The 80 series has a mechanical lspv - what does the 100 series do? How does it work with lifts etc?
How does the load sensing brake distribution stuff work in the hundy? (1 Viewer)
- Thread starter nukegoat
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I'm pretty sure the 100 doesn't have a mechanical lspv, since all model years came with ABS. So, no need to mess with anything in the breaking system after a lift, ABS has got your back
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- #3
Ok. So its a fixed proportioning? Seems like the failure mode is no brake pressure to the rear, based on the fsm?
I guess you could call the proportioning fixed? The ABS system measures wheel speed and sense sa wheel locking up, then opens valves to reduce braking at that specific wheel. I guess you can just think of ABS as a really sophisticated lspv system?
Failure mode of what? The entire braking system? Or the ABS system itself?
- Thread starter
- #5
Like without booster pressure
For some of the non USA 98 & 99 models it is similar to the 80 with a mechanical lspv (for those years part # 47910-60120). Those 98 & 99s might need some adjustment of the mechanical LSPV after a lift. The USA 98 & 99 models handle it electronically, don't know how it compares to 2000 and later system.
[Edit 10-23-2018] update to show USA 98 & 99 models are electronic.
In 2000 and later, along with adding separate lines to rear brakes, VSC, and ATRAC, the electronic proportioning may be improved from 98 & 99 system. With individual control of each brake and ABS sensors the brake computers can figure out the correct proportioning. This system is independent of lift so it does not need readjustment. It is not fixed proportioning, as the computer is making continuous proportioning adjustments based on its sensors, which is how it deals with load and road variations.
[Edit 10-23-2018] update to show USA 98 & 99 models are electronic.
In 2000 and later, along with adding separate lines to rear brakes, VSC, and ATRAC, the electronic proportioning may be improved from 98 & 99 system. With individual control of each brake and ABS sensors the brake computers can figure out the correct proportioning. This system is independent of lift so it does not need readjustment. It is not fixed proportioning, as the computer is making continuous proportioning adjustments based on its sensors, which is how it deals with load and road variations.
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- Thread starter
- #7
Other than wheel speed sensors, what data does the computer use?
I'm pretty sure that on the early models, wheel speed sensors compared to trans speed is all the computer uses. I'm not sure about the newer models with Atrac
Know 2000+ has a deceleration sensor and a yaw sensor. The deceleration sensor is used for normal braking. The yaw sensor could be used for normal operation, but may only be used for VSC operation of the brakes.
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- #10
So how does it know if youre towing a trailer other than "brake till it skids" ??
The system doesn't care what you are doing, the computer is sampling data and comparing values, doing math, and adjusting valving accordingly. It's primitive but it works. A more sophisticated system may allow you to put the vehicle in "tow mode" which would change the parameters in the various systems so that the braking may behave differently... but that was not something the early 100's had, and I don't think the later hundreds had anything like that either.
It doesn't need to know about the trailer, to the system it is just like a different load in truck.
Only light weight trailers do not have trailer brakes, on trailers with brakes most all its braking is done by the trailer brakes.
So trailer just acts like some reasonable load in the truck.
I remember hearing that the 100 brakes the rear a bit before front, if I was writing the software (don't know what Toyota did), from that known rear braking and input from deceleration sensor I would have a good idea of load, and therefore how much to apply the front brakes in the right proportion. No skidding required, but if the road has some slip that will come into play for ABS.
Only light weight trailers do not have trailer brakes, on trailers with brakes most all its braking is done by the trailer brakes.
So trailer just acts like some reasonable load in the truck.
I remember hearing that the 100 brakes the rear a bit before front, if I was writing the software (don't know what Toyota did), from that known rear braking and input from deceleration sensor I would have a good idea of load, and therefore how much to apply the front brakes in the right proportion. No skidding required, but if the road has some slip that will come into play for ABS.
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Is anyone else's 99 only wearing the front pads and not the rears? I've changed the front pads and rotors but never the rears since factory.
