Brake Issue

[NRX]

Guys. I had a problem with my brakes that the pedal is low and soft and the brake power was weak. I took the car to reputed place in Yakkala. Replaced a leaky (very small leak) wheel cylinder, rebuilt the master pump with new siekens washer kit (The bore was good), refilled with fresh brake fluid, bled all 4 wheels number of times, still the pedal is low and soft ( but a bit improved). Few things I noticed.

1. Bit lower braking power when the AC is switched on

2. If you apply brake very fast the car will stop easily ( Sometimes causing the wheels to lock) , but applying a constant pressure slowly causes less than ideal brakes.

3. Hissing sound when applying brakes from the brake pedal area ( Booster ?)

4. Booster rod was not visible after removing the master pump from it, they adjusted it fully but still it is only 1-2 cms long.

Guys could you please help me to identify the issue ?

The car is a Petrol FB13.

[VVTi]

The hissing sound is from a leaking diaphragm in the booster. You will need to replace the booster. Don't try to 'fix' it as it does not work.

[NRX]

  On 3/3/2013 at 4:18 AM, VVTi said:

The hissing sound is from a leaking diaphragm in the booster. You will need to replace the booster. Don't try to 'fix' it as it does not work.

I wonder why the mechanic couldn't identify it, the sound is very audible, BTW VVTi do you know the average price of a recon booster ? I'll be going today to the mechanic so it's good to know the prices beforehand to avoid being cheated

[Rumesh88]

  NRX said:

I wonder why the mechanic couldn't identify it, the sound is very audible, BTW VVTi do you know the average price of a recon booster ? I'll be going today to the mechanic so it's good to know the prices beforehand to avoid being cheated

NRX, didn't u know that the mechanics are immune to vehicle noise for that's what they hear all day? However, apart from audible noise one can see if the booster is operational and airtight by doing a simple test.

1. before you start the engine, press the break pedal a few times. Pedal stroke (travel) should be the same each time.

2. With the pedal depressed start the engine, the pedal should go down slightly. This is the normal operation.

3. Release the pedal and allow the engine to run idle for a minute of so and then depress the pedal fully and switch off the engine while keeping the pedal depressed with constant force (better do it barefoot). The pedal stroke should remain at the same position (meaning it should not come up)for about 30 seconds. if the pedal comes up you have a leak in the booster.

4. Release the pedal and start the engine again for about 2 min and switch off. The press the pedal consecutively for about five times. During first few strokes the pedal should come up progressively each time. This again confirms if the booster is airtight.

If 3 or 4 above is not OK follow VVTi's advice and never compromise on the breaking system. I once learned a bitter lesson and met with the only road accident ever due to my fault, because I drove a car knowing that the pedal was a bit spongy.

BTW how many pipes are connected to the master cylinder (2 or 4)? Just to know whether you hv proportionating valve built-in or separate.

[NRX]

  On 3/4/2013 at 5:36 AM, Rumesh88 said:

NRX, didn't u know that the mechanics are immune to vehicle noise for that's what they hear all day? However, apart from audible noise one can see if the booster is operational and airtight by doing a simple test.

1. before you start the engine, press the break pedal a few times. Pedal stroke (travel) should be the same each time.

2. With the pedal depressed start the engine, the pedal should go down slightly. This is the normal operation.

3. Release the pedal and allow the engine to run idle for a minute of so and then depress the pedal fully and switch off the engine while keeping the pedal depressed with constant force (better do it barefoot). The pedal stroke should remain at the same position (meaning it should not come up)for about 30 seconds. if the pedal comes up you have a leak in the booster.

4. Release the pedal and start the engine again for about 2 min and switch off. The press the pedal consecutively for about five times. During first few strokes the pedal should come up progressively each time. This again confirms if the booster is airtight.

If 3 or 4 above is not OK follow VVTi's advice and never compromise on the breaking system. I once learned a bitter lesson and met with the only road accident ever due to my fault, because I drove a car knowing that the pedal was a bit spongy.

BTW how many pipes are connected to the master cylinder (2 or 4)? Just to know whether you hv proportionating valve built-in or separate.

