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Old 10-03-2022, 11:53 AM   #1
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1978 28' Ambassador
NE , Oklahoma
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Bringing (some of) the original hydraulic disc brake system back from the dead (1978)

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!
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Old 10-03-2022, 11:57 AM   #2
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Impressive! You are a master craftsman!
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Old 10-03-2022, 12:28 PM   #3
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I admire you taking on this project as I have done many crazy restoration projects too. I believe most folks have abandoned this system years ago due to lack of parts and not wanting to be stranded somewhere with no ready access to parts.
You will have a lot invested in this semi-old system when your finished. If the system works ok then you may want to consider finding some spare parts to have on hand for the "just in case" issues on the road.
Post a few pictures if you think about - this seems like an interesting project.
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Old 10-03-2022, 03:55 PM   #4
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1978 28' Ambassador
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I didn't get too technical on the workholding for these rotors but only after re-reading the first post did I realize my mistake. Hopefully this will be seen and no one out there goes and turns their rotors on a standard metal lathe with a setup based solely on what is pictured above.

I took care to check the runout of the rotor face when I was mounting it in the chuck. I got each one within a thousandth of an inch of runout before I removed any material. And as I had mentioned above I turned both sides without rechucking it to ensure both surfaces remained parallel. This was not enough...

While the surfaces are clean and smooth now, and both sides parallel, nothing I did ensured that those surfaces spin true to how they will when riding on the bearing races. Like you know, while doin' 65 mph with the family.

I chucked the rotor by clamping the hub casting and bumped it around until the rotor face was nice and even. I wasn't too surpised it had such good runout for being 45 years old, I think the pads I took off of it were original and still had a bit of life left in them.

An actual brake lathe would have mounted these by using cones that seat against the wheel bearing races, runout on the rotor face at that point wouldn't matter too much to some degree because it would be resurfaced with the races being the datum. Nice and true.

Before I reinstall them I am going to chuck them up again the same way and double check runout against the race. It isn't perfect but maybe I'll be able to sleep at night knowing this glaring oversight I've made... Hope the information is useful to someone out there.
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Old 10-04-2022, 11:13 AM   #5
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Originally Posted by mindheavy View Post
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 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!
Did you try checking interchange catalogs for some compatible sized rotors that could be adapted? You might have to machine bearing holes or replace stud locations but there should be something in the catalogs that is close enough to adapt. Looking at the pics maybe an older model Nissan, Mazda, or Toyota 1 ton truck part or similar would be close.

https://www.thewrenchmonkey.ca/produ...change/search/

https://my.hollandersolutions.com/do...o+Number+Guide
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Old 10-04-2022, 11:25 AM   #6
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1978 28' Ambassador
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Looking at the pics maybe an older model Nissan, Mazda, or Toyota 1 ton truck part or similar would be close.

https://www.thewrenchmonkey.ca/produ...change/search/

https://my.hollandersolutions.com/do...o+Number+Guide

Thanks. That's a good idea to try cross-referencing these. I believe the hubs are Kelsey-Hayes units. I haven't spent too much time looking into them since mine seem to be usable but I'll keep it in mind for the future.
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Old 10-04-2022, 11:39 AM   #7
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1978 28' Ambassador
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This morning while I was cleaning up down in the shop I put the rotors back on the lathe and bumped them around until I had runout on the rotor face back to less than a thou. This re-established the work I had done before.



I moved the indicator to start taking some readings down near the bearing race. I spun the rotor with the indicator on the race where the bearing rides, the face or ridge of the race, and on the machined surface face that the race is installed in, if that makes sense.



All of the readings I was taking were within a couple thousandths so I think I should be okay here. No harm in double checking the work..

As well, I referenced the service manual and they detail the procedure for checking rotor runout once installed so I plan to do that once I get them put back on the trailer - it should only take a couple of seconds to verify runout with a dial indicator once they are reinstalled.



The service manual wants rotor runout to be less than 0.020" so I've got a pretty big margin there.
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Old 10-05-2022, 01:05 PM   #8
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Thanks. That's a good idea to try cross-referencing these. I believe the hubs are Kelsey-Hayes units. I haven't spent too much time looking into them since mine seem to be usable but I'll keep it in mind for the future.
.020 runout is pretty rough that will cause the rotors to warp or get hot spots after a while under .005 is much better. Too much runout can also cause uneven tire wear, and possibly tyre casing problems, by placing uneven loads on different parts of the tyre.

You should be able to get to about .002 or better on a good lathe easily; which is the recommended runout amount for a passenger car; if you can get it to .0005 you will not feel the drag-slip-drag-slip effect at all even under the hardest braking

https://www.brakeandfrontend.com/rot...0manufacturers.
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Old 10-05-2022, 03:40 PM   #9
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1978 28' Ambassador
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You should be able to get to about .002 or better on a good lathe easily; which is the recommended runout amount for a passenger car; if you can get it to .0005 you will not feel the drag-slip-drag-slip effect at all even under the hardest braking

I didn't take the time to put a tenths indicator on the rotors after turning them - it would have been jumping a lot even with the fresh surface on cast iron. I wasn't going for a mirror finish but it is smooth. A good trip will let the new pads and rotor surface wear together and will become that familiar shiny surface with a little time.


I was however able to get within or under 0.001" after turning using my thousandths indicator (workholding issues aside as I mentioned in a previous post).


