| Re: [GMCnet] update on master cylinder replace [message #197947] |
Sat, 09 February 2013 12:00  |
KB
Messages: 1262
Registered: September 2009
Karma: 0
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Senior Member |
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Jim Hupy wrote:
> By far the worst way to bleed them is to gravity bleed
> them, followed quite closely by pumping the brake pedal and releasing the
> bleeders, and third by using a "mity vac" type vacuum pump bleeder on the
> bleeder screws. By far the most efficient method of bleeding the system, is
> a power bleeder.
I was just reading in the "Brake Handbook" by Fred Puhn
that the author didn't recommend a vacuum bleeder. Apparently the
cup seals (on the rear wheel cylinders) can let air in since you're
pulling instead of pushing the fluid and the cups don't seal well
in that direction. (Maybe not a problem with disc calipers
which use o-rings.)
all I know on the topic.
Karen
1973 23'
1975 26'
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Karen
1975 26'
San Jose, CA
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| Re: [GMCnet] update on master cylinder replace [message #197951 is a reply to message #197947] |
Sat, 09 February 2013 12:35  |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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I blew a wheel cylinder at Rayne.
After fixing it, I borrowed a vacuum bleeder from Emery.
It made quick work of the bleeding job. If you think there is air sucked in past the cups, when you are done it would be a simple one squirt job to step on the brakes and open the valve under pressure.
I have done GMC brakes all of the different ways. They all work. I like the pressure tank.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] update on master cylinder replace [message #198025 is a reply to message #197947] |
Sun, 10 February 2013 09:42 |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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| KB wrote on Sat, 09 February 2013 13:00 |
I was just reading in the "Brake Handbook" by Fred Puhn that the author didn't recommend a vacuum bleeder. Apparently the cup seals (on the rear wheel cylinders) can let air in since you're pulling instead of pushing the fluid and the cups don't seal well in that direction. (Maybe not a problem with disc calipers which use o-rings.)
all I know on the topic.
Karen
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Karen,
What you know is more than most, but I have to disagree with both Fred and Jim.
I have never had an occasion that I did not get to clear - bubble free fluid coming out of the wheel cylinder (except the time I forgot to grease the bleed screws  ). This is one method I have been using successfully for many years. It is particularly well suited to dealing with strangely placed plastic fluid reservoir installations. It is also very good for those installations where reservoir access is less than great or clamping the bleeder plate is difficult.
I will also suggest that a sealing system to reliably hold 12~1500psi positive should be good for 15psi negative. (Or it might not even hold out atmospheric moisture.)
The real important thing with vacuum bleeding is to seal the bleed screw threads. I use grease, Chuck Boyd uses teflon tape. (I think I like the teflon tape idea a lot, but I didn't think of it first..... )
On something the size of a GMC, it is also good to have someone to watch and keep the reservoir level up. (If you don't you have to start over. expletive deleted)
This is also a very good method when filling the system of antique vehicles with DOT 5 (that used to cost <30$/qt) as you don't have to buy the extra to fill the pressure can.
You don't need a killer vacuum pump, just a little thing that maybe does 28" at low flow is all it takes.
Matt
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
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| Re: [GMCnet] update on master cylinder replace [message #198032 is a reply to message #198025] |
Sun, 10 February 2013 11:48 |
Surbo
Messages: 213
Registered: February 2004
Karma: 0
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[quote title=Matt Colie wrote on Sun, 10 February 2013 09:42Karen,
What you know is more than most, but I have to disagree with both Fred and Jim.
I have never had an occasion that I did not get to clear - bubble free fluid coming out of the wheel cylinder (except the time I forgot to grease the bleed screws ). This is one method I have been using successfully for many years. It is particularly well suited to dealing with strangely placed plastic fluid reservoir installations. It is also very good for those installations where reservoir access is less than great or clamping the bleeder plate is difficult.
I will also suggest that a sealing system to reliably hold 12~1500psi positive should be good for 15psi negative. (Or it might not even hold out atmospheric moisture.)
The real important thing with vacuum bleeding is to seal the bleed screw threads. I use grease, Chuck Boyd uses teflon tape. (I think I like the teflon tape idea a lot, but I didn't think of it first..... )
On something the size of a GMC, it is also good to have someone to watch and keep the reservoir level up. (If you don't you have to start over. expletive deleted)
This is also a very good method when filling the system of antique vehicles with DOT 5 (that used to cost <30$/qt) as you don't have to buy the extra to fill the pressure can.
You don't need a killer vacuum pump, just a little thing that maybe does 28" at low flow is all it takes.
Matt [/quote]
Matt;
If I recall correctly, the factory fill used to be by vacuumn, is that method still used today?
Bob Drewes in SESD
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| Re: [GMCnet] update on master cylinder replace [message #198050 is a reply to message #198032] |
Sun, 10 February 2013 16:58 |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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Senior Member |
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| Surbo wrote on Sun, 10 February 2013 12:48 |
Matt;
If I recall correctly, the factory fill used to be by vacuum, is that method still used today?
Bob Drewes in SESD
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Bob,
I all honesty, I cannot confirm that. 15 years ago, I did work with two of the Jeep assembly plants and they used vacuum to fill both the brake fluid and the engine coolant. They also had mega-buck hardware that set up the exact amount of each fill. There was no art to it at all.
Matt
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
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