This is the third in a series of articles, over the course of several months, that focusses upon the repair, maintenance and troubleshooting of the braking system of Series I, II and III Land Rovers. August's focus was upon squealing brakes and binding brakes. September's focus was upon brake pedal travel being excessive or spongy. We look at two further possible topics of concern with the braking system this month.
Brake pedal pressure required is excessive
Despite all models of Series Land Rover having hydraulic brake systems, more brake pedal pressure is required the earlier the Series model is.
Since it is friction between the brake lining and the drum surface that produces the braking effect, then any reduction in frictional properties at this interface should be our first suspicion as to the cause. Poor quality brake linings - i.e. cheap ones, will not have the desired frictional properties that the better quality ones have. Never be tempted to buy cheaper quality brake system components but go for OEM or best quality ones.
The brake drums need to be removed and the linings inspected. If they are excessively smooth or glazed over, then they can be roughened with sand paper to effect a temporary cure. A word of caution though on the dust from the linings; modern brake linings are asbestos-free, but there may be some OEM stock available still in various points around the world that has some asbestos content. A closely fitting facial dust mask is a sensible precaution because asbestos is a known cause of lung cancer. Brake linings should, of course, be renewed if they show signs of wearing thin.
It may be that more pedal pressure is required because not all brake linings are contacting the drums; a wheel cylinder could have seized, so preventing one lining from producing the required friction against the drum. Usually, if this is the case, then you would also notice the Land Rover pulling to one side as the brakes are applied (see below). You may be able to confirm this diagnosis by jacking up each wheel in turn and rotating it whilst a friend presses the brake pedal. The real confirmation though is to remove each brake drum in turn and inspect the operation of the wheel cylinders - be careful to only press the brake pedal slightly, else with the drum removed, the wheel cylinder piston will travel further than intended and admit air to the system. Seized wheel cylinders should be replaced rather than serviced.
A brake servo was fitted as standard to Series Land Rovers from 1969 but they were always standard on the 2.6litre engine models. Some servos are operated by a butterfly valve situated in the exhaust manifold that is thermally controlled by a bi-metallic spring (part No. 217818); if this is not operating correctly then vacuum will be lost. Sometimes the butterfly spindle can corrode and not move easily. This can be checked by loosening the screw in the counterweight, removing the weight, spring and serrated adjustment plate and then checking the ease of rotation of the spindle. The operation of the butterfly mechanism is particularly critical when fitted to diesel engines. Whatever engine is in the vehicle, it is important that all connections and tubing in the vacuum system are sound as reduced vacuum means a less effective servo and so more pressure required at the brake pedal.
Most Series III Land Rovers were fitted with a dual braking system; if one circuit failed then required brake pedal pressure may increase. A warning is fitted on the dashboard of such vehicles which should indicate a system failure.
Finally, a check should be made for leaking brake fluid at joints and there is also the possibility that a rubber seal in the brake master cylinder could have perished, allowing fluid to bypass the seal rather than carry the pressure on.
Brakes pull to one side
The most common cause of this problem is to do with the brake lining. You need to take off the brake drums on the opposite side to which the Land Rover pulls towards. Look for excessive wear, oil/brake fluid contamination or glazing on the surface of the linings. You can achieve an immediate temporary solution by using sandpaper on the linings (see earlier warning about possible asbestos dust). The correct procedure is to fit new brake shoes/linings as a complete axle set, even if the problem has been identified as one brake lining on one wheel.
The next likely cause is that the brake shoe adjustment is incorrect, so that unequal pressure is being applied to the brake linings on opposing wheels. You will need to jack up each wheel in turn on the opposite side to which the vehicle pulls towards and turn the brake shoe adjuster bolt clockwise until the wheel cannot be rotated any more by hand, then back off the adjuster bolt until the wheel is free to rotate. Finally, road test the brakes again.
If combined with increased brake pedal pressure needed, then see the comment above concerning "wheel cylinder could have seized".
Seriously unbalanced tyre pressures can cause the problem and even a visual comparison check could reveal this as a possibility in severe cases. But checking with a with a tyre pressure gauge is required.
A less likely cause is a damaged inner lining to a brake drum. This may be indicated if there has been a lot of brake squeal in the past, caused by small stones embedding in the brake lining and scoring the drum surface, so producing ridges and reducing the effective frictional area. Remove the brake drums on the opposite side to which the vehicle pulls towards and inspect for deep grooves. The solution is to fit a new brake drum or get the drum lining re-surfaced at a workshop.
Finally, it is possible, but rare, for an internally damaged or partially blocked flexible brake hose to cause the problem. Consider this option last, as you will need to bleed the brake system after inspecting the brake hoses.
109in Series Land Rover front brakes
(To see previous homepages visit the Homepage Archives link)