Replacing Rear Bump Stops

active.world

active.world

Active Member
I am planning to replace my rear bump stops (the upper one?... i saw mention of a lower elsewhere, but i dont have that). I have new OEM parts - MR210482. The bump stops appears to be held in place diagonally by one end of each pair of u-bolt on the rear axel. A few basic questions:
1) does the van need to be jacked up to remove this or is there any danger in disassembling the bolt from only 1-side of the u-bolt without lifting? Shop manual does not specify any pre-removal instructions.
2) are there any "gotchas" i should be aware of before doing this?
3) finally, just to confirm i'm reading the correct spec (highlighted in green)... the nuts on the u-bolts get torqued down to 61-80 ft.lbs?
Screen Shot 2023-08-16 at 9.06.14 PM.png

Every other bump stop has been incredibly simple, so hoping its the same here. Thanks!
 
I would normally take the load off the springs when doing this kind of thing, there can be a lot of stored energy there to accidentally move things otherwise. I read the torque values as you state from the diagram.

It's generally recommended to replace the u-bolts when you've de-torqued them, particularly if they've been on the vehicle a while, as they can develop stress cracks around the threads once you re-load them.
 
Thanks for that Terry. Do you know if there are standard sized U-bolts that i can pick up from local auto parts store, and if so, what that spec is?? I consider myself a total beginner/dummy when it comes to vehicle suspension. I've not done any work on my rear axel/suspension besides put on Monroe shocks a year ago and add IronMan helper springs, so the u-bolts are most likely what was put on the van when it was built.
 
L300 U-bolts are re-usable, but replacement is always a good idea. They are not a standard US size. I would either replace them with OEM Mitsubishi bolts, or re-use them. I wouldn't fit aftermarket bolts.

For just removing the bump stops on a 4WD L300, I would keep the springs loaded with an axle stand under the axle. If the axle is hanging when you undo the nuts, it can move out of alignment and make reassembly difficult. Final re-torquing of the U-bolt nuts should always be done with vehicle weight on the axle (This is the opposite of most leaf-sprung vehicles, where the axle is mounted above the spring).

Loosen all four U-bolt nuts by 3-4 turns, and then fully remove only the two nuts that retain the bump stop. That'll take the load off the U-bolts but should keep everything else together. Re-tighten the nuts in stages (40ft.lb, 50, 55, etc) and check that all four nuts have the same amount of threads protruding; it's easy to tighten one side too much, which pulls the U-bolt out of square.
 
Is this something that i should consider visiting an wheel alignment shop after doing? I've previously only ever gotten the front wheels aligned, but now I'm a little worried I could throw things off in the rear. Would the rear axel/wheels only get out of alignment if I similarly can not get the u-bolts put back together smoothly?
 
No, the rear axle can only go together one way and realignment is not required (or possible).

The risk I'm referring to comes when you do a partial disassembly (like loosening the U-bolts to remove the bump stop). There's a locating pin that goes through the leaf spring pack, which locates the spring to the axle and the top plate, but there is also a rubber isolator between the two: if the axle or top plate become loose and the axle twists, the rubber isolator can get pinched and the axle will not re-seat correctly when you re-tighten the U-bolts.
As long as you support the rear axle to keep the spring at least slightly compressed, there should be no risk of this happening. Leaving two of the u-bolt nuts in place will also keep everything together.

If the axle does twist and doesn't go back together straight, you just have to remove the U-bolts completely, lower the axle, and reinstall it straight. Easy, but extra work.
 
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