8.4 Drive Axle Lubrication, Fill Procedures, Leaks, Carrier Removal, Housings, Lube Pumps, and Temperature Indicators

8.4 Drive Axle Lubrication, Fill Procedures, Leaks, Carrier Removal, Housings, Lube Pumps, and Temperature Indicators

Six of the 20 drive axle tasks on the ASE T3 list are about keeping the axle lubricated and sealed. They cover: checking and repairing leaks at covers, gaskets, vents, magnetic plugs and seals; checking fluid level and condition with the correct fill procedure; removing and replacing the carrier; inspecting housing mating surfaces and alignment; servicing lube pumps, troughs, collectors, coolers, lines, slingers, tubes and filters; and testing the axle temperature sender and gauge. The specifics below come from Meritor's maintenance manuals.

1. Lubricant and Temperature Limits

• Hypoid drive axles use API GL-5 extreme-pressure gear oil (Meritor lists GL-5 hypoid gear oils in grades such as 75W-90 and 75W-140) or the synthetic oils Meritor approves for extended drains.
• Temperature: Meritor says its axles can operate above 190°F (88°C) without damage. However, if the oil temperature reaches 250°F (121°C), stop the vehicle immediately and find the cause, because damage can result. The axle sump must never exceed 250°F.
• Common overheating causes: low or excessive oil, the wrong oil, an IAD lock left engaged, mismatched tandem tires or ratios, overloading, and dragging brakes.

2. Checking the Level and Filling Correctly (Meritor)

1. Park on a level surface and block the wheels. The axle must be cold or near room temperature. When hot, the oil may be 190°F or more, can burn you, and does not give a correct reading.
2. Clean around the fill plug and remove it from the differential carrier or the axle housing bowl, depending on the axle. Do not remove the temperature indicator plug.
3. The level must be even with the bottom of the fill plug hole.
4. To add oil, fill until it is even with the bottom of the fill hole, then wait to let the oil flow through the axle and recheck.
5. Forward-rear tandem axles: if the inter-axle differential has a top fill plug hole, add an additional two pints (0.946 L) of the same oil into the inter-axle differential housing.
6. Install the fill plug and tighten it to 35–50 lb-ft (Meritor Maintenance Manual 1).

Two more Meritor details matter on tandems:

• Capacity changes with pinion angle. When the drive pinion angle changes, so does the amount of oil the axle holds. Always fill to the plug rather than pouring in a book quantity.
• Separate IAD housings: some forward-rear carriers (Meritor lists the SLHD, SQHD, STDD and SFDD models) have separate inter-axle differential housings. Their baffles and dams hold a reservoir of oil that can also trap wear particles, so always purge these reservoirs when changing the axle oil. They have their own drain and fill holes.

After a carrier installation, Meritor has you road test unloaded for 1–2 miles at no more than 25 mph, then recheck the oil level and fasteners.

3. Magnetic Plugs, Breathers, and Leaks

• Magnetic drain plugs: inspect them at every oil change. Meritor gives a reuse test for its front drive axle plugs: they may be reused only if, after cleaning, they still pick up at least 1.5 lb of low-carbon steel. Never substitute a pipe plug for a drain plug — it will leak.
• Breathers: a plugged breather traps expanding air as the axle heats, and the pressure pushes oil past the wheel seals and pinion seal (section 8.3). Keep breathers clean and replace damaged ones.
• Leak diagnosis: clean the area, run the vehicle, and trace the oil to its highest wet point. Common sources are the pinion seal, carrier-to-housing joint, cover plates, axle flange gaskets, wheel seals, fill and drain plugs, and the breather. Overfilling and plugged breathers cause leaks from otherwise good seals.

4. Carrier Removal and Installation (Meritor)

1. Drain the oil. On axles with a DCDL, lock it first — the locked position gives the shift collar clearance to remove the axle shafts and carrier.
2. Remove the axle shafts (loosen the tapered dowels with a brass drift or air hammer, never a chisel), and disconnect the driveshaft.
3. Support the carrier with a jack or lifting tool, remove the fasteners, and remove the carrier.
4. Housing prep: clean the housing and its carrier mounting surface, inspect the housing for damage, and check for loose studs. Loose studs are removed, cleaned, and reinstalled with liquid adhesive until no threads are exposed.
5. Sealant: apply a continuous 0.25-inch (6 mm) bead of silicone gasket material to the housing's carrier mounting surface. Meritor warns that using more can let pieces break off and plug lubrication passages. Work in a ventilated area, because some silicone gasket materials give off acid vapor as they cure.
6. Install the carrier, tighten the fasteners to specification, and install the axle shafts. Wait for any sealant or adhesive to cure as specified — Meritor's forward carrier manual calls for waiting a minimum of 60 minutes after applying some thread sealants before filling. Then fill and road test.

5. Housing Mating Surfaces and Alignment

• Inspect the carrier mounting face for nicks, burrs, warpage, and cracks, and check the bowl, tubes, spring seats, and wheel-end spindles for damage.
• Check alignment when there is uneven tire wear on one axle, repeated wheel bearing or seal failures, or after an accident. Compare with the OEM specification using suitable alignment equipment.
• Meritor's rule: always replace a damaged drive axle housing. Do not bend or straighten it, because that can misalign or weaken it and voids the warranty. Do not repair axle components by welding or heat-treating, except where Meritor's instructions allow.
• Welding near axles: follow the approved weld locations and procedures, and remove the brake air chambers first — Meritor warns not to expose a brake chamber to more than 250°F.

6. Lube Pumps, Filters, Troughs, and Slingers

Many forward-rear tandem carriers have an oil pump in the input bearing cage. It feeds pressurized oil to the inter-axle differential and input shaft bearings, often with a pressure relief valve in the cage. Some axles add an oil filter and external lines or coolers.

• Inspect the pump drive, the relief valve (plug, spring, and valve), and the O-rings whenever the input bearing cage is serviced.
• When installing a new axle oil filter, Meritor's procedure is to tighten it an additional 3/4 turn after the gasket contacts the carrier.
• Troughs, collectors, and slingers route splash oil to the pinion and through-shaft bearings. Keep them clean and correctly positioned. A misplaced baffle or collector can starve bearings even with the correct oil level.

7. Axle Temperature Sending Unit and Gauge

Many Meritor axles have a tapped hole in the housing for a lubricant temperature indicator or sender. Test the sender against the OEM resistance-versus-temperature chart and check its circuit for opens, shorts, and a poor ground, just as for transmission senders (section 5.5). A sudden high reading with a cool housing points to the sender or circuit. A genuine 250°F reading means stop and find the cause before the axle is damaged.