| Re: [GMCnet] Brake Bleeding 101 [message #364971 is a reply to message #364946] |
Thu, 24 June 2021 21:08   |
Larry
Messages: 2875
Registered: January 2004
Location: Menomonie, WI
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Tom Katzenberger wrote on Thu, 24 June 2021 09:23Guys,
While bench bleeding a new master cylinder (P30) I only get flow out of the front chamber. No action in the rear chamber. I do get one single bubble in the rear chamber each stroke. Is the master cylinder toast? Did I blow the rear seal?
Thanks,
Tom K.
Tom,
Several years ago I decided to try a P30 MC with my rear disc brake system when my stock MC had a pedal that under constant pressure went slowly to the floor. The P30, on bench bleeding, I could not get the rear chamber to bleed. So, I took it back to Auto Value for another one. The next one did the same. Returned it for another, and another. I also asked the counter guy that I had known for years (and also an excellent mechanic) to try it himself, and he had the same results....rear chamber would not bleed. I called Dave L and he told me to put a lever on the bleeding arm and push HARD. Eventually it broke loose and bled. While the P30 was a commonly used MC back in the 70's, it is not so common now and is a MC that does not move...sits on the shelf. Conclusion we came to is that the MC's that I got had been sitting on a number of part house shelves for many years and that back chamber piston had corroded in the bore, was frozen in place on all of those MC's. With the corrosion in that rear bore, that rear bore was compromised. After talking with Dave at some length, I chose to obtain a stock MC from a friend, bench bled it successfully, installed it and went on my way. The P30 has an inherent issue that makes it prone to sudden failure. Personally, I would reconsider the use of that P30 and go back to the stock MC. Just what I'd do.
Larry 
78 Royale w/500 Caddy
Menomonie, WI.
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