Both Rear Upper Control Arms Sheared off? WTF! - Page 6 - Toyota 4Runner Forum

02SE · 10-23-2022, 06:01 PM

Quote:

Originally Posted by TRD PANTHER

Thanks for that link. It was a very interesting and informative video on the KDSS system. That helped a lot. I always hear the pros and cons of the system, but I honestly don’t pay much attention since I don’t have it. I see the pros. What are the cons?

Not a cheap option.
Another system that can potentially have issues.
More involved to lift beyond 2-3".
Harsher ride in certain conditions such as washboarded roads. Aftermarket items are available to alleviate that.

Despite the potential downsides, I still like having it.

honda250xtitan · 10-23-2022, 10:31 PM

Quote:

Originally Posted by TRD PANTHER

I need to watch a video on the KDSS system. Thanks

naw. its just a sway bar with 2 fixed links and 2 pistons. hydraulic fluid flows back and forth/locked in position via valves. done. everyone hypes up how complex it is (it's not)

Shamish · 10-23-2022, 11:16 PM

Quote:

Originally Posted by Jetboy

FWIW - It's very likely the result of the bushings. Poly bushings are not an upgrade in many cases and are not appropriate for the rear control arms. The rear control arms require more complex motion than a simple hinge joint like the front suspension. The ends need to both hinge around the center bolt but also twist axially as the link rotates and flex out of alignment as them move through the various suspension motions.

The flex out of alignment with the bushing pivot bolt is probably what caused this failure. Because the bushing wouldn't flex enough to accommodate the angles needed, the solid rod was bending at the top of the weld bead. That's where the load would be maximum and there's a stress riser. So most likely that's where you started to get metal fatigue after repeated bends, just like breaking a paperclip. And eventually it failed.

Fortunately it sounds like it wasn't on the highway in an emergency maneuver or something like that.

Looks like you have some replacements. I would put some washers in or you may be able to collapse the brackets enough to tighten up. I would not let them float loose on the collar of the through bolt.

Good luck.

You can see some of the classic metal fatigue in those ends, although it's hard without a bit more resolution than you end up with over the forum. There are pretty clear progression zones and then an area of fracture when it broke completely.

I think an engineer would call this a "high cycle low stress fatigue fracture". But I'm not an engineer. So I call it a paperclip break. The main takeaway is that it wasn't from hitting something hard. It was from lots of small back and forth bending over time where the poly bushing wouldn't flex enough and resulted in the shaft bending back and forth.

If it were a result of an instant impact where it pulled so hard on the end that it ripped apart it would look more like this (ductile fracture):

I am an engineer and I once worked with an engineer who diagnosed a situation where bolts on electric transmission line structures were failing in a similar manner. You basically nailed the situation. Thanks for explaining it in clear terms!

MidniteTRD · 10-24-2022, 08:46 AM

Quote:

Originally Posted by comtn4x4

I got the arm installed today. Yes that's right @honda250xtitan you got your wish. Only the passenger side arm installed. However, that wasn't my intent initially. My local Toyota dealer only got me one set of hardware so I could only do one, and I need the truck. I may install the second one later. I did install 2 washers on each joint to take up the slop. Took a test drive and she's running great! Thanks to everyone especially @MStudt for getting these to me on the fly.

Mike these are really well made and really competitive in price. I'd recommend them to anyone who's interested. I'll report back as time goes on regarding performance and maintenance.

kinda off topic but you might want to reposition that rubber line from touching the exhaust.

glad you got the new parts in, and thanks for having the guts to show us all the carnage so the community can learn from this.

MStudt · 10-24-2022, 09:57 AM

Quote:

Originally Posted by honda250xtitan

I used to build traction bars for some of the titan guys back in the day. I alwasy did one end with Heims and the other end with a poly bushing. those traction bars didnt twist as much as the 4runner links, but same idea. I'd love a full of arms from Mstudt, they look killer. Heims are pain to keep noise free with age but they work so well.

That's why I don't use heim joints on control arms. The Flex Joints that I use from Summit Machine are vastly different than a heim joint, and hold up extremely well to abuse and miles.

Quote:

Originally Posted by comtn4x4

Although, shiny new parts are lots of fun!
Looking at the Overland Custom Design lower control arms, I'd have to do some more investigation. If you orient the heim joints so that you can access the zerk fittings they'll be in a potentially vulnerable position on both the axle and frame mount. And it looks like on the frame mount end the zerk would be really close to my mount guard during down travel. If you turn the heim so the zerk is on the other side you'd have to remove the arm every time you wanted to grease or inspect it. I've already had problems bashing those areas. Maybe @MStudt can speak to that.

