Broke my M's rear pinion shaft..

[achiem37]

While out for a drive in my CDN 52' M-37 to get a nice soft ice cream cone I stopped at a red light for a left turn. The light turned green and I started to move in 2nd gear like always.. I let the clutch out easy as always and then heard a bang in the tranny area. The truck would not move. I tried 1st gear and same thing... the engine revved but no motion. So I coasted the truck to the shoulder ( luckily it was a down hill grade) and engaged the parking brake. I then noticed that the truck still moved forward with the hand brake on. I rechecked the hand brake to be sure it was engaged and again it rolled forward. I rolled the truck to a curb edge and parked the front wheel against it. I got out and looked under the truck , no signs of oil or driveshaft damages. I checked the main short driveshaft and it was good as well. I checked the transfer case linkages and they were good. I released the parking brake and then found I could rotate the rear driveshaft by hand. The truck did not move but I could spin it relatively easily 2 or 3 turns. I thought " REAR AXLE SHAFTS " could be the problem. So I engaged the front axle and drove home carefully the 15 KM or so. I could not hear any grinding or any signs of the shaft ends causing trouble. I dumped the oil in the rear diff and found no metal debris or chunks of any kind. Seemed strange to me so I pulled the short side shaft and found it to be intact with no signs of twisted splines or funny wear patterns. I then pulled the long shaft and found it be intact and not showing any funny wear signs as well. I thought OH NO it must be in the gear set .... So I have not pulled the carrier yet but has anyone ever had this happen to their trucks.. I will keep the update going once I get into the gears and see what's up.. Terry

[Lifer]

Be sure to let us know what you find. (Include pics, too, please!)

I'm inclined to believe that your initial diagnosis of a failed pinion shaft is correct. Unusual, but correct.

Happy wrench bendin'!

[MSeriesRebuild]

While out for a drive in my CDN 52' M-37 to get a nice soft ice cream cone I stopped at a red light for a left turn. The light turned green and I started to move in 2nd gear like always.. I let the clutch out easy as always and then heard a bang in the tranny area. The truck would not move. I tried 1st gear and same thing... the engine revved but no motion. So I coasted the truck to the shoulder ( luckily it was a down hill grade) and engaged the parking brake. I then noticed that the truck still moved forward with the hand brake on. I rechecked the hand brake to be sure it was engaged and again it rolled forward. I rolled the truck to a curb edge and parked the front wheel against it. I got out and looked under the truck , no signs of oil or driveshaft damages. I checked the main short driveshaft and it was good as well. I checked the transfer case linkages and they were good. I released the parking brake and then found I could rotate the rear driveshaft by hand. The truck did not move but I could spin it relatively easily 2 or 3 turns. I thought " REAR AXLE SHAFTS " could be the problem. So I engaged the front axle and drove home carefully the 15 KM or so. I could not hear any grinding or any signs of the shaft ends causing trouble. I dumped the oil in the rear diff and found no metal debris or chunks of any kind. Seemed strange to me so I pulled the short side shaft and found it to be intact with no signs of twisted splines or funny wear patterns. I then pulled the long shaft and found it be intact and not showing any funny wear signs as well. I thought OH NO it must be in the gear set .... So I have not pulled the carrier yet but has anyone ever had this happen to their trucks.. I will keep the update going once I get into the gears and see what's up.. Terry

Several issues could be going on. Could be the shaft, could also be in the core of the unit, spider gears, shafts, etc. Complete disassembly will be a must to check everything out. If the shaft is broken, I would bet there are some spider gear / thrust washer issues that helped bring that on.

[achiem37]

UPDATE I took apart the rear diff today and found to my surprise all the ring gear bolts had sheared off. The ring gear was spinning on the surface of the carrier. It appears to have not damaged much inside. I found the locking plate had passed thru the gears but no teeth are broken or chipped off. The bearings roll smoothly but may need to be flushed to be sure. The carrier housing is missing the three dowel pins that hold the case ends from spinning. The holes are still aligned which is good but the pins are chewed up. I was hoping to install the new ring gear bolts , check the bearings and backlash and reinstall the unit . The case will be redowelled and staked around the pins. I really don't see any damages and I really wanted to avoid pulling out the ring gear and carrier assembly. I will check the carrier for face runout where the gear seats and see if it has been bent or scored up. I can send pics if someone can post them for me.... Terry

[MSeriesRebuild]

UPDATE I took apart the rear diff today and found to my surprise all the ring gear bolts had sheared off. The ring gear was spinning on the surface of the carrier. It appears to have not damaged much inside. I found the locking plate had passed thru the gears but no teeth are broken or chipped off. The bearings roll smoothly but may need to be flushed to be sure. The carrier housing is missing the three dowel pins that hold the case ends from spinning. The holes are still aligned which is good but the pins are chewed up. I was hoping to install the new ring gear bolts , check the bearings and backlash and reinstall the unit . The case will be redowelled and staked around the pins. I really don't see any damages and I really wanted to avoid pulling out the ring gear and carrier assembly. I will check the carrier for face runout where the gear seats and see if it has been bent or scored up. I can send pics if someone can post them for me.... Terry

If the taper pins are out of the case/cap assembly, you had better find out why. This is an extremely critical issue, there is always a reason for it, although you may have to disassemble the inner case to figure it out, most likely there is some thrust washer issues in play. Did the ring gear bolts have the locks in place? Are the bolt holes pulled (slightly out of round or wallowed) in the carrier flange, if so you will never keep the ring gear tight. Once this has happened the assembly will always move instead of being held rigid. This is what causes bolts to loosen and break and they will do it again, even with new bolts and locks in place. This is the most expensive gear box on the truck to rebuild, not addressing all the issues right the first time is generally a real heart breaker.

