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Brakes still spongy after fluid change

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#42 ·
@vmmf WRT the rotors, I am unsure if the coating is meant to be removed - if it is an oil based coating, then yes, but this seems to be a full manufactured coat. Read the instructions with the rotors, the coat may just wear off with use - I can not be sure as I do not know these
 
#44 ·
Also be glad you have all discs. Drum brakes are more of a pain with the wheel cylinders, 2 shoes, springs, retainer clips and automatic break adjusters. Also should check any emergency brake cables with drums.

I think you will find this a rather simple job. Just lube any mounts that move. On the car Imjust did it's simply 2 lots to lube called sliders.

If nobody else explained what sliders are here goes.

When you step on the brake of a vehicle they are not like that of a caliper brake on a bike where both sides get pulled into the wheel.

A brake caliper has one piston. So when you are driving the calipers are basically micro fractions off the rotor so the brakes do not pre mature wear and so the rotors do not get hot and warp. Warping is what causes the pulsating pedal feel.

So when you step on the brake the pressure on the fluid forces the piston out. This in turn will force the calipers to slide which is how the front pad gets it's pressure so the car will stop.

Unlubed sliders will either cause the calipers to totally freeze in place meaning only the inside pad is doing most of the work , this can also cause brake drag which leads to the above issues.

It's simple really once you understand the process. The master cylinder is what pushes the fluid, think of it like the cable on a bike that pulls the calipers instead of pushing.

The booster is simply a vacuum canister of sorts that multiplies the force of your peddle kind of how an air compressor can fill a basket ball better than you could do by mouth.
 
#45 ·
Now for the vacuum test. I turned the car in. Shut off waited 10 seconds, had one full peddle push, one just under and another partial before stiff peddle.

Turn car on, turned off sat 15 minutes and the results were the same. If you can't do that get a new check valve after all other work is done. Look for rust on the booster and see if any pin holes. You could check the vacuum line attached to the check valve for damage.

Lastly you could get a new vacuum booster. I have never changed one before but it seems like it's easy. There should not be any fluid in the booster unless the master cylinder is leaking.
 
Discussion starter · #47 ·
Just Another Guy said:
Also be glad you have all discs. Drum brakes are more of a pain with the wheel cylinders, 2 shoes, springs, retainer clips and automatic break adjusters. Also should check any emergency brake cables with drums.

I think you will find this a rather simple job. Just lube any mounts that move. On the car Imjust did it's simply 2 lots to lube called sliders.

If nobody else explained what sliders are here goes.

When you step on the brake of a vehicle they are not like that of a caliper brake on a bike where both sides get pulled into the wheel.

A brake caliper has one piston. So when you are driving the calipers are basically micro fractions off the rotor so the brakes do not pre mature wear and so the rotors do not get hot and warp. Warping is what causes the pulsating pedal feel.

So when you step on the brake the pressure on the fluid forces the piston out. This in turn will force the calipers to slide which is how the front pad gets it's pressure so the car will stop.

Unlubed sliders will either cause the calipers to totally freeze in place meaning only the inside pad is doing most of the work , this can also cause brake drag which leads to the above issues.

It's simple really once you understand the process. The master cylinder is what pushes the fluid, think of it like the cable on a bike that pulls the calipers instead of pushing.

The booster is simply a vacuum canister of sorts that multiplies the force of your peddle kind of how an air compressor can fill a basket ball better than you could do by mouth.
Click to expand...
Thank you very much for this magnificent explanation. I disassembled the wheel where the rotor seemed worst on the pictures to lubricate the caliper piston and 2 bolts. You know the caliper piston is hollow. Well a lot of rust came out of that hole and a part along the edge that should touch the pad fell. The piston is on a very bad shape. Literally falling apart. I'm glad I just ordered new ones. I also detected the following:
  1. After a 10 minute ride and stopping the car I do get the same results as you for the vacuum test. Approximately 2.5 full brake pedal pushes before it turns hard. This just doesn't seem to be happening if I turn on and off without a short ride first.
  2. The interior brake pad (the one not visible from the outside) was worn unevenly. Along the longest axis (you know the pad is approximately rectangular) with the longest dimension vertically, the top part was about 1.2 the thickness of the bottom part. I'm not sure why, perhaps I didn't mounted it staright when I put it new. After lubricating, I tried replacing that pad with others I had that were evenly worn and the result was a very loud noise if I drove the car above 70 km/h. Something like tac-tac-tac-tac. The faster I drove the more frequent the tac-tac-tac. It seems like something on that wheel is not turning even, like it is closer at one point and far away at another. Even putting the original non-uniform pads back didn't completely fixed the noise. I don't know if the part of the piston that fell is responsible for this. I will take the car for wheels alignment after I install all the new parts.
  3. I noticed that after driving 15 minutes and braking a few times to test the brakes the 2 front calipers where warm and the 2 front rotors burning hot. However, the rear caliper on both sides was cold, not even room temperature, cold. Ambient temperature was 12 C (53.6 F) this morning. And the rear rotors barely warm. I feel on a FWD the front brakes are more important but is this like this by design or each wheel should be responsible for 25% of braking the car?
 
