I thought it was the brake booster but what I can’t figure out is when i put the old master cylinder on then the entire system works just fine & the rotors don’t heat up but the brake peddle goes almost to the floor when it starts slowing down but could it really be that all 5 of the new master cylinders i put on be bad?
If the brake fluid is seeping past the seals around the pistons in the master cylinder, the hydraulics may not transfer to the brake lines enough of the gradual force being transmitted from the booster. In other words, the booster is slowly trying to pull the brake rod forward but rather than slowly applying the brakes the MC is allowing the fluid to bypass the pistons, not enough force is being applied to the brake lines to apply the brakes.
With the old MC, your foot pressure can’t apply the brakes.
With the new MC, even the pressure being applied by the booster is enough to apply the brakes.
Would a broken speed sensor cause the brakes to stick & then lock up?
A broken speed sensor could cause one wheel to begin to pulsate, but cannot cause the braking system to lock up. Generally a broken sensor will simply trip the ABS warning light. The ECU is pretty smart about that.
The concept behind ABS is simple. Each wheel has a speed sensor. The computer compares the speeds of the different wheels. If one stops turning, the system assumes that it’s slipping on ice or whatever.
The brake system contains a device (modulator) that has one hydraulic line going in from the brake master cylinder and four going out, one to each brake. Each line going out has a solenoid-operated valve where it goes to the caliper. When the computer detects a wheel not turning appropriately, it sends an electrical wave to the solenoid-operated valve on that wheel’s brake line, causing the hydraulic pressure to pulsate.
The computer is able to detect the difference between a slipping wheel and loss of the wheel speed sensor signal.
The speed sensor on the tire is the only thing that i can think of that would be the problem because for instance today, I was able to drive about 4 miles in the snow & the tires started locking up to where the RPM was at 3 but I was only able to go 25mph (put the car in drive & it won’t move until the gas is pressed) but a couple days ago when i was driving(not in snow) then the tires would not lock up but they would stick after about 5 miles & heat up the rotors but it wouldn’t cause them to slow the car down & the RPM only went up 1/4 at 45mph instead of 1/2- 3/4 at 45mph,
when i put the car in drive when the brakes are sticking then the car would move on it’s own without me touching the gas but when it’s locked up then the car won’t move at all until the gas is pressed,
& then comparing the old master cylinder to the 5 new ones that I had put in, the old one was working just fine without the rotors or anything heating up unlike the others but the old MC had the peddle almost to the floor.
I don’t think that it’s the master cylinder, the brake calipers, brake booster or the brake hoses. It has something to do with the pressure of the brake fluid
but the ABS modulator holds the brake fluid until i start driving & then it starts going low/empty. Took 4 driving attempts of 20-25 miles in 4 days for the ABS modulator to run low on fluid.
My theory is that the broken speed sensor is telling the ABS modulator to apply more brake fluid which is causing the brakes to press against the rotors & heat up after a while cause what else would cause the brakes to lock up today (driving in the snow) instead of sticking like it did a couple days ago(driving not in snow)?
Plus the speed sensors on the tires are only on the front.
The front heats up before the back does which is to be expected since it’s front wheel drive.
I’m thinking that either just the front right wheel speed sensor would cause this problem & if not then maybe the front left wheel speed sensor needs to be replaced as well.
The modulator does not apply brake fluid or pressure. It can only inhibit fluid or pressure.
Then what would cause the Break pressure to increase to lock up when driving in the snow & stick when driving in normal conditions?
What would cause the ABS modulator to lose fluid then? It’s not leaking.
Based off of the tests I’ve done the ABS modulator is pressing the brake fluid into the lines when I put my foot on the brake peddle & turn the car on but the ABS modulator is not leaking fluid
This says there is a pump in the modulator, so it very well might be able to put the brakes on:
https://automotix.net/usedautoparts/1994-honda-accord-abs_control_modulepump-inventory.html
But why one master cylinder doesn’t allow the lockup is a real puzzler.
Then why doesn’t it apply the brakes with the old master cylinder?
The old master cylinder worked great compared to all the others except for the peddle going so far down.
