Blocks under jacks, coach wheels off the floor. What holds the rear axle up.

[Guest Ray Davis]

Thanks Harry, actually it does make sense.  I couldn't get my brain straightened out for a while.  Sometimes ya gotta get away from it and when you return it's clear.

 

[96 EVO]

2 hours ago, Happycarz said:

 

Once the anchor points are attached, install the chains. Attaching the chains can be another story. To each, their own!

Would be cool if someone who's coach came equipped with limiting straps / chains, could post a picture. 

[vanwill52]

On 5/22/2023 at 8:48 AM, Ray Davis said:

Ok, I'm not quite getting the vision here,  how do we have a single chain on both driver & pass side, while placing the chains in the middle fore & aft?

I envisioned placing a chain on each side of the axles ( 4 chains ) but now I wonder did you place yours to hold up the H frame and thus the axles too? 

Ray, I'm not sure I'm explaining this explicitly.  But yes, there are a total of FOUR chains on my coach...one on each side of the front H-frame, and one on each side of the rear H-frame.  They are all attached to the H-FRAME, and then to the COACH FRAME.  NONE are attached to the axle itself.  "In the middle fore and aft" refers to the chains being attached at approximately the center point (for and aft) of the H-frame, which also equates to approximately at the location of either the front or rear axle.  Each one is APPROXIMATELY centered over the respective axle.  Since the trailing arms make the movement of the H-frame into the movement of a parallelogram (verical movement only--no tipping fore or aft) ONLY ONE chain is required on EACH SIDE of the front H-frame, and ONE CHAIN on EACH SIDE of the rear H-frame.

Actually, in all honesty, I must admit that my technically astute partner Paul Whittle (who was assisting in this procedure), asked, "Why are you putting two chains on EACH side of the H-frame?  Due to the trailing arms, the H-frame is moving vertically, NOT on an arc (neglecting the minor effect of the Panhard bar), so ONE chain will suffice.  Much like a four-legged chair, only three legs are guaranteed to touch the floor, until the chair frame bends and allows the fourth leg to touch the floor.  Had I installed two chains on each corner (total of eight), probably only four of them would be under tension.

The important thing is that you be sure that the single chain is tight and supporting weight BEFORE the shocks bottom out and possibly put all that weight on the upper shock mounts in the front.

Does that make sense?  Sometimes pictures or drawings are better at explaining this stuff, but I'm really pressed for time in the next few days, doing some physically taxing work for some church friends before I leave on my short trip.  If this still does not make sense to you, let me know, and when I return from my short trip, I'll try to post pix.

Thank you for being one of the "gentlemen" on this forum.

[Guest Ray Davis]

Van, yes it absolutely does make sense.  Thanks for taking the time to explain.  Pictures are always nice,   you know the saying about a thousand words,  but don't go to the trouble on my account.   Get your work done and have a nice trip.   

[Jim Pratten]

34 minutes ago, Ray Davis said:

Van, yes it absolutely does make sense.  

Ditto and thanks @vanwill52 

[DavidL]

There is no concern about a shock not able to hold the weight of the axle up in the air.

Keep in mind the suspension system is designed to "bottom out" (shocks completely compressed / axle hitting it's "bump stop") AND "top out" (axle at the total limits of either the shock / strap).  These are dynamic loads while driving that WAY exceed any pressure an axle exerts on a shock while sitting still.  An analogy is having a baseball bat "pushed" against you vs. swung at you.

There is so much "lore" in this issue on RV forums.

And, like others have said, don't get underneath an RV / car / truck if the tires aren't on blocks and the suspension is aired down, OR the chassis is suspended by properly rated jack stands on firm ground.

I wouldn't use chains as limiters at all.  Way too abrupt stop.  That's how things break.  Straps at least have a little give.  Plus chains are noisy and can get hooked on things and cause damage.  Chains are used in off road vehicles, but the primary reason is to keep the axle with the vehicle IF the suspension points break (due to excessive force).

The only ill factor I can think of from extended axle hanging is the air bag is extended as well.  If the bag is old / brittle, then it can then be damaged...but if it's old / brittle, time for a change (one of my projects for this Spring)

If the vehicle uses springs / leaf springs, then it will enjoy not having any weight on them.

Edited May 24, 2023 by DavidL

[vanwill52]

David, I respect your knowledge and experience, but what you describe has never happened to me.

In my fifteen years of RV experience, I have never once "bottomed out" or risen high enough to reach the point at which shocks would be extended to their limit.  Nor have I known anyone who has.  My restraint chains are for nothing but keeping the load off the shocks, and ESPECIALLY the upper shock mounts, when I am STATIONARY, and using my hydraulic leveling jacks to pick the wheels off the ground before I insert jack stands under the coach prior to crawling underneath it.

There are many instances reported on this forum and iRV2 of upper shock mount breakage, especially the FRONT cantilevered ones, and I doubt even one of them was caused by a HUGE vertical "leap" of the coach under driving conditions.  So far, all damage I have ever read of, was caused by lifting a wheel off the ground with the hydraulic leveling jacks.  And, as I said, the upper mounts are a BITCH to repair, as they require welding in a very confined space...ask me how I know.  I have repaired one of these upper mounts (NOT on my coach), and even with the Miller "confined spaces helmet", if you don't have a welding blanket to cover yourself, you will at the least have BB holes in all you are wearing, OR something you are wearing will begin smoldering.

And as far as the noise chains might make, I mentioned that concern myself in a post when I was installing them.  However, I found that even when trying VERY HARD to notice the noise chains might make, I've heard NOTHING.  I had expected to have to enclose them in rubber tubing to diminish the noise.  That proved to be totally unnecessary.  I had the same experience when installing 3/4" diameter restraint "rods" (as opposed to chains) on Paul Whittle's 2004 (?) Sig.  The rods were easier to install (still required welding), stronger even than the chains, and were TOTALLY silent.  They performed the same function as the chains--when raising the coach by external means (with or without hydraulic jacks), the rods took all the load off the shocks for supporting the weight of the axles when wheels were raised above the ground. 

I have so far found NO negative aspects to having "restraint chains", but considerable benefit when crawling under the coach.  And I bet I have removed wheels from my coach more than 99% of owners.  I remove them simply to make polishing my (non--coated) wheels easier to polish with a home-built/welded) wheel spindle, or to make access to under-coach systems more accessible.

So, I just want to say, David, I read all your posts because they contain valuable info and insight.  But I think on this one subject you have missed the point.  The restraint straps/chains/rods have NOTHING to do with suspension movements DURING TRAVELING.  They are simply to prevent damaging shocks or, more importantly, the shock mounts themselves when the coach is being raised for service and the wheels are being raised off the ground level.

Thank you for your many insightful contributions.