How to Fix the Infuriating Squeak in a Unimog ALB Modulator
Diagnosing the Squeak: The ALB Linkage
If you drive a Unimog U1300L, you spend a lot of time finding and eliminating noises. I had a high-pitched squeak that was louder than the engine and drove me crazy over every tiny bump. I finally tracked mine down to the ALB Modulator, and here is how I silenced it for good.
My goal is to take it apart and grease everything. Based on the manual it seems like I can take off the “actuating linkage” with no problem. I I had some questions though about some aspects, especially the part with the spring.
Questions I had about Disassembling the ALB Linkage
1. Can I just disassemble this whole thing and then reassemble? Or will I need some special tool to get the spring back on?
Yes you can – no special tools needed. At least, not on mine.
2. Do I need to worry about the spring taking my head off if I unbolt the wrong thing?
No. There was no tension on the spring at all. Check yours though.
3. While I am in there, should I replace anything? Maybe #918 in the diagram – is that a plastic bushing?
Yes, it is a hard plastic bushing. It would be nice to replace the bushings, but I couldn’t find the parts. I could have probably ordered a rebuild kit from Germany or Australia but I didn’t have the time to wait.
4. Lastly, can I accomplish all of this without opening the brake lines – having to bleed?
Yes! No bleeding necessary unless you take apart the modulating valve which is unnecessary for eliminating the noise I had, or servicing the bushings.
What is an ALB Modulator?
The ALB Modulator—short for Automatisch Lastabhängige Bremse (Automatic Load-Dependent Braking) is the mechanical “brain” that prevents your rear wheels from locking up when the truck is empty.
In a heavy-duty vehicle like a Unimog, the weight distribution changes drastically between an empty state and a fully loaded state. Without an ALB, applying full brake pressure while empty would cause the rear tires to lose traction and skid, as there isn’t enough downward force to maintain grip.
The ALB Modulator acts as a variable pressure reducer. It monitors the distance between the vehicle chassis and the rear axle. As you add weight, the suspension compresses, and a mechanical linkage moves a lever on the valve, signaling the modulator to allow higher brake pressure to the rear circuit.
Related Manual Pages
Disassembly
I found that there was play between the spring end and that round bushing (looks like a spool) it attaches too. That means no tension – so I went ahead and took everything apart. I found the squeak was most definitely the big main pivot point. There was a ton of rust on that main (chrome?) pivot rod, so obviously that is where the noise is coming from.
I was told there is a service kit available somewhere but I couldn’t find any of the parts at Expedition Imports, so I am just going to clean up all the rust, repaint, grease it up really well, and put it back together. This isn’t really a precision part – so as long as it doesn’t squeak any more I think it will be fine. Sometimes the time and cost of special ordering parts from Germany just isn’t worth it (for me).
Weirdly one of the balls wouldn’t come out of the end of the adjustment rod. I don’t want to risk breaking or bending it (A new one might be weeks away), so I am just going to pack it with grease and call it a day. I did find much later that there is actually a tiny metal ring inside the ball cavity that seems to be holding in the ball. I don’t know how to release it so I just continued with my plan of packing it with grease.
Reassembly
Here are the parts ready for reassembly. Nothing too interesting here. Just CLR, wire wheel, a sander, and some elbow grease to clean up everything. Then primer, paint, and clear coat. Everything went back together very easily and no complications. If it weren’t for the painting, this project would take about an hour.
The Best Grease for Unimog Bushings: Super Lube
I used Super Lube to grease everything up because “it is the absolute best product for this specific job.” – according to Gemini.
- Plastic Compatible: Super Lube is the “gold standard” for Steel-on-Plastic interactions. The PTFE (Teflon) is incredibly slippery and will eliminate the squeak instantly without swelling the plastic.
- Longevity: Unlike anti-seize or cheap lithium grease, synthetic Super Lube does not dry out or gum up over time. It will stay fluid inside that bushing for years.
- Waterproof: It is excellent at repelling water, which will protect those freshly painted rods from rusting again.
Conclusion
The squeak is gone! This thing is now dead silent. The fact though, that there is no tension on the system makes me think:
- The system is not functional
- The system needs adjustment
- I don’t have enough load on the back of the truck yet to make this system work
- All of the above
I am not really worried about it though, my braking is definitely good. This thing stops on a dime.
I also completely ignored the heart of this system, the brake proportioning valve. That is the rusty thing with brake lines running into it. Expedition Imports does have this part in stock, but it is way too much money to be spending on a part that, to my knowledge, is not broken.
To me, this system seems pretty useless to anyone with a camper. As long as we have our house on the back, our weight will never change. But what do I know?
Parts list – Main Transmission
| Part | Cost | QTY | Source | Photo |
|---|---|---|---|---|
| Super Lube Multi-purpose Synthetic Grease | $10.28 | – | Amazon | |
