Part I described what I went thru for the removal, repair, and replacement ot a damaged hydraulic cylinder. Part II described the forces generated when the cylinder is in motion. This final Part III will tell what I ran into while fixing the cylinder. OK, here is what I found.

A. Pulley Head: The steel pulley head is attached to the cylinder rod by a 3/4" threaded conn. The pulley head slides smoothly ( hopefully ) over the 3/4" guide rod. On my 1702T the pulley head hole had very close clearance to the rod. ( a few thousands ) The 3/4" hole also had very sharp edges that could catch on the guide rod if there was any distortion. In other words if the pulley head became slightly "cocked" it could hang up. This could cause bending and distortion of the guide rod and the piston rod that carries the pulley head. SOLUTION: I took a grinder and enlarged the hole in the pulley head. I also chamfered or beveled the edges of the hole so it would not hang up.

B. Guide Rod: My guide rod was corroded, dirty, ungreased, and bent out of line by 1/2". Looked like a dog-leg. SOLUTION: Hack-saw to remove and junk it. Got a new rod ( chrome plated ) and installed.

C. Piston Rod: My piston rod was bent 1/2" out of line and the cylinder was jammed and inoperative. Junk it, remove and replace. See Part I for details. SOLUTION: Had to be replaced, could not repair.

D. Top Alignment: My top was 2" lower in the front. The cables were not equal tension. This caused, during certain phases of the raising and lowering, that there may be an off-center pull ( eccentric loading ) on the rods which could cause bending of the rods, guide and piston. SOLUTION: Adjust the cables per the manual.

In my case, I believe that some combination of factors caused a bending and distortion of the rods, guide and piston. Even if it is only a small distortion, during the subsequent cycles of raising and lowering the distortion and bending could get worse and worse. From Part II, there are considerable forces that the pump can put out. If there is a hang-up the pump will put out more and more pressure up to the relief setting. The forces are more than enough to severely bend and tear up the rods. They did in my case. Remember the pump is a positive displacement type and will put out pressure.

Recommendations:

1. Clean and grease the guide rod per the manual.

2. Adjust the cables so the top is level and the cables have equal tension. There are procedures for this in the manual and on the forum.

3 Be careful of climbing on the roof when it is in the raised position hanging on the cables. I estimate each cable has a load of about 300#. If you climbed up on one corner, you could easily double the load. Old rusted cables could break.

4. Watch out for overloading the roof with snow falling off the house. Could over load the cables.

5. If you get a chance, crawl under the trailer and observe the cylinder during a cycle of raising and lowering. You may be able to spot an incipient problem.

GOOD LUCK !

Agreed! Nice writeup Ed. I take it you don't feel there will be any "wobble" in the pulley head due to the larger hole? Or, if there is, it will not cause problems?

And, I don't suppose it would be possible to get a picture of what you are talking about there?

I've already decided to do some thorough maintenance on our Hi-Lo when we get back from Yosemite next month. And, I'll definitely crawl under it and have Janet raise and lower it (as you suggested). I've been meaning to do something like that for a while now, since I haven't yet figured out quite how the cables are "pulled"/"wound up"/whatever to raise the top.

I had adjusted my cables to correct a low condition at the front, but it's come back (about half-way) again. In the collective experience of everyone, does this seem to be a normal symptom of cable stretching, or should I start getting worried about something else?

- Jack

I just took a few thousands on the hole. I believe the big improvement is the bevel or chamfer on the hole edge. This keeps the pulley plate from "digging in" if it gets a little misaligned.

From my experience if the cable adjust changes in a short time there is a problem developing. If I were you I would crawl under and look at everything before a trip, if cables are rusty they are not going to last long, a broken cable while on a trip is no fun. I have had a cable break on two different trips. If you are a DIY person, the cable can be replaced by getting a length of 3/16 cable at Lowes, the original cable is 5/32 but 3/16 will work and cable clamps also buy some lengths of 2X3 to hold the trailer top up, use your tow truck jack and wood and the lift to get it up, try to keep the top level a few inches at a time, not a fun job but it can be done in 2 to 3 hrs. Spare cables on hand is best even if you take to a RV dealer for repair, as they would have to order the cable and it could lay you up several days.