Transmission Problems

NDT

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With the truck idling in park, the torque converter is transmitting motion to the planetaries in the transmission as well as the transmission oil pump.
Resealing the transmission is not too difficult, remove the transfer first, then slide the transmission back onto a stack of wood.
 

MarcusOReallyus

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It's still leaking after adding more fluid, so a seal must have either dried out or given out. I'm not outfitted to drop a transmission and replace seals, so this will likely go in to a professional. For the time being I'm going to add some stop leak/seal conditioner and hope is slows the leak.
AT-205 might be the ticket for you.

But on another note, I have replaced a transmission in a Ford (can I say that here?) E350, working on a gravel driveway with just jackstands. It can be done.


There isn't any connection between the engine and transmission that would transfer heat from one to the other though?
Yes, there is a very direct connection. The transmission fluid is circulated through a heat exchanger in the radiator, so, once the engine warms up, heat from the radiator will be transferred to the trans fluid and from there to the trans.
 

ezgn

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It's still leaking after adding more fluid, so a seal must have either dried out or given out. I'm not outfitted to drop a transmission and replace seals, so this will likely go in to a professional. For the time being I'm going to add some stop leak/seal conditioner and hope is slows the leak. I was getting close to putting it up on jack stands for the winter anyways to keep the tires from getting flat spots, so this might have to wait till next spring.


Side question, as I got reading into the issue more. Multiple places reccomend letting the engine warm up before taking a reading or trying to shift gears. There isn't any connection between the engine and transmission that would transfer heat from one to the other though? If the trucks just idling, the torque converter hasn't locked up, so nothing is spinning in the transmission, including the transmission oil pump? So how does letting the engine warm up change things?
First off, where is the leak coming from. It must be coming from the transmission pan gasket. That is an easy fix. You should be able to tell where the oil is leaking from. Clean and wash the area from fluid, run the motor and see where the leak is coming from. As the motor and fluid warms up and gets hot the fluid expands thus giving you a higher reading on the dip stick, this is why you get an accurate reading when the engine is at operating temperature. You really need to determine where the fluid is leaking from before you can begin to diagnose a possible solution.
 

cucvrus

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Im sure you know this, but just in case you dont.
When you add fluid start up the truck and move through the gears but dont drive around. I move through each for 3 seconds then back through each to park for 3 seconds before double checking fluid level. You can leave the engine running when you add fluid.

[U]SomeNewGuy[/U] That is a good point. At this point the leak must be stopped and I agree that the transmission has internal issues with seals. I have had it happen several times with the reverse hesitation and inability to smoothly shift into reverse without slamming or not responding at all. Anyway. I always think that it is less expensive and easier to have a transmission refreshed and gone over when small issues arise then it is to run it till it don't move at all. But be that as it may. There are lots of doped up transmissions out there running on borrowed time and will fail when most inconvenient. Don't be one of them owners. Get it fixed and done right the first time. Take Care and Be Safe.
 

Mullaney

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Don't think I am being a smart-a$#, but most dipsticks on GM vehicles actually say "check fluid level when hot". Idling in the driveway will warm it up enough and the fluid should feel warm to the touch.
 

Bob H

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It's still leaking after adding more fluid, so a seal must have either dried out or given out. I'm not outfitted to drop a transmission and replace seals, so this will likely go in to a professional. For the time being I'm going to add some stop leak/seal conditioner and hope is slows the leak. I was getting close to putting it up on jack stands for the winter anyways to keep the tires from getting flat spots, so this might have to wait till next spring.


Side question, as I got reading into the issue more. Multiple places reccomend letting the engine warm up before taking a reading or trying to shift gears. There isn't any connection between the engine and transmission that would transfer heat from one to the other though? If the trucks just idling, the torque converter hasn't locked up, so nothing is spinning in the transmission, including the transmission oil pump? So how does letting the engine warm up change things?
The trans fluid will heat up as the pump circulates the fluid wil the engine idles, trans fluid expands with heat, so at ambient temps a pint low is about right.
I have had vehicles with TH400 transmissions for the last 40+ years. Once I thought I broke one, but it was the torque convertor that I twisted to pieces! Never had one fail on me yet. Just keep the fluid up to spec.
 

ezgn

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Don't think I am being a smart-a$#, but most dipsticks on GM vehicles actually say "check fluid level when hot". Idling in the driveway will warm it up enough and the fluid should feel warm to the touch.
When I check my transmission fluid when it is warm and it reads low, if I don't have any fluid on hand I just drive it until it's hot then check it, problem solved.
 

Skinny

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When I check my transmission fluid when it is warm and it reads low, if I don't have any fluid on hand I just drive it until it's hot then check it, problem solved.
My head hurts now... 🤣

Yeah this isn't rocket science. Warm the truck up, move the shifter thingy around a few times, return it back to it's home, pull the stick. If you put a gallon of fluid in and it's not on the stick then she is very low to the point of not functioning at all. Not much more would come out of the pan during a drain and fill.

