Air brake canister 1993 917 AF

[VerMonsterRV]

Another issue has come this morning in my right rear brake.
My truck was parked on a mountain for about 4 days for snowboarding. Snow accumulated to just over 2’/half meter around where it was parked. After I left, I noticed the parking brake would not fully engage. I made it a truck shop where my friend works and they were nice enough to look at it although they would not be able to work on it (they do fleet service only). They did not take anything apart for inspection. But they believe the recent/newer air canister is working. But the service or parking brake is not engaging in the right rear. The mechanic suspected a brake failure but cannot 100% confirm. There is plenty of pad life.

I’m wondering if anyone had a line on replacing any associated hardware, springs, etc. I would likely have a shop service both sides as a preventative maintenance. I’m also very open to feedback/suggestions.

This is my first big diesel truck and very much still on the learning curve.


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I just replaced the drums, wedge units, linings and the actuators. When I removed the wedge units the rear ones were toast, the internal springs were in bits caused by rust. We did the job ourselves. The air canister contacts a rod from the wedge unit, which then forces a "wedge" between the upper and lower cylinders that move the brake shoes in/out. I also noticed that the pivot points for our shoes were pretty stiff, so the spring wasn't returning quickly when the brake was released (once apart I cleaned the rust and greased the pivot points). One thing I found with shops is they are concerned parts will be difficult/time consuming to source (which they are). My thinking with our brakes, the truck is 35 years old and we travel up/down roads that would be fairly dangerous without brakes. Given the shipping time needed I ordered all new parts in preparation. My friend that helped has a 1113 and thought I was going a bit overboard, until we took things apart. I am glad it is all new now.

So, if you can't find a shop, I would order all the parts, then print our the workshop manual for the brake job and walk in with these things in hand. I would bet you would have a much better shot at getting the work done. This is how we got our engine worked on at a Volvo truck dealer a few years ago after many attempts at other shops.

You are correct, you should always do both sides at the same time so there is a good balance. One other thing I learned with our truck is we have the optional 4 wheel parking brake and also load compensation for the rear brakes. I just recently adjusted the rear compensation mechanism as we have replaced the leaf springs which caused less rear service brake braking force since the chassis rides a bit higher from the axle. Just something to try and learn about for your specific truck so you understand your brakes better. Like you, this is our first larger truck and it is definitely a steep learning curve.

 

[Joe917]

If the parking brake is not working properly the rear brakes may need adjustment. Front wheels chocked, parking brake off, neutral. The wheel needs to be lifted off the ground . There is a rubber plug in the dust cover that gives access to the adjuster. While turning the wheel rotate the adjuster with a large slot screwdriver until the brakes start to drag. Back off a bit. repeat on other side.

 

[theangrychicken]

Do you have a line on where you sourced your parts? The shoes look like they have pad life and don’t need to be replaced.
But I’d like to be a able to service/replace anything else within the drums.

Joe, the mechanic at the shop and I talked about adjusting the brakes. But he was thinking there might be a part failure since neither the parking or service brake was moving. He “felt” movement in the canister so he thought that was likely working.


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[theangrychicken]

Do you have a line on where you sourced your parts? The shoes look like they have pad life and don’t need to be replaced.
But I’d like to be a able to service/replace anything else within the drums.

Joe, the mechanic at the shop and I talked about adjusting the brakes. But he was thinking there might be a part failure since neither the parking or service brake was moving. He “felt” movement in the canister so he thought that was likely working.


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[Joe917]

Rob Pickering in Colorado is the only mech in the USA I know that I would trust.
He can order parts for you and get them drop shipped anywhere. It would be worth the time to go to La Junta. Go to the dinosaur tracks in Picket Wire canyon, check out Bent's fort and maybe if you're lucky Rob will take you for a spin in one of the Haggerlands.

Terry Lee Enterprises: Home Page 2014

 

[theangrychicken]

Hey Joe, I would actually love to have someone that knew these rigs go through it, help with repairs, and do preventative maintenance.
But I’ve had near zero luck with communication at that site. I don’t question their knowledge or experience. But it’s a long way travel to get to shop that doesn’t respond or follow up. I simply can’t plan around that.

