80 series CDL SWITCH TRANNY (1 Viewer)

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Hi all,
I recently just installed a center differential lock switch it went in very smooth I took the truck out for a ride and I noticed it was shifting hard when I got it home the transmission fluid smelt burnt could this be a coincidence or is the switch directly involved with this?
Should I change the fluid?
I have no history of fluid issues
93 LC 80 series
 
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Apache Junction, AZ
Hi all,
I recently just installed a center differential lock switch. It went in very smooth. I took the truck out for a ride and I noticed it was shifting hard. When I got it home, the transmission fluid smelt burnt. Could this be a coincidence or is the switch directly involved with this?
Should I change the fluid?
I have no history of fluid issues
93 LC 80 series
 
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Jul 26, 2020
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642
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Juneau, Alaska
The switch should only actuate the center diff lock. Need more information.

How was the truck driven before installation? Daily? Rarely?

How did you drive it after installing the switch - did you engage the center differential, or just install it and drive like normal without pressing the new button?

Did you smell the ATF specifically, or just noticed a smell in general?

Did you do anything else recently?

You say no history of fluid issues, but do you have a history of fluid service? Is the transmission fluid old? Have you checked the fluid level in the proper manner?
 
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I have not done anything else!
No fluid service history
I rarely drive it 2k a year. I have it 2 years

After I installed it I was engaging switch in and out.

I pulled dipstick out and it smelt like burning rubber no codes on dash. Fluid was above hot line.

Switch works I tested it by turning in circle no binding when I shut it off.
 
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So the fluid is of unknown age, and the truck doesn’t get driven much?

Did you check the fluid level after a full warm-up, with the engine still running?

Hopefully we can help you get to the bottom of this, but in your position, I would first do a few drain & fills of the trans fluid to gently get new stuff in there with some driving time (do not have it “flushed”). Who knows if it will help or fix the issue, but it sounds like the current stuff is cooked to some degree, and likely old.
 
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So the fluid is of unknown age, and the truck doesn’t get driven much?

Did you check the fluid level after a full warm-up, with the engine still running?

Hopefully we can help you get to the bottom of this, but in your position, I would first do a few drain & fills of the trans fluid to gently get new stuff in there with some driving time (do not have it “flushed”). Who knows if it will help or fix the issue, but it sounds like the current stuff is cooked to some degree.
Fluid is unknown and truck does not get driven that much!
I checked fluid with engine warm and engine off.
 
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Truck should be warmed up & running when checking transmission fluid, on level ground & in park - I would do it again to get a better idea of fluid level. If it’s correct, I would still drain & refill with correct fluid a few times as mentioned, to offset the old stuff, driving a while in between drains. Hopefully that’s all it is (old fluid, low fluid, or both) and there’s no damage, but one step at a time

Is there any other relevant history you can tell us? I assume you didn’t notice this before?
 
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Truck should be warmed up & running when checking transmission fluid, on level ground & in park - I would do it again to get a better idea of fluid level. If it’s correct, I would still drain & refill with correct fluid a few times as mentioned, to offset the old stuff, driving a while in between drains. Hopefully that’s all it is (old fluid, low fluid, or both) and there’s no damage, but one step at a time

Is there any other relevant history you can tell us? I assume you didn’t notice this before?
No I did not notice this at all kind of annoying 2 pick up on it after a mod was done .Iam going2 do fluid change when I get home.
Thank-you
 
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Strange just finished fluid change I think I had too much fluid in there it was at the hot mark after lc sat 14 hrs, anyway I did change drove 11 miles and she is shifting great ran it into low as well, shifted fine!!


Any explanation?
Can fluid turn from sitting?
It smelt bbq burnt but was red!!
Confused as always
I did not touch the CDL switch.
 
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Had you started the engine before you checked it?

Anyway, too much fluid can cause problems, just like too little. My guess is the fluid was old and essentially worn out, not providing proper lubrication, and perhaps the level was wrong too - now that you have the correct level and at least some fresh fluid, the transmission is happier. I would drive it more often and do a couple more drain & fills over a few weeks or so, to replace more of the old fluid that’s still in there.

I don’t have a scientific explanation off-hand, but generally speaking, yes automotive fluids can and do slowly degrade over time when sitting
 
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Iam ignorant I apologize, it is coincidence that I installed the CDL switch?
Is there a way it could be responsible for this?
 
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You’d have to get an expert to chime in, but I don’t really see how, as all it’s used for is locking & unlocking the center diff.

If you drove on dry pavement with it locked, and were turning a bunch (which you should not do) it might be able to put enough stress on the driveline to eventually heat the trans more than usual? But that would be due to the way it was driven, not the switch itself. Even then, I don’t know how likely that is unless it was prolonged. It’s probably just coincidental timing.
 
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