Bleeding Trailer Brake system

[Cajunhunter67]

I thought I would put this up for anyone that may struggle bleeding the BCB trailer brakes.I have a 2011 single axel trailer for a Sabre FTD. After purchasing the boat, first thing I did was disconnect the trailer electric connector. I than put the truck in reverse and backed up. The trailer brakes did not grab as they should, thus I knew the brakes were not working. I opened the reservoir service point. Empty! Broke the bleed valve loose on the left caliper. Only a few drops of oil, and water came out. So I knew the system was pretty empty.I had a large bottle of Brake fluid. I attached a hand pump (The one used to service the lower unit oil). It fit perfectly in the large brake fluid bottle. I added a clear hose from the pump to the left bleed valve. The trailer light connector must be hooked back up to the truck, and the truck shifted into reverse to activate the reverse valve. It can be done with the truck not running, with the parking brake activated, but key must be in the on position. I did not have the trailer hooked to the truck Just the trailer lights connector.Place a bucket on the ground under the oil reservoir. I than started pumping brake fluid thru the system. Do it slowly. I made sure to keep constant pressure from the hand pump. It keeps air from entering. I pumped till the reservoir was full and overflowing into the bucket. I pumped slowly and closed the bleed valve at the same time. Clean up the mess. I hooked the trailer to the truck. Did three or four hard stops from about 55 mph. Disconnected the trailer light connector from the truck. Put it in reverse. Brakes grabbed hard. Job done!!!

[oldtimer57]

sounds like an idea to fill from the rear. But why the reverse stuff? The normal config is the master cylinder is “open” when sitting, so that pressure can be relieved and the brake calipers will retract.I assume you did both caliper bleeders? Necessary to get the air out of the second caliper, at least on my classic. metal brake line goes to a T, with a separate line from there to each caliper.2008 Pantera Classic2014 Mercury Pro XS 200

[oldtimer57]

I see a potential issue in this approach. The calipers are mounted with the bleeder up and the brake line down. How will you ever purge all the air from the caliper when you are putting in brake fluid (which is heavier than air)??? Purging from front to back I can see as you are pushing new brake fluid in to the bottom of the caliper, and the air sits on top of the fluid until it is all evacuated…After thinking about this, I cant see how it can work… Unless you have calipers mounted upside-down (which is possible). If the brake line enters on the bottom, this seems to be problematic to me…2008 Pantera Classic2014 Mercury Pro XS 200

[Bass Cat Boats]

Nice write-up Cajanhunter.If the right side is jacked a little higher than left and tounge of trailer is higher than that your mesthod works well. Tapping the calipers and lines will dislodge any trapped air bubbles and send them out through the recervoir. Flushing will also assist with some water removal but Im concerned if the caliper was full of water. That may need to be removed and bench serviced to get all the water removed.Practice Angling CPRCatchPictureRelease2010 PIV 200SHO

[Bass Cat Boats]

Brakes that sit and are not used often can loose their charge (gain air) or seal. You will notice this in many master cylinder types of brakes, be those vehicle or trailer. Thus occasionally you might have to bleed that stored muscle car or boat trailer. On the muscle car or truck, you notice a soft pedal that gains pressure when pumped a few times. The master cylinder is mounted on the firewall uphill from the brakes and lines with many of these dveloping air bubbles being able to migrate up the lines and into the ports. Since brakes on a trailer dont have the master cylinder uphill from the system, the air bubbles can not drift uphill. They simply get trapped in the lines and remain there till the pocket works to the master cylinder or wheel cylinder. The parallel lines of the trailer are why brakes seem more fragile on the parallel systems.

[BIGCATTER]

Hand vacuum pump with catch reservoir inline . — Fill master with fluid . — open bleeder and connect vacuum pump . ( best to use clear tubing ) — Pump until line runs pure fluid , making sure not to let master run dry . — tighten bleeder — repeat procedure on opposite side . — done in 10 minutes . — Hoss

[Bass Cat Boats]

Does anybody gravity bleed anymore. Awhile back I bled mine just to run new fluid in the lines. I done it 1 slow pump at a time. I know “old fashion”. But works.2013 PANTERA 2MERCURY 200 PRO XSMINNKOTA 80LB FORTREX25 fury

[Bass Cat Boats]

Might work alright if you jack the nose of the trailer up quite a bit.

[Cajunhunter67]

The system would not allow me to pump fluid till the reverse valve was activated. My Sabre trailer has one, single bleed point. The left caliper. The line runs from the left caliper to the right caliper, than to the master cylinder.I did tap the calipers to break loose any trapped air. Bleeding from the rear is standard practice in many aviation applications. It worked great on the trailer. Especially with the system having very little oil left in it.

[oldtimer57]

Theres got to be something wrong in your system then. When the master cylinder piston retracts it HAS to uncover the orifice in the bottom of the reservoir to release pressure, otherwise the brakes stay on. UFPs instructions mentions this. Are you sure the M/C piston is fully retracted (i.e. you have pressed the break-away brake release on the bottom of the tongue? If that is not released all the way, I could see how your problem happened.As far as the other post above, you are not going to convince me forcing fluid from the caliper above will work. Bleeder is on top. Brake line is on bottom. No way to force air DOWN and out into the main brake line, the fluid will run around the air and out the brake line, leaving the air in place. Not the way to get a solid brake circuit.2008 Pantera Classic2014 Mercury Pro XS 200

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