Cat 140H final drives failing

Oldhx · Oct 14, 2020

Hi Everyone
I have a Cat 140H CCA seriel number that has had numerous final drive failures .
The problem is the planetary gear thrust washers are failing every 2,000 hours . 3 failures in 5,000 hours. 2 on the right hand side and 1 on the left.
I have exhausted any ideas for a explanation and have asked all the gurus that I know.
Has anyone seen this or can help with a logical explanation it would be very much appreciated.
Thanks

Per Eriksson · Oct 14, 2020

Did a quick search and there's not much written on the subject other than they had an issue with the dimensions of the carrier and/or surface finish.
finish 2.5 µm (100 µinch)
minimum width 60.45 ± 0.13 mm (2.38 ± 0.005 inch)
maximum width 62.95 mm (2.48 inch)

Are the carriers replaced on yours?

Oldhx · Oct 14, 2020

Hi Per
One carrier has been replaced 1,000 hours (12 months) ago and after dismantling ,the thrust washers appear to be on the way out already. It is the opposite side (LH final drive)that has failed this time. The carrier on the side that has failed this time has done 10,000hours at least that we know of .
The finish on the carrier where the thrust washer contacts is less than desirable from factory but surely there are thousands with the same finish. The carrier we replaced 1,000 hours ago we know did at least 8,000 Hours service before we replaced it and the finish on the thrust surface was identical to the genuine replacement carrier
Each failure has been identical in its pattern. ALWAYS the thrust washer on the tandem side of thrust. And out of the 3 planetary gears one washer has worn out , the next planetary gear the washer is about to fail and the last gear the washer has slight wear . All washers on the inside thrust (Diff side) are in perfect condition.

Nige · Oct 14, 2020

Has anyone checked the sag in the tandems (fibre bush).?

Oldhx · Oct 14, 2020

The tandem bushes have been replaced and are in good condition. They were actually replaced previous to the first ever failure.
There was no evidence of wear on pivots when changed .
The tandem drive axles have had There cups and cones replaced not from wear but as a precaution.

Cmark · Oct 14, 2020

So you're saying it ran around 8000hrs before the first failure, then multiple failures since?

Just off-hand I'm thinking of maybe some misalignment of the sun gears. Any history of diff repair? Any noise from the diff? How are the transmission oil samples looking?

Oldhx · Oct 14, 2020

The diff was rebuilt 6,000hours before the first failure. ( a piece of tooth on the crown was found in the screen)
I have placed the sun gear which is also the first axle out of the diff back In and there is substantial movement between the differential side gear which has the internal axle spline and the 4 spider gears.
A mirror and torch thru the opposite side where the sun gear (axle) would normally be showed only movement between the 4 spider gears and the side gear.
The side gear doesn’t appear have a located position in any way except the 4 gears on one side and the axle ( sun gear) on the other side holding it up . The side gear does look to have a bronze thrust washers nits outside face against the diff carrier that appears in good condition.
No oil samples have been taken but the screens and trans filter are done each 500 hours.
The screens and filter housing is immaculate until pieces of plastic thrust washer is found.

Oldhx · Oct 14, 2020

Here are 2 images from the previous failure.
It always leaves the washer intact around the roller bearing cage but wears out the area that contacts the gear

Cmark · Oct 15, 2020

I was thinking more along the lines of the entire differential/crownwheel assembly being out of alignment with the final drive sun gears.

For example;
Crownwheel bearings loose?
Diff housing mis-aligned in the case?

The possibility of both final drives suffering from the same unusual failure mode at the same time seems pretty remote. Look for the common denominator.

Nige · Oct 15, 2020

Those photos suggest misalignment to me. If it's not at the tandem end then as my learned colleague above says the diff is the only other alternative, and coincidentally it's the one common thing connected to both final drives. I would suggest that you need to think seriously about pulling it for a look ASAP.