[W_A_Watson_II]

I'd suspect the taper pins caused the ring gear issue. One of the units on my 46 PW was serviced and the pins not properly installed and came out, and I have several broken ring gear bolts as a result.

[Lifer]

I'm glad you found out what the problem is.

It shouldn't be too terribly hard or expensive to fix, and it will give you yet one more opportunity to become familiar with the innards of your truck.

[achiem37]

the rear diff was rebuilt using NOS parts such as studs, nuts, locking tabs and torqued with loctite to 40 ft-lbs on the ring gear bolts. The case was apart and new spider gear assemblies installed. The carrier does have 4 holes that are wallowed out so maybe this piece is scrap.. any luck redrilling and sleeving these holes Charles???. The end cap has not moved as I did find the third dowel still installed , it was just a little deeper down the hole. The dowels did leave a mark on the oil gallery casting section. I guess the pin came loose and broke off causing the rest of the turmoil. I will have to pull the carrier and check for these parts now to be sure they are located. Terry

[MSeriesRebuild]

the rear diff was rebuilt using NOS parts such as studs, nuts, locking tabs and torqued with loctite to 40 ft-lbs on the ring gear bolts. The case was apart and new spider gear assemblies installed. The carrier does have 4 holes that are wallowed out so maybe this piece is scrap.. any luck redrilling and sleeving these holes Charles???. The end cap has not moved as I did find the third dowel still installed , it was just a little deeper down the hole. The dowels did leave a mark on the oil gallery casting section. I guess the pin came loose and broke off causing the rest of the turmoil. I will have to pull the carrier and check for these parts now to be sure they are located. Terry

It will be pretty amazing if you don't find a damaged flange with too much run out to be able to get a proper gear set up. If the diff was rebuilt as you say, what happened? Was it not done correctly, doesn't sound like it. If I were you, I'd be leaning on the builder. 40 ft lbs is too much torque for the ring gear bolts, they should never be pulled more than 35, as they are ungraded fasteners and simply won't stand excess torque, this could well be part of your issue. A much better option is to install new grade 8 bolts with self locking nuts. I've seen quite a few with the taper pins out and the casting grooved as a result. I've never seen ring gear bolt damage that could be attributed to a taper pin coming out. I'd almost be willing to bet the bolt holes were wallowed when the ring gear was installed, and is the more likely cause of the issues you have now. This I have seen many times.

[achiem37]

Looking into the rear diff further I found the 5 of the holes to flared over when the ring gear spun. It has gouged the mating face for the gear as well. This unit had new spiders installed 8 years ago and they are in great shape. The case cover was fairly easily removed as well. Should I attempt to machine about 0.005-0.010" off of the mating face to true it up , clean up the bolt holes and use metal permatex when installing some grade 8 bolts for the next time? Or should I look around for a decent condition carrier and install that one. The problem is the spider gears and thrust washers may be in sad shape and require the end cap removal as well. We'll see what happens with the search. Terry.

[MSeriesRebuild]

Looking into the rear diff further I found the 5 of the holes to flared over when the ring gear spun. It has gouged the mating face for the gear as well. This unit had new spiders installed 8 years ago and they are in great shape. The case cover was fairly easily removed as well. Should I attempt to machine about 0.005-0.010" off of the mating face to true it up , clean up the bolt holes and use metal permatex when installing some grade 8 bolts for the next time? Or should I look around for a decent condition carrier and install that one. The problem is the spider gears and thrust washers may be in sad shape and require the end cap removal as well. We'll see what happens with the search. Terry.

The fact is you simply can't tell what condition the spider gears, side gears, and thrust washers for each are in unless you go into the case and do a visual inspection, plus measure washer thickness, etc. I wouldn't even think of running the risk of not having a look. Definitely do not install a take out carrier without inspecting the internals. From your description, I'd say the carrier is thrashed to the point a proper gear set up will be almost if not certainly impossible to achieve. We have built many differentials from the spider gears up, trust me,and take this next statement to the bank. Something was not done right during the build or you would not be having these issues now, things always happen for a reason. Don't set yourself up for the same thing again.

[paul]

where are you located ? i have a few carrier dissasembled , if you need one

[achiem37]

Paul ; I am located just east of Toronto . I have been asking around here for some parts but no has got back to me yet. I have a connection for a set of axles from a 45' WC 51. These are the same size as my Power Wagon ones and would be nice spares. I just have to convince the guy to sell them. I was also looking at installing a air operated locker that I have seen on this site. I believe the guy still has two left. I'm not sure the $1000 or so is worth the trouble as I don't seriously offroad the truck. If you have a good used spare carrier and the shipping is not too extreme maybe we can swing a deal. My postal code is L0A 1J0. Let me know what you want for it and the shipping costs if possible. Ground mail is probally the lowest prices.. Thanks Terry

[paul]

nice i am in new brunswick so shipping should not be to bad, not looking at getting rich, i took 5 axle appart to find a good set of gear so i must have a good carrier or two, ill check tomorow and will get back to you about it , cheer!

[paul]

here is a pic of the 2 i have that seem to have good hole and nice mounting surface, they are both empty case, you can pick one and i can post it to ya if needed