Hi Rumesh,

I've tested the booster as per the service manual ( same as what you have mentioned here) and the booster is airtight. BTW #1 and #4 contradicts no ?

The normal booster operation consists of taking fresh air (atmospheric pressure) at a rapid pace ?, so isn't it natural to make the hissing sound when the air intake happens ?

Mine has 4 pipes connected to the master cylinder. BTW what was your incident ?

Edited March 4, 2013 by NRX

[Rumesh88]

  NRX said:

Hi Rumesh,

I've tested the booster as per the service manual ( same as what you have mentioned here) and the booster is airtight. BTW #1 and #4 contradicts no ?

The normal booster operation consists of taking fresh air (atmospheric pressure) at a rapid pace ?, so isn't it natural to make the hissing sound when the air intake happens ?

Mine has 4 pipes connected to the master cylinder. BTW what was your incident ?

No. 1 should have read before you start "in the morning" or similar to indicate that any residual vacuum fro a previous drive has all but disappeared not to confuse with No. 4. The booster takes vacuum through a non-return valve from the inlet manifold and use this vacuum to push a diaphragm whenever you apply break thus assisting you with additional power on the mater cylinder. You cannot hear a hissing sound.

BTW did you have any problem other than the booster? Did you take a look at the old washers removed from the master cylinder to confirm that they are uniformly worn out. I have come across a Nissan master cylinder where there had been an air bubble in the original casting (one in a million case I thought)which caused washers to wear out unusually.

As for the "incident", I set off on a rainy evening, postponing bleeding of the front cylinder to another day, only to find myself ramming into a van near Mahara junc. That was my FB13.

[NRX]

  On 3/4/2013 at 8:21 AM, Rumesh88 said:

No. 1 should have read before you start "in the morning" or similar to indicate that any residual vacuum fro a previous drive has all but disappeared not to confuse with No. 4. The booster takes vacuum through a non-return valve from the inlet manifold and use this vacuum to push a diaphragm whenever you apply break thus assisting you with additional power on the mater cylinder. You cannot hear a hissing sound.

BTW did you have any problem other than the booster? Did you take a look at the old washers removed from the master cylinder to confirm that they are uniformly worn out. I have come across a Nissan master cylinder where there had been an air bubble in the original casting (one in a million case I thought)which caused washers to wear out unusually.

As for the "incident", I set off on a rainy evening, postponing bleeding of the front cylinder to another day, only to find myself ramming into a van near Mahara junc. That was my FB13.

I'll check that out then Rumesh.

I thought the booster works by the pressure difference between vaccum and the atmospheric pressure, where the pressure difference causes the diaphragm to move.

The old washers were worn out uniformely but the rubber properties were gone ( Mechanic said 'washer thambilaa' )

BTW so the air bubbles caused your brakes to fail or the brakes were weak ?

EDIT: nice animation about the brake booster operation http://auto.howstuffworks.com/auto-parts/brakes/brake-types/power-brake2.htm

Edited March 4, 2013 by NRX

[Rumesh88]

  NRX said:

I'll check that out then Rumesh.

I thought the booster works by the pressure difference between vaccum and the atmospheric pressure, where the pressure difference causes the diaphragm to move.

The old washers were worn out uniformely but the rubber properties were gone ( Mechanic said 'washer thambilaa' )

BTW so the air bubbles caused your brakes to fail or the brakes were weak ?

EDIT: nice animation about the brake booster operation http://auto.howstuffworks.com/auto-parts/brakes/brake-types/power-brake2.htm

You are right about the way booster works. Did I say anything contrary? On one side you get vacuum and on the other side you get atmospheric pressure. You canot hear a hissing sound "unless there is vacuum leak"

Air bubble issue was in another Nissan hatchback car (not mine) but I took hell of a lot of trouble to trace that issue. Air bubble had cause a wall between two oil paths to fail thus causing the oil to return to reservoir. Also it caused washers to wear out quite fast.