Discussion starter · #49 ·
Bigphil555 said:
@vmmf WRT the rotors, I am unsure if the coating is meant to be removed - if it is an oil based coating, then yes, but this seems to be a full manufactured coat. Read the instructions with the rotors, the coat may just wear off with use - I can not be sure as I do not know these
Click to expand...
Apparaently not. The coating is supposed to prevent the rust after they are installed
 
#51 ·
@vmmf I did check their website out of interest. It is no worry though, as they are well known for good quality work. Looks like you made the right choice to swap out the calipers - it will give you full confidence for the future.

As for brake temps, 80% plus of the brake force is on the front brakes, hence they will be well warm. Well done on the lube too :)

Let us know how the brakes are after the service - once they are bedded in, it will be a world of difference
 
Discussion starter · #52 ·
Bigphil555 said:
@vmmf I did check their website out of interest. It is no worry though, as they are well known for good quality work. Looks like you made the right choice to swap out the calipers - it will give you full confidence for the future.

As for brake temps, 80% plus of the brake force is on the front brakes, hence they will be well warm. Well done on the lube too :)

Let us know how the brakes are after the service - once they are bedded in, it will be a world of difference
Click to expand...
I have found this great article about brake force distribution

brakeexperts.com

Front vs. Rear Brakes: Does it Even Matter? | Brake Experts

Even though most modern cars are built with brakes on all four tires, If you have ever needed to replace the brakes on your vehicle,…
brakeexperts.com brakeexperts.com
 
#54 · (Edited)
I'll answer you. I think i know what the issue is.
I have a rav4 3.5 and the problem was the brake booster, not the brake lines, neither the brake pump. I'll tell you why:
1.- When the brake lines have remanent air in the lines, it could feel soft and underpowered.
2.- When the brake pump is damaged, the pedal goes all way down and you have to pump continuosly to achieve the braking effect.
3.- When the ABS is damaged, it causes to show some led in the dashboard, and if you have DAC (downhill assist control) it won't work.
4.- A normal brake booster:
A) gets suction from the engine to amplify the brake power, so it won't be hard when you brake.
B) can be tested like this: with the engine powered off, pump many times until it gets hard (good sign of a good brake pump and no air in the lines); when you step on the pedal with the engine turned off, is usually hard, but when you turn on the engine, the pedal goes down (only halfway) and gets soft but at the same time has a strong braking effect.
C) sounds only a bit when you press the pedal (like a brief "poof"), but it doesn't leaks air (like a constant "hisssss", bad sign btw), try listening carefully the zone near the pedal while doing this.
5.- When a brake booster is damaged in any part as diaphragm or valve, or disconnected from the suction hose:
A) the pedal won't go down when turning on the engine
B) the pedal unpredictably can go hard when driving and braking (too dangerous)
C) the pedal leaks air ("hisssssss" sound when holding down the pedal)
D) the brakes get very hard, so hard that you have to push with all your weight on the pedal to achieve some braking effect.

I ordered a new brake booster from amazon, and guess what... it was also damaged. But it could be repaired at my local brake shop. I threw away the old one.
After that... all good! Just a little pressure on the pedal and whoa! brake like a dream.
 
