question MB Jeep Gearbox

[KMF]

I have a 42 Jeep. It has a problem with the gearbox. It is jumping out of second gear when on the over run, it does not do this all the time but it does do it. Whilst slowing down from third, then into second and slowing down it sometimes jumps out of second gear. Is this a common problem? Does it mean the gearbox is ready for a rebuild? I have been told that it just a common problem that Jeeps suffer from. Any coments are welcome

[Willyslancs]

mine use to jump out of top mate , till it was rebuilt,been ok since (not much fun driving from the lakes , whilst holding it in gear).....

[Nick Johns]

If it only occasionly happens its usually caused by worn or weak syncro unit, or could be a broken selector spring but first worth checking the mainshaft nut. Remove the PTO cover on back of the transfer box and check if there is any end float in the mainshaft gear, can you detect any movement pulling/pushing on the the gear, if so remove the split pin and see if the nut will tighten further. there should be no perceptable fore & aft movement. As bearings and shafts wear it allows end float to develop in the mainshaft which can cause the selector to come out of gear. If this is not the case alas a gearbox overhaul is required

Edited October 20, 2010 by Nick Johns

[deadline]

If its popping out of gear something is loose (worn). Shift forks (bent or the pads are worn) is also a common cause.

 

My tranny was popping out of 2nd I did three things (I have no idea which one fixed it, but it is fixed now)

 

1 New input shaft

2 New small parts kit

3 New mainshaft

 

I measured the shafts as per the TM and both were way out of spec (the previous owner had a bushing in the input shaft). Now I am good in all gears.

[deadline]

If it only occasionly happens its usually caused by worn or weak syncro unit, or could be a broken selector spring but first worth checking the mainshaft nut. Remove the PTO cover on back of the transfer box and check if there is any end float in the mainshaft gear, can you detect any movement pulling/pushing on the the gear, if so remove the split pin and see if the nut will tighten further. there should be no perceptable fore & aft movement. As bearings and thrusts wear it allows end float to develop in the mainshaft which can cause the selector to come out of gear. If this is not the case alas a gearbox overhaul is required

 

There are no thrust washers on the input/main shaft. The only wear point is the main shaft where the tip goes into the input shaft (the 13 needle bearings). The only thrust washers are on the idler/counter shaft (at the bottom of the tranny).

 

The TM lists the most common causes for popping out of second gear:

Bent fork

Weak poppet sprint

Worn Gear

 

But to add to that any part that touches those is worth looking at (ie a shift rail may have worn ridges at the shift detents, the spines on the gear where it contacts the main shaft might be worn etc).