Edited March 4, 2013 by Rumesh88

[VVTi]

  On 3/3/2013 at 5:23 AM, NRX said:

I wonder why the mechanic couldn't identify it, the sound is very audible, BTW VVTi do you know the average price of a recon booster ? I'll be going today to the mechanic so it's good to know the prices beforehand to avoid being cheated

My E39 booster failed once on the way back from Anuradhapura. Agent wanted 110K, got one from SGP for less than 50K. The Alfa also had a Booster issue and I bought a recon part from Holland for 16k. Reason being that part is no longer available brand new.

My advise is buy a good recon one or if the car is a keeper, a brand new part. Brakes are there to save your life. Don't skimp on it.

[HardHat]

I guess the direction the thread is going with attention to break booster is right.

Just out of interest while we are on the subject, could a fault in ABS alter the pedal travel and feel?

[VVTi]

  On 3/5/2013 at 1:53 AM, HardHat said:

I guess the direction the thread is going with attention to break booster is right. Just out of interest while we are on the subject, could a fault in ABS alter the pedal travel and feel?

Pedal feel is normally linked to a booster fault or, bubbles in the lines or even worn pads. before you go to the ABS diagnostic you check the basics first. If your brake fluid has turned dark or you can see little particles, that usually means your washers are shot and is not sealing the piston properly and it is a matter of time where you will get a pedal to the metal situation.

best is to eliminate the basic stuff first. Check the pads, check for leaks, check the booster vacuum lines, and then check the ABS. If you are feeling a pedal wobble when applying brakes, sometimes it could be a warped disc also.

Edited March 5, 2013 by VVTi

[Rumesh88]

@NRX, if you find your booster is air tight and the tests mentioned in the manual are OK, before deciding to change the booster you need to confirm if your master cylinder is OK. When you apply brakes to stop the car (Not just to slow down)do you get the feeling your front or rear wheels get locked while other two remain in motion?

Locate the two oil inlets to the master cylinder at the reservoir bottom. If the fluid is clear you can see them from top when you take off the reservoir lid but if not, you can reduce the oil level (use a syringe to remove oil taking care not to spill)to few mms from bottom. Then with engine off ask someone to press the pedal hard (almost standing on it) while keeping a close eye on the two inlets for any inward movement of oil back to reservoir on ONE of the inlets. (When this happens it will be only on one because that's how it is designed with redundancy). Keep your eye on floating particles for evidence. Worth checking this too before investing on a booster.

[Sylvi]

Members,

I do not want to write much of this brake problem because most experienced members had given their ideas on the matter.

I have written under early and there was plenty of opposition from few members on the modification I did.

About forty years ago I had this problem in a commercial vehicle. Vacuum was not building up correctly due to leaks due to faulty exhauster unit drive shaft seals.

The vehicle was a D/D GUY bus sold by CTB. Person converted same to a lorry, unable to get a certificate from RMV to use same due to poor brakes.

I got down 13 very good mechanics from CTB 12 of them failed. 13th Mechanic very senior person problem was detected.

He said he will come next day. keep a vacuum meter and some copper and high pressure Rubber hoses ready he will inform what to do.

He connected the vacuum meter to exhauster supply line, started the engine vacuum did build up to 10 on the meter. Was not sufficient for efficient brakes.

His diagnosis was correct, and wanted me to examine the exhauster. I had to rebuild the exhauster with different modified seals for air not to suck in.

Few months back one A/L member contacted me for his brake problem. I informed him to get his vehicle down to Colombo to have a look.

I examined the vehicle there were brakes but the vacuum build up was not enough due to a very small vacuum tank.

Therefore I decided to add a bigger tank which was very expensive. Then only thing was to modify to a small shell domestic gas cylinder which cost was Rs:2000/=.

I instructed to my workers they did this job satisfactory, with a vacuum gauge fitted so that driver can observe his vacuum build up and operation.

He has become a family friend of mine was with me last Sunday discussing some other matters. Instructing me for a electric fence, which he has done.

Sylvi Wijesinghe.

[Watchman]

We would really like to see a photo of this gas cylinder brake booster. I'm sure others like me are genuinely interested in seeing this contraption. Maybe you can share some photos with us?

Thanks!

[Crosswind]

  On 3/6/2013 at 12:43 AM, Sylvi said:

Therefore I decided to add a bigger tank which was very expensive. Then only thing was to modify to a small shell domestic gas cylinder which cost was Rs:2000/=.

