# Glossary > Working vocabulary for specialty vehicle repair. Source: https://ocrv.info/resources/glossary ## Delamination A bonded wall losing its bond. Skin, adhesive, substrate and framing stop behaving as one panel, so the surface flexes on its own and reads as a bubble or a long ripple in reflected light. Water causes most of it. Impact causes the rest. ## Gelcoat A pigmented polyester surface layer molded into a fiberglass part rather than sprayed onto it later. It is thicker than paint, it goes chalky under sustained UV, and it crazes into fine webs wherever the laminate underneath has been flexing. ## Azdel A polypropylene and fiberglass composite board used as wall substrate in place of thin plywood. It neither absorbs water nor rots, so a leak in an Azdel wall does far less collateral damage than the same leak in a plywood wall. It costs more and weighs more per sheet. ## Lauan Thin tropical plywood laminated behind the exterior skin on a great many RV walls and floors. Light, inexpensive and thirsty. Once it takes on water it swells, loses fastener grip and never regains structural value, which is why wet lauan gets removed rather than dried in place. ## Filon A fiberglass reinforced plastic sheet used as the exterior skin on laminated walls. It arrives as a roll, gets bonded to substrate under pressure, and is painted rather than gelcoated. It repairs well across a flat run and poorly across a molded radius. ## EPDM A synthetic rubber roofing membrane, usually white, fastened at the edges and bonded across the deck. It weathers by chalking, which streaks the sidewalls below it, and it thins gradually until a seam or a penetration edge finally lets go. ## TPO Thermoplastic polyolefin roofing membrane. Its seams can be heat welded rather than only taped, and the surface holds reflectivity longer than rubber. It is stiffer to work with, less forgiving over an irregular deck, and it does not chalk the way rubber does. ## Lap sealant The self leveling compound run along horizontal roof joints and around every penetration. It flows out to bridge a gap and then skins over. A non sag version exists for vertical surfaces. Neither replaces correct bedding underneath, and neither belongs on top of silicone. ## Schwintek An in wall slide mechanism using two vertical gear racks driven by synchronized motors set into the side jambs. Compact and common on lighter rooms. Its signature failure is tooth wear on one column, which lets the room walk out of time and bind on the next cycle. ## Kingpin The hardened vertical pin under a fifth wheel's forward overhang that engages the tow vehicle hitch jaws. Wear, an out of tolerance diameter or a cracked mounting plate is a structural finding rather than a cosmetic one, and it changes how the entire tow load is carried. ## Pin box The bolted or welded assembly holding the kingpin and transferring tow loads into the trailer frame. It absorbs the worst of a jackknife or a hard chuck. It also hides damage well, since the visible plate can look straight while the frame behind it is bent. ## Betterment A deduction an insurer applies when a repair leaves you with a component in better condition than it was before the loss. Tires, roof membrane, awning fabric and batteries draw it most often. The carrier pays for the damage and you pay the depreciated share. ## Supplement An addition to an already approved estimate covering damage found after the first inspection. On laminated bodies this is normal rather than exceptional, because the boundary of the damage is invisible until panels come off. Photographs and written measurements are what get one approved. ## Actual cash value Replacement cost minus depreciation. It is the settlement basis on most standard policies and it explains why a total loss check on an older coach surprises the owner. Comparable listings for the same model and condition are the practical currency in any argument over the number. ## Agreed value A policy structure in which the insurer and the owner fix the settlement amount in writing at issue. Common on collectible and high end coaches. It removes the depreciation argument entirely, at the price of a higher premium and a periodic revaluation of the unit. ## Appearance allowance A cash amount an insurer offers instead of paying for a cosmetic repair, generally where the defect is minor and the correct fix is disproportionate. Accepting one closes that item. It is a legitimate tool and also a common way for small damage to leave a file quietly. ## LKQ part Like kind and quality. An original component pulled from a salvage unit and supplied in place of new. On discontinued molded panels it is frequently the only path that exists at all. Condition varies enormously, so an LKQ part should be inspected before anyone plans around