The SL3 and LM100 are manually controlled boxes, readily identified by having a long gear lever which is attached to the selector shaft externally, immediately
by the side of the gearbox casing. The SL3 is the first version of the box; the LM100 the later version. Most faults and fixes are the same for both, unless stated.
The LH150 is hydraulically controlled and has a short selector lever secured by four small screws, to which (typically) a Morse type control cable will be attached.
Roughly in order of occurrence -----
Slipping in reverse. SL3 and LM100 Generally, unless caught early, you will be looking at having to replace the brake band. The friction lining is very thin and if there has been any degree of prolonged slippage will typically have worn through to the metal at the 'half past' position.
It is not entirely uncommon to find the reverse band lining has completely delaminated from the metal backing. In this event, replacement is the only option.
To adjust -- SL3 and LM100. Remove gearbox top cover. The reverse band selector lever is the one closest to the edge of the casing. Undo the locknut on the actuating roller and adjust the roller outward toward the lever. Adjust in small increments. It should not be necessary to use excessive force on the gear lever to engage the gear. When neutral is selected, the reverse brake band must not be binding on the drum. Tighten the roller locknut once you have the desired adjustment.
If adjustment does not produce a result, or you find the band is already adjusted as fully as possible then replacement is the only option. On both the SL3 and LM100 this necessitates removal of the box and a full strip down of the reversing gearbox.
LH150 Generally, the hydraulic actuation of the brake band takes care of any wear automatically, so if it starts slipping it is usually game over. If however you want to try adjusting the band it is fairly simple. Before starting the job ensure you have a new top cover joint to hand. The joint is an integral part of the functioning of the hydraulic system and while you may get away with re-using the existing piece, you don't want to count on it. Never use any form of sealant or gasket compound when replacing the LH150 top cover as there is a danger any excess will find its way into the hydraulic circuit and cause problems.
You will see a small dome on the cover of ther LH150; it is this area within you will be looking at to complete the adjustment. Remove the top cover and old joint. Take care not to allow any dirt to enter any of the hydraulic passages. You will see the reverse adjustment thread and locknut pointing upward. Using a well fitting screwdriver in the slot at the top of the thread, hold the thread still and turn the nut clockwise until you feel the band has tightened up against the drum. Next, again holding the thread still, slacken off the nut approximately three and a half to four full turns. This completes the adjustment. As with the manual gearbox, if you are able to see that the lining has delaminated from the backing then replacement is the only option.
Replacement of the brake band on the LH150 requires removal of the gearbox, but not a full strip down.
Slipping in Ahead. SL3 and LM100. Usually a sign of a tired ahead clutch cone, but you have nothing to lose by checking the adjustment. Remove the box top cover and this time you are looking at the inner selector lever on the cross shaft, This lever is used to obtain neutral by pulling the clutch cone out of engagement with the drum. Slacken the roller locknut and adjust the roller inwards toward the cross shaft. Ensure the ahead cone is not binding when neutral is selected. Note -- the manufacturing tolerance of various parts of these boxes seems to have varied considerably and you may find there is no further adjustment to be had. In this case, or if an adjustment has not produced a result, then clutch cone replacement is going to be the answer. This is a box out and full strip job.
LH150 If your LH150 is slipping in ahead then almost always it will be a case of replacing the clutch cone. There is an adjustment for the ahead / neutral piston within the box but it would be very unusual were this the issue. If you do want to check this adjustment, remove the top cover (see note above regarding the joint). The lever and piston are to be found in the top rear left hand corner of the box. To check the clearance between the piston pushrod and the lever, first ensure the piston is fully home within its bore. You may find it easier to push it fully home if you remove the hydraulic test point plug in the middle of the piston bore rear cover on the outside of the box. The gap between the lever and pushrod should be 2.5mm. If adjustment is needed, take care to have well fitting spanners as required.
Stuck in Ahead. SL3 and LM100. Usually, just one of two causes. If the box has been unused for some time and moisture has been present within the box, the ahead cone lining may have rusted to the drum. This is a case where you may or may not get lucky. Run the engine up to temperature (remember the prop is turning) and try selecting neutral. Do not use excessive force on the gear lever -- you may break the selector roller). Give it several goes; if it comes free then that's it - job done. If that does not work, drain the oil from the box and try filling it to the top with diesel. Leave to soak for a day or two, drain and try again. For the purpose of trying if it has worked you may as well put the old oil back in (to the level on the stick). If you have a result, then drain the oil and replace with fresh. If this shows signs of residual diesel after having run, drain and replace until just clean oil emerges. If you are unable to get it free, then it's box out and a complete strip down.