I instructed to my workers they did this job satisfactory, with a vacuum gauge fitted so that driver can observe his vacuum build up and operation.

He has become a family friend of mine was with me last Sunday discussing some other matters. Instructing me for a electric fence, which he has done.

Holy mother of god!

sylvi, u do realize that a gas cylinder, even an empty one, can cause an explosion...

[NRX]

  On 3/5/2013 at 4:24 AM, Rumesh88 said:

@NRX, if you find your booster is air tight and the tests mentioned in the manual are OK, before deciding to change the booster you need to confirm if your master cylinder is OK. When you apply brakes to stop the car (Not just to slow down)do you get the feeling your front or rear wheels get locked while other two remain in motion?

Locate the two oil inlets to the master cylinder at the reservoir bottom. If the fluid is clear you can see them from top when you take off the reservoir lid but if not, you can reduce the oil level (use a syringe to remove oil taking care not to spill)to few mms from bottom. Then with engine off ask someone to press the pedal hard (almost standing on it) while keeping a close eye on the two inlets for any inward movement of oil back to reservoir on ONE of the inlets. (When this happens it will be only on one because that's how it is designed with redundancy). Keep your eye on floating particles for evidence. Worth checking this too before investing on a booster.

Hi Rumesh,

I checked the #1 item of your check list. The car was not started for 2 days, the peddle strokes were same each time I press it, pedal feel was same as the pedal feel I got after testing #4 item of your check list ( That is after pressing the pedal 4,5 times)

So basically every test is passed.

As per your question, no I don't feel a drag when the wheels are locked, but I feel that only the front wheels are locked ( tire marks on the road)

[harshansenadhir]

I too experienced this hissing sound from the booster of one of 504s I used. I thought it's the booster but later it was revealed that, the valve which opens when you press the brake pedal (don't know the name, that's the valve which allows atmostphere air pressure) was faulty and causing the hissing sound.

[NRX]

  On 3/6/2013 at 6:39 AM, harshansenadhir said:

I too experienced this hissing sound from the booster of one of 504s I used. I thought it's the booster but later it was revealed that, the valve which opens when you press the brake pedal (don't know the name, that's the valve which allows atmostphere air pressure) was faulty and causing the hissing sound.

mine could be a similar case since the booster airtight test is alright according to the service manual. :|

[Sylvi]

  On 3/6/2013 at 2:34 AM, Crosswind said:

Holy mother of god!

sylvi, u do realize that a gas cylinder, even an empty one, can cause an explosion...

Crosswind,

Yes it was a empty one I bought for the said amount, then removed the top brass adopter fitted all units bought from Thahir's

They supply units and all accessories for Boiler and steam operators. From year1930.

It was not necessary to turn out any thing for the modification. If any one wants can get Pictures from the A/L member who is using that Mitsubishi jeep.

I did not want to take any pics because I have done this several times successfully.

My spray painting compressor tank is also a bigger domestic gas tank.

Which was modified to a air receiver tank, when the original tank gave away due to corrosion after 5 years.

Gas tanks are build with thicker gauge of iron sheets and tested for high pressure. Do not require very high pressure for spray painting.

Sylvi Wijesinghe.

[Rumesh88]

  NRX said:

mine could be a similar case since the booster airtight test is alright according to the service manual. :|

If the hissing is due to a problem at the atmospheric port you may hear a hissing sound but only for couple of second as you press the pedal. If you don't feel your wheel are not dragging, what exactly do you mean by "brake power is weak"? Did you do the test in post #12? When you do it light up the reservoir sufficiently so that you can see movement of floating particles suspended in oil inside (Like "Brownian motion" in Physics).

[HardHat]

  On 3/5/2013 at 2:51 AM, VVTi said:

Pedal feel is normally linked to a booster fault or, bubbles in the lines or even worn pads. before you go to the ABS diagnostic you check the basics first. If your brake fluid has turned dark or you can see little particles, that usually means your washers are shot and is not sealing the piston properly and it is a matter of time where you will get a pedal to the metal situation.

best is to eliminate the basic stuff first. Check the pads, check for leaks, check the booster vacuum lines, and then check the ABS. If you are feeling a pedal wobble when applying brakes, sometimes it could be a warped disc also.

