Auxiliary trans seized (1972 gmc 6500)

I just bought this old gravel truck with a steel box and got it running. I went to move the thing home, but only made it about 5 miles or so before something broke in the auxiliary trans and brought me to a very abrupt stop. Before this happened it stared shaking like crazy at anything over about 35 km per hour, and I thought I must have a flat tire. It stopped so fast I didn't have half a chance to move to the side of the road. First thing I did after it stopped was restart it and try reversing a little with the hopes we could get it to the side of the road that way. I only moved a few feet in reverse and that seamed to work okay so I tried moving ahead. It wouldn't move ahead and it locked up completely solid and wouldn't reverse either. First off I suspected something broke in one of the diffs, but we noticed a clunking sound when trying to move forward or in reverse Which turned out to be the auxiliary trans floping around.The auxiliary trans actually tore a 9/16 bolt on one of the trans mounts clean off as well as shearing 2 half inch ones in its haste to bring the thing to a stop. We pulled off the drive line beween the auxiliary trans and front dif and were able to pull it off to the side a half mile down the road were it would draw less attention. The auxiliary trans is completely solid at the rear output shaft, but I think I was able to turn the front shaft a little. Has anyone experienced something like this? I'm guessing I need to find a replacement for that trans, but I'd like to know what went wrong. I'll likely drop it down when I have time and dissemble it to figure out if it's repairable. All tires on the rear axles had turned at least one round while sliding as noted from marks on the tires. I didn't notice any recent oil leaks or broken spots on the trans. Anyone who has an idea what is going on with it please reply.

6041 spicer? low on oil and running in od caused the pilot bearing rollers between the input and the mainshaft to fail causing catastrophic failure of several parts? just a WAG

I'll have to see if I can figure out which trans it is. I was think a bearing as well, but I don't THINK I was in od.

Depending on engine size it could be any of three common auxiliary gear boxes used at the time. Most common 8341, and any of those were single counter shaft models. There should be a
six bolt pto/inspection plate on the side, some had a plate on each side. I would drain it and take a look see for scrap metal inside. It almost sounds like it tried to go into two different gear ratios
at the same time, but like said above input and main shaft failure. Not knowing how many speeds are in that box, I'll guess four- if you were in third/direct the input-main shaft are 1 to 1. So
For failure like that to occur you would have to been in second/under or fourth/over.

if I recall, in that size truck, it would have had a 427 gas, so my guess is the 6041 or maybe 7041 spicer. in those trucks they were a 4 speed with the single countershaft although I have seen 2 slightly different shift patterns with D and OD reversed but then again my memory may be hazy

Thats right 427 gas is what I've got. I believe I was in 2 gear due to how slow it was with the main in 5th. 1st and 2nd were working fine and not really that hard to shift, I tried several times to find 3rd and 4th but the leaver simply wouldn't go side to side at all. Am I right in thinking the pattern is 1st at forward left position, 2nd ar rear left, 3rd at forward right, and 4th at rear right? Same as say a 4 speed in a small car would be right? I'm thinking there was something going on with it before I started out.
I haven't had a chance to look at it again yet. What am I looking for to identify which model it is? What are the chances of being able to rebuild it/find parts for it?

3rh and 4ty may be reversed. Forward for 3, backward for4

https://lkqheavytruck.com/part-deta...AUXILIARY-TRANSMISSION&make=SPICER&model=6041

find the tag on the case- upper side just below the top cover. I don't remember which side. under the grime it will have the model number and most important the b/m number(bill of materials) which is used to look up parts for that particular transmission. talk to the Gear Centre in G.P. on those trucks, when the shifter gets well-worn, it is common when making a sloppy shift for the stick to slip between the two rails and then it is stuck in one gear. the quick solution is to crawl underneath and use a long screwdriver or prybar and pry the two rails back into alignment with each other at the auxiliary trans end of the shifter rods. engine shut off, main trans in neutral, and park brake applied(if it works) otherwise block wheels. there is a hidden grease fitting on the shifter assy that rarely gets greased that keeps the shifter rails lubed, otherwise they get worn and sloppy. old gravel trucks usually have worn-out shifters because that stick has been rowed a bazillion times

oh ya- that roller pilot bearing between the input and mainshaft is spinning in all gears except direct

I got a chance to have a look at it today. My bad I was in a hurry to get it off the road the other day, and apparently its the input shaft which is seized and output is mobile. I pulled off the side cover and drained the little bit of remaining sludge since it hardly qualified as oil anymore. there are no broken pieces laying it the bottom, and I didn't notice any filings. Nothing seems to be broken and it seems like the only thing which won't move is the input shaft. Im hoping I can just replace the bearing or bearings on the input shaft. what do you guys think?

Thanks a lot for all your help guys. I figure the right thing to do would of coarse be to replace all the bearings, but if I can get away with it Id like to try just replacing the input one(s)

You need to disassemble it first before you make any decisions and all parts inspected. A shock load such as the one that trans experienced needs careful examination.

Thanks again for all you help. I found the main input bearing had siezed due to lack of oil and moisture damage. Good thing I didn't check the oil as the input gear pocket bearing between the input and output shafts was siezed with corosion and turned on the output shaft. If I had added oil I wouldn't have noticed the turning pocket bearing until it ripped the thing up. Fortunately nothing turned much and everything is quite salvageable. The only thing that looks questionable is the output shaft looks like it got heat damaged. I might replace that if I happen to snag one on Ebay.

The main input shaft bearing is $399 at A1 driveline in Grande Prairie, but I found one on ebay for $121 shipped.

The secondary input shaft bearing is just a 6210 which I ordered a new SKF to replace.

The input gear pocket bearing is $171.65 at A1 driveline. The original is a cylindrical roler bearing with a removable outer race and a snap ring on both side to facilitate the removal of the outer race. I can't find anything but the spicer and gm part number, or a bearing to match the snap ring removable outer race. A1 didn't seem to want in give me part numbers so I didn't ask them.
I'm thinking to order something like http://www.bearingscanada.com/mobile/Product.aspx?ProductCode=Kit14437
to replace it. Its rated 46000n dynamic load.

The output bearing is a BCA 1312L or a SKF 312 and is $572 from A1 driveline.
I'm thinking of replacing it with https://www.bearingscanada.com/mobile/Product.aspx?id=41585
The original SKF 312 is rated somewere between 78000 and 85200n static load and has 12 balls. The Nachi 6312 is rated 82000n dynamic load, but has only 10 balls. Would this 6312 Nachi bearing be adequate on the output shaft?

It's a spicer 7041

That is actually an SKF 312nr because it has the snap ring on the outside diameter.
An SKF 6312nr is a 10 ball, but is rated for 85200n
Any reason I can't go with this?

bearings with the fill-notch have more balls. more is better. did you check gear centre prices? those bearing prices seemed quite high or was that for a re-bearing kit? also you might check Applied Technologies in G P and just give them the bearing numbers

that SKF 312 bearing at $572 sounds like gouge-the-oilfield price

For some reason I don't get emailed when you guys reply, so just seen you replies now. Thats about right, this is Grande Prairie everything is gouge-the-oilfield price around here. Can anyone tell me what oil I need to run in this when I finally get it back together? I read somewhere it requires 30, 40, or 50 wieght mineral oil. Can I just run 85/90 gear oil since thats pretty standard stuff?

85w/90 GL5 gearlube is all I've ever seen used in those transmissions