The other typical cause of this failure is when the ahead cone lining starts to fragment. Pieces of lining may become wedged between the remainder of the lining and the drum, such that even though the selector lever pulls the cone to the neutral position, drive is still transmitted.If you go on to select reverse, it is likely the engine will stall. Sometimes, if it is a disintegrating lining the symptom may disappear if a piece that has been wedged is dislodged and falls into the main part of the gearbox. This is not a fix. Once the linings start to disintegrate it is only a matter of time before the problem reoccurs. The only fix is cone renewal, which requires box removal and a full strip down.
LH150 Normally, the cause will be as for the manual boxes above and the solution the same. The classic symptom with the LH150 is stalling of the engine when reverse is selected. As the LH150 is hydraulically actuated there is however one additional thing to look for. If it is stuck in ahead and there is no perceptible effect if reverse is engaged, this indicates a lack of hydraulic pressure. Check the oil level and if low, top up to the mark and try again. Generally, the hydraulic aspect of the LH150 is pretty trouble free, so it will be unusual if this is the cause of the problem.
Mechanical Noise, particularly in reverse. All versions -- all these boxes are relatively agricultural in terms of their construction and decades of use will inevitably give rise to wear and a degree of noise. This is usually most noticeable when reverse is engaged. Selection of reverse brings the clutch hub planetary gears into play and a combination of the engagement of the straight cut gears running on (likely) slightly worn bushes on a hub which itself is likely running on worn bushes is a recipe for added noise. The good news is that generally, the box will continue running and functioning perfectly well for a considerable period like this. Unless absolutely excessive, or unless a sudden new noise has appeared, we recommend just living with this issue until such time as the box may need attention for something else. Important ! Never use any additives in the reversing box to try and fix the noise -- they may react with the friction linings, leading to glazing and a loss of drive.
Reduction Box Output Flange Problems. SL3. The SL3 differs from the other boxes here in having an output flange that is mounted on a parallel shaft of a smaller diameter than the later boxes. The nut that secures the output flange also serves to tension the thrust bearing which sits behind the oil seal. Problems here tend to be inter-related and the sooner repair action is taken the better the chance of preventing further damage.
Leaking oil seal. This may simply be due to age. Fixable externally. Uncouple the propshaft flange; make a tool to hold the output flange still and then undo the centre retaining nut. Remove the flange and the seal is accessible. It is in the course of doing this job you will become aware of other issues that may be present. Before undoing the centre retaining nut, grasp the flange and check for any lateral movement. A very small amount is not unusual given the age of the box and will usually signify a worn thrust bearing. Ideally, get it fixed as any lateral movement will shorten the life of the oil seal, but if it is not immediately practical to make a repair, then providing the movement is only very slight you have a little breathing space.
Generally peculiar to the SL3 assembly is play due to wear between the output flange and the shaft. (i.e. the flange rocking on the shaft, rather than the flange and shaft together rocking in the thrust bearing) If the play is purely confined to a rotational slackness, this may be down to a combination of inadequately tightened end nut and worn Woodruff Key and may be repaired externally. If however the flange is generally slack on the shaft, this requires prompt rectification; it is not uncommon for the shaft to break on these boxes. This will require the dismantling of the reduction box and an assessment from a suitable engineering shop about the best way forward. (Or we are able to supply a new custom made shaft, to order). If you need to undertake this job, it is definitely time to replace the thrust bearing.
Loosening of flange to flange coupling bolts. Over time, we have heard from various customers of ongoing issues regarding couplings loosening off. Four steps to rectify this. First - check for and fix any of the issues mentioned above. Second - with the propshaft disconnected, check for excess lateral movement of the shaft. Resolve if present. (not applicable if a proper external thrust bearing is fitted). Third -- ensure correct alignment of the two flanges. This means they should mate exactly; completely flat, face to face. If you are unable to push the bolts through the two flanges all the way, by hand, they are not right. Using a flexible coupling is not an acceptable substitute for correct initial alignment. Fourth -- use new fastenings. Correct new bolts and locknuts just make sense -- the originals have likely done over 50 years and been on and off who knows how often.
