Text and Pictures by Mark Trotta
In 1951, Harley Servi-Cars were upgraded to hydraulic rear brakes. The same system was utilized until 1973, when rear disc brakes were fitted.
This article covers 1951 through 1972 Servi-Car rear brakes.
Removing Rear Drums
Before the rear drum comes off, the castellated axle nut and cotter pin need to be removed. Do not try to bang off the drum with a hammer if it doesn't come off easily - it's a tapered fit on the rear axle. You will need to use an appropriate puller to remove the drum - a slide hammer with puller attachment works well.
Once the brake drum is removed, you will find an axle shaft spacer behind the drum. There is a square keyway that fits into a slot on the axle shaft. Apply a thin coating of anti-seize on the end tapers when re-assembling.
Keyway size is 1/4" x 1/4" x 1-3/4"
Rear brake drums from 1951 through 1972 measure 9" inside diameter and are 2-1/4" deep. They carry HD part #83800-51.
Servi-car Wheel Cylinders
Rear wheel cylinders for Harley 45 trikes have a 7/8" bore and are the same from 1951 to 1972. The wheel cylinder part number is #83460-51, but very often they're rebuildable. You may still be able to buy rebuild kits from a good auto parts store (try a NAPA store).
Read: Rebuild Wheel Cylinders
Rear Brake Hardware
Brake shoe hardware for 1951 through 1972 Servi-Cars includes one (long) return spring on the top and one (short) retainer spring on the bottom for each side. There are also four brake shoe hold-down clips, two for each side (one for each shoe).
If needed, shims are installed behind the rear backing plates. These are a "use as required" part to correctly space the backing plates from the flange mounts on the axle tubes.
Rear Brake Shoes
Rear Servi brake shoes are 9" x 1-3/4". To install the rear shoes, first attach a front and rear shoe at the bottom with the shorter spring. Then install the hold-down clips.
Next, line up the brake shoe "ears" into the sides of the wheel cylinder. You will need a pair of brake spring pliers to install the top (longer) spring.
Servi-Car Master Cylinder
No longer available from Harley-Davidson, the master cylinder can still be obtained through most auto parts stores. Originally, 1951 through 1955 models had a removable top, later master cylinders were one piece with a threaded cap. These two styles will interchange.
Many Harley Servi-car brake parts are the same as certain 1948 through 1963 Willys Jeeps. These include master cylinder, wheel cylinders, and brake shoes. Harley-Davidson did not produce these parts, they bought them from an outside source.
There are more (and better) Classic Jeep suppliers than there are Servi-Car suppliers. Kaiser Willys Auto Supply is a reputable company that (unknowingly) sells Servi-car brake parts. I've gotten parts from them on several occasions.
The aftermarket Wagner master cylinder FE2693 fits 1951-1972 Harley trikes, as well as certain 1948 thru 1963 Willys Jeeps. Center-to-center bolt hole length for the Servi master-cylinder is 3-7/16".
Note: Earlier 1941-1947 Jeep master cylinders are nearly identical, but have a bolt center length of 3-1/8" and the front mounting hole is threaded. Although it would work on a Servi-car, it would not fit the frame bracket correctly.
Rear Servi brake shoes are 9" x 1-3/4" and appear to be the same as Willys model M38A1 (part #807376).
Servi-Car Steel Brake Lines
You can buy or fabricate steel brake lines. Three are needed, left-side, right-side, and master cylinder to junction block.
Read: How To Make Brake Lines
There is a rubber brake hose runs from the back of the master to a four-way junction block mounted to the rear axle. Also on this junction block is a hydraulic stop-light switch, which lights up the brake lights when pressure is applied.
The right-side foot-brake linkage connects the front foot lever to the rear pivot bracket. It is comprised of pivot lever OEM# 83525-51, pivot bolt #83528-51 (with grease fitting), and clevis pin kit #42269-30.
Bleeding Servi-Car Rear Brakes
Because the Servi-car master cylinder sits lower than the wheel cylinders do, bleeding brakes by gravity is not possible. Here's an optional way:
Attach a length of 3/16" clear tubing (from an aquarium pump or something similar) to the bleeder screw, and submerge the other end into a clear container filled with a couple inches of brake fluid.
Doing one side at a time, open the bleeder, and depress the pedal. Close the bleeder before you release the pedal. Repeat this procedure until you get fluid with no air bubbles, then go to the other side. Go back to the first side and check that no air from the other side entered that line. If your master cylinder is in good condition, bleeding the brakes should only take 10-15 minutes.
Servi-car Brake Pedal Adjustment
With the back of the trike up on jack stands, rotate the rear wheels and check for excessive drag. The brake rod should be adjusted so the brakes don't take effect until the foot pedal is about an inch down. When properly adjusted, the brakes should be fully applied before the foot pedal goes all the way down.