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Rear hydraulic brake line
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Supporting Member of Barthmobile.com 10/08
Picture of MWrench
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For the last weeks I have been doing some long needed repair and upgrades to the Breakaway.

I have just finished replacing the hydraulic brake line to the rear. I replaced the brake line which was 3/16" with 1/4". Every time I bled the brakes, the rear always was much slower and the fluid would not flow with as much force as the front.

I reasoned it was because of the nearly 20 feet of very small tubing and the possibility of some blockage due to corrosion.

I used some PVC flexible tubing from front to rear and then fed the brake line thru that. The PVC tubing will prevent any possibility of scraping/rubbing/vibration effects to the steel brake line.

The 1/4" line made a HUGE difference in the flow when I bled them last night. Pressure/flow at the rear now is very close to the pressure/flow of the front. Front still has 3/16" line but is very short.

Driving later this week will be the final test for this.


Ed
94 30' Breakaway #3864
30-BS-6B side entry
230 Cummins, Allison 6 speed
Spartan chassis
K9DVC
 
Posts: 2020 | Location: Los Gatos, CA | Member Since: 12-08-2005Reply With QuoteReport This Post
Supporting Member of Barthmobile.com 4/08
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A few years ago I installed a new front to rear brake line and fed it thru tubing to prevent damage. Two years later I had to pull it out. The brake line had massive corrosion and had to be replaced.


'92 Barth Breakaway - 30'
5.9 Cummins (6B) 300+ HP
2000 Allison
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Posts: 967 | Location: Minneapolis/Yuma | Member Since: 08-17-2006Reply With QuoteReport This Post
Supporting Member of Barthmobile.com 3/11
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Brake lines are also dependent on whether you have discs or drums. With a matched set you do not need a proportioning valve but if you have front discs and rear drums it is mandatory. Drum brakes travel further and require more volume. Disc brakes will suffer if larger lines are installed because pressure is inversely proportional to the id of the line. Stainless steel tubing is available and not difficult to bend. Never use a rubber or braided hose for the long runs. Those are limited to the connection from the frame to the wheel because of the necessity for flexibility. In non irs rear ends the only flexible line should be between the frame and the hard line that is mounted on the axle assembly, not at the wheels.


1993 32' Regency Wide Body, 4 speed Allison Trans, Front Entry door, Diamond Plate aluminum roof &
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Posts: 1441 | Location: Houston Texas | Member Since: 12-19-2006Reply With QuoteReport This Post
Supporting Member of Barthmobile.com 10/08
Picture of MWrench
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quote:
Originally posted by Tom and Julie:
Disc brakes will suffer if larger lines are installed because pressure is inversely proportional to the id of the line.

That is not correct. In a closed or blocked system with non compressible fluid, pressure is equal throughout the system, input to output. If you were referring to flow rate then yes, it takes more pressure to force fluid thru a smaller ID tube, and more time to build pressure at the end of a smaller ID, longer line to equal the input pressure.


Ed
94 30' Breakaway #3864
30-BS-6B side entry
230 Cummins, Allison 6 speed
Spartan chassis
K9DVC
 
Posts: 2020 | Location: Los Gatos, CA | Member Since: 12-08-2005Reply With QuoteReport This Post
Supporting Member of Barthmobile.com 2/16
Captain Doom
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Once the brakes are bled, the master and slaves can't tell the difference between brake line sizes in terms of pressure. As Ed mentioned, flow restriction could be noticeable in terms of time lag from actuation to engagement because the slave cylinders have to move, which requires a volume increase.


Rusty


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'94 28' Breakaway: MilSpec AMG 6.5L TD 230HP

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Posts: 8380 | Location: Brooker, FL, USA | Member Since: 09-08-2005Reply With QuoteReport This Post
Supporting Member of Barthmobile.com 9/17
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[quote]Ed mentioned, flow restriction could be noticeable in terms of time lag from actuation to engagement because the slave cylinders have to move, which requires a volume increase.[/quote

I have a slight delay in my front brakes (disc) on the right side, a little pull to the left when I first brake, then it goes away, if I pump once or so it is a nice straight stop, I wonder if perhaps I have a restriction in the right side line. Any thoughtsssssssssss? I had considered it was just the shoes.