LM100 and LH150 The reduction box used with these gearboxes is a beefed up version of the unit above, with the output flange being a taper fit onto a stronger shaft and with bigger bearings. There is a double oil seal arrangement, but generally with this later version if it has got to oil leak time it will be ready for a general overhaul. The exception may be where the box has been unused for a long period and moisture may have got into the leather seal lips and corroded the seal land. Either way, it's a strip down. One thing it does share with the earlier box is the requirement for correct alignment (see above).
Gradual Oil Loss. All versions. All versions of the reversing gearbox when fitted with a reduction box share a similar set up; the mainshaft passes through a bearing in the casing and a seal land and oil seal are fitted on the outer side of the bearing. Age, play in the shaft and sometimes moisture induced corrosion can all take their toll on this seal, which if it starts to fail will allow migration of oil from the reversing to the reduction box. It is generally a very slow process and most people comfortably live with it until a general overhaul is undertaken. Manage the situation by keeping an eye on the respective oil levels.
Oil Pump Failure / Damage. LH150 only. Being hydraulically actuated, the LH150 has an oil pump fitted low down at the front of the casing. The pump has a protruding shaft and gear which engages a drive gear fitted to the main input gear. The oil pump shaft is a very small item and easily damaged and this inevitably occurs during fitting or removal of the gearbox if care is not taken. When removing or replacing the LH150. it is essential to keep it square to the engine for the first three or four inches of travel. This is to allow the oil pump gear to fully clear its driving gear. If it does not and the box is lifted at an angle, the small shaft gets bent. It might break at that point, or if refitted in bent condition is highly likely to break later on.. If it does break, you will still have forward drive, but no neutral or reverse. Repair / replacement of the oil pump requires removal of the box but not a full stripdown. (in fact, it's one of the easiest jobs on the LH150).
The LH150 is a fairly heavy (abt. 45kg) awkward shape lump to handle and a second pair of hands is useful, especially given the necessity of keeping it square to the engine. If possible, when fitting an LH150 have someone turn the engine slowly, by hand. This helps ensure the two oil pump gears mesh satisfactorily and thereby avoid the bent shaft scenario. If correctly fitted, the box will slide right up to the adaptor flange. Under no circumstances use use the studs / bolts to draw it in. If it has not gone fully home, it is because the oil pump gear has not meshed.
Selector Valve Stiffness. Gear selection problems. LH150 only. First - disconnect the cable control from the gearbox selector lever. You will now be able to establish whether the stiffness is caused by the cable or the selector valve. If it turns out to be the cable, then either find the kink in it, or replace. If your problem has been poor selection of a gear, check the cable is satisfactorily fitted to give a full range of movement.
The LH150 selector valves vary in stiffness of operation. As an almost literal rule of thumb, if you can move the selector lever through its range of travel by pushing it with your thumb, it's in the acceptable ball park. Stiffer than that, or having to tap it with something to get it to move and it needs looking at. They are a precisely machined item, but our experience suggests a degree of individual fettling at the factory, as they definitely vary between different cases. A box in fairly regular use with a nice easy valve action is not likely to stiffen up. Prolonged standing with moisture present may cause issues, or the O ring seals.
The valve spool. is removable externally without any need to remove or strip the gearbox, but if you decide it needs to come out, be sure to have the appropriate new O rings for reassembly first. Generally it is a trouble free item and the only likely reason to remove it is to investigate stiffness. The problem is, of course, that if it is stiff to turn, it will also be stiff to extract. There is a small spring loaded ball bearing seated partly in the spool retaining collar -- take care to catch it before it pings away, never to be seen again. If refitting the valve spool, try it first without the O rings fitted, just to confirm no basic issues between the spool and the bore. It is imperative to offer the spool in squarely and also ensure it is in the correct orientation (location dimples for the spring loaded ball bearing facing downward).
Can I remove the box myself ? Can I fix the box myself ?
Removal. SL3, LM100. Before removing the box, you will need to arrange support for the rear of the engine, as this is normally achieved by the feet on the gearbox itself. If you can reach the gearbox drain plug, time to drain the oil. If you don't, it will drain itself on separation from the engine.
