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Lister LM100 gearbox slipping in reverse


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A couple of questions about my gearbox, which I suspect is slipping in reverse. Firstly, is the gear ratio the same in forwards and reverse? I measured the prop shaft speed with a laser tachometer and it rotates about 20% slower in reverse than in forwards, in which case it has the same speed as the camshaft.

 

If it is slipping, do I need to adjust the roller that acts on the rockers in the gearbox? How do I know how much?

 

I took the cover plate off and removed the screw from the keyway to try to slide the operating lever across but it won't budge. It feels like there is a lot of force on the rollers preventing any movement. I tried all lever positions. Have I missed something?

 

Cheers,

Joe

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A couple of questions about my gearbox, which I suspect is slipping in reverse. Firstly, is the gear ratio the same in forwards and reverse? I measured the prop shaft speed with a laser tachometer and it rotates about 20% slower in reverse than in forwards, in which case it has the same speed as the camshaft.

 

If it is slipping, do I need to adjust the roller that acts on the rockers in the gearbox? How do I know how much?

 

I took the cover plate off and removed the screw from the keyway to try to slide the operating lever across but it won't budge. It feels like there is a lot of force on the rollers preventing any movement. I tried all lever positions. Have I missed something?

 

Cheers,

Joe

Reverse slip will be caused by a worn out brake band lining or a weak or dislocated brake band tension spring, or too much free play at the reverse roller-lever. The reverse band roller adjustment (clearance) is to stop the band from binding on the drum when forward gear is selected which can cause serious damage. With the gear lever in full forward gear you need to adjust the reverse band lever roller so that there is about an inch backwards and forwards of free play movement at the gear lever knob when the lever is at its full forward position.

Edited by bizzard
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Ok, for that I'll need to draw the operating shaft across so that the rollers are clear of the rockers, but I can't move the shaft at the moment. Having removed the set screw from the casing, should it be free to move when in forwards, or neutral perhaps?

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Ok, for that I'll need to draw the operating shaft across so that the rollers are clear of the rockers, but I can't move the shaft at the moment. Having removed the set screw from the casing, should it be free to move when in forwards, or neutral perhaps?

There's probably wear grooves on the shaft ends that are baulking up in the casing holes. These ends should be oiled now and then. A sharp knock with a mallet should move it. However its only necessary to shift it to make a roller adjustment and both adjustments might be within tolerance.

Forward gear adjustment is checked by there being 1'' play at the lever knob when in full fore gear, no less than1/2''

Reverse band adjustment is best checked by selecting astern gear and and attempting to turn the prop shaft with a long lever or large Stilsons. If the shaft via the gearbox tries to turn the engine as well then the reverse brake band is gripping the drum ok and is unlikely to slip.It is best to lock the engine in some way for this. If it slips around without turning the engine then there's either the band lining is worn down and knackered or adjustment is needed. If only adjustment is needed the reverse lever roller needs screwing out until a firm band to drum grip is gained. But make sure it releases clear of the drum when neutral or forward gear is selected. A very very slight rub is permissable.

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  • 3 weeks later...

As it seems to have a reduction box bolted to the end I very much doubt its 1:1. Chalk mark the gearbox coupling and the flywheel (through the holes in the guard) and turn the engine one complete turn. see how far the gearbox coupling has turned. That should allow you to see if its 2:1 or 3:1 near enough.

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The reduction box is 2:1 as prop shaft speed is the same as cam shaft speed when in forwards (measured with a laser tachometer). My query is because prop shaft speed is about 20% lower than cam shaft speed when it's in reverse, and I'm wondering whether it is meant to be or whether the clutch is slipping.

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