The zerk fittings are always supposed to be facing upward for that reason. Even a random rock kicked up from the road can break a zerk, and having them at the highest point is best. You can add 45* zerks to the joints to make them easier to access, but it not required. With a 45* zerk you'll be able to access the frame side on the lower by giving the axel a little droop. Unfortunately the axel side you won't be that lucky on.

Mike

comtn4x4 · 10-24-2022, 10:03 AM

Quote:

Originally Posted by TRD PANTHER

Thanks for that link. It was a very interesting and informative video on the KDSS system. That helped a lot. I always hear the pros and cons of the system, but I honestly don’t pay much attention since I don’t have it. I see the pros. What are the cons?

I think 02SE hit it pretty well. One additional plus I rarely see mentioned is if you carry a lot of weight on your roof rack or have a RTT KDSS will be a godsend.
My opinion is lifting with KDSS up to the 3" is threshold requires no more thought than lifting a non KDSS rig up to that same height. (Which is how almost all 4runners are lifted) KDSS blocks aren't necessary unless you're neurotic about the lean and the KDSS switch isn't necessary but it's really nice. (All these KDSS improvements are relatively new in terms of how long KDSS has been available. ) Where KDSS gets complicated is if you want to be lifted and have it preform REALLY well, full potential droop in the rear end and return the system to level front and rear. And it gets really complicated to do a long travel set up, debate-ably not worth it.

baldrik78 · 10-24-2022, 10:55 AM

Quote:

Originally Posted by comtn4x4

I do have the Sonoran Steel KDSS adjustable trac bar. It's positioned as it is supposed to be. I also have a KDSS spacer block. Are they what is causing the issue? Good question, I don't think so bit it's certainly possible.

It could be a combination of the added flex from the trac-bar/KDSS spacers with the less flexible poly bushing.

Products that look good in a vacuum can have vastly different outcomes when stacked with another non-oem product.

jbtvt · 10-27-2022, 07:10 PM

From your pics showing intact paint it doesn't look like those arms were heated to remove the old bushings, and it wouldn't be expected. The shop would've been a cloud of black smoke from burning rubber long before the metallurgy was affected. Map gas will burn off paint pretty easily and it's hard (impossible?) to get a piece that size anywhere near red hot with a standard tip, oxy acetylene torches paint almost instantly

comtn4x4 · 11-10-2022, 06:03 PM

I was e-mailing with Steve from Sonoran Steel the other day about this and here's his take on it:

"As for the links coming apart, yes I have seen that before. But not how you think. In the year 2000 with the 3rd gen 4Runner Toyota had issues with the welding on the upper rear links. This only happened to model years 2000-2002, in that case the weld on the end tube did not penetrate. In your case the weld did not penetrate the small center rod.

If you look at the breaks they had rust in them prior to coming apart. The small silver areas are where the welding penetrated the center rod, these are the areas that actually held them together. If these were welded correctly, then the bushings would have sheared and split from over twisting. You could clean them up and re-weld by someone who can weld correctly and then side twist and spit the bushings. Toyotas part supplier probably uses a computer welder but the machine/robot seems to be set wrong from time to time lacking penetration and they don't seem to do destruction QA testing.

The upper links came apart because of very poor welding. That is disappointing that they are still having this happen. There is no way a soft poly bushings will hold up to welded steel, the poly will fail first."

jbtvt · 11-13-2022, 11:31 PM

I think he's mistaken. Those welds look good to me, and though we can't really tell from the photo angle, the break appears to be through the solid bar stock itself above the weld. The only way you'll get that "high cycle low stress" fracture pattern as jetboy so eloquently described is if the weld is holding and the bar itself is being torqued beyond its yield point. The rusty one I thought was established was likely broken for a while and you didn't notice symptoms until the other one also gave out.

comtn4x4 · 11-14-2022, 11:08 AM

Quote:

Originally Posted by jbtvt

I think he's mistaken. Those welds look good to me, and though we can't really tell from the photo angle, the break appears to be through the solid bar stock itself above the weld. The only way you'll get that "high cycle low stress" fracture pattern as jetboy so eloquently described is if the weld is holding and the bar itself is being torqued beyond its yield point. The rusty one I thought was established was likely broken for a while and you didn't notice symptoms until the other one also gave out.

That's very possible. I'm not sure if we'll know for certain.

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