RACKING and TWISTING WHEN LEVELING

[timeforus]

I have a 05 Dip. and when leveling there is an issue with racking and twisting. Wondering if I'm doing something wrong. Just the slightest movement will rack the basement doors and the upper right corner of the windshield shows twisting. Stopped using the on-board level and now use my iPhone with an app that has a level, placed in the refer. Seems to do a little better, but if I need to do anything more than stabilizing then there is windshield and compartment/s (between the wheels) movement. Have had the rig for two summers now.

[RCLImperial]

A few years back, I had my '04 Holiday Rambler 40 ft imperial up on jacks and I extended one of the slides and the upper passenger side of the windshield cracked. I lived with that windshield until it started to generate glass splinters on the dashboard. After that, I was careful to only extend/retract the slides only when the air suspension was at ride height, which was the Monaco recommendation. One of the things I noticed was that the windshield shifted around a great deal while the coach is being moved.

When the windshield was replaced, the shop was careful to glue it into the rubber gasket. I questioned them and they said that glueing was the recommended installation process. I don't recall if the casket was glued to the fiberglas opening, bit I'm pretty sure that it is. Now nothing shifts around during leveling. The windshield has held up for a couple of years and some 12k miles of travel without incident. I'm beginning to believe that the windshield is an integral structural element of the coach and that glueing contributes to the stiffness of the coach. I also suspect that even though the jacks are a three point system, they can induce some twisting moment to the structure, perhaps caused by the fact that they lift the frame directly, rather than the air bags which act as a more distributed force.

Dick L

[walt2137]

When parking slide out then level by front jack down to at least touch then level with rears, leaving start the coach jacks should retract air up slide in.

[timeforus]

Thanks for your responses. I always retract or extend the slides when bags are powered up. After extending the slides, I dump the air then always extent front jack first, then rears as needed. Seems like the more the rears are extended the more the basement doors rack.

[walt2137]

That is a unusual, I'm sorry but The only thing I can think of is To get under the coach and inspect everything looking for a crack on suspension or frame.

[ShapeShifter]

Originally Posted by RCLImperial

I also suspect that even though the jacks are a three point system, they can induce some twisting moment to the structure, perhaps caused by the fact that they lift the frame directly, rather than the air bags which act as a more distributed force.

There are those who say that racking is not possible with a three point jack. They are wrong: it can and does happen. I've seen it.

It definitely happens if you don't extend the front jack enough to act as a pivot. If the site has a significant lean to it, you must extend the front jack enough so that neither front axle bump stop comes into play. If you raise the lower corner so much that it pivots on the front jack and then then the high corner hits the front axle bump stop, you will get a lot of twist.

The hardest sites to level on are where the back end is lower than the front, and the site also slopes to the side. That was exactly what we ran into last weekend. The issue is that you need to raise the front enough so it has room to do the sideways pivot, but you don't want to do that because it means that the back needs to be even higher. But the need to pivot trumps all. I ended up driving my rear wheels up on the blocks I normally carry, and borrowing some concrete blocks from the campground to put under the rear jacks. However, I still couldn't get completely level: I raised the front quite a bit to give me a pivot, and the front axle still hit the high side bump stop before I was level side to side. I finally did get it mostly level side to side, but I had to raise the front enough that I spent the weekend with a bit of a front/back slope.

I was on the proper three point pivot with the front axle free of the stops, yet the coach still had a noticeable rack to it - the top passenger corner of the windshield was a bit out of place, and the driver side basement doors had enough of a rack to them that when opened they didn't clear the bottom of the slide. There was no permanent damage, but racking can and does happen on particularly difficult sites.

Originally Posted by walt2137

then level by front jack down to at least touch then level with rears

Not just touching, but raise the front of the coach at least an inch or two after touching, then level with the rears. But as described above, if the side-to-side level of the site is very bad, you will have to raise the front more than an inch or two, even if it's the front side that's high.

The best bet is to find a site that's level in both directions. If that's not possible, my preferences are a site that's lower in front than in back and pretty level side to side, followed by a site that's only slightly lower in back than in front yet still fairly level side to side. My last choices are sites that have a significant side to side lean, especially if they are low in back.

I've found that it's the side to side adjustment that causes the most racking.