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Supporting Member of Barthmobile.com 1/18
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Several members have had problems with the front brake hoses. Apparently they can collapse internally and cause blockage, dragging brakes, etc. Try a search. Mechanic


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"98" Monarch 37
Spartan MM, 6 spd Allison
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Posts: 3637 | Location: Kalkaska, MI | Member Since: 02-04-2011Reply With QuoteReport This Post
Supporting Member of Barthmobile.com 10/08
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Further work! noticed while bleeding the brakes a black particle residue was coming out. Clear now but I suspect it is hose residue. I will take off the hoses and get some new ones made. If I can I will have them made in stainless.

I will replace the rubber lines in the rear with steel lines. I agree with Tom, there is no reason for rubber to be used on a solid axle. It is the way they built it, makes it easier to remove the caliper and if the caliper ever comes loose, I have had this trouble before but hopefully have all the shims required so it will stay in place.


Ed
94 30' Breakaway #3864
30-BS-6B side entry
230 Cummins, Allison 6 speed
Spartan chassis
K9DVC
 
Posts: 2020 | Location: Los Gatos, CA | Member Since: 12-08-2005Reply With QuoteReport This Post
Supporting Member of Barthmobile.com 10/08
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I tried a few more things to verify where that black residue was coming from. The fluid draining out with gravity bleed was had cleared up and stayed clear while draining about 150 ml from each caliper. Did this on both the front and rear calipers.

I closed the system and then actuated the brakes several times, really hard. The peddle was a bit soft as it always has been and then about half way down it gets harder. My normal brake use is always in the softer region and only get to the stiffer region for quicker stops.

Went back to the calipers and started the gravity bleeding again, the fluid was now darker and black particles were back. Same both front and rear.

Took the front hose off and went to Royal Brass and had them make 3 Stainless hoses. Two for the front and one for the rear that goes from the !/4 inch line I just installed to the divider on the diff. Installed the front hoses, while draining the calipers lots of black particles and darker fluid came out. Flushed the calipers and installed the hoses. After seeing that I decided to replace the 2 small hoses that connect the divider in the rear to the calipers as well as the chassis to diff hose. All now are stainless.

I saved all the fluid while doing the bleeding process for later evaluation of the particles. That did confirm the black particles were rubber.

It took nearly 300 ml of brake fluid for each caliper to get clear fluid.

I should mention at this point that I had previously measured the air actuator movement with the old rubber hoses attached before removal. There is a rod exposed that shows the movement of the air actuator and really easy to attach a magnetically held recording micrometer.

All new stainless hoses installed and gravity bled the system, micrometer back on. Brought the air pressure back up to the governor shut off of 120 PSI and started to press the brake actuator peddle. First thing I noticed was the brake peddle didn't go near as far down. This was also confirmed by the micrometer, the air actuator was traveling slightly less then half of the distance with old rubber hoses. Solid firm brake peddle and no further dark fluid or particles in the fluid.

Road test today or tomorrow.

I know this is wordy but it does show that rubber brake lines need attention well before I changed mine. Royal Brass guys told me that rubber brake lines over 10-15 years are waiting to fail!!! I already knew that but just wasn't on my radar.

Further, I suspect that those that are complaining about brakes pulling from a side but not from mechanical problems should replace their lines, and of course if older than 15 years! I am not saying it is needed to go the the extreme that I did with stainless hoses, just get new ones. I don't believe hoses will collapse during usage, I believe the interior of the hoses are disintegrating and the hoses start to get blocked by particles of the hose inside causing reduced pressure or fluid movement to the brake calipers or drum cylinders.

I will post part numbers (rear calipers require a new connectors) and pictures late after I put up the process on my website.


Ed
94 30' Breakaway #3864
30-BS-6B side entry
230 Cummins, Allison 6 speed
Spartan chassis
K9DVC
 
Posts: 2020 | Location: Los Gatos, CA | Member Since: 12-08-2005Reply With QuoteReport This Post
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