VVTI you are absolutely right. ABS should be about the last thing to be checked here and I wasn't suggesting to jump ahead of the game.

The reason for asking that question is one of my mates had an old beat up Holden Commodore and it developed a break issue - sudden and unpredictable loss of pedal feel along with no or very little breaks! The breaks were ok for 95% of the time but would suddenly give up the ghost when you needed them most. Driving that car was like playing Russian rulet.

Long story short, went through all the basic stuff - the pads, disks, brake cylinders, washers, hydraulic lines, master cylinder and the lot but the problem was still not solved.

The only thing which hadn't been checked by that time was the ABS but the guy sold the car before we could get into that - he gave fair warning to the buyer on the problem of course.

Nevertheless, we were not convinced that there could have been any problem with the ABS anyway, as if there was any ABS issue, the symptoms could have been different to long travel of break pedal and loss of break feel.

[NRX]

  On 3/7/2013 at 2:50 AM, Rumesh88 said:

If the hissing is due to a problem at the atmospheric port you may hear a hissing sound but only for couple of second as you press the pedal. If you don't feel your wheel are not dragging, what exactly do you mean by "brake power is weak"? Did you do the test in post #12? When you do it light up the reservoir sufficiently so that you can see movement of floating particles suspended in oil inside (Like "Brownian motion" in Physics).

Hi Rumesh, Yes the hissing sound can be heard only for a half a second or less when pressing the pedal, not when keep holding it. To put it simply the sound comes only when the pedal is travelling not while holding.

Sorry for the confusion, what I meant by 'wheels are not draggin 'is this. When I apply a heavy force to stop suddenly, the front wheels get locked and the car is really stopped and not dragging forward. Rear wheels don't get locked btw ( Is it ok ? )

But when I apply brake slowly I feel the brake power is not enough. Dammit! Am I applying the brake in a wrong way ??

I'll do the reservoir test on weekend and update you

[Rumesh88]

  NRX said:

Hi Rumesh, Yes the hissing sound can be heard only for a half a second or less when pressing the pedal, not when keep holding it. To put it simply the sound comes only when the pedal is travelling not while holding.

Sorry for the confusion, what I meant by 'wheels are not draggin 'is this. When I apply a heavy force to stop suddenly, the front wheels get locked and the car is really stopped and not dragging forward. Rear wheels don't get locked btw ( Is it ok ? )

But when I apply brake slowly I feel the brake power is not enough. Dammit! Am I applying the brake in a wrong way ??

I'll do the reservoir test on weekend and update you

Ideally all four wheels should get locked at the same time although the brake force on rear wheels is less than that on front wheels. It is the purpose of the proportioning valve to distribute correct brake force to front and rear wheels depending on the weight distribution. You can try braking on a gravel road or a ground and see if the tyre marks are of equal length.

Another thing to confirm down the line is whether your idle throttle position and ignition timing is correct. This has a significant impact on intake vacuum which should be in the region of 18 - 22 Hg.in. Anyway first check your braking system.

Edited March 8, 2013 by Rumesh88

[The Don]

  On 3/7/2013 at 5:17 AM, NRX said:

Hi Rumesh, Yes the hissing sound can be heard only for a half a second or less when pressing the pedal, not when keep holding it. To put it simply the sound comes only when the pedal is travelling not while holding.

Sorry for the confusion, what I meant by 'wheels are not draggin 'is this. When I apply a heavy force to stop suddenly, the front wheels get locked and the car is really stopped and not dragging forward. Rear wheels don't get locked btw ( Is it ok ? )

But when I apply brake slowly I feel the brake power is not enough. Dammit! Am I applying the brake in a wrong way ??

I'll do the reservoir test on weekend and update you

The hissing noise can always be a leaky rubber boot on the rod to the master cylinder, so might not be connected to an actual fault.

[Sylvi]

Members,

Will get that A/L member to upload a picture of the vacuum tank mini Gas cylinder under the foot board. Of his jeep.

I will upload a picture of the compressor what I have modified.

Sylvi Wijesinghe.