We recommend removing the box complete with its feet, so it is a good idea to slacken the engine front mountings also, to allow the engine to tilt up a little at the flywheel end such that the feet on the gearbox are just clear of the bed. If you have an absolutely rigidly fixed exhaust (not a good idea), this may not be possible without disconnecting the exhaust. With the propshaft disconnected and moved back out of the way, undo the fastenings that secure the gearbox to its adaptor. This is the smaller circle of bolts. The larger circle fastens the adaptor to the flywheel housing. While it is possible to remove the box and adaptor as an assembly, we don't recommend it -- it tends to be markedly more difficult and the only advantage is that if you have not drained the oil, the oil is retained. If you do remove it complete, take care to pull the box back squarely until it is completely free -- you are clearing the adaptor oil seal from the input gear. These boxes are around 25kg - 30kg; heavy enough, but not unmanageable.
Repair. SL3, LM100. Unfortunately, as you will have read above, pretty much all the ailments on these boxes require the stripping of the box. As a very broad guide, if you would be happy changing the clutch on your car, or doing the cam belt, then this box is quite 'doable'. (Clearly a different thing to a clutch or cambelt, but a comparable skill level). If you are going to tackle it, you ideally want the appropriate imperial spanners; circlip pliers; drift set (preferably brass); bearing puller kit; ideally, the means to compress the mainshaft assembly spring pack on reassembly of the whole shaft back into the casing. These items will see the most common repair jobs -- cone and brake band replacement and bearings replacement. Deeper repair, such as planetary gear shafts and bushes often require specific bespoke machining and are generally outside the scope of DIY.
Reduction Box, SL3. Although simpler than the reversing box, repairs here are likely to be more involved, particularly if output shaft wear is present. Additionally, the upper bearing in the reduction box (engages the end of the reversing box mainshaft) is blind and may present challenges in removal.
Removal. LH150. The LH150 with reduction box is a heavy-ish (45kg) awkward lump. As previously mentioned, it is crucial it is withdrawn and replaced squarely.Bearing this in mind, removal is as for the LM100 (above), except you will need to disconnect the selector control cable. The LH150 should always be removed from the adaptor. The presence of the oil pump drive gear within makes it virtually impossible to remove it complete with the adaptor, without significantly damaging something. A second pair of hands is a defininte asset in removing and refitting the LH150. Once removed, take care not to place the box such that the oil pump gear / shaft is damaged.
Repair. LH150. See above for the LM100 and then add in being comfortable fitting pistons and overhauling a brake master cylinder to the skillset. (Again, not directly comparable, but indicative of what you need to be comfortable with). There are two bits of good news with the LH150. If you have been unfortunate and suffered damage to the oil pump, this is easily replaced once the box is out. Likewise, if the reverse brake band has expired, it too may be changed without a full strip down. You need to be reasonably dextrous and used to assembling awkward springy things ! The internal construction of the LH150 differs from the manual boxes, but the essentials of stripping the mainshaft to replace a clutch cone are the same.
All Versions. Having rebuilt numerous boxes of all variants, there is one big 'But' to be mentioned. Combinations of original manufacturing tolerances, wear and slight variations in replacement parts may lead to a situation where although carefully assembled, your repaired box just won't play quite properly. In the workshop, although aggravating perhaps, it's no big deal as we test all the boxes before they go out and make any necessary adjustments. It's not quite so funny if you have struggled to remove and replace the unit in a tight engine space, only to find it's not right. On all the boxes you can torque test the ahead drive to confirm good engagement between cone and drum. On the SL3 and LM100 you may also test the reverse band,
On all versions, it is essential to ensure the clutch cone is able to slide freely on its splines. Exchange cones will typically have a protective paint finish and it may be necessary to remove this on the splined surface. You may find a cone operates more smoothly in one particular orientation on the splines. Although clutch drums are usually re-usable, it is good practice to check that the new cone does not bottom out in the drum and ideally that there is correct contact across the width of the friction lining. Take care to fit the cone withdrawal bearing the right way round and ensure there are no problems with the circlip groove on the end of the cone spigot.
A bit vague ? We hope you find the above useful, but understand you may think it's just a little too generalised and doesn't give a nut and bolt description. That's true, but there is a reason for that. Not to put too fine a point on it, if you need more hand holding to decide whether or not to tackle the box, then it's probably not for you. You are welcome to mail any questions you have and we will happily provide any information we can, but you do need a degree of mechanical experience and skill to make it worth the cost and effort of tackling the job yourself.
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