Unimog 242.121 with brake and ex - Off-Road Forums & Discussion Groups
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post #1 of (permalink) Old 05-18-2010, 12:56 AM Thread Starter
Join Date: May 2010
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Unimog 242.121 with brake and ex

My 424.121 mog has been sat unused for two years now, ( I was away traveling, by boat). Please bear with me whilst I explain the sequence of events;

It started great, however the parking brake seems to have "siezed". By that I mean that the air pressure no longer gets high enough (6bar) to turn out the red light on the dash and release the brakes.

When I started the engine the first time, the throttle stuck full down. I took this opportunity to disconnect the linkage on the right hand side of the engine, lubed it and put it back together. Engine started fine and ran at idle.

Having started the engine with no problems I then shut it down using the button on the cab floor to actuate the exhaust brake and shut the engine off. Thinking it might be a hung valve somewhere in the air brake system I then hooked up my air compressor to first the left hand air tank (that runs the regular brakes) then the smaller tank on the right hand side. (This is when I discovered I can only get just under six bar on my portable compressor, (of course the truck is parked in a corner of my field away from all power etc.).

Tried to shut down using the footswitch/exhaust brake. No reaction, stalled the engine, (easy as the brakes are locked), and investigated the exhaust switch system.
Air switch dismantled, blown through, all ok.
Line followed forward to inside the engine bay, found a pressure switch (marked 0.1 bar-0.5 bar) disconnected the electrical connection on engine bulkhead, cleaned, reinstalled, physical air passage confirmed through the union. followed airlines until they disappear back over the top of the gearbox, under the cab where cannot be traced, but appear to lead to an actuator that can almost be accessed by taking off the panel in the middle of the cab.

Panel off, looking forwards, on the left hand side of the engine is the foot throttle & hand throttle (this is a LHD vehicle) linkage, it passes through the rear of the block, then goes forwards to the fuel p/p.

On starting the engine, starts first hit, but am not able to increase rpm using either the hand or foot throttle, all movement is stopped by this "actuator" on the left hand side of the engine block, in the engine bay, just underneath the panel I have removed.

Sorry for the length of the post, but wanted to include all the details. My questions are;

1. What purpose does this linkage to the exhaust brake perform?
2. How do I get it to release?
3. What is the pressure switch for?
4. Any ideas on how to release the parking brake?
5. Can I start and run the motor once I have tilted the cab forwards?

Thanks for getting this far! Any suggestions greatfuly received.
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