Other Technical Discussions A place for technical discussions NOT related to Porsche or BMW. Other makes, home DIY, etc. |
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How to: Replacing and adjusting trailer brakes
As unluck would have it, my trailer lost its electric braking capability about 10 miles into my trip up to the Glen a couple of weeks back.
Fortunately, I had just replaced the brakes on my truck. Made it there and back with minimal fuss (though I got very good at downshifting). Upon closer inspection, I could confirm the brakes were still getting a signal from the controller but nothing was happening. In removing the drum, I saw that I had successfully worn away all pad material, and that the solenoid had short circuited and stopped working. Fortunately, replacing the brakes on a trailer is easier than on most drum brake-equipped vehicles, for a couple of reasons: 1) It's most cost-effective to replace the entire backing plate assembly -- which includes the magnet/solenoid, shoes, springs, wiring, etc. all pre-assembled into a tidy package. If you've ever done drum brakes before, you know that while it's not necessarily difficult per se, it is a PITA...not least because of the brute strength required. 2) There's generally more available space for your working area. I had been experiencing a speed-dependent low-Hz vibration under braking previously, so I also took this opportunity to replace the drums (which come with new bearings!). In case you're not aware, electric brakes on a trailer operate identically to a drum brake on a car, but the actuator mechanism is not hydraulic -- it is electrical. My trailer has Dexter axles/brakes, which are (by far) the most common axles on trailers. The whole kit (backing assembly, drums, bearings, etc for one axle) cost me about $250 total. Step 1: Remove the wheel and hub cap The hub cap is just a press-fitting and can be chiseled off with a thin screwdriver or, well, a chisel. This will expose the stub axle and bearing assembly. To remove the drums, you will need to remove the cotter pin, castle nut, and D washer holding the bearing assembly/drum to the axle. You will then be able to pull off the drum; it may require whacking the drum a couple of times with a dead-blow hammer or rubber mallet. Step 2: Remove the backing assembly There are four nuts holding the backing assembly to the axle. Once removed, don't forget to snip the wiring to the axle (be sure to leave enough for you to splice the new brakes in). Step 3: Install the rear bearing + seal On the inside of the drum, you will need to install the larger of the two tapered bearings. Be sure to pack the new bearing well (HF sells a cheap bearing packer that works quite well). Install the seal, taking care to orient the seal with the inside face down. To aid with installation, be sure to lightly lube the surfaces of the seal and hub of the drum. I use a chunk of wood to aid with installation; it evenly distributes the load. Step 4: Wire the new backing assembly and install onto axle Use Anti-Seize! There is no need for positive/negative (at least on these brakes). Once the backing assembly is installed and tight, be sure to tie up the wiring to ensure it does not hit any moving parts. Step 5: Initial adjustment of shoes The shoes will need to be adjusted properly, such that you can feel a slight drag on the drum when assembled. The adjuster is at the bottom of the backing assembly, below the magnet. You may use an actual brake adjuster tool, although a screwdriver/small pry bar works well. There is also an adjuster opening on the backing plate itself, so as to access the adjuster when the drum is assembled. You will likely need to fine-tune your adjustment once the drum is installed; the opening will likely have a rubber plug that will need to be removed. Step 6: Install the drum and secure the hub/bearing assy Once the adjustment on the shoes is to your liking, install the small tapered bearing, followed by the D washer and castle nut. Do not install the cotter pin yet. Torque the castle nut to ~50 ft-lbs (i.e., good 'n' tight) while spinning the hub. This is an important step, in that it seats the bearing properly. Then remove all torque on the nut and finger-tighten until snug. Then back the nut off until the hole in the stub axle aligns with the first opening of the nut. Don't worry if the nut has play at this point -- this is how it's supposed to be. Step 7: Install hub cap and wheel; torque. Step 8: Bed brakes and ensure adjustment So, Dexter does not explicitly require bedding of brakes. It's likely not a particularly fancy material, and the braking forces are not insane. That said, I still recommend it -- it will also give you the opportunity to ensure everything is working properly. Before leaving to confirm function, I drew a series of lines radially on the tire. This will be helpful when determining left-right adjustment balance. First, bed the brakes by driving around and conducting heavy braking five or six times (without locking up the wheels) in quick succession from ~30-40 mph. Then drive around for 5-10 minutes with as little braking as possible (I just turned off my brake controller for this) to allow the brakes to cool. Next, we will determine left-right balance -- i.e., which wheel is locking up first. Crank up the power on your controller and proceed to stop. By watching in my side mirrors, I was able to see which wheel locked up first by noting when those lines I had drawn on the tire come into focus (you will not be able to see the lines when the wheels are in motion). At this point, I had good confirmation that my balance was respectable. After driving around for a while longer, I stopped for good and measured the temperature of the two drums, and found that there was, in fact, a difference of about 8 degrees between the two. I added one more click of adjustment to one of the sides and lo and behold -- the temperatures came in line with one another! Being this anal about left-right brake balance is likely overkill, but it will help ensure the brake wear remains even.
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Collin M. I wear a cowboy hat. '86 951: lucky number 13...rare 6.0L edition. '06 M3: hers. |
#2
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Quote:
I made the same decision for the same basic reasons when I 1st bought my aluminum trailer. Nice to have all new everything! Mine had surge brakes which made it even easier. You forgot to mention you also get new wheel bearings! A real plus on older, possibly less well maintained trailers
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David I hope to arrive to my death, late, in love, and a little drunk! Just because I don't care doesn't mean I don't understand... Homer Simpson "That's what's keeping me out of F1.... Too much mental maturity...." N0tt0n Some cause happiness wherever they go; others whenever they go. CHAOS, PANIC, AND DISORDER my work here is done... Live without pretending, Love without depending, Listen without defending, Speak without offending |
#3
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I adjust my brakes by having Jamie @ FTRS (Freeman Trailer Repair Service) check them during an annual repack service
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Stephen www.salazar-racing.com 1970 914/6 - 3.0L GT 1983 911SC - 3.32L IROC 1984 930 2008 S2R1000, dirt bikes (some gas, some electric), Sherco trials bike Sold: 2001 Boxster (hers), 2003 996tt x50 , SpecE30, 1996 E36M3 GTS2 racecar, 2015 Mustang GT |
#4
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Nice writeup !
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We will now use the power of the Continuum Transfunctioner to banish you to Hoboken, New Jersey. BMW Spec E46 #609 |
#5
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Well, you see, I made the naive assumption that they last forever. Or at least long enough that I didn't need to inspect them immediately!
Ironically, when I bought the trailer I actually repacked the outer bearing...but didn't bother removing the drum. Sigh. Quote:
And I did mention we get new bearings with the drums: Quote:
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Collin M. I wear a cowboy hat. '86 951: lucky number 13...rare 6.0L edition. '06 M3: hers. |
#6
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I bought my steely new so everything was new... in 2002 Moved the rear lights so I could back in drive, added tyre rack and nice big toolbox.. There are times I wished I still had it. Then I need to move the aluminum one around and don't need my truck or several friends to make it happen.
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David I hope to arrive to my death, late, in love, and a little drunk! Just because I don't care doesn't mean I don't understand... Homer Simpson "That's what's keeping me out of F1.... Too much mental maturity...." N0tt0n Some cause happiness wherever they go; others whenever they go. CHAOS, PANIC, AND DISORDER my work here is done... Live without pretending, Love without depending, Listen without defending, Speak without offending |
#7
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Collin: excellent writeup, tailor-made for der Vorganger. You can send it to one of the new editors.
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Richard Curtis Fairfax Station, Va. '93 911 C2 |
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