Out of what i can tell with what I’ve researched is that since the passenger speed sensor being broken is telling the ABS modulator that the roads are unsafe & is applying more pressure(I am convinced that the ABS modulator does apply brake pressure) & if it’s only supposed to react towards the one tire then how would the system affect all 4 tires?
That’s why I am thinking that because the one wheel speed sensor is gone then the sensor is telling the modulator that the roads are unsafe & are applying braking pressure to all 4 tires which is causing it to lock up but the front is locking up before the back which makes sense since it’s front wheel drive & the sensors are only on the front but the FL & RR are on the same line & the FR & RL are on the same line.
This is a 1994 Honda Accord LX
Which is why I am nearly convinced that replacing the wheel speed sensor would fix all the problems.
Well, “fixing what you know is broke” IS an old and wise maxim…
;-]
No, it simply calls it a modulator/pump. Perhaps because its pulsation of the fluid resembles the function of a pump. If you can offer a technical explanation of where and how it could accumulate and store the pressure to supplement the brake fluid pressure, and how it does so, and why, I’d be open to learning.
Because the old master cylinder is no good. It cannot move fluid pressure down the brake lines. It simply allows the master cylinder pistons to move through the fluid without moving the pressure to the brakes.
The new MC causes the lockup in response to the bas booster because it does have the ability to move the pressure to the cylinders.
I wish I could use a whiteboard here. It’d be easier to illustrate than to explain.
I was able to drive 20 miles in one trip with the old master cylinder & nothing was wrong except for the peddle going to far down. I put the car in drive & it moves on it’s own, I push on the brake peddle & 2/3 way down the brakes start stopping the car normally & when i pushed the peddle all the way down then the car would come to a sudden stop but i was only able to get my toes under the peddle when it’s down all the way
Out of what I can tell you is that when the car is off & I press on the brake peddle then the peddle becomes stiff & solid. Turn the car on then the brake peddle goes down like it should but 1/4 of the brake fluid in the ABS modulator is gone after that. I’ve read that the fluid is stored in the Accumulator when the brakes are pumped & then released when the car is started
If i am right then the difference between the old & new master cylinders is the pressure that it generates.
The pressure is put into the ABS modulator & because the wheel speed sensor is broken then the modulator is pushing more brake fluid(pressure) into the lines causing them to stick/lock up. The old master cylinder isn’t applying as much pressure which is causing nothing to go wrong except for the peddle.
Since the wheel speed sensor is broken then It’s telling the modulator to apply more pressure & the pressure is taken from the MC
This might get you killed if you continue driving it this way.
Where do you believe the accumulator gets its pressure? Through what process do you believe the modulator applies more pressure?
I’ve tried to explain how it all works. Apparently without success. I might as well bow out now.
I do hope you take this to a reputable shop and get it properly diagnosed and repaired. A brake system that’s failing, regardless of the reason, is endangering everyone you share to roads with.
I truly wish you all the best, but clearly cannot help.
If there is a missing or broken wheel speed sensor the ABS warning light should be on and the system disabled. If in doubt drive with the pump and modulator unplugged.
When the brakes are dragging do they continue to drag after shutting off the engine? If so try loosening the nuts holding master cylinder a couple of turns and pull the master away from the booster. If you can now rotate the wheels by hand this suggests there is an adjustment problem with the booster push rods (input or output) or an application problem with the replacement master cylinders.
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the accumulator gets its pressure from the master cylinder when the peddle is pushed but in this circumstance i think it’s either pulling pressure from the master cylinder into the modulator or some how creating its own pressure in the modulator.
I really don’t know. I’m just a novice when it comes to mechanics. I know how & can build a car from scratch but that’s without the computer system.
I’ve only worked on a 1991 Honda civic, 1995 Honda accord LX & now a 1994 Honda accord LX
Yes the ABS light is on. It’s been on since i broke the wheel sensor. Wasn’t on before that.
Yes the tries still drag when i turn the car off but after the car is off & cools down then they don’t stick anymore until it’s turned back on. I’ll try that one. I did put the master cylinder on pretty tight