Cause of transmission failure

[Goldnboy 920]

For those who have repaired 8 speed transmissions what items are the source of failure? Forks? Cluster gear? Bearing?

 

Water is obviously enemy #1

Along with no oil as #2

[doc724 925]

My very limited experience is that needle bearings seem to be the weak points.  Seal failure happens first.  Fluid leaks out and dirt gets in.  Not a good combination.  Water incursion is almost always at the shift boot.  They do not last forever and most are rotted out after 15-20 years

[pfrederi 17,741]

  Axle needle bearings !!

[953 nut 55,261]

The other major problem area with transmissions is the nut behind the steering wheel!    AKA the driver.               

Some people seem to want to speed shift these transmissions on the go and end up ruining the 3522 and 3523 gears. This is true of three speed and eight speeds.

[stevasaurus 22,745]

Forks and cluster gear are never the problem.  Shifting on the fly is probably the one thing that ruins these transmissions (grinds the gears).  The major weakness is the hi/low shifter plate...it is thin and can be either bent or broke by shifting on the fly.  The other thing to think about is whether you have an 8 pinion of a 10 pinion differential in that 8 speed transmission.  You did not differentiate.   These guys that are talking about needle bearings are correct, but you are dealing with a transmission that has been around for 50 or 60 years...of course bearings are going to be worn and seals will be old and dry...especially if the horse has been setting. 

[Goldnboy 920]

Thanks this will be helpful when evaluating a roller in the future for a parts machine.

[The Tuul Crib 7,336]

5 hours ago, Goldnboy said:

Thanks this will be helpful when evaluating a roller in the future for a parts machine.

 Here's a pic of my dipstick out of my 312-8 that I just picked up. I called this  tractor my hundred dollar turd but it obviously was abused and sat out in the weather a lot. The dipstick was rusted out really bad so I wasn't sure  if any water got into the transmission. After a couple of diesel fuel fill ups  and drive arounds the trans seems to be ok. The old fluid  didn't have a lot of water in it. So  hopefully he's OK !