Page last updated 25 Sept 97. Fixed typo in acknowledgment, removed email addr.

Brake System Observations

[Thanks to Ron Miller for contributing this section. --Pat]

404.1 Brake details, Info & Learnings obtained from a 404.115 and a 404.114

Brakes are a simple single-circuit hydraulic arrangment. Each wheel has a leading and trailing shoe. Rear brake also has mechanical handbrake linkage. (There is no info here on air-assist brakes. I haven't seen them.)

Adjusters are mechanical snail-shell like cams that are turned via hex heads on the brake backing plate. The mnemonic for adjustment is: "tighten up" Put the wrench on the adjuster in the standard way and move the wrench up to tighten. (19mm) Each shoe is adjusted individually (8 shoes total)

Bleed screws are 9mm. 1 on the master, one on each wheel another on the hydraulic/air valve if present. A box wrench can get to it. There is limited wrench swing due to the clearances of bolts and banjo fittings around the bleeders at the wheels. Crescent wrench probably can't do it if you put a hose over the bleeder which I recommend to keep brake fluid off your wheels and driveway.

Wheels weigh about 130lb (60kg) each. 15/16" lugnuts.

The two flathead screws shown in the manual on the brake drum hold the drum to the hub. Need a BIG flat-blade screwdriver to undo. Actually, a large flat-blade in an impact driver may be the only way to get a stuck screw loose. Once these screws are removed - the holes are not the jacking bolt points. The jacking bolt holes are 90 degrees from these and M10 x 1.5 x 50mm would work fine as jack bolts.

Front brake shoes are not connected to each other except by the retract spring.

Rear shoes are linked by the handbrake linkage. It is not necessary to unhook this to remove the shoes. The pair can be wiggled free as an assembly. This saves readjusting the handbrake on reassembly. Handbrake adjustment is made both at each wheel and at the lever assembly. Each wheel has a rubber plug at the backing plate by which access to a star wheel is gained to adjust the individual wheel. The pair are adjusted at the handbrake lever.

A long, thin, flexible screwdriver seems to be the spring tool required to re engage the retract spring.

Shoe pivot pins are held in place by a cotter pin in a groove. To remove pivot pins, remove the cotter pin, and thread the M10x1.5 bolt used to press off the brake drums into the pivot pin. The bolt now gives purchase to pull (while turning and grunting) the pivot pin.

There are 4 flexible hoses in the system. One at each front wheel, one where the lines run from the chassis to hard piping down the front torque tube and likewise for the rear torque tube.

Hard piping fittings are 12mm (for your flare wrench). Male flex hose ends are 14 mm and the female ends are 19mm. The female hose ends are captured with an E clip to hold that end against structure where it mates to the metal piping.

Reservoir to master connection is 22mm hose coupling. (access from behind cab in spare wheel well unless you have the battery ground switch in the way. Turning this coupling is not trivial due to limited swing clearances.)

Master is held to frame by 17 mm bolts threaded into frame. (suggest loosening brake hose pipe couplings but don't separate until mounting bolts removed so you aren't working in a shower of brake fluid.)

Master is quite large diameter. Interior can be swabbed clean with wood dowel & lint-free rag. You might find sludge on the brass screen that is the bleed-thru port on the piston. Clean this gunk off to restore full volume pressure bleed.

Problems I have seen:

Generic Brake Advice: When rebuilding master or slave cylinders, use "Cup Saver" PAC-10 from United Brake Parts. This is brake system assembly fluid. Has the consistency of 90wt oil but is brake compatible. Makes the rubber cups move smoothly in the bore. Comes in little gelcaps for about US $.10 each. Use one capsule per cyl.

Brake Linings

[Thanks to Manfred Princz for this information. --Pat]

There have been several enquiries recently about brake lining thicknesses on Unimog-S 404.

In order to compensate for brake drum wear and allow machining to remove any ridges, 3 repair sizes are available.

When replacing linings, it is always necessary to measure the diameter of the drums to determine the thickness of the lining required. Please note: ex-military Unimogs may have had the drums skimmed previously and thicker linings already fitted.

Drum diameter       Lining thickness required
mm                  mm

349.2 + 0.3         6.0
350.0 + 0.3         6.4 - 0.2
351.0 + 0.3         7.0 - 0.2
352.0 + 0.3         7.5 - 0.2
To our friends in the US: 1" = 25.4mm

Take me back to the Unimog-S 404 FAQ.
Patrick Tufts