it. ## ADAS recalibration Resetting the aim and reference of driver assistance sensors after a repair moves the surfaces they look through or sit behind. A windshield replacement, a bumper reinstall or a mirror change on a modern chassis can all require it. Skipping it leaves a system reporting normal while aiming wrong. ## Blend time Refinish labor spent fading new color into the adjacent undamaged panel so that no boundary is visible. It is a separate line from panel refinish, it is among the most disputed items on an outside estimate, and leaving it off is the usual reason a repair looks like a repair. ## Substrate Whatever a finish or a skin is bonded to. On a laminated wall that means the plywood or composite board behind the fiberglass. On a painted panel it means the primer and the material under it. Repairs fail at the substrate far more often than at the surface. ## Sikaflex A family of polyurethane structural adhesive and sealant products used for bonding panels, bedding windows and sealing seams that move. It cures tough and stays flexible. Surface preparation and the correct primer decide whether it holds for years or peels within a season. ## Butyl tape A non curing rubber tape laid under anything that bolts through the skin, from windows to roof vents. It never hardens, which is exactly the point, because the joint moves. It is a bedding compound rather than a topical sealant and it belongs under hardware, not over it. ## Dry rot Shorthand for two unrelated problems. On tires it means UV and ozone cracking in the sidewall and tread grooves with no relation to remaining tread. On wood it means fungal decay in substrate that stayed damp. Both are driven by age and exposure, and neither reverses. ## Soft spot A floor or wall area that yields underfoot or under hand pressure. It marks substrate that has lost fiber strength to moisture. The affected area is nearly always larger than the part that feels soft, which is why probing past the obvious edge belongs in any honest estimate. ## Tap test Running a plastic mallet or a coin across a laminated surface and listening. Sound material returns a sharp, bright report. Delaminated or saturated material returns a dull thud. It costs nothing, it takes minutes, and it locates a repair boundary better than looking ever does. ## Moisture meter An instrument that reads water content in a substrate. Pin type meters measure resistance between two probes and leave small holes. Pinless meters read capacitance through the surface without damage but respond to whatever sits behind. Useful shops record readings on a grid instead of quoting one number. ## Unibody Construction in which body panels and floor carry structural load instead of sitting on a separate frame. Sprinter, Transit and ProMaster vans are built this way. Repairing one means measured pulling against reference points, not simply replacing whichever panel looks bent. ## Subframe A secondary structural assembly bolted or welded to the main frame to carry one specific load, such as a slide room, a generator, a liftgate or a suspension group. Damage here is easy to miss, because it sits above or behind the parts that actually show the impact. ## A-pillar The upright structure on each side of a windshield. On a cab chassis coach or a van it carries roof load and defines windshield geometry, so a tweaked pillar usually announces itself as a windshield that will not stay sealed rather than as a visible bend. ## Front cap The molded fiberglass shell forming the nose of a coach or trailer. It is one large part with compound curvature, it is expensive, and on older units it is often out of production, which turns cap damage into a repair decision rather than a parts decision. ## Basement bay The pass through storage compartments below the floor of a coach. They also carry tanks, plumbing runs, electrical distribution and sometimes the generator, so an impact to a bay door frame is rarely only an impact to a bay door frame. ## Slide topper A fabric awning above a slide room that unrolls automatically as the room extends, keeping debris and standing water off the room roof. When its spring tension drops the fabric pools, and pooled water goes looking for the top seal. ## Wet bolt A greasable replacement for the plain shackle bolts in a leaf spring suspension. It carries a zerk fitting and a grease groove so the bushing surface stays lubricated. Fitting them is the standard cure for the ovalled holes and squealing shackles common on multi axle trailers. ## Shackle The link connecting one end of a leaf spring to its frame hanger, letting the spring change length as it flexes. Worn shackles and elongated bolt holes produce axle misalignment, uneven tire wear and the clunk owners describe as a loose feeling trailer. ## Leaf spring A