I reinstalled the road side rotors and calipers yesterday and used the same indicator once installed to measure runout as referenced by the wheel bearing surfaces. Both front and rear rotors had about 3 to 4 thou runout which I am happy with.



I took a few pictures during install, I will try to do another small write up on that later tonight or tomorrow.
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Old 10-07-2022, 01:03 AM   #10
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1978 31' Excella 500
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Too bad you are a few years late. A phone call to Andy at Inland would have fixed you up. I sent him one of my rotor pads for him to use for a model to get some pads made up.
You haven’t mentioned brake actuator yet. There are some out there. The Actibrake that Andy sold me with new axles back in ‘07 failed this summer. I found a new actuator on Amazon. Good service and the actuator works. It lives under the same cover as the vacuum booster had.
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Old 10-07-2022, 01:10 AM   #11
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Ah, I just looked it up and you asked for a photo. I’ll try to find the photo, but not for a few days
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Old 10-07-2022, 10:19 AM   #12
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1978 28' Ambassador
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Too bad you are a few years late. A phone call to Andy at Inland would have fixed you up. I sent him one of my rotor pads for him to use for a model to get some pads made up.
It is evident after spending only a few minutes poking around these forums, or searching for practically anything airstream related on google, how great of a resource Andy was to this community. I'm glad his knowledge is still here informing new comers like myself to the airstream community.

Luckily on my model the brake pads (and caliper assembly) are manufactured by Ausco – new pads and caliper rebuild parts are available for purchase. On the brake actuator, I ordered a new 1,600 psi unit from e-trailer last year. https://www.etrailer.com/Brake-Actua...tar/HBA16.html, it seems well built.

This brake job is sort of half restoring the original system, half building a new system. I bought the brake actuator by itself and am running my own new line to the axles, to flex lines, and then to the calipers. I don't want to have any of the new work relying on 45 year old brake lines and fittings that I can't inspect under the belly pan.

I would have liked to put my actuator in the old vacuum booster box but I ended up sticking a battery there when we first got the camper. The original battery box on ours is small. I'll get into the front section of this brake system in another post soon after I put a few pictures up on the reinstall of the calipers and rotors.
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Old 10-07-2022, 10:41 AM   #13
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A few days ago I was able to get out and install the rotors and rebuilt calipers. I took a few pictures during the process that I will try to turn into some coherent order of operations here. As anyone that has done a wheel bearing job knows, even with the best intentions it can get greasy so I didn't pick up the phone for pictures every time I thought about it.

I used a bearing packing tool that easily and fully packs a roller bearing in a few seconds. They work well and save a huge amount of time and mess when there are eight bearings to clean, inspect and pack. The bearing race gets a light film, bearing is packed, and a few scoops with a finger to put a little extra grease inside the hub area - mostly to clear out the extra from the bearing packing tool. Not too much, not too little.



New wheel seals got knocked in place and a light film of grease helps the seal get into place without catching on the axle.





Anything can be a decent seal installer if you try hard enough..

After getting the rotors installed on the axle and the axle nut tightened, I moved on to checking rotor runout.



The (flawed) method I used to turn these two road side rotors resulted in a maximum runout of around 0.004". I'll try to mount the curb side rotors a little more precisely when I turn them in a couple days.

The calipers slide on next, I ended up finding a permatex caliper lubricant. I'll see how it performs, it can always be changed later pretty easily.



Pads and other hardware installed and it's finally starting to look like a proper brake system again.



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Old 10-07-2022, 10:57 AM   #14
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Cool project and great problem solving!
Good job keeping old technology working!
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Old 10-08-2022, 10:51 AM   #15
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A few days ago I was able to get out and install the rotors and rebuilt calipers. I took a few pictures during the process that I will try to turn into some coherent order of operations here. As anyone that has done a wheel bearing job knows, even with the best intentions it can get greasy so I didn't pick up the phone for pictures every time I thought about it.

I used a bearing packing tool that easily and fully packs a roller bearing in a few seconds. They work well and save a huge amount of time and mess when there are eight bearings to clean, inspect and pack. The bearing race gets a light film, bearing is packed, and a few scoops with a finger to put a little extra grease inside the hub area - mostly to clear out the extra from the bearing packing tool. Not too much, not too little.



New wheel seals got knocked in place and a light film of grease helps the seal get into place without catching on the axle.





Anything can be a decent seal installer if you try hard enough..

After getting the rotors installed on the axle and the axle nut tightened, I moved on to checking rotor runout.



The (flawed) method I used to turn these two road side rotors resulted in a maximum runout of around 0.004". I'll try to mount the curb side rotors a little more precisely when I turn them in a couple days.

Pads and other hardware installed and it's finally starting to look like a proper brake system again.
The best way to turn rotors/drums would be to build a tool that indexes and mounts the disk on the lathe using the bearing bore as the ref CL. Then all machining would be done ref to the rotational axis and runout would be exact. If you have the type of rotor that is a simple disk using the bolt circle or index at the hub use those ref points to make a true CL.


found this interesting slide show online that explains in detail with good drawings, would be worth d/l and put in the archives under tech ref section or similar

https://slideplayer.com/slide/5806326/
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Old 10-11-2022, 09:32 PM   #16
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The Hydrastar 1600 is made by Carlisle. Andy sold me one in 2010 and knock on wood it has performed well.
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