Regular Suspension on Mojave

[chr15m]

I should add this, perhaps the most important part IMO.

If youve ever removed a bolt that had the middle threads shaved off, you'll know why this isnt a risk worth taking on cramped space, with large bolts and high fastening torque values.

Have a saw and torch ready.

Sponsored

 

[outdoor.adventures]

Thanks for the additional knowledge, @chr15m .

Also worth saying: None of this should really dissuade someone from putting Mojave suspension on a Rubicon or any other trim. It's not much of a headache. The complete solution with the right bolt size isn't a big task - just requires a drill bit (9/16" I believe is the easier to find match) to enlarge the existing shock mount holes where applicable on the front, and the right M14 hardware themselves. Not bad at all.

 

[Wheelin98TJ]

If I understand what is being said, if a smaller diameter bolt is used to fasten thru an larger diameter mounting point there will be a couple possible issues.

First, while the fastening static force is applied to the outer fastening surfaces, any slack between them will still allow for movement. They may not "become loose", as in the bolt can remain at initial torque settings, but the tolerance between the bolt and bushing in this case will still allow vibration and movement between the two. Eventually this will wallow or ovalize the two and eventually increase the movement between them. It'll be fine initially, but wear will occur and will accelerate the wear rate the longer it is left. Eventually fracturing the bushing most likely and resulting in some of what we've seen on here with Billstien bushings cracking.

I've had bolts loosen and wallow, within a hundred miles the bushings and frame flanges were damaged. It can happen quickly. Bad experience with a bad tech when I was careless enough to not do the work myself.

Second, it may be possible that the increased tolerance between the bolt and bushing could reduce the fastening surface and allow more of the force to be located on the frame flanges, possible resulting in deformation. While the first will happen eventually. The second is an assumption, but may also occur, and has under different circumstances for me.



Static fastening force does this at the bolt head and the flange of the nut or in our case the surface surrounding the welded/threaded frame nut. Most likely those would stay the same, even with the improper diameter bushing. If the length was wrong, then this changes the clamping force as well.

The bolt and bushing are also subject to shear forces, this is where you would want as much reinforcement or shear strength as possible, coupled with low tolerance between parts. Tolerance or gaps allow potentially uneven dispersal of force and possibly allow greater torque to exist than designed to allow when those gaps allow parts to become fulcrums that weren't intended to be. If the gap between the bolt and bushing were increased the bushing could be allowed to achieve greater angles and place greater torque values on both parts as a result. The gaps also allow increase occurrences of these torque values, accelerating wear. Both the bolt and bushing would incur more stress and vibration.

There are bolts everywhere that don’t perfectly fit the holes. And places that see a lot more force than shock bolts. You need a pressed fit to achieve what you want and you can’t have that everywhere.

 

[chr15m]

There are bolts everywhere that don’t perfectly fit the holes. And places that see a lot more force than shock bolts. You need a pressed fit to achieve what you want and you can’t have that everywhere.

But you can have it on shocks, where the bushing and machine bushing are press fit.. Beyond that I'm not sure I follow the press fit "bolt" concept you imply, unless you mean a shouldered bolt, a compression or carriage style bolt. Even with shouldered bolts being 2mm smaller in diameter you'd have the same issues.

As far as force, the suspension components, after the axle hub have some of the largest and highest fastening torque of all the parts of the vehicle due to the force they are subject to.

I routinely install fasteners that are required to have essentially nearest to no tolerance and seal to prevent atmospheric leaks while also being subject to constant 24/7 movement. Improper tolerance between bolts and fittings is a common failure I see junior techs make, so I'm not unfamiliar with this specific question. The greatest concern though again remains, the frequent cycling combined with any slack or hysteresis in the mechanical system. There is more wear generated when there is room for deviation to occur, that's the short of it. I'd say it occupies a good 10-20% of the failures in my daily work. Lots of moving parts, like shocks that simply make constant strokes, any slack beyond intentional design is a guarantee for premature failure.

The bolt diameter delta between m12 and m14 isn't just about the visible size. The sheer strength between the 2 is easily more than 20% greater for the m14. Grade dependent, some other exceptions, but like bolts compared, yeah easily more than 20%.

The reason Jeep opted for the M14 bolt was done along side the changes in the reinforced shock mounts, both upper and lower, to withstand higher sheer and impact forces from driving offroad at higher speeds.

Of course YMMV based off your use, but at the very least, improperly matched bolts and bushings will accelerate wear.

 

[Gregj]

I’m sure the FAD housing will be broken long before the shock bolt, LOL.
Gregj

 

[Wheelin98TJ]

But you can have it on shocks, where the bushing and machine bushing are press fit.. Beyond that I'm not sure I follow the press fit "bolt" concept you imply, unless you mean a shouldered bolt, a compression or carriage style bolt. Even with shouldered bolts being 2mm smaller in diameter you'd have the same issues.

As far as force, the suspension components, after the axle hub have some of the largest and highest fastening torque of all the parts of the vehicle due to the force they are subject to.

I routinely install fasteners that are required to have essentially nearest to no tolerance and seal to prevent atmospheric leaks while also being subject to constant 24/7 movement. Improper tolerance between bolts and fittings is a common failure I see junior techs make, so I'm not unfamiliar with this specific question. The greatest concern though again remains, the frequent cycling combined with any slack or hysteresis in the mechanical system. There is more wear generated when there is room for deviation to occur, that's the short of it. I'd say it occupies a good 10-20% of the failures in my daily work. Lots of moving parts, like shocks that simply make constant strokes, any slack beyond intentional design is a guarantee for premature failure.

The bolt diameter delta between m12 and m14 isn't just about the visible size. The sheer strength between the 2 is easily more than 20% greater for the m14. Grade dependent, some other exceptions, but like bolts compared, yeah easily more than 20%.

The reason Jeep opted for the M14 bolt was done along side the changes in the reinforced shock mounts, both upper and lower, to withstand higher sheer and impact forces from driving offroad at higher speeds.

Of course YMMV based off your use, but at the very least, improperly matched bolts and bushings will accelerate wear.

I might’ve strayed a little. I was talking about how critical the size of the mounting holes are. I thought that’s what you were talking about when you said mounting point.

I agree the bolt and bushing should match.

 

[RudeJeepin]

I'll either press them out and replace with M14 size bushings or drill and sleeve the frame threads to reduce down to M12. Bushings probably make more sense, but we'll see!

If you got the new shocks from a place like AccuTune, I'd bet they could put the right bushing in them. Then it would be a simple bolt up.

 

[chr15m]

I might’ve strayed a little. I was talking about how critical the size of the mounting holes are. I thought that’s what you were talking about when you said mounting point.

I agree the bolt and bushing should match.

Likewise, no worries, all here to help.

Sponsored