Wondering why it jumps out of gear.

[kshansen]

We have a Yale KGP51AT-40 S/N 551398

Can't believe the local dealer says parts are not available

It has been jumping out of low forward for a year or two, anyone have some ideas?

Below is a picture of the gears in the transmission, anything look out of the ordinary?



Have been told several times over the last 10 years that a newer one has been approved in the budget. Maybe I should have been dumpster diving for deposit bottles all these years could have purchased a new one by now!

 

[old-iron-habit]

Looks like if it stops in the right spot it won't even move.

 

[Nige]

I think I can trump that. We had a 789 the other week that wouldn't build air. The initial diagnosis was a seized air compressor but when the compressor was pulled out the boys discovered that the idler gear between the crankshaft and the compressor drive gear had no teeth on it whatsoever............l
The best part was that the crankshaft gear didn't have as much as a scratch on any of the teeth.

 

[JDOFMEMI]

Looks like a visit to a scrap yard is in order. Drop a whole "new to you" tranny in it instead of hunting for ghost gears.

 

[JDOFMEMI]

I think I can trump that. We had a 789 the other week that wouldn't build air. The initial diagnosis was a seized air compressor but when the compressor was pulled out the boys discovered that the idler gear between the crankshaft and the compressor drive gear had no teeth on it whatsoever............l
The best part was that the crankshaft gear didn't have as much as a scratch on any of the teeth.

I would count that a a very lucky find. Did you decide to buy a lottery ticket after that one?

 

[Delmer]

Is that frosting and sparkles? Are you secretly practicing to be a cupcake artist?

 

[overworked]

Well looks like it is low on oil?.

 

[lantraxco]

Hydrolube, that is mostly water and air with a bit of gucky grease and rust flakes for giggles.

Build those teeth back up with some modified stainless, Eutectic 680 or similar, grind them into shape, or find a good machinist, put some good old roller lube in there, LOL.

 

[mitch504]

that's just those tapered gears, designed to take the place of synchronizers.

 

[Nige]

The best part of it is I now have to make a plan to inspect 34 engines in service using a borescope to see if we can see any initial signs of the same failure mode on any others, starting with those engines we've already had rebuilt and where the gear was reused, many of which are well past 20k hours by now. Apparently it's a "known problem" but the failure mode is so random that there is no official service support, just an agreement to support any engine where this gear fails. Neither is there a way of predicting it from oil sampling, but we're planning on fitting a mag plug into the oil pan just below where this gear runs in case it might just pick up some fragments and give us a heads up ........

The other issue is that if the gear fails the particles that air produced from the initial stages of the failure get sucked up by the oil pump and scratch the crankshaft bearings, so that's engine out time. Even if it can be picked up at any early stage the air compressor, fan drive, aux water pump, front engine mount, and crankshaft damper have to come off just to get at 2 of the 3 bolts that hold the shaft for the idler gear in place. Once the shaft is out the gear will slide sideways then come out the hole where the air compressor mounts.

 

[Nige]

A large handful of these is what came out of the oil pan ...........

 

[overworked]

I have seen that before in a 3176C, loose idler shaft bolts in that case, wallowed out the block where shaft sits in.

 

[Nige]

Nothing loose, no bearings worn out, just the teeth totally missing off one gear in a set of 3 ..................

 

[lantraxco]

Too hard, or not hard enough.. weird.

Nige, what's your sampling interval?

 

[mitch504]

Hey Nige,

Maybe you could grind that gear smooth, er, smoother, then wrap a bunch of layers of old inner tube around it, then patent it as a "friction compressor drive", no wait, a silent compressor drive?

 

[overworked]

Like you said Nige, fatigue. Compressor surely been changed several times, crank maybe reworked or replaced at rebuild? Overworked

 

[lantraxco]

Reminds me of a Deutz engine in the old Terex artics, guy laid one over, filled the air compressor with oil... the drive gear had a torque limiting setup with a large belleville washer, when the compressor hydro-locked the clutch popped over, saved the whole gear train from catastrophic failure. Sometimes ya just gotta love those crazy Germans and their over engineering.

 

[Nige]

Nothing so exotic. Rather than being a forging or a milled blank it's a powdered metal gear, made in a press. Every so often one comes out of the mould that hasn't been squeezed quite tight enough.

 

[Nige]

Too hard, or not hard enough.. weird.

Nige, what's your sampling interval?

250 hour oil sample interval. The only one that showed a jump in iron, and even then it still wasn't enough to trigger a monitor compartment alarm, was taken 5 days before all the teeth landed in the oil pan.

 

[Nige]

Like you said Nige, fatigue. Compressor surely been changed several times, crank maybe reworked or replaced at rebuild? Overworked

Cranks are all original. Never replaced a single one out of all the fleet, well so far anyway.........air compressors we have very little trouble with, despite the engines being air start.