For those that have broken axleshafts...

[steved]

...tell me a little more about the cause...

Is the truck stock?? Open or locked differentials? Oversized/aggressive tires? Engine still stock, or is it a swapped powerplant???

Trying to get an idea if a stock truck with open diffs would suffer a broken axle under normal offroading? Does the stock 6-holer actually have enough grunt to break them?

How often do the tracta joints cause issues?

Thanks,
Steve

[M376X6]

1965 M37, 318 V8, Stock tranny, xfer, and open thirds. 20 inch tires, power steering. Run most Colorado trails and Moab, no broken stock axles.

1963 M37 6X6, 360 V8, stock tranny, xfer, and open thirds, 11.00-16 tires and power steering. No broken axles, abuse it all over New Mexico, Colorado, Wyoming, and Utah. When I say abuse, we tore out three of the four motor mounts on boulders and trails this last hunting season. I'm still sore from all the banging around.

Getting ready to install air lockers on both thirds in the 65 4X4, will run after market shafts in the rear. Never had or seen any problems with the front shafts or joints.

I have been blowing up Superwinch hubs over the last 2 years, have since gone to Selectro's.

[steved]

OK, that what I sorta figured...open diffs are always easier on the axleshafts. Just didn't know how much abuse they could take.

steved

[M376X6]

I really work my trucks hard sometimes. I should say play with my trucks really hard. Hunting, fourwheeling, etc.. Yet I have heard some guys practically just look at their trucks and the shafts break. Completely stock original trucks. It has been a puzzle to many of us on the various versions of the M37 sites over the years. Some feel it is always the short shaft that breaks, others always the long shaft. No one really knows. I have spun the 20" tires on dry pavement with my 65 and no problems. Had the truck bouncing in the air climbing the toughest trails at Moab. Yet one fella broke his shaft dropping down a gear to get compression slowing on a hill near his home in a residential area. No rhyme or reason for any of it.

Regards,
Bryan Sage

[robi]

I have broken two rear shafts. One broke while while starting from a stop sign in a residential zone about a block from my house. No hot rodding , just a normal start and BANG! I had to put in 4h to get home. That was with a completely stock, original, never messed with, engine and drive line.

The other time was a few years later at Hungry Valley. I had replaced the shaft with an stock shaft. I had also put 4:89 gears and a Power-Lok in the rear. I was just driving down a dirt road when this one let go.

Both times it was the driver side rear that broke. I now carry a spare axle and my special axle stub removing tool with me at all times. All that was about 20 years ago. I haven't had a problem since (knock on wood).

BTW, the first one broke at the diff, the second one broke at the hub.

[Dicktater]

One of the first upgrades I did to my truck was to replace the long axle with one made of modern alloy,never had a problem.

[MSeriesRebuild]

...tell me a little more about the cause...

Is the truck stock?? Open or locked differentials? Oversized/aggressive tires? Engine still stock, or is it a swapped powerplant???

Trying to get an idea if a stock truck with open diffs would suffer a broken axle under normal offroading? Does the stock 6-holer actually have enough grunt to break them?

How often do the tracta joints cause issues?

Thanks,
Steve

Just scanned the post in this thread quickly, we've seen a bunch of broken shafts over the years. Fact: using the automatic lockers in the differentials is an axle shaft KILLER, so this explains the problem someone had with that one. No rhyme or reason, well sometimes it seems that's the case, however if you look far enough most times there is a reason to discover. Abuse can surely break them, even with stock power, however a good driver even in abusive environments usually doesn't have problems. I have found that if all drivetrain components are tight & set up in the proper working order, breakage is much less likely, almost "0" unless an abusive driver is behind the wheel. Loose motion in differentials, drive shaft slip joints, u-joints, etc. is also a big killer of axle shafts. A sudden slap to the axle shaft takes place everytime you let out the clutch as the loose motion is taken up before power can be transferred to the ground. Add just a mildly abusive driver to this mix & you have lots of problems. I have a Cummins powered M37B1, purchased the truck stock in the early 80's, still has the same axles it had when purchased. Using good common sense in a good condition truck, you'll do just fine with stock shafts. If problems start, look back over the list of probable causes, you won't have to look far to figure out what is going on.

[steved]

Thanks for the replies...

