1998 LMTV Hot transmission - No drive

[MrGoldman]

Hi everyone,
I am in the process of un hack jobbing my 1998 LMTV, previous owner did some questionable things, I've already replace the motor due to a cracked block.
I had the driveshafts balanced and then did a test drive, transmission felt great - smooth shifts and no issues over 50 or so miles.

The next day I went on about a 120 mile highway and city trip, about 60 mi in I got a transmission temp light and wasnt able to pull over right away but when I did it shut off. Fluid level looked good (maybe a bit high) right before and during this entire trip, it was 95F outside. Engine temp crept near 195 for a bit but never over that.

Once I got to my destination, I noticed the transfer case was smoking and leaking a bit out of the case seal, thermal gun showed the transfer case was 325F, Let it cool for an hour or so and then started the drive home, took back roads and checked the t-case a few times, always around 220f.

I was 20 miles from home and it came up with a trans temp light and went into "6" on the controller, 100 yards later It lost all forward motion and gears. I re-started the truck and would have gears for 10ft or so but very weak.

Had it towed and drained all trans fluids as well as the t-case, nothing came out to indicate a C6 needle bearing failure (diagnosed by the LMTV facebook group), Filters look fine, scavenge line is clear and scavenge pump looks fine. Fluid smells terrible. Got about 7gallons out total.

What else should I check before putting new filters and fluids in and trying to drive it again? I didnt pull codes before pulling fluid out but can once I re-start it.

 

[MrGoldman]

Dug a bit deeper, Found the oil screen on the transmission to transfer case scavenge line.
Chunky metal, looks like bearing. Anyone have experience with this ? Was going to pull the upper rear cover next.

 

[Ronmar]

oh darn...

there are a few discussions on it including one couple's saga with their failure and repair(the failure wiped out the P6 casing)...

 

[Skyhawk13205]

Dug a bit deeper, Found the oil screen on the transmission to transfer case scavenge line.
Chunky metal, looks like bearing. Anyone have experience with this ? Was going to pull the upper rear cover next.

What is your transmission SN? Looks like the C6 thrust bearing. Usually that is a rebuild of the 6 clutch assembly which requires to remove the transmission. Check out Allison service letter 17-wt-11 it specifies an updated c6 thrust bearing to a composite washer. Also see service letter 28-wt-96 it gives the SN breakpoint for the bearings that are subject to increased failure.

 

[MrGoldman]

What is your transmission SN? Looks like the C6 thrust bearing. Usually that is a rebuild of the 6 clutch assembly which requires to remove the transmission. Check out Allison service letter 17-wt-11 it specifies an updated c6 thrust bearing to a composite washer. Also see service letter 28-wt-96 it gives the SN breakpoint for the bearings that are subject to increased failure.

Ill grab the SN in the morning when I get back to the truck, Do you think this overheating could have caused further damaged to the internal clutches?

Where would I find those Allison service letters? A quick google is not finding them for me.

Is their a guide somewhere that would cover the rebuild? I can get the trans out pretty easily but would need something before I pulled it apart.

Thanks!

 

[Ronmar]

you don't have to pull the transmission, but you will probably have to lift the subframe to get enough clearance to remove the P6 cover

 

[MrGoldman]

you don't have to pull the transmission, but you will probably have to lift the subframe to get enough clearance to remove the P6 cover

That sounds like more fun than pulling the transmission, I've spent a lot of time under the truck today, getting to be a second home for me.

 

[Keith Knight]

Find a donor vehicle and buy the used transmission.

 

[Skyhawk13205]

Here are my copies of the service letter.

 

[Ronmar]

here are some of the discussions on this with lots of excellent pics...

M1078 A1 transfer case

Had some codes come up the other day on the transmission 2511, 2533, 5633. I pulled a cover that is next to the output shaft going to the rear axle. From what I can tell the gears look fine but something probably a bearing came apart and bounced around and you can see where the parts were...

steelsoldiers.com

M1078A1 "Pandora" Build | 2024-??? | ***Picture Heavy***

Greetings SS community ! I wanted to start a build thread before I got too far behind the power curve. I'll be posting updates here and on my website (Aviator4x4.com). Table of Contents Chapter 1 | Electrical PPD & Cabling - (Forum Posts #3-5) Battery Box - (Forum Posts #31-32, 40-49, and...

steelsoldiers.com

 

[MrGoldman]

here are some of the discussions on this with lots of excellent pics...

