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Suspension Bolt Sizes?

RustyC

RustyC

Knucklehead
Joined
May 20, 2020
Member Number
733
Messages
390
Loc
Alabama
Linked suspension systems.

What is the proper size bolts to use for connecting control arms to the chassis / axle?
Obviously a race car or bouncer needs massive bolts to match their application. What is needed for the rest of the vehicles out there on the trail?
Myself I feel like a 5/8" or 16mm is the smallest I"m comfortable with on a lower link. I think using a 3/4 or 18MM offers a bit more confidence for resisting breaking from impact to a link from landing on or hitting a rock.

What about upper links? They should never see impact forces. So how small is too small?
9/16 or 14mm is the smallest for uppers in my opinion.

What about the upper link in a 3 link? Is 9/16 or 14mm enough then?
Bushing type suspension joints would cushion the mounting hardware a bit but for this discussion let's focus on hiems or uni-balls.

How small can you go to save weight before it compromises durability or potential failure?

If you have had a link / control arm bolt failure please chime in!
 
Weasel said:
3/4" all the way limits the number of bolts you need.
Click to expand...
X2. I like 3/4 inch bolts because you can torque them properly and they don't have a tendency to loosen. I don't know why, but it seems like when I torque check 3/4" bolt they are rarely loose. I use 3/4" bolts in every location, upper, lower and steering.

I also absolutely hate 9/16 bolts. Try finding a replacement for that in a hardware store in Harlan, KY when you need it.
 
I ran 5/8 all around on my old Silverado with 3 link. My new trail rig has 4 link front and rear and also uses 5/8 bolts for the links. 3/4 are the Hydraulic steering attachments.
I wanna talk link material sizes..... should i start a new thread???
 
The 3 times i took my old rec buggy to the hammers, i broke the chassis end 3/4 bolt on the single upper. I got lucky both times and the bolts got trapped in position. IMO link bolts are not a place to save weight, the link yes but not the bolts.
 
My XJ on tons will be using grade 8 9/16” bolts. When I asked about bolts for links in a previous thread I made people told me to make the grip length the width of the bracket. No one mentioned bolt size mattering. A lot of it might depend on rig weight. I’m not doing heims. I’m doing Metal cloak joints. My brain tells me “if Johnny Joints come in a 2 5/8 width and 9/16 bolt then 9/16 bolts are good enough for me” especially when lots of brackets come with a 9/16 bolt hole.

edit: I agree with the statement “finding 9/16 sucks” because it does. Caterpillar dealers are open on sundays and sell 5/8 in every size and have them in stock. Finding 9/16 fine thread isn’t easy.
 
3/4 for steering, 5/8 for links, 1/2 for most other things is sorta my thinking unlesss it's litle stuff.
 
Same as the above for me. 3rd gen runner, 3 linked on 40s...

Fine thread bolts also seem to hold their torque much better than a coarse thread bolt.
 
I have 1" bolts on my buggy. Everywhere.

If I had to do it again I'd go 3/4" everywhere with RPI bolts.
 
It's a brand that makes high end fasteners.

Kinda like ARP, yeah, but they are very much oriented towards offroad racing vs ARP. They know about proper grip length etc.

And the owner is even active on RDZ.
 
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Tensile strength of a fine thread 5/8” bolt seems pretty astronomical to me.


I’d argue that the average recreational rig would be just fine with hardware store 9/16” hardware in the links. Those of us who like to drive by braille, 5/8”. Ultra4, CAT 5/8” and/or 3/4”. Bouncers 3/4”.

It’s all dependent on the use of the vehicle.
 
I'm using 5/8 bolts in my metal cloak joints for my 1 ton chevy on 40s. but at the rate im going i dont think it will ever leave the garage.
 
CAT 3/4"
Byro said:
Tensile strength of a fine thread 5/8” bolt seems pretty astronomical to me.


I’d argue that the average recreational rig would be just fine with hardware store 9/16” hardware in the links. Those of us who like to drive by braille, 5/8”. Ultra4, CAT 5/8” and/or 3/4”. Bouncers 3/4”.

It’s all dependent on the use of the vehicle.
Click to expand...

Links are typically shear ~ 60% of YS. And TS isn't much use, if it hits that point your bolt isn't holding the clamping load.
 
RustyC said:
Everyone loves Caterpillar hardware. I work for a CAT dealer. Lock nuts are the bad ass all metal design.
Click to expand...

The flex lock type ? Those are cool.

6751816-23.jpg


Do you have the same chart with fine threads ?
 
No the non clamping side of the nut is domed and ovaled just a bit. Repeated removal and installation wears the threads on t he bolt a bit. I'll go get a photo.
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Last edited:
12 point Oil and Phosphate and Oil coated. Course and Fine thread.
Screenshot 2022-06-02 082241.jpg
 
The nuts are stamped in the red area. It distorts the threads just enough to lock in place.

Screenshot 2022-06-02 093211.jpg
 
Does anyone know of anyone who offers a thick weld washer that has an internal hex design?

A weld washer with a 1.125" hex would prevent a 3/4" nut or bolt head from turning allowing the hardware to be easily torqued and prevent the hardware from turning. This could be stacked on top of a standard weld washer.

Some equipment manufactures use square stock welded so the one or more of the flats of the hardware is held form turning. This is very helpful in very tight locations when there is little room for tooling.
 
I tried to post the One Safe Source to the resources tab but never could get it to upload.

I order mine through the CAT parts Store Online, goes to my local dealer and picked, bagged, and ready to pickup in 30 mins or less usually. Also will tell you if it's in stock or not. If it's not in stock, 90% of the time it will be shipped and available next day. Santa has nothing on CAT shipping program.
 
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