M923 MPG and Differential Oil Seal Leak

[GHall]

Thanks for the info. My thoughts are that if a $60K F350 quad cab 4X4 gets 12-ish I might as well get something with similar mpg for $5K.

I like it...

 

[phat6]

Just picked up an M925A2. I drove it back from Georgia, a little over 500 miles. I had it floored most of the way and was running 65 on most stretches. When I got home and took a look around, I noticed a great deal of oil spatter on the back of the truck. It appears to have come from the rear differential. I joined the forum today and have been poking around looking and have seen everything from you shouldn't drive faster than 60 or you will aerate the gear oil and toast, to the CTIS sends air through the diff and could have blown the seal, to the seal could just be bad, to clogged vents could have caused the seal to blow. I understand all of those, but I was hoping to find two things from this forum of wisdom, which I have not been able to find. Perhaps this is just because I am the n00b. I am looking for:

1. What is the most common cause of a blown seal (what is real, what is folklore?)?
2. How do you replace the seal? Is it a PITA or relatively easy? They put all those massive bolts on there just to make me stay away? Most forums I have frequented have these great, experienced folks who put all the nice pics and videos together, so my ignorant, lazy a$$ can just follow their nice easy, step-by-step, guided directions--after I watch the whole thing and decide whether or not I can do it or if I take it to someone who knows what they are doing!

Also poked around for a few other things and found some useful information on these--thanks!:

• A ladder or steps to get into the bed easily
• How to add more power to the Cummins 8.3L Turbo Diesel
• Tires - will 16.00R20's fit, which I found a yes answer, but still not seeing it, at least not without removing some stuff like mud flaps and their brackets.

Some topics I have not yet started researching, but are definitely on the list:

1. Better seats: more padding, less "bouncy", further back for more leg room
2. Removing or relocating the window crank--it digs into the side of my leg. I have a nice bruise there from the drive.
3. Better seat belts (3-point or 5 point)
4. Digital gauges / replacement instrumentation
5. Changeover to synthetic fluids (gear, trans, xfer case, diffs, power steering, waterless coolant, etc)
6. And this one perhaps will make the traditionalists cry out: painting, chroming, modifying

Ya, you can probably tell I am not an "all original" / traditionalist--let the mods begin! This thing seems like the right canvas for building the ultimate truck. I love the truck, but holy cow is this thing intimidating. It is massive. I think I need a new garage, new tools, new jacks, new lift . . . all bigger, and more expensive. Man, what was I thinking!

 

[Coffey1]

That's the 5 ton club welcome to the heavy madness.

 

[Coffey1]

And by the way ,wait until you knock an upper dog bone off and have to figure out how to get it back on andmake it stay.

 

[M925]

I would think that if the a2 is like the a1, you should slow'er down.....but that's up to you.

 

[juanprado]

Sounds like the differential seal where the driveshaft goes onto the pumpkin. There is a seal on the front and back of the truck on each differential. The back still has a seal under the pancake looking flange even if nothing is attached. With that much oil, it should be easy to run a finger and find the leak. There is also a plate on the top of the pumpkin with a gasket and a gasket on the chunk but unlikely for either to have caused the leak.

I would think the truck sat up for a long time, the seal got hardened or stuck to the shaft and then you drove it causing the leak. Unbalanced driveshaft or bad u joint could put stress on the seal. Easy to find seals, and not too hard to change.

Need a large socket for the nut, don't recall off hand maybe 2 5/16. All other tools are common socket/ratchets.

Pull the driveshaft if leak is in between axles, usually 10 bolts and pull to side, unscrew big nut, pull pancake, then knock tin plate off. Seal in plate. This is the nickel tour. Check tm for complete repair.

If you do it yourself, one piece of advise I learned the hard way. The front facing seal is in a tin plate that just knocks off a metal spacer ( don't recall technical name). Do not try to pull the plate with a gear puller as the tm describes. It will make a mess of the shims and does not need to be pulled. Tin plate literally will knock off with a screwdiver/punch hammer easily as it a slightly pressed fit.

Rear facing seal is even easier than the front in my opinion.

 

[juanprado]

The real problem driving with super singles is that the tires are only rated for 55 even though the truck can do 65. Check sidewalls for speed rating.

I don't think your speed was the differential leak, just old seal whose time was up.

 

[jvandal]

My 923A0 just round tripped from Knoxville to the GA rally at 7.5mpg which was a little lower than I normally see.... 8-8.5mpg's.... I got very excited on the drive home from Huntsville as it appeared that I got well over 10.... but the reality is... 8-8.5... of course mine will only top out at 57mph.....

 

[phat6]

And by the way ,wait until you knock an upper dog bone off and have to figure out how to get it back on andmake it stay.

