not impressive...dealer bleed and nose print on the steering wheel.

See attached snip from Alldata.