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TFX gear/throttle control adjustment


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Long story short, old gearbox and drive plate chewed themselves to pieces, had an engineer come out and replace both. The old one was a PRM80 (which for all this time I have though was a 120, because 120 was the first 3 digits on the serial plate) which was replaced with a brand new PRM90. 

 

Reading through the manual, it states the gear cable for this model should be set so it pushes the gearbox selector leaver all the way to the stop in both directions. The current adjustment only allows it to go most of the way in forwards and stops about 10mm short in reverse. 

 

I'm not sure of the exact model of the TFX control leaver and I've not actually been able to find any manuals for anything of use to see how to adjust the amount of movement of the gear cable in each direction. Looking at the control I can't see any obvious way of doing it either, any help muchly appreciated! 

 

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You're already adjusted for maximum travel at the lever. (outer of two holes)

 

Othe way of increasing travel is to shorten the lever at the gearbox end.  Are you sure the gearbox lever goes to a stop? On the (few!) PRMs I've seen, the gearbox lever moves to engage gear, then goes loose, which gives a bit of leeway on cable adjustment. If a cable is adjusted to push/pull against a stop, very slightly too much movement will wreck the cable in fairly short order.

 

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Moving the gearbox lever by hand in either direction, you can feel when it has engaged and, as you say, when you push it further there's an extra bit of travel which causes the lever to move forwards or backwards as far as it can go, and also pushes the lever outwards away from the body of the gearbox.

When I operate the control in forward or reverse I now have it adjusted so when I pop off the cable attachment, I can still move the gearbox lever a short distance to the end of its maximum travel, which is as you have suggested sounds correct. 

 

It was the bit in the manual which had me questioning if it was set up correctly as it suggests:

 

"Care must be taken to ensure that the cable moves the gearbox operating lever approximately 2mm short of its forwards or backwards travel, to prevent the lever being brought hard-up against its end stop with every gear shift. This does not apply to PRM60/90/125 which must be adjusted against the stop in both directions. Failure to correctly adjust the shift lever may result in premature wear to the drive train and gearbox failure. 

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The PRM 90 is a mechanical cone clutch. If there is any loss of movement on the gearbox leaver when it is in either forward or reverse the danger is that the cone will be slipping and wearing all the time.

 

Shorten the distance from the center of the gear lever to the attachment of the cable end by drilling another hole. 

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There's actually another hole already on the gearbox lever. I changed it over to this one, but even with micro adjustments of one turn on the cable attachment, I can feel resistance on the control lever in either forward or reverse, I can't get it to eliminate both. As Iain said above, I don't really like the idea of that much strain or compression on the gear cable with every change. So I guess I get a choice of either prematurely wrecking the gearbox or having to regularly replace gear cables. 

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2 hours ago, Rumsky said:

There's actually another hole already on the gearbox lever. I changed it over to this one, but even with micro adjustments of one turn on the cable attachment, I can feel resistance on the control lever in either forward or reverse, I can't get it to eliminate both. As Iain said above, I don't really like the idea of that much strain or compression on the gear cable with every change. So I guess I get a choice of either prematurely wrecking the gearbox or having to regularly replace gear cables. 

 

Try it on the short throw pin position on the morse control and the short throw hole on the gearbox lever.

 

You'll probably have to do a lot of screw adjustment, but if it doesn't work on morse long throw and gearbox short throw it's worth a try.

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Depending upon access a mild steel gear lever should not be that hard to drill for a better hole placement unless the two are so close together you can't get another one in.

 

I don't see how not going to full travel on the ever will wreck the gearbox as long as the lever is in the slack area beyond the gear selection. Admittedly the slack might et taken up as the clutches wear and cause slip that would wreck the clutches so if the slack was taken up it would be time to think again.

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I don't really fancy drilling any extra holes at the minute and invalidating the warranty seeing as it's a brand new box. I tried putting the connectors on the two inside holes, still doesn't comfortably hold it up against the stop. I've put it back on outside hole of morse control and inside hole of gear lever and fine tuned it as best I can so the cable doesn't feel like it getting squished or stretched too much. When put into forward and reverse I can feel a tiny bit of wiggle on the ball and socket connector on the gearbox lever, so hopefully this means the cable isn't getting abused too much. 

Edited by Rumsky
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When I had a PRM120, I gave up trying to get everything perfectly adjusted in both forward and reverse.  I made sure that the forward adjustment was best as it most used. I also got into the habit of taking the control beyond the idle position every time I put it into gear, so that all the slack was taken up, and the gearbox lever was against the stop. I still do it even though I have changed the box for a 150!

Richard 

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