massey 135 Trany slips out of gear

Jeff345 · May 16, 2011

In reverse i cansometime watch the shift lever slowly slide into neutral. Seems like there is presure on the gear. What would cause this? What should hold it in gear?

DavidP, South Wales · May 16, 2011

Hi Jeff,
At the front of the gearbox casing are 3 spring-loaded 'bullets' or plungers which locate in cut-outs in the selector shafts. The spring pressure should hold the gears in engagement. Even bullets with extreme wear will hold engagement.
I suspect that a more likely cause is chamfered wear on the gear teeth so that in effect you have two tapers sliding against eachother under load. If this is the case it has probably been caused by prolonged 'crashig' into reverse. This may have been caused by hard fast gear changing when using a front end loader perhaps.
DavidP, South Wales

Jeff345 · May 17, 2011

Thanks for the responce David. What is the fix? Split the tractor and re-work the gears or pull the top cover, which on this model includes the steering gear. Thanks Jeff

DavidP, South Wales · May 18, 2011

Hi Jeff,
Removal of the steering box cover will allow you to remove the detent springs and plungers. Cover the inside of the casing to ensure that you don't lose any springs or plungers. The plungers should be fairly pointed. If the point has gone that may be part of the problem. You should be able to see the condition of the rail notch as well. Drain the oil and inspect the gears. Engage reverse by moving the RH rail rearwards and observe which gears mesh and the condition of them.
DavidP

Masseynut(Australia) · May 18, 2011

Just to add to David's answer here, there could also some problem with the splined mainshaft.
The splines on the mainshaft are"back-cut" where the first-reverse and 2nd-3rd gears sit respectively, when in their engaged position. The splines on this shaft are back-cut on both sides, so the sliding gear "locks" both in the drive and overdrive positions. The detent plungers don't do the whole job, in stopping the gear from "moving" out of mesh, when either in the loaded or overdrive situation.
I had experience way back with an M.F. 168, four x two speed box. We replaced the mainshaft when rebuilding the transmission, with an aftermarket shaft. The splines were NOT back-cut in production.

The machine "jumped" out of all gears under load. The problem was finally tracked down to this mainshaft.
The back-cutting on the splines is very minimal, and hard to pick-up, but is necessary for the transmission to perform correctly. Has your tractor done a lot of hours? Wear in this area may be the cause of your problem, along with worn detents as well,

my two cents worth,
Evan.

Jeff345 · May 18, 2011

David, I can see some wear on one of the gears through the oil fill plug. If I need to replace some of the gears what does it entail? I would not be doing it for fear that I would mess it up more. Just wanting to have an idea of what would need to be done. Then I could cost it out. Thanks Jeff

DavidP, South Wales · May 20, 2011

Hi Jeff,
I've attached a cut-away image of the 6-speed transmission. This may be helpful. There is very little that can be done without seperating the engine from the gearbox and the gearbox from the centre casing. The 6-speed is straightforward but a good workshop manual is essential. A reasonable range of basic tools is needed as is the necessary lifting tackle, axle stands, blocks of wood etc.
Most parts will be available from non-genuine suppliers. As mentioned, removal of the steering box (it has to come off anyway) will reveal more.
DavidP, South Wales

massey 135 Trany slips out of gear

Jeff345

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