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Re: [GMCnet] Maintaince [message #288832 is a reply to message #288817] |
Thu, 15 October 2015 18:05 ![Go to previous message Go to previous message](/GMCforum/theme/default/images/up.png) ![Go to next message Go to previous message](/GMCforum/theme/default/images/down.png) |
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Matt Colie
![United States United States](/GMCforum/images/flags/us.png) Messages: 8547 Registered: March 2007 Location: S.E. Michigan
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Ken Henderson wrote on Thu, 15 October 2015 16:24Darn you, Jim! You kept me awake last night! Thinking about the "fix" for your brakes.
I hate to break it to you (and probably start an argument), but changing the lines should not affect the performance of properly bled brakes. In fact, you could connect them with either 0.010" ID lines or 1.0" ID lines without affecting anything except response time or required force on the MC.
Look at it this way: In a sealed system like brakes, a caliper responds only to the volume of fluid and pressure supplied to it. So, if the MC supplies 1 ci of fluid, the caliper will receive that 1 ci, no more and no less, regardless of any intervening rigid container, such as the brake lines. (The 1 ci is an arbitrary volume -- obviously the caliper will receive only enough volume to move it the distance imposed by the force applied; the point is that the volume can only be exactly what's supplied by the MC, in every case.)
I yield the podium.
Ken H.
Ken,
This not an argument. It is merely another look at the entire picture.
While I also don't believe that the root cause has been correctly identified in this case, there could be an issue with brake lines that are too thin a wall. Please note that I am not talking about the tubing ID in this case. Tubing ID comes in only because the OD of the tubing is controlled by the related hardware. There have been cases where the tubing did expand under load and cause those involved serious headaches until the issue was identified. Brake lines do expand, this fact was used for an electric brake controller that failed in the market place in the late 60's. It was a line pressure responsive control that starred a strain clamp that was placed on a line out of the master cylinder and electronics with adjustable gain to convert that to a signal for the trailer brakes.
Another case I am most familiar with was a small diesel engine (DB OM328) family that had a smoke issue when it should not have had same. While the pressures were higher than GMC brakes, I am sure that the case is still valid. In this case, the injection lines were 6mm OD and 2mm ID. With some very expensive equipment we demonstrated that the fuel injection rate did not match the high pressure pump output curve at many loads. They had to be changed to a 1.5mm ID.
How could this be? The injectors opened a the correct pressure? Yes, but nobody had counted on the elasticity of the injection line. So, as the fuel line pressure rose, it did not get to the cracking pressure of the injectors when it should have, it was late.... And, when the injectors did finally open, the balloon effect of the fuel line caused the delivery of gobs more fuel in the early part of the cycle than the burn process could manage. Worse still was that the technician that set up the engine had realized that timing was wrong, so he cranked the pump ahead a couple of degrees.
Now, if this sort of a situation existed in a vehicle service brake, it would result in an always soft pedal and not a declining pedal height. The only way it could cause the symptoms as described would be is the steel line were continuously deforming. I believe that any common metallic line that did so would fail in relatively sort order. It would also be very visible, much as when a copper water line that gets frozen.
If all he has changed the steel lines and absolutely nothing else, I still do not believe that the case is closed by any means. Were line deformation a real root cause, I would start by looking at the flexible components first, their elasticity has a way lower threshold than any steel line at all. I did work in foundation brakes for a little while, and we measured this sort of stuff for certification.
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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Maintaince
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Re: Maintaince
By: thesmith on Thu, 15 October 2015 07:40
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Re: [GMCnet] Maintaince
By: bdub on Thu, 15 October 2015 08:03
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Re: Maintaince
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Re: [GMCnet] Maintaince
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Re: [GMCnet] Maintaince
By: USAussie on Thu, 15 October 2015 16:44
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Re: [GMCnet] Maintaince
By: k2gkk on Thu, 15 October 2015 17:08
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Re: [GMCnet] Maintaince
By: USAussie on Thu, 15 October 2015 17:28
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Re: [GMCnet] Maintaince
By: k2gkk on Thu, 15 October 2015 17:36
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Re: [GMCnet] Maintaince
By: USAussie on Thu, 15 October 2015 17:52
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Re: [GMCnet] Maintaince
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Re: [GMCnet] Maintaince
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Re: [GMCnet] Maintaince
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Re: [GMCnet] Maintaince
By: thesmith on Fri, 16 October 2015 07:44
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Re: [GMCnet] Maintaince
By: powerjon on Fri, 16 October 2015 13:00
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Re: [GMCnet] Maintaince
By: KB on Fri, 16 October 2015 14:38
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Re: [GMCnet] Maintaince
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Re: [GMCnet] Maintaince
By: powerjon on Fri, 16 October 2015 17:01
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Re: [GMCnet] Maintaince
By: KB on Fri, 16 October 2015 17:35
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Re: [GMCnet] Maintaince
By: powerjon on Fri, 16 October 2015 18:43
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Re: [GMCnet] Maintaince
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Re: [GMCnet] Maintaince
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