M/C change without bleeding at the wheels? - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 03-16-2008, 09:43 PM   #1
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Default M/C change without bleeding at the wheels?

I was discussing my '93'* apparent master cylinder failure with my brother, who is a mechanic. He said that it'* a very easy job. I replied that I was only really worried about how rusted stuck my bleeders might be after 15 years.

He said that bleeding at the wheels wasn't necessary. Just crack the lines at the ABS unit or something like that, and that'll get the little bit of air out. Apparently that'* the way it'* done in some shops.

Of course, that freaked me out. I've never heard of such a thing. It does seem far easier though...

Anyone ever heard of doing a M/C without bleeding every line out? Or better yet - anyone here tried it?

I'm all for doing things the right way, but if my bleeders won't budge, I'd rather not have to buy all new cylinders and calipers just to change out a M/C. Not on my work "beater", anyway.

Any and all thoughts are appreciated in advance.
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Old 03-16-2008, 10:32 PM   #2
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Pardon the person shot at your brother, but he'* a fool.

You have to disconnect the brake lines to change it.

Yes, you HAVE to bench-bleed the MC first, then bleed to ALL 4 wheels. That'll fully bleed your system because you introduced air into the farthest upstream point.
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Old 03-16-2008, 11:19 PM   #3
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Thanks, Bill.

No offense taken at the personal insult - It'* not his shop, he just does as he'* instructed.

Apparently this works for them though. Seems that if it gave them much trouble, they wouldn't do it that way.

Yet of course, logic does point toward air entering the system. It seems possible that the air could escape through a loosened fitting to the ABS unit, but not a sure thing in my mind.

I suspect that I'll do it the tried and true (and PITA) way. I just wanted to bounce this idea off of you guys anyway.
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Old 03-16-2008, 11:33 PM   #4
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I've heard of a couple of shops who have bled the air out of the line between the master cylinder and the ABS unit the way your brother described, and it seems to work for them. Personally, when I changed out mine, I did the 4 wheel bleed anyway - mainly because the other way makes me nervous. Having a power bleeder made it a lot easier, too. If some good soaking with PB Blaster doesn't free up the bleeders, you may want to give his way a try, being very careful to test your brakes when done before driving it anywhere.
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Old 03-17-2008, 12:00 AM   #5
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Quote:
Originally Posted by Archon
I've heard of a couple of shops who have bled the air out of the line between the master cylinder and the ABS unit the way your brother described, and it seems to work for them. ... If some good soaking with PB Blaster doesn't free up the bleeders, you may want to give his way a try, being very careful to test your brakes when done before driving it anywhere.
Ah. Good to hear that my bro isn't the only "fool" out there.

I think this seems like a good plan of action. I'll take wheels off first, make sure the bleeders will crack open. If they do, great. I want to replace the (who knows how old) fluid anyway if possible. If not, I'll give the "foolish" ghetto method a try.

A little bit of air can't be much worse than what I've got now. I'm up to two-step braking. One quick stab to build some pressure, then the actual braking press of the pedal. Works fine since I know to start early, but it would give a whole new meaning to the term "panic stop", if the need for one of those came up.
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Old 03-17-2008, 04:51 AM   #6
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It is a good idea to bleed the brakes at the four wheels using enough new fluid to flush the system of the water, oxides, and crud in old brake fluid that settles to the wheel cylinders and calipers over time. Bleeding Procedure Provided in This Thread
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Old 03-17-2008, 12:01 PM   #7
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Default Well, there is an old-school way..

While certainly bleeding everything is the way to go, if for no other reason than getting all the old stuff out, and this is rather easy to do, if you have everything apart, and does not require that much fluid... But, I have changed probably 100 master cyls in my lifetime on everything from old Chevys to my '99 Olds eighty-eight, and in a pinch to get up and running to get to work the next day...

Remove the two lines from the old master cyl., don't touch anything else in the brake system.. If the fluid can't go anywhere (like leak out at a lower point) then the fluid will still be up nice and high in the lines. If the lines are angled at the MC such that they could drip out, bend them up very slightly and carefully so they can't drain. Bench bleed the new MC, bolt to the car. Have a friend SLOWLY press the brake pedal to the floor and hold it there. (This has to be done slowly so the brake fluid does not spurt all over the place, and, catch the fluid that dribbles out with a rag.. Then, while the brake pedal is on the floor, reattach the brake lines firmly, then slowly release the brake pedal. Any bubble of air that was at the top of those brake lines will be sucked up and into the MC. Wait a little bit to allow the air to bubble up, then you should be good to go.

If unsure about how much air is at the top of the lines, you can always pull a front and back wheel, then collaps the wheel cyl / caliper until fluid goes out those lines... but if you get that involved, then you might as well just bleed them.
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Old 03-17-2008, 02:53 PM   #8
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I agree with troyport, I havent done it hundreds of times but I have done it at least 5 times. In fact my bonneville master cylinder was installed just as he described. Been that way for about 5 years(and 40,000 miles) now and I always have a full stiff pedal when I want to stop. The most important thing is to bench bleed the crap out of that new master. Like the others said; if you want the old fluid out, bleed everything. But by no means would I call the other way a foolish way to do it.
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Old 03-17-2008, 03:03 PM   #9
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Any remote chance for air in the system is bad news. These are your brakes.

Any contamination (water, etc) already in there should be removed periodically.
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Old 03-17-2008, 03:42 PM   #10
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Thanks for the additional comments and experiences guys.

The TROYPORT method of air removal seems reasonably sound to me, if I can't get my bleeders all loose.

I guess the end test is how the pedal feels. As long as I end up with a firm pedal (and can stop with one push), whatever I did must have worked.

But as mentioned, I DO want to replace the fluid anyway, with it being 15 years and 190,000 miles old for all I know. The brakes are terrible anyway (vibrations, clunks, and the like), and I can't tell if it'* warped rotors, bad drums, or whatever yet. I might as well make sure the hydraulic part of things is in prime shape, make sure it'* not a factor.

Thanks again. I think I'll get 'r done the next warm day that I can find a friend willing to sit in a car pumping the brakes all afternoon.
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