M1078 A1 transfer case

Had some codes come up the other day on the transmission 2511, 2533, 5633. I pulled a cover that is next to the output shaft going to the rear axle. From what I can tell the gears look fine but something probably a bearing came apart and bounced around and you can see where the parts were...

steelsoldiers.com

M1078A1 "Pandora" Build | 2024-??? | ***Picture Heavy***

Greetings SS community ! I wanted to start a build thread before I got too far behind the power curve. I'll be posting updates here and on my website (Aviator4x4.com). Table of Contents Chapter 1 | Electrical PPD & Cabling - (Forum Posts #3-5) Battery Box - (Forum Posts #31-32, 40-49, and...

steelsoldiers.com

Thats incredibly helpful, thanks. It looks like a tear down is in my future, I'd rather replace a $300 bearing than a $3000 transmission. Worth a shot at least.

 

[Ronmar]

the issue is that for the parts you found in the strainer to exit the P6 housing, they have to chew their way thru the clutch pack and splined aluminum housing/cover, with the aluminum housing being the weakest link...

 

[MrGoldman]

the issue is that for the parts you found in the strainer to exit the P6 housing, they have to chew their way thru the clutch pack and splined aluminum housing/cover, with the aluminum housing being the weakest link...

Gotcha.... So buying a used trans is my best opinion probably. And changing the c6 out before it fails if it's in the range

 

[MrGoldman]

@Ronmar

Got my C6 out, ended up just cutting a small piece off of the bed.

Not terrible inside but not great either, need a few new clutches and a new hub, i'm about $1500 in parts, Can get a trans for $3k, Ill immediatley swap out the bearing of death before installing. Its the same truck my engine came from, 1k miles on it

I think im going to slide the bed back and try to go out the top if possible. Probably keep it with motor oil and not swap to ATF.

Does anyone know where i could put some temperature probes in the trans and T-case for cab gauges?

 

[Skyhawk13205]

@Ronmar

Got my C6 out, ended up just cutting a small piece off of the bed.

Not terrible inside but not great either, need a few new clutches and a new hub, i'm about $1500 in parts, Can get a trans for $3k, Ill immediatley swap out the bearing of death before installing. Its the same truck my engine came from, 1k miles on it

I think im going to slide the bed back and try to go out the top if possible. Probably keep it with motor oil and not swap to ATF.

Does anyone know where i could put some temperature probes in the trans and T-case for cab gauges?

I saw on FB that you replaced your engine due to a crack in the block. Have you had your drivelines rebalanced?

The 4x4s seem to have more vibration related damage and also a C6 thrust bearing failure, I have wondered if the vibration causes that thrust bearing to fail sooner.

Were you able to find the SN of your transmission, I wanted to see it is within the replacement range?

Looks like removal via cutting the bed storage is easier than removing the transmission

Hope you get it resolved soon.

 

[MrGoldman]

I saw on FB that you replaced your engine due to a crack in the block. Have you had your drivelines rebalanced?

The 4x4s seem to have more vibration related damage and also a C6 thrust bearing failure, I have wondered if the vibration causes that thrust bearing to fail sooner.

Were you able to find the SN of your transmission, I wanted to see it is within the replacement range?

Looks like removal via cutting the bed storage is easier than removing the transmission

Hope you get it resolved soon.

When I bought the truck it quite the dent in the rear driveshaft, it would rattle the mirrors so bad at 45 you couldnt see out of them... I have no idea how much the previous owner drove it like that but it was 100% the cause of my block issues. I wouldn't be surprised if it caused the trans issues as well.

I bought a used non dented rear shaft and had both balanced locally. It was amazing, I put 100 or so miles on it before the C6 failure and it was smooth at any speed.

SN attached

Yeah it was much easier, took me 20 mins to get it out. now i get to pull the trans out and have that fun as well. I'm sure I could fix up the C6 and drive it again but as many people said its just a ticking time bomb now, I only found about 60% of the bearing.

 

[Skyhawk13205]

When I bought the truck it quite the dent in the rear driveshaft, it would rattle the mirrors so bad at 45 you couldnt see out of them... I have no idea how much the previous owner drove it like that but it was 100% the cause of my block issues. I wouldn't be surprised if it caused the trans issues as well.

I bought a used non dented rear shaft and had both balanced locally. It was amazing, I put 100 or so miles on it before the C6 failure and it was smooth at any speed.

SN attached

Yeah it was much easier, took me 20 mins to get it out. now i get to pull the trans out and have that fun as well. I'm sure I could fix up the C6 and drive it again but as many people said its just a ticking time bomb now, I only found about 60% of the bearing.

Yeah, I would imagine a vibration contributed to the failure. Most people who have posted a tear down of their C6 as a preventive measure has not seen any issues.

Your C6 has prob failed a while ago and the only symptom was the scavenge screen getting clogged causing the overheat.

Your SN is in the updated range so it is good to realize that even if you have the updated PN it does not mean you are not safe from failure,until you have the composite washer.

Looks like a lot of work but you are making progress, keep us updated.