I'll be adding more to this as I go along.. and some of this work took place last year. I'm just now (October 2022) about to reinstall the calipers and rotors and tie it all in to a new electric actuator.
I have been in the process of going through the brake system on our 1978 Ambassador 28'. We got this trailer a year and a half ago, before that it apparently sat stationary for about 17 years in a RV/Trailer park. It was used and kind of taken care of a few weekends out of a month off and on over this time as a guest house next to the owners larger RV.
And to give some context, this camper is in pretty decent condition overall. Perfectly usable inside, everything aside from the propane system pretty much functions. Original Armstrong AC keeps us nice and cold, and the fride/freezer gets nice and cold after a couple hours on shore power. The plan is that while our four kids are young, we're going to camp every chance we get and maybe in 5-10 years this turns in to one of those cool shell-off builds we all love.
On to the point of this post..
It had the original vacuum assisted hydraulic disc brake system, and it was completely inoperable. Yeah, towing this home was exciting..
Hmm, let's take a look under the hood. It's all tucked away behind those propane bottles.
Last year I took all of this stuff off. Capped off the hydraulic brake line and removed the master cylinder, vacuum booster, propane regulator, mounts and hoses. This freed up pretty much the entire tongue of the trailer. The original electric jack was also removed and replaced with a new electric unit. I also put a larger deep cycle battery in the box that the brake system sat in (for now).
After clearing all that away I started inspecting the axles and brake system back there. The axles (surpisingly to me) have a decent amount of bounce or flex to them when towing or raising the frame to take off wheels. I'm going to run these for now as they seem to be functioning just fine. I'll probably throw some new shocks on it just for kicks.
And that leaves the calipers and rotors. Here is one from the curb side before any work was done. They all pretty much looked like this except both on the road side were more heavily rusted and took more work getting the calipers freed up.
Looks pretty bad but at this point I had confidence I could probably get them cleaned up and rebuilt as long as I could find the parts. I spent a few months off and on reading and familiarizing myself more with this brake system. I found that Ausco manufactured the calipers and started the search for parts. I ordered new pads, pistons, and seals for all four calipers from Ausco through a distributor. Here's a good idea of old versus new.
After I pulled off the rotors, soaked them in evaporust, and cleaned with a scotchbrite wheel, I was looking at the surface of the moon.
And since to my knowledge I can't go buy replacements, I disliked the idea of taking these precious chuncks of cast iron to some knucklehead at the parts counter and asking them to be turned. I double checked the measurements, minimum rotor thickness comes in at 0.940" and mine measured right around 1.100". Cool, plenty of material to give this a shot. And this is a clear case of smoke 'em if you got 'em...
It took a good hour or two one evening to find the right setup that I could turn both sides of the rotor without removing it from the chuck. This would ensure parallel surfaces. It's a capable old lathe and it had the capacity to turn these 11" rotors, but the workholding and tools required to reach the backside while still clearing everything is a little less straightforward than using a proper brake lathe.
Anyway, I was able to get it done, and once I figured out the setup, it only took about 15 minutes or so to turn each rotor.
Rebuilding the calipers was pretty straight forward. I cleaned the housings as much as I could, lubricated and installed the o-ring and boot, and then installed the new piston. I also replaced the upper and lower bleeder screws with new ones. These calipers are the type that slide on two pins mounted to the axle. The service manual asks for a lubricant with molybdenum. I got a bottle of this stuff called Dri Slide. It seems like good stuff but it is moly suspended in mineral spirits. When the spirits evaporate it leaves behind a dry moly coating that isn't supposed to attract dirt/grit. I'd be interested to hear any recommendations on a better grease as this stuff has a very low viscosity and runs/drips off everywhere.
And that brings us to today. The next task is to get the parts back out to the camper and put the rotors and calipers back in their rightful homes. Then install new braided steel flex lines and hard line to the front where it will hook up to the actuator. Bleed the brake system and see if I can do a burnout with the camper holding me back!