Maintenance Q&A
Torn trailers, bum batteries and out-of-whack adjusters

By Paul Abelson, senior technical editor

Q. I have a small fleet and buy used equipment. We do a lot of drop and hook at public warehouses one of our shippers uses. We often get holes punched in our trailers.

Of course, no one knows who drove the forklifts. The warehouse operator doesn’t keep records of who loaded any particular trailer, and the shipper claims no responsibility.

What is the best way to fix the holes in the trailers? I really don’t care about appearance, but I want the repairs weatherproof.

A.  I don’t have that much personal experience with trailer walls, so I turned to my “Brain Trust” –retired TMC Silver Spark Plugs Carl Tapp, vice president of maintenance with P.A.M. Transport, and Tom Tahaney, Kenworth regional service manager. They agreed that for a quick repair, use sheet metal and pop rivets.

Start by cutting out any jagged or bent metal around the hole so you are left with smooth, flat metal with a smooth hole. Don’t leave any overlapping cuts or sharp corners in the base metal. These can become stress risers under the patch. As the trailer experiences road shock and vibration, cracks and stress fractures will start at those points and grow, often beyond the repaired area.

Use similar metal for repairs (steel on a steel trailer, aluminum on aluminum, and stainless on stainless) so the metals expand and contract at similar rates. It will minimize stresses at the fastener holes.

Create a template to cut the patch. It should be at least two inches larger all around than the trimmed hole to allow space to the patch. Mark where the rivet holes should go on the template to make sure they are at least one inch away from the edge of the patch and one inch away from the edge of the hole.

Cut the patch out of the appropriate metal and drill holes for the rivets. Apply RTV (room temperature vulcanizing) silicone sealer to the outer edges of the hole and the patch. Make sure there is a continuous bead of sealer on both pieces. Press and hold them together for a few minutes to let them set.

Once the patch can be left without shifting, use the drilled holes in the patch as pilot holes to continue drilling the rivet holes.

Then use a pop-riveter to permanently fasten the patch in place. Use similar metal-rivets. Stainless steel pop-rivets can be found in marine supply stores.

Of course, duct tape gives the quickest repair. It may get you home (once) with dry cargo, but replace it immediately.

Q. I spent a lot of money switching batteries from four 675 CCA lead-acid, regular batteries to four new absorbed glass mat (AGM) batteries to power my 12-volt air conditioner.

Rated at 1000 CCA, they are supposed to give longer life. The salesman said they combine high cranking power, long life and extra deep-cycling, but after a few weeks they died. The dealership replaced them and everything was fine for a while. Then the new batteries failed just like the others. This time the dealer said no adjustment, so I went back to the old-type batteries. We’re still arguing over the money. Can you help?

A. I can’t get between you and your dealer, but according to my Brain Trust, this has more to do with truck architecture than with the batteries. AGM batteries are very sensitive to heat. They are completely sealed and have a minimal amount of electrolyte paste between their pure lead plates. This paste can cook when heat is too high, weakening the batteries’ ability to accept a charge or produce power.

In some trucks, the diesel particulate filter (DPF) is next to the battery box, or right under it, often with only a sheet of metal – itself a heat conductor – between the batteries and the DPF. When the DPF regenerates, its internal temperature is raised to close to 1,000 degrees to convert soot to inert carbon dioxide. Even though the outsides of the DPFs are well insulated, they still get as hot as a typical truck muffler. Placing batteries over the heat is what cooked them.

If you still want the advantages that AGM batteries offer, you could try insulating the battery box or, better yet, relocating the batteries farther from the DPF.

Q. One of my slack adjusters on my 2009 Freightliner Coronado always seems to be out of adjustment. The others work just fine. They all get serviced and checked the same way, but the left front drive axle always wears quicker. Why?

A. There’s usually an underlying problem in the foundation brake. Today, just about every truck has automatic slack adjusters, and as the name implies they take up slack caused by brake wear.

If one regularly goes out of adjustment, that brake is wearing more than the others. Check the spider plate for bends or cracks. It holds the brake components in alignment. Check to see if the S-camshaft is bent. Even a 1/8-inch misalignment will create problems. And, of course, check that the slack adjuster has been properly greased and is functioning on each stroke.

These are critical components. Brackets and spider plates cannot be straightened if bent. When in doubt with brake parts, it’s always best to replace them. Do it in pairs to avoid future problems. And always look for underlying causes. LL