For this, I’m thinking of scoring the needed parts. Correct me if im wrong, but this is something any truck shop can handle. Im also wondering now if the parts are unique to our brakes? Or is this something most shops might be able to tackle without Benz specific hardware if we aren’t doing drums/rotors?

I’ve actually gotten quite a bit of parts help with Unimogcanada. Have you had any mechanical work done by them before?


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[Joe917]

It is too bad, Rob Pickering is a great mechanic, but he always seems to be a one man show. Once you get to know him you are set. It is a long way to go, if you are ever out that way stop in.
Unimog Canada is Hans Mross in Langley BC. We dropped in on his shop on our way through. Hans is typical German. He would be a great guy to take the Heffalump to.
I have very little faith in "any" truck shop. They often seem to be nothing more than random parts changers.

 

[Neil]

When adjusting the brake shoes be very careful , The adjusters on these drums can be sized and stiff and easily broken.
You should never wind the shoes out against the spring , this is the easiest way to break them.
The easiest way on the rears is to put the parking brake on so the shoes are at their max against the drum . You can then easily wind the adjuster out with no adverse pressure from the springs . Once the adjusters are out , you can take the parking brake off and then you can back off the adjuster until the desired clearance is achieved. By doing it this way you are working with the spring and not against it . Its so much easier and less likely to break the adjuster.
You can do the same on the fronts, but need someone to press the foot brake at the start to get the shoes out to the max
Hope this helps
Neil

 

[where_the_heffalump_roams]

Joe: From what I've read, Rob is a great mechanic and really knows his stuff. I don't contest that at all. I've just had very little luck with communication when trying to make an appointment to come bring my truck to him or when trying to secure parts. He is difficult to reach by phone and email. During the 1-2 times I've received responses, I've not had follow up with request to purchase parts. It's a 1200+ mile drive for me to bring the truck there, with the communication history, it's a bit risky for me.

Neil: That does help somewhat. I've had no past experience with these systems. I'm assuming something internal to the drum brake has failed as there is no service or parking brake activation. The mechanic that looked at it did not want to remove the drums as he was certain this was would be more than a simple adjustment and they would not be able to secure parts or work on my truck. His thought was if the brakes were not moving at all when the parking brake or service brake was applied, an adjustment would not be effective.

So my thought process is this. I'm hoping to find parts to overhaul the brakes at all 4 corners with the expedition of pads/drums as they appear to have plenty of life. Vermonster mentioned encountering a lot of rust/corrison when he serviced his brakes. So it might be proactive to have al the parts to overhaul the brakes while it's on jacks just in case. I'm very open to feedback and thoughts. Thanks!

 

[RoamIt]

Brakes are on my to-do list, setting a baseline for maintenance. If you come across a site that sells the parts for an overhaul ,please share!

 

[VerMonsterRV]

My advice for anyone owning a truck like ours in North America is the get the EPC/WIS off eBay. Usually less than a $10 download. Once you get it installed and used to how it works it is the best money/time you will ever spend on your truck.

With the EPC you will see the parts break down with part numbers. Then use Google to search, you will usually find some OEM parts, and a lot of aftermarket, but usually in Europe. With the WIS you get the workshop manual with not only the process but also needed specialty tools and torque specs.

It is not the easiest software to use but it is all there. Even if you don't plan on doing any of the work yourself a good mechanic that is unfamiliar with the truck will appreciate it. So search the EPC for parts, find them in Europe (or if you're very lucky North America, mainly the engine parts), order them up, print out the section for the repair out of the WIS and present that to a good mechanic. I would bet they would then be willing to work on your truck. Actually ask your friend about this, he may even agree to work on it.

One thing to think about with the brake linings, they need to be riveted on. You will need to know a shop that can do this for you before you start. They are not that common in the USA. I chose where I did the brake refresh so I could be close to a shop to do the relining. I didn't want to ship our shoes out, causing delay and potential loss.

 

[where_the_heffalump_roams]

Vermonster, I've found a few shops that can reline the the pads and I've bought/downloaded that software from eBay. But I'm still trying to access it with my Mac. I do have photos of the brake mechanisms and access to ordering parts through unimog Canada.
But I'm wondering if you would be able to share with the group exactly what parts you purchased when you did your brakes?
A shopping list for those of us who want to refresh our brakes would be awesome and we would really be grateful for the guidance since you have done this recently.

