Yes, its old. It has 225k miles and I am trying to get it to 300k. (on its original transmission too)

I am having problems with the rear shock absorbers. The bolts keep breaking off flush with the mount, which results in me having to drill it out. Ive done this twice with the passenger side and once now with the driver's side, and its getting old quick. (I can never get the extractors to bite enough)

The shocks themselves are still good, the van doesnt bounce at all when I jump on the trailer hitch. I am thinking maybe they are TOO stiff for the van - I bought some fairly expensive HD shocks and put them on since I was/am using it to haul equipment for work. The equipment itself isnt over 300lbs - way below the payload rating for that Van. I dont use the trailer hitch for anything; it was there when I bought it used.

Ive used the equilvalent of grade 8 bolts in it and torqued then TO specs, then over specs after the first breaking.

Ive noticed some funny things about the design down there too - one leaf spring...? It has a higher payload rating than my small pickup yet the pickup has 3 leaf springs on each side. This makes no sense to me. Also, the shocks point forward, and IMO they should point rearward from the bottom so it actually supports the rear of the van, not the center. It looks like an inferior design for something thats supposed to haul 7 passengers to me.

 

Grade 8 bolts are stiffer than Grade 5, it MAY be that when torqued to specs, THEN a load is placed on it, the bolts cannot stretch and break.

POSSIBLY you can try grade 5 bolts, torque them to spec, and when under load it may be within it specified limits and not break.

OR the heavy duty shocks may need stronger/different design bolts since under load more stress is put on the bolts.

OR your torque wrench is not calibrated right and may be over torquing the grade 8 bolts.

I added rear monroe coil over load leveling shocks on my 96 gc, with stock bolts and have towed a light ( 1000 pound ) trailer without a problem.

Hope this helps

 

The bolt strength makes total sense. I downgraded to metric 8.8 which should put me around SAE grade 5 or 6. I looked and the passenger side has metric 8.8 in it and that has held since the last time I worked on it. The driver's side sheared off when I hit about a 12" pothole at 35mph so I cant really blame the bolt, though it was definitely old.

Hopefully I was just trying to make it too strong before, not giving it the little 'wiggle room' it needed.

 

Sounds like you were doing the right thing going stronger, It could be that the particular grade 8 bolts you got may have a lower stress limit due to length or application?

Could also be the TYPE of forces placed on it, SHEAR strength may be less THAN compression strength for the same type of bolt, it may just be why different strength bolts are used in different places, each has it's designated rating for that type of particular load.

Check with Rancho suspension or other off road shock makers or forums and see what they use it may help!!

 

Grade 8 bolts are made harder so they won't stretch. This also makes them more brittle and therefore reduces the shear strength. I think you'll be fine if you go to the softer bolts.