#55 ·
Jack Daniels said:
sometimes air can get in while bleeding if the reservoir gets just a shade too low. This may require bleeding all 4 calipers again.

also air can get in around the outside of the nipple thread. Install any new nipples with ceramic brake grease on the threads, this will make that joint fluid tight at the low pressure used for bleeding.

Also never shake the fluid bottle, don't let it splash into the reservoir, any bubbles in the reservoir will take ages to dissipate so if you see any, take a coffee break until they are gone.
Click to expand...
There's a really good video on YouTube about the very same issue you are having. I can't remember the guys name but, he has a ton of repair videos. He's in Houston. His Rav4 started getting spongy brakes shortly after a complete brake job. I had similar issue with my 2011. The master cylinder was the culprit.
 
#56 ·
Wayouttawarranty11 said:
There's a really good video on YouTube about the very same issue you are having. I can't remember the guys name but, he has a ton of repair videos. He's in Houston. His Rav4 started getting spongy brakes shortly after a complete brake job. I had similar issue with my 2011. The master cylinder was the culprit.
Click to expand...
Agree, spongy brake = master cylinder
Hard brakes, maybe brake booster
 
#57 · (Edited)
Just Another Guy said:
Now for the vacuum test. I turned the car in. Shut off waited 10 seconds, had one full peddle push, one just under and another partial before stiff peddle.

Turn car on, turned off sat 15 minutes and the results were the same. If you can't do that get a new check valve after all other work is done. Look for rust on the booster and see if any pin holes. You could check the vacuum line attached to the check valve for damage.

Lastly you could get a new vacuum booster. I have never changed one before but it seems like it's easy. There should not be any fluid in the booster unless the master cylinder is leaking.
Click to expand...
Changing a vaccum booster, in my rav4 3.5 was a pain in the a...
It's difficult because of the small space to maneuver. I needed to unscrew the ABS unit so the metallic brake lines coming from will not be damaged. I suppose in the 4 cylinder version could be easier.
 
#58 ·
Btw, when changing brake pads, you should never press the brake piston into place without bleeding the brakes at the same time. If you do so, the plunger in the brake master cylinder gets damaged and appears the spongy feel.
So, loosen the bleed screw first, putting a hose to drain the brake liquid into a can, then press the brake piston in position.
 
Discussion starter · #60 ·
shruen said:
I'll answer you. I think i know what the issue is.
I have a rav4 3.5 and the problem was the brake booster, not the brake lines, neither the brake pump. I'll tell you why:
1.- When the brake lines have remanent air in the lines, it could feel soft and underpowered.
2.- When the brake pump is damaged, the pedal goes all way down and you have to pump continuosly to achieve the braking effect.
3.- When the ABS is damaged, it causes to show some led in the dashboard, and if you have DAC (downhill assist control) it won't work.
4.- A normal brake booster:
A) gets suction from the engine to amplify the brake power, so it won't be hard when you brake.
B) can be tested like this: with the engine powered off, pump many times until it gets hard (good sign of a good brake pump and no air in the lines); when you step on the pedal with the engine turned off, is usually hard, but when you turn on the engine, the pedal goes down (only halfway) and gets soft but at the same time has a strong braking effect.
C) sounds only a bit when you press the pedal (like a brief "poof"), but it doesn't leaks air (like a constant "hisssss", bad sign btw), try listening carefully the zone near the pedal while doing this.
5.- When a brake booster is damaged in any part as diaphragm or valve, or disconnected from the suction hose:
A) the pedal won't go down when turning on the engine
B) the pedal unpredictably can go hard when driving and braking (too dangerous)
C) the pedal leaks air ("hisssssss" sound when holding down the pedal)
D) the brakes get very hard, so hard that you have to push with all your weight on the pedal to achieve some braking effect.

I ordered a new brake booster from amazon, and guess what... it was also damaged. But it could be repaired at my local brake shop. I threw away the old one.
After that... all good! Just a little pressure on the pedal and whoa! brake like a dream.
Click to expand...
I will focus on the booster and master Cylinder after I'm done with the calipers and rotors

I have 1 question for you though:
If the brake booster is there to make you have to do less effort. Why would the brake pedal get hard when driving? Without the booster help shouldn't it go soft requiring more strength from you sinking the pedal deeper?
 
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Just Another Guy
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