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Car Forum / Australian Car Forums / 4x4 Cars (Australian group) / January 2006Any L'Cruiser brake gurus about? re:HZJ75 load balancing +Rear Drums
Hoping for some input on a problem with rear brakes on a troop carrier [2/91manuf]. Original problem was the escape of the leading shoe on RT/HND Rear set from the slave , creating a jammed wheel. On inspection of all parts the system was found to totally inundated with signs of moisture stress. A complete clean [blow-job] together with master cylinder and load sequencing valve replacement delivers this new (?) problem, as put here The brake system bleeds normally as in pedal to master cylinder reaction when releasing and pressurizing the system.. When the system is closed the brake pedal reacts normally. On starting the engine the pedal depresses the standard amount. With the vehicle stationary the pedal travel is acceptable. With the vehicle in motion the pedal travel extends beyond 50% and only the front discs are activated on any attempt to brake (measured or emergency). The rear drums appear to have no pressure whatsoever exerted on them. I am casting a suspicious eye at the load sequencing valve, primarily because I do not understand how it works (hydraulic). I am looking for someone to explain the theoretical design of such a contraption :-) In the event I have missed something very obvious I would appreciate a complete jerk back to reality. thanks. crusty Back in the 70's on domestic vehicles, they started using a proportioning valve for the rear brakes on station wagons and pickups at first. This valve senses the amount of pressure going to the front and read brakes and shunts the pressure so the rear shoes will not lock up the rear wheels. This is a safety thing so the vehicle doesn't have the rear end trying to pass the front end. With a vehicle jacked up, the front wheels lock and the rears appear not to stop. When it is in motion, this changes because it take more pressure to stop the fronts so the rear sees a lot more too. Even on gravel or snow the rear wheels are never supposed to lock except when coming to that last little bit of a hard stop. I don't know if this answers your question or not. Mike 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's Canadian Off Road Trips Photos: Non members can still view! Jan/06 http://www.imagestation.com/album/pictures.html?id=2115147590 (More Off Road album links at bottom of the view page) > Hoping for some input on a problem with rear brakes on a troop carrier > [2/91manuf]. [quoted text clipped - 23 lines] > > crusty Mike Romain <romainm@sympatico.ca>,went to some trouble to offer: >> Hoping for some input on a problem with rear brakes on a troop carrier >> [2/91manuf]. [quoted text clipped - 36 lines] >to stop. When it is in motion, this changes because it take more >pressure to stop the fronts so the rear sees a lot more too. yep..all of the above is in my database [pre-existing]. >Even on gravel or snow the rear wheels are never supposed to lock except >when coming to that last little bit of a hard stop. K...my experience is different, maybe the 'gadget has not been adjusted correctly on my other Tojos? >I don't know if this answers your question or not. nup..I was really looking for a 'technical' explanation of the hydraulics of this contraption. The Gregorys I have says "70mm clearance at the shackle for 75series, testing and further adjustment by a qualified operator only". I reckon if I can understand how the contraption works I can soon rig some test gear and at least determine/eliminate the valve as a factor in my problem. btw...in all of the repair I have spoken to a number of "qualified" peers, none have ever seen the escape of a shoe from the slave trunnion on a 'Cruiser. As to how it happened they say "beats me"..beats me too, women drivers? <G> thanks crusty > Mike Romain <romainm@sympatico.ca>,went to some trouble to offer: > [quoted text clipped - 61 lines] > trunnion on a 'Cruiser. As to how it happened they say "beats > me"..beats me too, women drivers? <G> Try refitting your old valve, if the symptoms change then you will know that the valve was the problem. Does the valve have a mechanical link to the rear suspension? The load sensing valve on most cars work by sensing the load by the angle of the rear of the vehicle but trucks usually have a link to the rear suspension which is more accurate. Jack the rear wheels clear of the ground, put it in gear and turn the rear wheels, apply the brakes and watch if the rear wheels stop. Daryl > > Mike Romain <romainm@sympatico.ca>,went to some trouble to offer: > > [quoted text clipped - 70 lines] > Jack the rear wheels clear of the ground, put it in gear and turn the > rear wheels, apply the brakes and watch if the rear wheels stop. If the rear wheels are clear of the ground then the proportioning valve would sense there is no weight on the back wheel and the valve will close preventing the brakes from working. The valve works by sensing the weight in the back. the more weight the more brake fluid is applied to the rear. It is operated by a lever which is attached to back axle. and the valve is attached to the body. the more weight, the closer the body is to the axle therefore raising the lever and opening the valve. If you give the car a suspension lift, this will alter the setting. just lift the end attached to the axle equal to the difference in spring size Ron > If the rear wheels are clear of the ground then the proportioning valve > would sense there is no weight on the back wheel and the valve will close > preventing the brakes from working. The brake force to the rear will be reduced but there still should be a small amount of rear brakes even with no load. Daryl > > If the rear wheels are clear of the ground then the proportioning valve > > would sense there is no weight on the back wheel and the valve will close > > preventing the brakes from working. > > The brake force to the rear will be reduced but there still should be a > small amount of rear brakes even with no load. Correct.. Maybe I should have said "preventing the brakes working to their correct capacity" Ron I don't know what system is used on the LC, but it is likely similar to the common Bendix type II where the parking brake actuator can cause the shoe to escape the anchor pin. What happens is that if the parking brake is adjusted before the hydraulic side is set, the parking brake actuator can be expanded far enough that the shoes actually rotate around lever and are not seated on the anchor pin when the brakes are at rest and the "fixed" end of the shoe can escape the anchor pin on actuation. Extreme case, but possible. Relax the parking brake, adjust the brakes shoes, then reset the parking brake adjustment. > Hoping for some input on a problem with rear brakes on a troop carrier > [2/91manuf]. [quoted text clipped - 23 lines] > > crusty  SignatureWill Honea |
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