stack of curved steel plates carrying axle load on most trailers and many chassis. They sag with age and overload, dropping ride height and changing axle spacing. A sagged pack is measurable by comparing free arch side to side, and it is not judged by looking at it. ## Torsion axle A suspension design in which rubber cords inside a square axle tube twist to absorb movement, with no springs, shackles or equalizer. It rides well and asks for almost no service. It also cannot be rebuilt, so once the rubber takes a set the whole axle gets replaced. ## Wheel bearing repack Removing, cleaning, inspecting and refilling trailer hub bearings with fresh grease, then setting preload correctly. Neglected bearings cause a large share of highway axle failures on trailers, and the service interval is measured in miles rather than in seasons. ## Shore power One hundred twenty volt utility power delivered to the coach through a cord and inlet, usually at thirty or fifty amps. It feeds the converter and the branch circuits directly. Inlet condition matters; a heat discolored contact at the inlet is a fire risk rather than a nuisance. ## Transfer switch The device deciding whether the coach draws from shore power or from the generator, and preventing both from feeding the panel at once. Automatic versions switch on their own after a short delay. Burned contacts inside one produce intermittent power loss that mimics a wiring fault. ## Inverter Converts twelve volt battery power into one hundred twenty volt alternating current so household devices run without shore power or a generator. Pure sine output matters for electronics and motors. Idle draw matters for anyone who leaves the unit switched on overnight. ## Converter Works the opposite direction from an inverter, stepping shore or generator power down to charge the battery bank and run twelve volt loads. A converter with one fixed output voltage will never bring a bank to full. A multi stage unit with a correct profile will. ## MPPT Maximum power point tracking. A solar charge controller that continuously finds the array voltage and current combination producing the most power, then converts it down to battery voltage. It beats a simpler controller by a wide margin on cold mornings and with panels wired in series. ## LiFePO4 Lithium iron phosphate battery chemistry. It delivers most of its rated capacity as usable energy, accepts charge quickly, holds voltage nearly flat under load and weighs a fraction of lead acid. It requires a battery management system and it must not be charged below freezing. ## Absorption refrigerator A refrigerator with no compressor. An LP flame or an electric element drives an ammonia solution through a sealed circuit to move heat. It runs silently and off grid, it wants the coach reasonably level, and it fails in a way that leaves yellow residue on the cooling unit. ## Hard start capacitor A capacitor added to a roof air compressor circuit to raise starting torque, helping the unit start on a marginal supply such as a small generator or a long cord run. It addresses a starting symptom and does nothing for a compressor that is already failing. ## Macerator A pump with a grinding impeller that reduces black tank contents to slurry so waste can travel through a small hose over distance or uphill. Convenient, and completely unforgiving of anything that should not have entered the tank in the first place. ## Black tank The holding tank for toilet waste. It is gravity fed and vented through the roof, and its level sensors foul routinely. A tank reading full immediately after a dump is nearly always a fouled sensor rather than a blockage, and the two get confused constantly. ## Gray tank The holding tank for sink and shower drainage. It fills faster than most owners expect, it produces the sour smell people blame on the black tank, and a restricted vent path is the first thing to check when a shower starts draining slowly. ## PEX Cross linked polyethylene tubing used for nearly all fresh water plumbing in modern coaches. It flexes, it survives a freeze better than rigid pipe, and it joins with crimp rings or expansion fittings. When it leaks, the crimp is usually at fault rather than the tubing. ## Hydronic heat A heating system that warms a fluid loop with a diesel or electric burner and circulates it to heat exchangers around the coach, usually producing domestic hot water on the same loop. Quiet and very even. Diagnosis means following the loop rather than replacing the part that is complaining. ## AquaHot A brand of hydronic heating and hot water system fitted to higher end coaches. It combines a diesel burner, electric elements and often engine coolant heat into a single loop. Servicing it means understanding the loop as a system, not swapping the component that is