Reverse gear is only shifting in one direction

thomashoebus

thomashoebus

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I took out my Hurth (ZF) reverse gear because it didn't shift 1 in 5 times in reverse. In forward there was no problem. I took it all apart and started with replacing the friction discs. Since it was the first time i opened up a reverse gear this looked a good place to start. Everything went fine and now i assembled the gear again and off course i still can't make it shift in the two directions (i began to suspect that the friction discs had nothing to do with it the moment i openend up the gear but the discs were already ordered). Depending how i position the cover plate of the lever it shifts forward but not backward and vice versa. I assume there are some pieces worn out. What should i do replace the shifting fork or should i replace also the shifting cam... At the end of the day i could perhaps better buy a new Hurth / ZF HBW 250. Please some advice on the technical part.
 
When you shift gear are you doing it directly by moving the lever on the gearbox itself, or via the remote lever in the cockpit? If the latter your problem may be the cable.
 
How are the cables? They could be out of adjustment. Maybe the travel lenght has decreased. Could be some loose cable clamps. If these are ok, is the shifter assembled correctly? I had a similar problem with my VP gearbox. A rogue VP dealer in France assembled the shifter with the pivot bolt to the wrong side. The selector shoe was to the rear of the slider instead of at the front where it should be. The result was that you could select reverse, but if you selected forward there was a delay before forward gear engaged. Worth a look if the selector assembly was worked on. Its a selector problem by the sounds of it. Are the pretension spring washers in the vertical shaft OK? If they are broken or weak it will cause problems. I am assuming the Hurth is similar to a VP reverse gearbox
 
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I took out my Hurth (ZF) reverse gear because it didn't shift 1 in 5 times in reverse. In forward there was no problem.

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Could it be the oil? I had a similar experience, changed the oil, careful to use the exact type, problem solved.

I know it's a bit simplistic, and you've probably already done it, (in fact, you must have done if you've had it apart).
 
I shift directly with the shifting lever. Since the gear is not yet installed. The shifting cam is in the right position, I tried it already the other way. There is no oil yet in the gear box could that be the problem. Nevertheless i oiled the parts before installation. The space between selector lever and cover plate is ok as described in the workshop manual. So I'm at a loss here.
 
I'm guessing that by the fact you've got friction disks (clutches) that this is a hydraulic gearbox. So the presence of oil is rather important!
 
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