[timeforus]

WOW! Thanks so much for what appears to be some very knowledgeable info. I usually make the front jack just make ground contact, raise the rears (even if it's just a little) and when I exit the rig, see that the windshield has moved in the upper curb side corner and basement doors are racked. I will try to raise the front a little more and then raise and level with the rears. What's your opinion on how the windshield must be installed, totally sealed or not. Again, thanks

[ShapeShifter]

Originally Posted by timeforus

What's your opinion on how the windshield must be installed, totally sealed or not.

That's a tough one, I can see both sides of the argument. Mine is not glued in place: neither on the glass nor fiberglass sides of the gasket. I can see the benefit there where it would allow the glass to shift around to relieve stress, but it allows it to pop out more easily. That happened to me where a corner came loose: took it to a glass shop, the worked on it a bit to get the glass back in the gasket and mostly in place, and didn't charge me for it. The flexing from driving home from the glass shop worked it back fully into place.

If it were glued in place, it would be less likely to pop out. But it's that movement the relieves the stresses, so I would think that a glued in windshield would be more likely to crack? It may get some extra strength from the body, and give some extra strength to the body to help absorb flex, but at some point it's going to be too much for the glass?

I only have two experiences with windshields under twisting forces: my non-glued windshield which popped a corner out, and was free ton fix, and a friends glued windshield which got a dozen cracks in it running down the driver's side where it curves back to the sidewall. I'm not disappointed that mine isn't glued.

[RCLImperial]

Been thinking about the racking of the coach and have come to some conclusions about the subject. When they put slides into a coach, you affect the structural stiffness. The coach is stiffer and more resistant to wracking when the slides are in. The stiffness is augmented by the close contact of the outer skin structure of the slide. In the out position, there is less structural support, because it relies on the inner frame of the slide. Anywhere in between in and out, there is little support, because the slide has little contact with the coach walls. I believe that this is the rationale for only extending the slides while the air suspension is at run height.

Another conclusion that I have come to is that the three point jacks can't protect against wracking. The coach frame has to be somewhat flexible, because the alternative is to beef it up until it is so heavy that it affected the weight and cost. Consider a flexible plate with a three point support, at three of the four corners. If you place weight at the unsupported corner, the plate will flex. Our coaches have the front support at the center line, but there is np guarantee that the side to side weight is uniform. This side to side imbalance can cause wracking.

In the case where I cracked my windshield by extending one slide when it was up on jacks, I think that the side to side weight imbalance was what caused the wracking. Also, during the slide extension, the coach stiffness was compromised by the slide no longer being in full contact with the walls.

These coaches are by their nature are fragile and need to be carefully handled, and everything in the structure is contributing to their resistance to wracking.

Just my thoughts...

Dick L. '04 HR Imperial 40 ft

[ShapeShifter]

Dick, I think you have some very valid thoughts. Yes, I agree that cutting holes in the sides of the coach for slides affects rigidity, that's one of the reasons I was afraid to go with the 40SFT model at the time I bought mine - it has a full wall slide, the first year that they did it (I think) and I was just to concerned about losing the structural integrity of the whole side of the coach.

You mention the added rigidity when the slides are in, I'm not convinced that really makes much of a difference. I suppose there could be a little in/out movement of a corner when the body is racked, and the flange of the slideout might help prevent that. But I'm thinking that any racking is going to have a tendency to affect the squareness of the slide opening more than anything, which will cause the wall to slide sideways compared to the slide flange, and and I don't see the wall/flange interface really doing anything to prevent that.

I agree with your comment about the three point system not preventing racking. I think it greatly reduces racking compared to an improperly deployed four jack system, but the possibility for twist still exists - especially if the front isn't raised enough and one of the front bump stops makes contact: that would turn the three point system into an improperly deployed four contact point system (three jacks and the bump stop.)

[wa8yxm]

First you need to understand your jacks.. Since I am not looking at your Rig I am not sure of your jacks, but there are basically 3 systems I will describe,, NOTE: Hydraulic or electric does not matter save for systems 1 and 3

1: 3-jack system, One front center, one on each side in the rear
2: 4 Jack system (Two front jacks work together however so act as one)
3: 4 (or six) jacks system, all jacks independent of the other.

Mine is #2 (power gear)

My PDI technician said he liked to put down the Rear jacks first, then the FRONT, then work to level it... WRONG

Put the FRONT down first on systems 1 and 2.. ON system 2 they balance and act like a single point centered.. This way the front of the RV can "Rock" side to side on that single point.. THEN use your rear jacks to balance front to back and side to side.

Alas, if you have independent jacks.. None of this helps.