I don't even know what that is yet, and based on the tone of the reference, I hope I never find out.

 

[Coffey1]

Go look at back bogies and there is a bone looking connector that's a dog bone

 

[phat6]

The real problem driving with super singles is that the tires are only rated for 55 even though the truck can do 65. Check sidewalls for speed rating.

Yep, 55 mph. Glad I didn't blow a tire. Why install a tire only rated for 55 mph on a vehicle capable of 65 mph? I guess it did not occur to me that someone would actually do that. Are there good 16.00R20's with great on/off-road traction that can do 65? Guess that is probably another thread and one to add to the list.

 

[Tow4]

I changed a couple of pinion seals on my M818. I think the axles are the same as far as pinion seals go. The process should be the same.

Here's the procedure for replacing the M818 pinion seal.

http://www.steelsoldiers.com/showthread.php?77513-Rear-End-Seal-for-M818#post979551

 

[jdknech]

Yep, 55 mph. Glad I didn't blow a tire. Why install a tire only rated for 55 mph on a vehicle capable of 65 mph? I guess it did not occur to me that someone would actually do that. Are there good 16.00R20's with great on/off-road traction that can do 65? Guess that is probably another thread and one to add to the list.

reason is the military didnt allow the trucks to go over 55mph.. and most times 45mph was it... so why worry about putting 65mph rated tires on a truck that is not allowed to go that fast... plus you will learn that the truck was not desinged to go that fast... it orignally had 11.00X20 tires on it.. so max was 55mph.. the 14.00X20 was a afterthought upgrade... and the bigger tire added speed... thats why it will go 65mph now..

now, all that being said, I used to drive mine at 67mph (the max it would go) all the time, but now i tend to keep it at 50-55mph... i have noticed my mpg's go WAAAAY up, and the truck seems to like it better.. every once in a while I will push its limits, but not often, and NEVER pulling a semi trailer.. (i have the tractor)

 

[TacticalDoc]

never took my M923 over 55. also make sure your hub is on tight enough. My rear axle wheels were wobbling when I lifted the axle. The 2 large locking nuts must have come loose. this wobbling must have blown the seal. So. I recommend lifting all the tires and see if there is any wobble. if there is and there is not any leaking you can tighten the nuts without changing the seals. Lift the axle high so the gear lube doesn't leak out.

As far as the vent goes...I put some tubing on to an elbow off the axle where the vent is. just take the vent off and bring it into the hardware store and match up the threads and get tubing. I connected all the tubing and ran it up the back of the cab. Allow for some slack as the axle will stretch the tubing as it moves. I put one of the vent caps at the end of the tubing once I ran it up the cab. Or you can just run the tubing up to the mushroom of the air intake and not put a vent on it.

the tank is 81 gal and the range is 350 miles. So, 4 to 5 mpg sounds about right. you can try diesel additives like diesel kleen to see if you get more range. it will also clean the injectors

 

[Karl kostman]

Tires as stated are ONLY rated to 55 MPH MAX, then the only thing you need to be aware of is the magic 2100 RPM on the motor, the 855 does not RPM higher than that, I do not know much about the 8.3 but I am guessing its going to be in the same area. You mention the size of the 939 series, yes they are big and do have good brakes but its not going to stop like a pickup from 65 MPH, its going to take some distance and some time, drive accordingly we do not want to read about something BAD happening! Good luck
KK

 

[M925]

I don't like for the tachometer to go over 2000 rpm....you know where the danger sticker is....but that's just me. I'm convinced on my first truck; that it didn't start smoking till someone drove it too fast....but that's just superstition.

 

[Artisan]

Burning Man just got added to my Bucket List.

A SS Contingent Convoying up there would be a real hoot, or
meet us there of course..

Any like minded folks are free to PM me, if enough interest
I will make a dedicated thread. No time frame, no time
limit but I HAVE to go... and if I do, we WILL be comfy.

Come Wind, Cold, Rain, Heat, or Zombies, we will be comfy!

Food, WATER, Power, Latrine, Tents, MKT trailer would be AWSOME.

This could be a LOT of fun.

GOSH how fun would it be for a HUGE convoy of MV's loaded to the hilt
w/ all the comforts of home, wagin' trainin' and gettin' to the livin'... BURNING MAN Style.

One truck filled w/ fire wood.
One truck filled w/ 5000? Gallons of water.
An MKT Mess trailer! LOL!
A/C
Power
Tents...

I bet ya everyone has a contribution...

Haul it in, haul it out, a CLEAN head too!

August 30 is not far, nor is it too close...

(PS, leave your inhibitions at home)

I am in SO Calif.