You don't have to dive deep into planetary operation and thermodynamics...
 

CivilEGR

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I had a chance to look at it again today. Whatever I put in a few weeks ago is now on the floor. I put another gallon in and let it run for awhile to warm up. It looks like the leak is somewhere around the vacuum modulator or above it where the oil lines to the radiator are. Either way, when it was running it is was just pouring out.
 

ezgn

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I had a chance to look at it again today. Whatever I put in a few weeks ago is now on the floor. I put another gallon in and let it run for awhile to warm up. It looks like the leak is somewhere around the vacuum modulator or above it where the oil lines to the radiator are. Either way, when it was running it is was just pouring out.
I don't think you would lose the same amount of fluid you put in without the engine running from the lines to the radiator. If it is all leaking out from just sitting there than it must be below the top of the fluid pan. You should clean all the fluid off the surrounding area then have someone start putting just enough fluid in until you can isolate the leak. Stay under the truck while fluid is put in slowly until you can determine where the leak is coming from. The vacuum modulator should be checked for the bolt being tight and the seal being in place on the base of the modulator. I take it your sure that all the pan bolts are tight and the leak is not from around the pan gasket?
 

nyoffroad

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I know this is not applicable to the OP's case now but I'm going to tell the story anyway.
Many years ago when I was young and broke I needed a car and couldn't afford much, I found a 73 Duster with a 225 six in it for $75! That was right up my ally, problem was it not only smoke badly but blew oil out the exhaust! It ran pretty good so I figured cheapest thing to do is an oil change I ended up getting a couple GALLONS of oil out of it instead of the 5 quarts it should've had. Turned the previous owner lost the dipstick and replaced it with one from a Ford. So what I'm saying if the fluid level is low but the vehicle runs/moves ok , check the DIPSTICK!
 

Mullaney

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I know this is not applicable to the OP's case now but I'm going to tell the story anyway.
Many years ago when I was young and broke I needed a car and couldn't afford much, I found a 73 Duster with a 225 six in it for $75! That was right up my ally, problem was it not only smoke badly but blew oil out the exhaust! It ran pretty good so I figured cheapest thing to do is an oil change I ended up getting a couple GALLONS of oil out of it instead of the 5 quarts it should've had. Turned the previous owner lost the dipstick and replaced it with one from a Ford. So what I'm saying if the fluid level is low but the vehicle runs/moves ok , check the DIPSTICK!
.
I wonder how many hundred times that has happened?

Similar situation that was on a friend's car and the transmission dipstick on the GM TH-350 had a little goofy cover. It was tack welded at the factory and the weld had broken. Cap (dipstick cover) slid up the the "ring" where you pull it out. Dipstick was always about an inch too far down into the pan.

CivilEGR You should really consider checking out your dipstick on that transmission. nyoffroad 's idea is pretty dang good. Especially if somebody near you has one of these trucks close by - so you could compare...

Oh, and there at the modulator, there is an o-ring to seal it to the transmission. Might be a cheap fix!
 

ardalan

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Last question from civilegr makes me wonder
I was always told to check transmission fluid when warm. Is that not correct and how would you get a pressure reading
I am new to m1123, 1998 with 4l80e that’s very low power in reverse and most likely drive too
I was told transmission capacity is 14 qts
 

MarcusOReallyus

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Ardalan, you don't need a pressure reading for daily maintenance. That's a specialized troubleshooting thing when you are having problems.

14 quarts is probably in the right ballpark. I checked the LO, and the -10, -20, and -34, and could not find any mention of the capacity.

Here is what the -10 says about checking the transmission fluid:

Transmission fluid level should
be checked with engine run
ning, parking brake set, trans
mission shift lever in “P” and ve
hicle on level ground, Fluid
l e v e l s h o u l d r e a d b e t w e e n
“ADD” and “FULL” on the dip
stick.
Check transmission fluid level.
If level is below “ADD”, add suf
ficient fluid to bring the level be
tween “ADD” and “FULL” mark.
N O T E
After completing transmission
fluid level check, turn off en
gine.
That's straight from 9-2320-289-10, Table 2-1 (page 57). Not one word about hot vs. warm. If it makes a big difference, that difference never made it into the TM.

However, the OP's problem is that he has a big leak. Until he finds that leak, nothing else matters.
 

ardalan

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Ardalan, you don't need a pressure reading for daily maintenance. That's a specialized troubleshooting thing when you are having problems.

14 quarts is probably in the right ballpark. I checked the LO, and the -10, -20, and -34, and could not find any mention of the capacity.

Here is what the -10 says about checking the transmission fluid:



That's straight from 9-2320-289-10, Table 2-1 (page 57). Not one word about hot vs. warm. If it makes a big difference, that difference never made it into the TM.

However, the OP's problem is that he has a big leak. Until he finds that leak, nothing else matters.
Thanks for checking on it
I heard 14 qts. From Midwest support.
Could this low power reverse be caul your limp mode.
would a 1998 m1123 6.5NA have computers?
 
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