~60% of braking force comes from the fronts, the rears will wear a lot less quickly all things considered. I think my brother just replaced the rear rotors on his 2001 and we are pretty sure they were the original rotors
Thanks for the info Somebodyelse5. I wonder if there's a solution to fix this.
hoser
SILVER Star
There is no solution needed because there is no problem. Electronic Brakeforce Distribution (EBD) maximizes every wheel's brake power. If the sole goal was to have all pads wear at the same rate, they would simply make the rear pads, much smaller... but there are benefits to a larger pad, as there are benefits to lower weight and cost. The percentage of brake force between front and rear does vary.... according to weight, center of gravity, driving style, terrain, etc.
I think that Electronic Brakeforce Distribution actually helps with the wear since it puts more braking force on the rear compared to mine but the problem is that the 99's don't have Electronic Brakeforce Distribution.
hoser
SILVER Star
I believe the term EBD was coined after 98-99 but I still think the early 100's have some form of EBD, except it only has 3 channels, not 4, as the rears are considered one.
Hmm, interesting. I didn't know about that. I'll still need to find a solution for this problem but it can wait for a while.
Nope, the general rule of 60/40 braking force distribution can fluctuate a bit but it's based on the center of gravity and the momentum of the vehicle. You move forward when you slam the brakes, so does your car...
Here is some good reading on the topic...
Brake System and Upgrade Selection
"
FRONT TO REAR BRAKE BIAS
Stability and control under heavy braking is at least as important as ultimate stopping
capability. All cars, from pickups to Formula One, are designed with the majority of the braking torque on the front wheels. There are two reasons for this - first, if we ignore the effects of aerodynamic down force, the total of the forces on each of the vehicle's four tires must remain the same under all conditions. When the vehicle decelerates, mass or load is transferred from the rear tires to the fronts. The amount of load transfer is determined by the height of the vehicle's center of gravity, the length of the wheelbase and the rate of deceleration. Anti-dive geometry does not materially effect the amount of load transferred - only the geometric results of the transfer. Second, when a tire locks under braking, braking capacity is greatly reduced but lateral capacity virtually disappears. Therefore, when the front tires lock before the rears, steering control is lost and the car continues straight ahead - but this "under steer" is a stable condition and steering control can be regained by reducing the pedal pressure. If, however, the rear tires lock first, the result is instantaneous "over steer" - the car wants to spin. This is an unstable condition from which it is more difficult to recover, especially when entering a corner.
Most mid-engine pure racing cars are designed with 55-60% of the total static load and 45-50% of the total braking torque on the rear tires. These cars feature literally tons of rear aerodynamic down force and the footprints of the rear tires are always significantly larger than those of the front. Most passenger cars are front engined; none of them have any appreciable download and almost all of them have the same size front and rear tires. In extreme cases (front wheel drive) they may have 70 % of the total static load on the front tires. They are therefore designed with a preponderance of front brake torque. Most current production cars feature anti-lock brake systems (all cars should). Sophisticated ABS systems ensure that, under heavy braking conditions - even braking with tires on different surfaces - each tire is braking at something very closely approaching its maximum capacity while the ABS system prevents lock up.
THE REAR BRAKE LINE PRESSURE-LIMITING VALVE
Since the load transferred from the rear tires to the fronts under braking decreases the braking capacity of the rear tires, a rear brake line pressure-limiting valve (often referred to a proportioning valve) is utilized to prevent rear wheel lock up on most passenger cars that do not feature ABS. Its function is to limit the amount of pressure transmitted to the rear brakes under very heavy braking. Assuming a tandem master cylinder with equal bores, front and rear line pressures are the same until some pre-determined threshold is reached. After this point, rear line pressure, while it still increases linearly with pedal effort, increases at a lower rate than the front. In a graph it appears as a distinct "knee" point where a further rise in pressure after the valve is noticeably diminished. The purpose is to avoid rear wheel lockup and the attendant unstable over steer at maximum deceleration rates when the weight transfer is greatly reducing the dynamic load on the rear wheels. It is not a good idea to remove the limiting valve from a road going automobile. Remember, under steer is stable, over steer is not. Without an effective anti-lock braking system, in any panic braking situation we must be absolutely certain that the unloaded rear tires cannot lock first. Therefore materially increasing the rear braking torque is not a good idea for highway use. If you feel that you must do so, consider removing the OEM rear brake line pressure-limiting valve completely and replace it with one of the adjustable units manufactured by Tilton Engineering or Automotive Products (now part of Brembo). Do not place a second pressure-limiting valve in line with the OEM unit."
