Check The Torque On Rear Leaf Spring U Bolts!

[quangdog]

After someone brought up in the discussion about start up shudder that their rear leaf spring U-bolts were not torqued correctly, I decided to check mine. I was a little surprised to see that mine were also not to spec, so I recorded the process of torquing them correctly on one side of the truck. The other side is done exactly the same way.

I have not noticed any change to my start up shudder, but I've previously also lowered my center carrier bearing which almost completely eliminated the start up shudder... it's barely a flutter now. I do plan to put my carrier bearing back to the stock height to see if it's any better now that the leaf springs are torqued down correctly... but I suspect it won't really have made much difference.

Anyhow, here is how to torque your rear leaf spring U-bolts, per the shop manual:

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[VAMike]

Morpheus asks: how do you know the shop manual is the one that's right?

 

[Bsqrd]

Morpheus asks: how do you know the shop manual is the one that's right?

Maybe quangdog could post the shop manual pages for us.

 

[janitorjim]

Maybe quangdog could post the shop manual pages for us.

https://www.ranger5g.com/forum/attachments/204-02-rear-suspension-shop-manual-zip.2977/

 

[janitorjim]

dammit Jim, he said Quangdog......why you gotta come in and show off like that?

post count who*e

 

[quangdog]

Morpheus asks: how do you know the shop manual is the one that's right?

I mean…you gotta trust something. Shop manual has been right for everything else I’ve done on this truck…

Also: based on the size of these bolts, frankly I’m surprised they don’t need to be torqued even more than 98ftlbs.

They were almost certainly under torque from the factory, or have loosened up a bit in the 16k miles I’ve driven it …

 

[Langwilliams]

I had to retorque bolts all the time on my Harley Shovelhead. Then god gas us loctite.

 

[VegasRanger]

My U-bolts were ridiculously lose. I didn't mess with this procedure though, I just tightened them all to 98 from the start. I noticed it improved my highway vibration issues I was having for sure.

 

[Trigganometry]

Depending on the temper of the U bolts they will stretch under normal use. Same as head bolts, they stretch too but you don’t want to be cranking them down to original specs again.

 

[TJ1]

Interesting write up Kimball. Looks like I'll be crawling under my 2019 Magnetic XLT with clicker torque wrench in hand even though there is no hint of any vibration.
Thought here is that if said bolts are too loose the axle assy could rotate under load/acceleration (pinion climb), this could then increase the pinion angle and drive shaft vibration. Hmmm ...
Tom Jacobi
Dallas, Tx

 

[landiscarrier]

Mine were 54 at best.

 

[quangdog]

i'd go with the loosen up after use theory. especially if you run the truck to the extremes. I wouldn't expect a mall crawler to have as many torque issues as someone bashing up and down trails every weekend, or other hoonigan type events.
pretty easy for that to happen i think.

if the torque was too high, could start crushing the tube from the force.

I deal with re-torque specs all the time with work.
basically as things get used, things can loosen. even self locking nuts are not all the same when it comes to their drag torque. I've seen videos of assembly lines and they do use proper torquing tools. of course there can be tool issues, or user issues, but they may be few and far between

I do take this truck offroad, but not to the extremes. However, I have (especially when I first got it) driven it over lots of washboard, single-track stuff up and down mountains around here. I think I'll give it 3-6 months and check the torque on these bolts again... if they have loosened up again, I'll either leave them alone or loctite them.

 

[jblc]

Depending on the temper of the U bolts they will stretch under normal use. Same as head bolts, they stretch too but you don’t want to be cranking them down to original specs again.

Does anyone know how would we know if we should tighten to the original specs, then, or keep them as we find it?

 

[jblc]

just a few things from standard practices on suspension u-bolts, including the tech manual
as you can see, its cut and dry to replace them....but, i am sure there are literally millions of home mechanics who never have.
and much like covid we could discuss the risk to ourselves and others till we are all blue in the face.

It sounds like re-torquing might not be a good idea, since it may be expected that the nut torque is lower through use.
But, that wouldn't explain why the vibe occurs with some people until they tighten down...maybe some are correctly torqued from factory, some not.

 

[Trigganometry]

Does anyone know how would we know if we should tighten to the original specs, then, or keep them as we find it?

You could try to re torque them but if they come lose again you know the answer. Metal fatigue is very unforgiving. When you really don’t want it to is when it will fail. Safest approach if it were me under those circumstances would be to get the proper replacements with new hardware and redo the assembly using factory specified specs.

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