Bleeding trailer brake actuator

ssobol

Chief Petty Officer
Joined
Sep 3, 2010
Messages
503
I found that the surge brake actuator on my MagicTilt trailer was not working. The mechanism is all rusted up.

I got new one (UFP-75a with backup solenoid). I installed it and bled the master cylinder according to the instructions (move the actuator rod with a screw driver until no more bubbles in the reservoir). Then I tried bleeding the brakes.

I opened the bleed valve on the caliper (self bleeders) and moved the actuator rod with the screwdriver. I noticed that the reservoir did not deplete much at all. I opened the bleeder more, and still no fluid went out of the reservoir. I opened the brake line at the first tee and tried again (to see if the line was blocked). Same thing, no depletion from the reservoir and no fluid out the line.

I removed the actuator, disconnected the outlet line, and moved the rod again. A little fluid comes out every once in a while when the rod is moved, but most strokes result in nothing happening. Sometimes I can hear a sucking noise when the rod is moved coming from the outlet. I can see the rod moving in the port at the bottom of the reservoir.

I expect that there should be a decent squirt of fluid whenever I move the rod, but this is not happening.

Is there some thing I overlooked or some trick to getting the actuator to work so I can bleed the system? Perhaps I have a defective actuator?
 

oldjeep

Admiral
Joined
May 17, 2010
Messages
6,455
Re: Bleeding trailer brake actuator

if you want to save yourself a LOT of future headaches bleeding brakes go pick up a mityvac kit... you can get one for under $50

https://www.google.com/shopping/pro...05&sa=X&ei=C099Udn2ComH2AXEEw&ved=0CGsQ8wIwAQ

It's a handheld vacuum pump.. fill mc res, remove bleeder, apply vacuum, refill mc res, dump fluid from pump res, move on to next wheel.


Or use a pressure bleeder - I've never had much luck with those vacuum things
0130 - Trailer Bleeder Kit Press Fit Reservoir Cap

I've got accessory connectors that fit all my master cylinders
 

UncleWillie

Captain
Joined
Oct 18, 2011
Messages
3,995
Re: Bleeding trailer brake actuator

You are on the right track, you just need a little more patience.

Manually bleeding is a 2 man job. It goes something like this.

Fill up the actuator reservoir.
Position one person at the bleeder fitting at the farthest wheel.
The other person compresses the actuator and maintains pressure.
The second person opens the the bleeder; Air/Bubbles/Fluid squirts out; and then re-closes the bleeder.
The actuator is then released and re-compressed. Repeat as needed.
The actuator will need to be topped off after every 3-4 pumps to prevent it going empty and pumping air.
The closest wheel will need to be bled separately after the farther one is completed.

It is not difficult, just tedious. Pump, open, close, release, repeat!
 

Thalasso

Commander
Joined
Jan 18, 2011
Messages
2,876
Re: Bleeding trailer brake actuator

place a jar with brake fluid in it, attach a hose the the bleeder and put it in the jar, pump the mc and watch the jar untill all the air bubbles are gone. close the bleeder and move on to the next one. One man job
 

ssobol

Chief Petty Officer
Joined
Sep 3, 2010
Messages
503
Re: Bleeding trailer brake actuator

I understand how brake bleeding is supposed to work. The issue I have is that even when the actuator is not connected to anything there is not a consistent fluid output when the rod is moved using a screwdriver to move it as shown in the instructions. Most of the time no fluid comes out. Once in awhile a spurt will come out. Since I have never worked on a trailer with surge brakes before (but have worked on the brakes on several make of cars), I was wondering if there is something I might be doing wrong or have overlooked. I happen to suspect that the actuator is bad, but I want to be sure I have covered everything before I try and send it back.

As I understand it, the backup solenoid is only energized when there is 12v applied. When energized the solenoid does not allow fluid to go the the calipers (returns to the reservoir?). When not energized there is no return of the fluid so the brakes will work. Bleeding the brakes should be done with the solenoid not powered, correct?

Thanks for your help.
 

smokeonthewater

Fleet Admiral
Joined
Dec 3, 2009
Messages
9,838
Re: Bleeding trailer brake actuator

not energized....correct


I think the issue you are having is that you are allowing air to be drawn back into the master when releasing the actuator
 

UncleWillie

Captain
Joined
Oct 18, 2011
Messages
3,995
Re: Bleeding trailer brake actuator

not energized....correct
I think the issue you are having is that you are allowing air to be drawn back into the master when releasing the actuator

+1
When the actuator retracts with an open brake line, the path of least resistance is to draw air up the opening instead of pulling fluid through the master cylinder valves.
Hook up the hoses and bleed all the way to the wheels.
When releasing the pressure either close the bleeder or use Thalasso's technique in Post #5 to prevent back drawing air.

Don't let the reservoir get too low, or you will have to start all over again.
 

dockwrecker

Lieutenant
Joined
Mar 10, 2006
Messages
1,392
Re: Bleeding trailer brake actuator

Pressure bleeders are the only way to go. Google "home made brake bleeder". $20. I don't know why anyone screws around with anything else.
 

ssobol

Chief Petty Officer
Joined
Sep 3, 2010
Messages
503
Re: Bleeding trailer brake actuator

I used the MightyVac pump that was recommended earlier. Very handy and saved a lot of time.

As I suspected some of the calipers are seized, so I'm just going to replace the calipers and the rotors and be done with it. The trailer is a MagicTilt. It uses UFP parts (calipers and actuator). The calipers have "UFP" on them, but no part number. MagicTilt has a part number of PG5003 for the caliper. I find UFP DB-35 and DB-42 calipers searching online. These are about half the price of the MagicTilt part number. I'm not sure whether my trailer uses the DB-35 or DB-42 calipers.

Anyway to tell which caliper is being used by looking at them?

Thanks.
 

bruceb58

Supreme Mariner
Joined
Mar 5, 2006
Messages
30,454
Re: Bleeding trailer brake actuator

If you are going through and switching calipers and rotors, I would switch to Kodiacs. Are your rotors bad? if they are OK, just replace the calipers.
 

Jonnybbad

Petty Officer 1st Class
Joined
Jun 10, 2011
Messages
210
Re: Bleeding trailer brake actuator

You may want to start off by bench bleeding the master cylinder. I would suspect a trailer would require a lot of work to manually bleed the brakes with all that brake line. You certainly would want to invest in a vacuum bleeder. Its manually operated by hand. They are not very expensive and can be found at Harbor Freight Tools or an auto parts store.
 

ssobol

Chief Petty Officer
Joined
Sep 3, 2010
Messages
503
Re: Bleeding trailer brake actuator

If you are going through and switching calipers and rotors, I would switch to Kodiacs. Are your rotors bad? if they are OK, just replace the calipers.

The rotors are rusty. They probably can be turned. If the price is low enough I'll probably just replace them when I do the calipers. I replaced the rotors on my Dodge Caravan a couple of years ago. They were only about $35 ea. For that money I'd just replace them.
 

UncleWillie

Captain
Joined
Oct 18, 2011
Messages
3,995
Re: Bleeding trailer brake actuator

... I'm not sure whether my trailer uses the DB-35 or DB-42 calipers....Anyway to tell which caliper is being used by looking at them?...

DB-35 = 9.75" Rotors.
DB-42 = 10.25" Rotors.
 
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