Servi-car Axle Overhaul
Text and Pictures by Mark Trotta
Just like Henry Ford's first automobile, final drive on Harley Servi-cars is a simple chain-drive mechanism.
The transmission output gear attaches to the rear drive sprocket with a chain, and both rear wheels rotate at the same speed.
This type of final-drive system was cheap to manufacture and very durable.
Differences In Servi-car Axles
Early Servi-car axles (1934 to 1936) have a big center, with a single mechanical drum brake inside the housing. This brake has two shoes and is internal-expanding on a fixed pivot. A parking brake is mounted inside the rear axle housing.
In 1937, the Servi's brake system was upgraded to a drum brake on each rear wheel.
Somewhere in the 1940s, the axle halves were welded together instead of riveted.
The 1941 to 1950 rear axles are slightly different than 1951-1972 units. They will fit up to 1972, but not be "correct".
Last-year Servi-car axles (1973) were disc-brake equipped and have six-stud wheels.
Truss Rods
The Servi axle has one front and one lower truss rod to keep the axle from bending.
There are four coupler nuts which have right-hand threads on one end and left-hand threads on the other end. To remove them, tighten (shorten) the shorter side of the rod, which creates slack on the other side.
The right front truss rod coupler is "smooth". This is for clearance and goes toward the center by the stoplight switch. This coupler has internal lock washers.
The other three couplers use external lock washers.
Unlike automotive differentials, Servi-car axles do not require gear oil. They are lubricated by wheel bearing grease (approximately four ounces).
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Servi-Car Axle Rebuild
To split the axle open, tap out the axle housing bolts and studs.
There are two bolts which measure 4-1/2" in length. The bolts for the nuts face the shorter (right) axle half. Two of the three studs measure 6" and the third measures 5".
The left axle is longer and measures 26-1/4".
The right (shorter) axle measures 20".
Both left and right axles fit 1941 through 1973 models. In the event one of yours is damaged, they were (and then weren't) available in the aftermarket.
I didn't need to separate my axles, but if you need to, there are nine bolts and nuts which need to be removed. A spring wire lock ring holds them in. This allows disassembly of the differential.
Note that there are small "C" clips at the end of the axles at the differential gears in the center section. These are referred to as axle lock half rings, or retaining clips. Two are used per axle.
Parts Inspection
Inspect all parts for pits, grooves, and gauges. Replace any parts if there is any doubt to their condition. After inspection, clean all parts with solvent and blow dry them with compressed air.
All bearings not needing replacement should be cleaned and repacked. Automotive wheel bearing grease is fine.
Before these old truss rods were reinstalled, they were ground down, filed, sanded smooth, primed and painted.
Remember to install the coupler, nut, and lock washer in the correct order, or you'll be taking them off again!
Slowly and evenly, loosen the low-end truss rod fittings, then tighten the high-end fittings until the rods are parallel with the axle. Do not over tighten them, as it may prematurely wear axle parts.
Before reinstalling the axle to the frame, check tightness of all bolts and install grease fittings. The axle housing takes about four ounces of grease.
NOTE: If you're replacing the axle grease fittings, you probably won't find them at the local parts store. They're a 1/4" fine-thread pitch with a head size of 5/16".
If yours are damaged or missing, Rear Axle Clamp Bolts for Harley Servi-Car 1942-1973 are still available.
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Servi-Car Rear Wheels (1937-1950)
Harley Servi-Cars 1937 through 1950 were fitted with 16" x 3" spoke rear wheels. These early wheels are a taper fit with key to the axle, and the hubs are specific to them.
Aftermarket spoke wheels are available and retail for about $1,000 each.
Servi-Car Rear Wheels (1951-1972)
From 1951 to 1972, Harley Servi-cars had automotive-style steel rims, which the factory referred to as "disc wheels". They are 16" x 3.5" and have a drop-center design.
Today, these wheels are hard to find and sell for inflated prices. Unfortunately, there is no automotive wheel that exactly matches them.
Last-year Servi-cars (1973) are unique in that they were the only year with rear disc brakes and had six-lug rear wheels.
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Rear Tires
For my 1961 Servi-car, I chose Dunlop D402 wide whitewalls, also available in blackwall.
Tire size is MT90B16, which fit the original 16 x 3.5 rear wheels. They require 5.10 x 16 center-valve tubes. Don't forget to install rim strips before mounting tires.
Servi-Car tire pressure chart.
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Speedometer and Gear
From 1947 to mid-1961, Servi-cars had a speedometer ratio of 2:1. The 2:1 ratio was actually used on most Harley models from 1936 to 1961.
Later models have the more common 1:1 speedometer ratio.
Speedometer Gear Ratio
Because there are two different speedometer ratios, there are two different speedometer gears. Note how many teeth your gear has. The 11-tooth gear is correct for earlier 2:1 ratio speedometers.
If you need to replace the speedo gear, measure the distance from the gear face to the end of the axle to be sure the replacement one is correct. The new gear needs to be pressed on. Grease the speedometer gear before installing in the rear axle.
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Related Articles:
Servi-Car Frame Identification and Inspection
Servi-Car Rear Brakes
Hydra Glide Front Drum and Shoes Installation
Motorcycle Tire Shopping
Servi-Car Exhaust And Why Getting Parts Is So Frustrating