Most of the responses were what I expected...driver input the biggest influence, probably followed by poor alloys (when compared to today's stuff) probably the other.

I sort of stockpiled some spare shafts...complete set of shafts (front/rear) and a complete set of axles (with shafts). I figured that was the weak link.

On a side note, my M37 has a gash in the floor (center hump I believe) from the center driveshaft letting go at some point in its life...

steved

[PoW]

Most failures are indeed in the rear shafts. The Tractas in the front are pretty robust, and I've never had one fail in 35 years of driving M37's.

I have seen several trucks with torn floors due to drive shafts coming loose, but that is always due to the four cap screws coming out. They will not stay tight over any length of time, and the handbook clearly states they along with the axle flange bolts should be torqued at intervals not to exceed 2,000 miles.

I have tried various schemes to keep them tight; locknuts, lockwires (they broke), locktite. I finally admitted Dodge was right and just hit them with a wrench every so often.

dg

[Dicktater]

Pow,
Thats some good info about the drive shafts bolts coming loose. Something alot of M owners don't even think about,thats something I check alot because of the damage it can cause,(there are always loose).
It will always happen when your driving down the road with a big smile on your face cause your truck is runnin so good,and then it sounds like you ran over a land mine.

[MSeriesRebuild]

True, we've seen many trucks with damage from a jack shaft getting free. It isn't something you have to put up with all this re-torqueing though. Most folks aren't aware these are special bolts & not just your normal grade 5 or 8 cap screws. The correct bolts have splines & must be pressed into the flange similar to a wheel stud. Once correct bolts are in place along with a "crush type" grade 8 lock nut installed using RED lock-tite, then torque properly; they will be there for the long haul trouble free. DO NOT USE NY-LOCK TYPE NUTS. What we usually find on trucks where folks complain they won't stay tight is where the wrong bolts have been used, they have been run loose & wallowed the holes out to the point even the correct bolts are no longer a press fit. This of course allows the 2 flanges to move because of over-size bolt holes. They will never stay tight if this happens. We have repaired many by welding up the bolt holes & re-drilling to the proper size to restore the press fit. They are as good as new after this.

[Rick C]

Charles, where can I get the proper bolts? I'm sick of tightening mine up every few months....
Rick

[Lifer]

I agree with Charles on the "mildly abusive" drivers adding to the problem, although I think I would have called them "mildly agressive," myself. "Getting on it" with a worn drive train is asking for trouble. Automatic transmissions amplify the problem, too. I have put many, many miles on old trucks with manual transmissions and bad u-joints or slop in the diff, knowing full well that they could fail at any time. I always managed to make 'em last until I was ready to do the needed repairs, though. Slipping the clutch to gently take up the slack will help make them last a little longer.

[Barley Pop]

I broke the rear shafts one of each and both went bang from an easy take off on pavement from a stop. So I figured they started to go over time and went in the same way due to low gearing and torque ??? one was completely stock truck the other was same truck with a 360 V-8 engine and 40's gamma goat set up. Saved the stubs for paper weights in the shop. My opinion on things to break, I'd rather snap an axle shaft then do damage to the rest of the drive line. It's a slow drive home in low running it in front wheel drive.

Barley...

[M376X6]

As you can read from the statements, sometimes there is no rhyme or reason for breaking a rear shaft. No abuse, no loose driveline, maybe a bad shaft from manufacture. No one really knows in some cases!

As far as splined bolts for the flanges on the driveline. Never made, never used, DON"T PRESS ANYTHING INTO THE FLANGES. It'll ruin them.
The part number for the screw (bolt) is 181668. The number for the regular lock washer is 120383. For the nut it is 120370. The bolt is a long shoulder type that is not available that I have found. I make them by cutting down the length of longer bolts to get the proper shoulder length to match the original bolts. Again, no splines on the originals. Don't waste your time looking for something that was never used and will ruin your flanges. If you do decide to make your own by modifying bolts, make sure they are very close to the same weight as each other when finished to prevent mismatched weight bolts, very common to find oddball bolts on these trucks, which will cause the shafts to vibrate leading to a lot of loosening problems on their own. The bolts are a fine thread and I have found over they years that proper torqing will eliminate loosening without the use of locktite or any type of locking nut which makes both it and the bolt one time use only. If you need the dimensions and and type of bolt to use please contact me.

Regards,
Bryan Sage