Hi. BJ 74.
[...]
Changed the master cylinder early this year. changed the wheel cylinders as well together with pads.
Brakes very weak. Handbrake does not work on steep hills. Pulls up but no brake. Only pedal will work. Emergency braking risky. At times have to pump the brakes, then pedal becomes really hard.
Guy who sold me the 2nd hand (cant get new) master cylinder / booster said to drain brake fluid and re-fill. Did that slight improvement then back to square one.
Put in another master cyl yest. seemed fine. took car for test. All 4 wheels got really hot and brakes started to jam.
tried again today with another mcyl etc. went well for around 10kms, then front and rear (frnt right / back left) brakes started to jam up. wheels extremely hot.
thinking, calipers maybe.. or .. pads are new..
basically am stumped!!
any ideas on what do to where to look?
So, we're working on a BJ74.
A number of points come up -
The parking brake mechanism must be working correctly for the rear brakes (drum type) to work properly.
It is extremely common to find that the bellcranks (pivots) at the backing plates are corroded and not allowing the bellcrank to move and actuate the parking brake mechanism inside the drum. The bellcrank and related hardware must be freed up so that the parts can move easily, with no binding or catching.
Another common issue is that many people attempt to adjust the parking brake system at the handbrake handle inside the vehicle. This is an absolute no-no. The consequences are that the parking brake pivots will sit away from the backing plates - this will either cause the shoes to drag and wear prematurely (and give poor fuel economy etc.) and/or it will cause poor brake pedal feel because the wheel cylinder pistons will not be returning to their normal resting position. The poor pedal feel is not always a problem...
So, the parking brake cables must be adjusted so that the pivots are resting against the backing plates - and this is done by adjusting (most often loosening off) the cable adjustment inside the vehicle.
Another problem that crops up is a seized or partially seized parking brake cable may be causing the shoes to intermittently drag against the drums. This will cause the brake to get hot, wear prematurely, and decrease performance and fuel economy. A seized cable must be replaced.
Another issue that shows up from time to time is that grit gets into the brake cable pivot that is attached to the rear axle. There are nylon bushings in the pivot and dirt will cause these to bind and/or wear out prematurely. Binding at this pivot will cause the brakes to remain on, and the braking effort may apply to one side or the other instead of both at the same time - the effect is generally similar to a seized parking brake cable. The pivot can be taken apart and cleaned of dirt/corrosion etc. and put back together again.
Other problems that we find:
- Brake fluid that is not changed often enough - this leads to corrosion of internal parts of the brake system and much more rapid than normal wearing of cylinders etc.
- Seized calipers - depending on the kind of use, the calipers should be replaced or rebuilt in the 180,000 to 220,000m km range. This mileage number should only be used a rough guideline as the type of usage you are putting your vehicle through may drastically reduce your service intervals.
- the "in drum" parking brake wires are off their pivot or are missing or broken. These are needed for the parking brake to work.
- Improperly adjusted proportioning load sensing valves on truck that are lifted or have really sagging springs.
Excessive pumping of the brakes which causes the pedal to become hard usually means that you have used up the vacuum faster than the vac pump can re-generate it. Overly long pedal travel from badly maintained and improperly adjusted brakes can contribute to the same problem.
Also, it is very common for us to find very badly adjusted front wheel bearings (as well as rear wheel bearings in Full Floater equipped trucks), and this leads to caliper kick back, premature wear and dishing of the rotors, bad road manners, and a spongy brake pedal (due to the caliper kick back)... This can also case the pads and rotors to get hot as the pads tend to drag a lot more than normal.
Anyhow, just a few thoughts about Land Cruiser brake stuff.
~John
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