85 Bluebird Minibird rear leaf spring failure

[Austin J Hampton]

Hi guys, as the thread title says, we've had a rear leaf spring U-bolt break. I've got several questions on the situation.
BACKGROUND: Buddy and I bought an '85 Bluebird Minibird in April 2023. 90K miles on it. Good bones - a PA school bus with remarkably little rust on the frame and drive train, only a few floorboard pinholes that were easily patched. We changed all fluids, put on new tires, shocks, steering damper, belts, hoses, etc. New water pump and fuel pump as well. On the road August 2023. It's a short trip vehicle, Chevy P30 platform, 6.2L diesel, turbo 400 transmission no overdrive, and the Rockwell 12 rearend with 5.13 gears. Not a turnpike cruiser but so far we put about 1200 trouble free miles on it. It spent this winter here in upstate NY parked on a crushed stone pad next to our driveway, my wife's objections notwithstanding.
PROBLEM: Yesterday I pulled it onto our blacktop to inspect and get ready for the season, and soon discovered a large bolt laying in the crushed stone, 3/4" dia x 12" long. Crawling underneath it quickly became apparent that it was half of one of the drivers side U-bolts that join the axle to the leaf springs. The other half was hanging there loosely, and the other U-bolt is now loose, lacking the force balance of the pair of them. The break appears to be (as expected) a tensile failure, maybe started after 40 years with a stress corrosion crack. Man were we lucky and blessed. It apparently failed shuttling around the driveway AND fell out there where it could be discovered immediately. What are the odds of that. As loose as the other bolt is now, I don't think the rearend would have stayed underneath long, and it probably would have let go without much warning. I've been able to figure out which U-bolt pair to order on Rock Auto, and it's on the way.
QUESTIONS for anyone who might know -
1) Is this a common failure mode for U-bolts in 40 year old buses? Anyone else seen this? Should I change the other pair on the passenger side? And the front U-bolts as well joining leaf springs to the solid front axle?
2) I had to cut the broken half to get it out through the plate. It looks to me like I can remove the other drivers side U-bolt and install the new ones with the bus on the pavement in the driveway, with appropriate safety precautions. Anyone else done this and have any suggestions?
3) I've sprayed the nuts on the other U-bolt with PBlaster and have a pair of MAPP gas torches to heat them with before trying to remove. Any suggestions on other pre-work rust treatments?
4) This is odd - the driver side leaf spring has 11 leaves and the passenger side has 10 leaves. U-bolt lengths are sized to match. Is it common to have mismatched springs? Or maybe one of the springs was replaced with an aftermarket one that is different from OEM?

Any answers to the above are appreciated, as well as advice on anything that I don't know that I don't know.
AJ

 

[magnakansas]

I have seen spring packs with unequal number of leaves. Not super common, but has been done before. My bus, I am certain, needs front springs replace due to fatigue. I think I have lost a couple of inches on the front ride height. In my case $1200 for a pair of new springs. I would be inclined to replace all four rear u-bolts. Looks like quite a bit of erosion more than enough to introduce stress point and begin a crack. Telephone if you want to talk about suspension failures. 7852077600

William

 

[Mr P]

A torch or cut off wheel will likely be easier/faster than turning the nuts on the remaining bolts. I fix automobiles, and it's somewhat common to find bolts that have rusted to about 1/5 their diameter...hanging by a thread....on trucks that are 30+ years old and have been used in the winter (salty roads) and muddy conditions.

After installation of new bolts/buts, retorque them after driving just in case there is rust between the spring leaves that "crushes" and loosens the bolts. (Old rusty leaf springs that are loosened and moved around will probably have some rust/scale that interferes with proper torque "memory". )

 

[Austin J Hampton]

Thanks for your replies, guys. We'll get the broken side fixed first and see what we learn before moving to the other side U-bolts. MA, I would like to talk. I'll give you a call later today.