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Hi, can anyone help. I have a S700 on a Mercedes chassis and have a problem getting 1st gear, the previous owner said he had changed a linkage on the gearbox and since then had trouble getting 1st gear all other gears are ok.
OK this should be pretty easy to fix. The crucial information is that you said "ever since" the previous owner had changed a linkage. In my book, that means he fitted it wrongly. The "left and back" first gear on the Merc box has always been a challenge for most, but it should work perfectly with practice - it isn't faulty by design. If you look at the side of the gear box you will see there are several arms about 6 inches long coming out of the side of the box, attached to rods running forward. If you get somebody to go through the gears (engine not running) while you look, you will see how the mechanism works, and you will see by a process of deduction which arm is responsible for selecting first gear.
The arms are attached to the little shafts that stick out of the box. Those shafts are splined - they have little grooves in them, and the round holes in the arms are similarly grooved where they locate onto the shaft. There is a bolt that attaches the arm to the shaft. It is my theory that the arm has been reattached to the shaft just a single groove (or tooth if you like) either way, incorrectly. So you should loosen the bolt and gently work the arm off the shaft, then relocate it one tooth to the left or right - I can't tell you from memory which way, you will have to do it by trial and error, but it will probably be in the direction which results in the arm traveling further, and thus engaging the gear more fully.
Having moved it one groove, either clockwise or anticlockwise, retighten it, and then jump into the van. Start the engine and depress the clutch, and then select first. You should notice straight away if you have got it right - first should select with a satisfying feel, no grinding of gears, and as you lift the clutch you should feel the power go to the wheels, without it jumping out of gear. If not, repeat the process one groove in the opposite direction. It is unlikely but not impossible, that you may even have to go two grooves - depending on how inaccurately it was originally fitted - but the fact that you say it is a problem selecting first gear, and not that you can't select it at all, indicates that it should only be one groove.
Of course I can't guarantee this fix, but from what you have said, and based on my own experience, it is certainly the favourite thing to try first. It is highly unlikely to be an internal problem in the box.
Somebody else mentioned bushes and it is also correct that the plastic bushes on the linkages can get worn, resulting in a similar problem, but on the basis of how you have described the problem, you should try this first.
If you are not mechanically minded, and in possession of a tool box, or at least a spanner, then just pop into your local or favourite garage and explain the problem, plus my comments, and they should be able to do all this in about 15 minutes.
The arms are attached to the little shafts that stick out of the box. Those shafts are splined - they have little grooves in them, and the round holes in the arms are similarly grooved where they locate onto the shaft. There is a bolt that attaches the arm to the shaft. It is my theory that the arm has been reattached to the shaft just a single groove (or tooth if you like) either way, incorrectly. So you should loosen the bolt and gently work the arm off the shaft, then relocate it one tooth to the left or right - I can't tell you from memory which way, you will have to do it by trial and error, but it will probably be in the direction which results in the arm traveling further, and thus engaging the gear more fully.
Having moved it one groove, either clockwise or anticlockwise, retighten it, and then jump into the van. Start the engine and depress the clutch, and then select first. You should notice straight away if you have got it right - first should select with a satisfying feel, no grinding of gears, and as you lift the clutch you should feel the power go to the wheels, without it jumping out of gear. If not, repeat the process one groove in the opposite direction. It is unlikely but not impossible, that you may even have to go two grooves - depending on how inaccurately it was originally fitted - but the fact that you say it is a problem selecting first gear, and not that you can't select it at all, indicates that it should only be one groove.
Of course I can't guarantee this fix, but from what you have said, and based on my own experience, it is certainly the favourite thing to try first. It is highly unlikely to be an internal problem in the box.
Somebody else mentioned bushes and it is also correct that the plastic bushes on the linkages can get worn, resulting in a similar problem, but on the basis of how you have described the problem, you should try this first.
If you are not mechanically minded, and in possession of a tool box, or at least a spanner, then just pop into your local or favourite garage and explain the problem, plus my comments, and they should be able to do all this in about 15 minutes.
Ron Bentham This is a picture of a 410D box, You can see where the arms attach to the box - the opposite end from where the rods are attached. You can see that moving the arm one groove to the left or right on the little shaft will have quite a big effect - it only has to be one groove out to cause trouble.
Further thoughts. It pays for Merc owners to be familiar with the gear linkage mechanism. Many a holiday has been ruined when after a long trip, especially on rough roads, suddenly you can't get a gear, or any gear, and the stick feels like a bag of spanners. The obvious reaction is that the gearbox is knackered and that this is going to be catastrophically expensive, especially if you are abroad. In fact total gearbox failure is extremely rare, and the Merc gearboxes are as good as the engines - I have run them for 400,000km with nothing more than oil changes.
Further thoughts. It pays for Merc owners to be familiar with the gear linkage mechanism. Many a holiday has been ruined when after a long trip, especially on rough roads, suddenly you can't get a gear, or any gear, and the stick feels like a bag of spanners. The obvious reaction is that the gearbox is knackered and that this is going to be catastrophically expensive, especially if you are abroad. In fact total gearbox failure is extremely rare, and the Merc gearboxes are as good as the engines - I have run them for 400,000km with nothing more than oil changes.
It is the linkages that cause the problems, as I have found out several times over the years. If the gear change is getting stiff, and giving the impression that it just isn't like it used to be, then it is usually just in need of a good clean. It is quite a complex mechanism that converts the movement of the stick into pushing and pulling the lever arms on the side of the gear box. If you look at the pic above, you will see that there is an assembly on top of the box that has the base of the stick sticking up out of it. This assembly contains a lot of levers and linkages that over many years can get very dry and dusty. There is a plastic cover about 3 inches by 2, which when removed exposes the mechanism - photos are hard to come by - it is not shown in the pic above, but if you get under there and have a good look, you will find it. The cover just pops off. Inside of there needs a good clean out and lube. You will be amazed at the difference.
The next problem is the dreaded "knackered box" scare. What has usually happened is that one of the selector arms, as in the photos, has simply worked loose and either started to slip, or even fallen off all together. If you are lucky you will find it still hanging around - if you are unlucky it will be gone, and it's a garage job, but won't be expensive. The problem is that if just one works off or loose, it is likely that the whole mechanism gets out of kilter and you can't select any gear. This happened to me in Italy once and the only gear I could get was third, but it was enough to limp off the autostrada, save myself a hefty fee, and limp to a local garage where they fixed it in 30 mins for 20 euros cash. I could have fixed it myself but it was raining and my back was killing me!
The selector arms attach with a single bolt - as detailed above, and they do have a tendency to work loose over the years. The problem when they come loose is getting them back on in the right position. I am sure there is a Merc workshop manual procedure for this, but out on the road you just have to do it by trial and error. Any decent rescue mechanic should be able to get you going again, especially if he is over 50!
Finally, another lesser known problem is that where the actual gear stick fits onto that stubby stick on top of the box, there is a rubber sleeve fitted to dampen the feel. This can also get very worn after 20 years, and can also create the impression that the box is sloppy and "on the way out" - a new sleeve for a few quid (if you can get one!) and the box feels like new again.
So be familiar with your gear selection mechanism and avoid that sinking feeling if it ever happens to you. It is usually always an easy fix, and of course regular maintenance is also important.
