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Cat 938G rough shifting transmission

Nige

Nige

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Jun 22, 2011
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G..G..G..Granville.........!! Fetch your cloth.
Jonathan Wurz said:
Just pressure tested it and I can't find anything leaking. I put a couple psi on it and sprayed it with soap, there was nothing, then I put 30 psi on it and put it in a bucket of water but still nothing. I guess that's out.
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Need to look inside the transmission if that is the case, because if I’m reading it right that tube directly connects to the pump. The only other thing would be to spray both ends with soap with the tube installed and the engine running & the transmission at convert stall to test the integrity of the seals/gaskets at both ends.
 
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Jonathan Wurz

Jonathan Wurz

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Oct 23, 2021
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66
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Montana
HATCHEQUIP said:
Was reading where you stated the foaming wouldnt start until stalled or loading the bucket.
Just thinking
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Either it got worse or I didn't check it enough when I started this thread but right now it will foam if I just let it idle. I can't see the foam in the sight glass until I stop it because there is no movement to get the bubbles into the sight glass. When I stop it, more oil moves into the sight glass and I can see the bubbles.

Or, I can drive it around and get them to move into the sight glass that way. Either way it doesn't seem connected to how hard I work it.

The gauges in the cab don't have numbers but it is in the normal range when I run it. I checked the temp of a fitting with an infrared thermometer when the gauge was at normal and it was between 170 and 180*F
Nige said:
The only other thing would be to spray both ends with soap with the tube installed and the engine running & the transmission at convert stall to test the integrity of the seals/gaskets at both ends.
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What would I see if it is sucking air, can you see the soap disappear? I'm not sure how I would do that since its not really accessible with the cab on it. I could spray it with soap but wouldn't be able to see what is happening.

The seals were new roughly 500 hours ago and they didn't have any trouble sealing on the blanks that I had bolted on.
 
J

JAJ

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Australia
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Owner operator of small fleet
Did you have any luck getting this sorted??
I am having similar ish problem with my 966G, I am pretty sure my problem is TC related but thought I’d see if you worked yours out.
I did have dramas with trans pumps on mine that were being killed by the main implement pump. But I don’t think you are having repeated trans pump failures are you?
 
Jonathan Wurz

Jonathan Wurz

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Oct 23, 2021
Messages
66
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Montana
JAJ said:
Did you have any luck getting this sorted??
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Nope, still has bubbles, I just stopped looking at it.
JAJ said:
But I don’t think you are having repeated trans pump failures are you?
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No, one right after I replaced the bushings and the second died after 50 hours. This one hasn't given any issues.
Never figured out what happened to the second one.
 
J

JAJ

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Joined
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Messages
182
Location
Australia
Occupation
Owner operator of small fleet
Jonathan Wurz said:
Nope, still has bubbles, I just stopped looking at it.

No, one right after I replaced the bushings and the second died after 50 hours. This one hasn't given any issues.
Never figured out what happened to the second one.
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Hey thanks for replying! Yeah ok that’s interesting, I have been doing similar letting it develop and it seemed ok but I’m pretty sure my torque converter has leakage problems now. I haven’t got back to it to finish troubleshooting yet but thought your problem may have led to other ideas to check. You spent a lot of effort trying to get it sorted.

Re pumps that’s good you have that sorted, mine had 5 trans pumps I think it was and two transmission overhauls before I purchased it being told it was good to go. I immediately had dramas and eventually found the shaft on the implement pump was preloading the trans pumps killing them. Anyway long story but sounds like that wasn’t your problem.

Thanks for you reply and best of luck with your machine, hope you get many trouble free hours!!
 
J

JAJ

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Messages
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Australia
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Owner operator of small fleet
Yeah sure I can do that.
You mean the problem and cause for the transmission pumps failing I assume, not the current problem I have?
I haven’t got to the bottom of the current issue yet, I am expecting it might turn out to be follow on damage caused from the pumps.
 
J

JAJ

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Joined
Mar 22, 2022
Messages
182
Location
Australia
Occupation
Owner operator of small fleet
Yeah I absolutely agree. From what I found when I looked up the parts diagrams for a 938g the other night it has a completely different transmission type. IIRC it looked like a countershaft type vs the planetary type in mine.
The pump issue I found could be common to any arrangement that has pumps stacked out on the same drive shaft I think, so that is why I thought I would mention it here in case it might help.

I do think I should start a thread to document what I found with the pumps, it may help someone out there. Cat actually fitted the pump that caused all the problems and subsequently a few people including cat spent a lot of time and money trying to find the “gremlin”.
At the very minimum it would be a good story to discuss and I may sort my current drama in the process.
 
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