Oldhx · Oct 15, 2020

Thanks for your ideas.
The diff is the common item .
I have tried to find movement in the crown wheel bearings with a bar with only slight backlash felt.
I were not involved during the diff repair 6,000 hours before the first failure so can’t comment on the care taken.
It did cross my mind that maybe debris (rust , dirt etc) was left between the diff carrier and case thru a section only ( not evenly around) which is not allowing the carrier to be square with case when bolted up.
I would think the oring that seals the carrier to case would not be a face seal .
Surely the oring would seal inside the case mating bore .
So if the case was not square with the carrier it would still seal ok and not leak any oil ?
On the other hand , large components usually are a tight fit inside its mating bore so mis-alignment is impossible ?

Nige · Oct 15, 2020

The distance between the mounting flange of the differential on the case and the centreline of the axle shafts is enough that IMHO it would only require a few thousandths out in installation for the alignment of the axle shafts to be off.

Oldhx said:
I would think the oring that seals the carrier to case would not be a face seal .
Surely the oring would seal inside the case mating bore .
So if the case was not square with the carrier it would still seal ok and not leak any oil ?

What if it was mounted with a smear of gasket sealer around the O-Ring.? It most likely wouldn't leak then.

I think you're between a rock and a hard place TBH. much though it pains me to say it the only way to eliminate any possibility of a problem (mis-assembly, misalignment, etc) with the differential is to pull it out and go through it.

Digtressing somewhat. Who else thinks that overhauling a differential at 6000 hours is awful low. Was there any particular reason why it was pulled at that time..?

Oldhx · Oct 15, 2020

True True
It wouldn’t take much to move the axle center line.
The diff was overhauled (I were not involved) because a piece of the crown wheel was found in the suction screen.

Nige · Oct 15, 2020

I wonder what else was put in it besides a replacement crown wheel.? New pinion I hope.?

Also wonder what caused a tooth to break at 6000 hours.? Usually a duff gear will spit a tooth much earlier than that, probably within the 1st 1000 hours or so.

Cmark · Oct 15, 2020

We did a diff rebuild in a 140H CCA at well under 10000hrs. From memory, something caused crownwheel/pinion tooth loss and the resulting carnage actually broke the diff housing.

The CCA 140Hs are Brazilian built. Notorious for poor paint quality and sheet metal that rusts badly even in our subtropical climate. Maybe some of the powertrain components are locally sourced and of questionable quality as well?

Oldhx · Oct 15, 2020

If the diff center(carrier) was slightly out alignment , would the final drive be able to compensate with all the play within the final drive.
The FD carrier fits over the tandem axle spline and a new carrier still has 3 mm of movement at its outer edge
The planetary ring gear has large tooth splines to locate it onto the stub housing and is pushed on by hand and held there by 8 3/8 bolts and is loose also. ( No visible wear)
What I’m saying is there is a lot of movement in the entire unit.
I’m not dismissing your suggestions ( greatfull for the help) but ?
Any idea is more than I have left.

Cmark · Oct 15, 2020

Yes, you're right with all those points but all we can do is consider the facts.

Planet gear thrust washer failure like this is unusual. (In fact I have never seen it before. Hs anyone else?)
Both sides have the same problem.
The only thing in common is the diff.

I'm not saying the problem is definitely in the diff, but I have no better ideas ATM.

Oldhx · Oct 15, 2020

Yes
Yes
And yes again
Thanks for pointing out the rule of troubleshooting Cmark.
Look at the Facts don’t guess !

Oldhx · Oct 15, 2020

If nothing is found to cause the plastic thrust washers failing , does anyone have a opinion on having some Brass ( Bronze, ) thrust washers made and install in place of said genuine washers .

Nige · Oct 16, 2020

Oldhx said:
If nothing is found to cause the plastic thrust washers failing , does anyone have a opinion on having some Brass ( Bronze, ) thrust washers made and install in place of said genuine washers .

That would certainly be a Plan B, and if the misalignment issue is not corrected maybe brass particles would give more advance warning of the thrust washer wear.

As CM rightly pointed out the known facts at this time all point to the diff, at least with a big fat question mark hanging over it. I’d also add that IMHO it is probably not coincidence that the FD issues apparently started after the diff was rebuilt.

Cat 140H final drives failing

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