currently loud. ## Onan A long established brand of recreational and commercial generator set. Owners use the name the way they use the word generator. Service work concentrates on fuel delivery, brushes and slip rings, control boards, and exercising the set under real load rather than at idle. ## Load bank A test device that draws a controlled electrical load so a generator or a battery bank can be judged under real conditions. Running a generator unloaded proves almost nothing. A load bank test finds the set that starts beautifully and folds at seventy percent output. ## Corner post The vertical structural member at each rear corner of a box body or trailer, tying the roof rail to the floor frame and carrying door hardware. It is the first thing a dock strike folds, and a bent post throws the entire rear door opening out of square. ## Roll up door A segmented overhead door on a box body, running in side tracks on rollers with a counterbalance spring. It jams when a track bends, when a roller seizes or when spring tension drops. Forcing a binding door bends more track and multiplies the repair. ## Reefer liner The interior lining panel inside a refrigerated body, generally a bonded fiberglass or plastic sheet over insulation foam. Its job is keeping moisture out of the foam. A torn liner lets insulation take on water, gain weight and lose thermal value permanently. ## Liftgate A powered platform at the rear of a truck or van for raising and lowering freight. Rail, tuck under and cantilever styles all exist. Failures cluster in hydraulic seals, bent hinge pins, worn rollers and the electrical path between the battery and the pump motor. ## Headache rack A steel or aluminum barrier mounted behind a truck cab to protect the rear window and the occupants from shifting cargo. Some carry lighting, tie downs or a rack for long material. Fatigue in the mounting hardware is the usual finding during a body inspection. ## DOT reflective tape Red and white conspicuity tape applied in a specified pattern along the sides and rear of larger trailers and box bodies so they are visible at night. It lifts at the edges, degrades with UV, and is destroyed by body damage, so it gets replaced whenever a panel is restored. ## Kick panel The lower interior trim panel below a dash or beside a footwell. It hides wiring bundles, relays and sometimes a fuse block, which makes it the first panel out on a twelve volt diagnostic and a reliable place to find evidence of previous repairs. ## Wheel well The formed housing over a tire, inside the body or under a fender. On a coach it doubles as a structural element in the sidewall and floor and sits directly in road spray, so corrosion and delamination frequently begin at its upper edge. ## Rocker The lower body section running between the front and rear wheel openings, below the door line. On a van it is structural and takes jack loads. On a coach the equivalent skirt area collects road debris and is the first place a curb strike registers. ## Quarter panel The rear side body section between the rear door opening and the back of the vehicle. On a van it is welded rather than bolted, so damage there means sectioning at an approved seam instead of unbolting a part and hanging a new one. ## Clear coat The unpigmented top layer over base color that supplies gloss and UV protection. It fails by delaminating in sheets rather than fading gradually, and once peeling has started the only correct fix is stripping that area to a sound layer and refinishing it. ## Orange peel A dimpled surface texture in cured paint, named for exactly what it looks like. Gun setup, reducer choice, film build and booth temperature all produce it. It can be cut and polished out when the clear film is thick enough to survive the sanding. ## Fisheye A small circular crater that opens in wet paint where silicone or oil contaminated the surface. It appears within seconds of the coat going on. Sanding the area and respraying is the only reliable fix, and the contamination source has to be found before the respray. ## Tack rag A resin treated cloth wiped across a prepared surface immediately before spraying, lifting the dust that blowing off left behind. Cheap, unglamorous, and responsible for more of the final finish quality than most of the equipment standing in the booth. --- OCRV Center. 23281 La Palma Ave, Yorba Linda, CA 92887. (949) 799-3387. info@ocrvcenter.com. Serving Eastvale, California in Riverside County, about 20 miles from the shop. All work is performed in shop at the Yorba Linda facility. No mobile, roadside or on-site service is offered. Scope is body, paint, structural, fiberglass, interior and vehicle systems work. Engine rebuilds, transmission rebuilds, drivetrain work, DOT inspections and emission testing are not performed.