Problems with Rear Suspension and Handling

[ryan-in-oregon]

In effort to check on the safety of the LR3 I want to revive an old thread on a control arm failure.....Clicky, Now I have read through all the postings on the two active threads on this forum as well as the one I just linked to. It is my opinion that the above linked crash is NOT due to a front control arm failure. (Thats the good news) However in looking through the pics you will notice that the right rear track rod has the same failed bolt that I and several others have had. When the bolt fails the rig tends to "wonder" on the freeway especially during left handed turns. I believe he lost control due to this failure and smacked the center jersey barrier, this in turn damaged the front suspension as evidenced by the damage to the lower section of the front bumper and caused the airbags to blow......If this is the case the NHTSA needs to be notified and something done to correct this problem......What do you guys think that have been looking into and following this topic???

 

[Rogo]

Ryan - thanks for resurrecting this. As you can see in my prior posts, I suspected something in the rear.

I concur - this is very likely related.

 

[ryan-in-oregon]

Ryan - thanks for resurrecting this. As you can see in my prior posts, I suspected something in the rear.

I concur - this is very likely related.

Is that your LR3?? At the time of the failure I actually agreed and thought the front control arm was the root cause. But not now!!

 

[Rogo]

Is that your LR3?? At the time of the failure I actually agreed and thought the front control arm was the root cause. But not now!!

It is my LR3.

Here is the discussion on this board http://forums.landroverworld.org/showthread.php?t=14917

 

[blackforestham]

Interesting. Glad you're ok! You may be onto something here Ryan. See other thread...

 

[Houm_WA]

Rogo, did you ever have an alignment done at an indy shop or otherwise have an occassion where that bolt would've been removed (like for a rear bushing replacement)?

 

[Geotrash]

Thanks for connecting the dots, Ryan. This is an interesting thread as are the others. Just read every post with great interest. Couple of observations. Looks like 2 folks have said that they found loose rear control rod bolts when they investigated a slight shimmy or directional instability. It definitely looks like a smoking gun for the control issues several have reported.

It's a very small sample size to suggest a root cause but looseness in this bolt is probably it. A loose bolt will not handle the shear loads that a properly torqued bolt will withstand, and so the failure sequence could be: 1/ bolt loosens 2/ shear loads increase on the bolt as the looseness causes rapid changes in tire tracking 3/ bolt fails and the truck is difficult or impossible to control at speed.

If this approximates the failure sequence then perhaps periodically checking the torque on the bolt would be a wise preventative measure.

The second observation is that corrosion could be a factor. If the corrosion is restricting the ability of the control arm to pivot freely on the bolt with normal suspension travel, then it would create a loosening torque on the bolt in the up direction of suspension travel on the right rear corner of the car. Since the up direction of travel is the direction of heaviest load on the bolt, it stands to reason that it would be the right rear corner that's been problematic.

All speculation based on limited information, but seems plausible. Whatever the root cause, it's scary stuff given some of the roads around Colorado.

Dave

 

[Houm_WA]

A few things....it isn't quite an increase in shear load if the bolt gets loose. Rather, you'd get a combination of shear and bending across the bolt. Even looking at the pics of the broken bolt you can see some "smeared" threads. This could be an indication of a slight bending moment across the bolt as well. The failure of a part when there is an interaction of two or more kinds of loads can be significantly less than if it was pure tension, compression or shear.
Either way, I agree that a loose bolt is the trigger for this issue.

The second thing, is that I wonder if it's good to check the looseness by re-torqueing. Could that hurt the bolt's integrity? Particularly, if it wasn't loose before and then it gets wrenched on? Not sure how that works...

 

[ryan-in-oregon]

To properly torque a bolt you need to loosen it then retorgue. Other wise you have to over come the friction holding it in place. As far as a corrosion concern there was absolutly none on the bolt or inside portion of the track rod when I had it apart. Also the rubber bushing is what pivots. So yes I agree that checking the bolts periodically is a good thing however we are in the minor few that will. As a safety concern for other people driving these (the ones that have no interest in mechanics and just use it as transportation) I still think this is something that needs to be brought to LR's attention...However they will likely brush me off so there will have to be multiple complaints....

 

[Geotrash]

The failure of a part when there is an interaction of two or more kinds of loads can be significantly less than if it was pure tension, compression or shear.

Particularly, if it wasn't loose before and then it gets wrenched on? Not sure how that works...

Couple of quick replies (eyes getting very sleepy)

1/ Yes, bending would be a factor the more the bolt loosens. Omitted for brevity.

2/ Unless it's a stretch bolt, the effects of loosening and re-torquing the bolt should not affect the bolt's strength, unless you over-torque it. Torque wrenches are one place in my toolbox I pony up to buy the best.

Ryan- If you plan to formally raise the issue, a proper letter to Land Rover North America is probably the best way to start, so that they can track the issue and have the chance to deal with it without the expense of added attention and press, I would include printouts of the forum posts describing the problem, and the photographs of the missing/damaged bolts. You can always notify the NTSB if LR doesn't respond.

Best,
Dave