 

[VerMonsterRV]

We are travelling with a friend with a Sprinter. He has a Mac and we got the EPC running on it. I have to say he did have troubles getting it to work as the instructions that were sent to him were wrong. We did get it working, but not using the supplied instructions. We had to use a different virtual machine than what was instructed to get things going.

So for our rear brakes, I replaced the drums, wedge units, linings and air canisters. But you really need to know your specific axle and what part numbers are needed. We have the simplex rear axle and I am not sure how common those are. I know on our truck there are at least 2 different rear brake setups. Also your truck has the factory single rear wheel axle, which may also be slightly different with the brakes. The only way to be sure is to get your VIN into the EPC and lookup your specific brake parts.

For the front axle I replaced the drums, linings, wedge units and rebuilt the original air canisters (just replaced the rubber diaphragm.

You should also replace the shoe return springs.

For us the rear drums/linings are different from the front (some axles use the same drums/linings front/rear). The wedge units were the same front/rear.

As you know I used the DT Spare Parts rear air canisters, the rest of the parts were from a few different suppliers as I had a hard time finding a single source. I didn't go with all OEM as I was trying to keep the cost down (it was still pretty expensive, just less so) and I have had pretty good luck with aftermarket parts. Heck, some of the "aftermarket" parts are the original suppliers to Mercedes.

To add to the list in preparation for problems I would also order a few of the brass air fittings that screw into the air canisters. The rear canisters are aluminum where the brass fitting screws in, ours were a bit corroded ad very difficult to remove (cold chisel, map gas torch and a big hammer). If I would have had spares on had (I have some now) I would have used them.

The reason I replaced the drums was when I removed the fronts to do the wheel bearings (which you should also do if it hasn't been done in a while) the drums were heat checked. You won't know this unless you remove the drums to inspect.

If you replace all these parts then your brakes at the axle will essentially be new. There is still the air system which feeds the canisters but that is a whole other ball of string that I have only recently started to unravel.

 

[where_the_heffalump_roams]

We are travelling with a friend with a Sprinter. He has a Mac and we got the EPC running on it. I have to say he did have troubles getting it to work as the instructions that were sent to him were wrong. We did get it working, but not using the supplied instructions. We had to use a different virtual machine than what was instructed to get things going.

Do you happen to know what he used to get things going?

This morning I got some help pulling the wheel/drum at freight company. The lower piston on the wedge is not activating is likely seized internally. The drum also shows sign of uneven pad were and heat damage. It's actually just a bit warped as well.

I've contacted Hans at unimogcanada and requested new wedges, springs, and drums.
For now, until the parts are received, I'm wondering if that wedge is servicable? If it just be cleaned and refreshed to get working for now that would be great! The guys at the frieght shop did not now how to service those units.

 

[VerMonsterRV]

Do you happen to know what he used to get things going?

This morning I got some help pulling the wheel/drum at freight company. The lower piston on the wedge is not activating is likely seized internally. The drum also shows sign of uneven pad were and heat damage. It's actually just a bit warped as well.

I've contacted Hans at unimogcanada and requested new wedges, springs, and drums.
For now, until the parts are received, I'm wondering if that wedge is servicable? If it just be cleaned and refreshed to get working for now that would be great! The guys at the frieght shop did not now how to service those units.

The instructions that came with his download specified to use a specific virtual machine. Problem was that the instructions mentioned that there were supposed to be specific files in his download which were missing. When I looked into it I found a txt file that had instructions that specified a different virtual machine, and the files were there for that one. So we downloaded it, attached the file and it was working.

If one side of your wedge unit doesn't work my guess is something is broken internally. I don't think Mercedes sells the internals, though I think at one time they rebuilt them. One of my rear brakes did the same thing (the other did even less). Aftermarket ones are not super expensive and I think (though I am not sure) OEM are no longer available. I saved our original front wedge units as they looked ok, though I did replace them with new ones.

Make sure you also get new linings and rivets. If you are replacing those other parts you might as well start with all new.