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Braking Power Varies With Time


NRX

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Guys!

My car's braking power varies with time, Sometimes it has enough brake power to swing you forward when you apply brake, sometimes just as low to make you afraid that you would hit anything. I replaced the rear brake shoes and refaced the drums as well. The mechanic bleeded air (rear side only) and topped up the lost brake fluid with new fluid. But didn't touch front brakes in the process. But he said "issaraha brake pads awulak na".

The braking power is generally on the low side as I feel. There isn't any fluid leaks.

Sometimes after a cold start the breaking power is fine, after riding for few minutes the power becomes low. This even varies day to day.

Any input on this matter is much appreciated.

BTW the car is a Sunny FB13 (Dr Sunny): Front disc and rear drum. :)

Edited by NRX
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Are you saying that the brake loses power at times and you have to press hard to get the car to stop?

Perhaps it is a vacuum leak / brake booster issue?

In your driveway with the car parked and neutral (engine on, press the brake pedal deeply a few times... if the brake gets very stiff soon and doesn't resume normal functioning perhaps this is a clue?)

Disclaimer - I'm no expert on this or any automotive area.

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Not a expert on this but generally I think you have to check your brake booster, master pump from a good mechanic to see whether it operates perfectly. Mostly if there are no issues on brake pads or whatever the things inside the wheel, It could be related to the booster or the pump or even may be the lines. :) I had a same issue on my vehicle which is very older than yours I think and basically I had to replace the booster and some parts. Hope this helps.

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Are you saying that the brake loses power at times and you have to press hard to get the car to stop? Perhaps it is a vacuum leak / brake booster issue? In your driveway with the car parked and neutral (engine on, press the brake pedal deeply a few times... if the brake gets very stiff soon and doesn't resume normal functioning perhaps this is a clue?) Disclaimer - I'm no expert on this or any automotive area.

Brake loses power and how quicker I apply the brake it takes its time to stop. The time it takes to stop varies from time to time The pedal is soft too, just like when you press the accelerator.

About the testing you mentioned; I haven't noticed any stiffening other than when you press brake several times when the engine is off :)

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Not a expert on this but generally I think you have to check your brake booster, master pump from a good mechanic to see whether it operates perfectly. Mostly if there are no issues on brake pads or whatever the things inside the wheel, It could be related to the booster or the pump or even may be the lines. :) I had a same issue on my vehicle which is very older than yours I think and basically I had to replace the booster and some parts. Hope this helps.

Well macahn, I tested the booster as mentioned in the service manual, and it was fine, have to check the master pump though.

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It was there even before the rear brake shoe replacement machan :) You meant the front ones ?

Ah ok, I had a problem with the previous car, where the garage had used some brand that wasn't very good & I had problems stopping the car in a hurry. At the beginning of the journey it was all good but as they got hotter it became worse. Changed it & it was all sorted.

Ya meant the front ones machan. But I suppose it could happen to the rear as well if its some inferior quality?? Have you changed the oil & flushed out the system recently?

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Ah ok, I had a problem with the previous car, where the garage had used some brand that wasn't very good & I had problems stopping the car in a hurry. At the beginning of the journey it was all good but as they got hotter it became worse. Changed it & it was all sorted.

Ya meant the front ones machan. But I suppose it could happen to the rear as well if its some inferior quality?? Have you changed the oil & flushed out the system recently?

Hmm, That may be a reason machan.

I wanted to flush the fluid and refill but the makabass only topped up fluid lost during the repair.

BTW machan what was the better quality brake pad brand you bought ? I bought FBK for the rear one.

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Not sure I'm understanding your problem?

If I have understood correctly when you first drive you car for first time that day etc tha brakes are great. Nice firm pedal feel and they work as they should.

But after a while of driving and using the brakes, the pedal goes soft and the brakes have very little stopping power?

If this is your problem, have your brake fluid changed.

It absorbs water naturally from the atmosphere and causes the fluid to boil when hot thus not operating the slave cylinders in your callers correctly as the gas just expands.

If this isn't what you mean please explain the problem a but more

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Hmm, That may be a reason machan.

I wanted to flush the fluid and refill but the makabass only topped up fluid lost during the repair.

BTW machan what was the better quality brake pad brand you bought ? I bought FBK for the rear one.

Machan can't remember the brand now machan, but now I just get the originals. They cost more, but they last longer & work far better too.

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Not sure I'm understanding your problem? If I have understood correctly when you first drive you car for first time that day etc tha brakes are great. Nice firm pedal feel and they work as they should. But after a while of driving and using the brakes, the pedal goes soft and the brakes have very little stopping power?

Yes! Except the brake pedal is soft all the time.

If this is your problem, have your brake fluid changed. It absorbs water naturally from the atmosphere and causes the fluid to boil when hot thus not operating the slave cylinders in your callers correctly as the gas just expands. If this isn't what you mean please explain the problem a but more

and the brake power varies from one day to another day, say I had good braking power on last satuday but sunday had terrible braking power. Hope I made it clear this time.

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Not sure I'm understanding your problem? If I have understood correctly when you first drive you car for first time that day etc tha brakes are great. Nice firm pedal feel and they work as they should. But after a while of driving and using the brakes, the pedal goes soft and the brakes have very little stopping power? If this is your problem, have your brake fluid changed. It absorbs water naturally from the atmosphere and causes the fluid to boil when hot thus not operating the slave cylinders in your callers correctly as the gas just expands. If this isn't what you mean please explain the problem a but more

same problem in my car also...

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Had similar sort of issue and corrected by repairing the masterpump using a rebuilt kit. According to my mechanic its due to worn out rubber seals which fails to hold the pressure and expand as they supposed to do. Does braking after paddling have an improvement on braking power? If so, its most probably the masterpump!

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Agree with H C. Ask a good mechanic to inspect the master pump and the washers(as everybody calls them) and replace if you haven't done it for a long time even if they look fine.

Also make sure to check the inside of the master pump to make sure there's no damage in the bore and replace all the fluid.

Use genuine sieken or nissan parts and you should be fine

One important thing is get this sorted out ASAP as you wouldn't want to be in an emergency braking situation with crappy brakes

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Had similar sort of issue and corrected by repairing the masterpump using a rebuilt kit. According to my mechanic its due to worn out rubber seals which fails to hold the pressure and expand as they supposed to do. Does braking after paddling have an improvement on braking power? If so, its most probably the masterpump!
Agree with H C. Ask a good mechanic to inspect the master pump and the washers(as everybody calls them) and replace if you haven't done it for a long time even if they look fine.

Also make sure to check the inside of the master pump to make sure there's no damage in the bore and replace all the fluid.

Use genuine sieken or nissan parts and you should be fine

One important thing is get this sorted out ASAP as you wouldn't want to be in an emergency braking situation with crappy brakes

Thanks guys! I'll check the master pump and do whatever is needed. Thanks for the help. :)

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  • 1 month later...

Guys. Little update. 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, 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 ?

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Since you mentioned you replaced the washers in the master cylinder, was there a leak in it as well? That in conjunction with the hissing sound leads me to believe your brake booster should be inspected as well, since you don't specifically mention it being checked out.

As for braking power with A/C, my car exhibits something similar but it's normal; the pedal goes down by about an inch or two whenever the compressor cuts out, which makes the car jerk forward if I've already stepped on the brakes about 70-80%.

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Since you mentioned you replaced the washers in the master cylinder, was there a leak in it as well? That in conjunction with the hissing sound leads me to believe your brake booster should be inspected as well, since you don't specifically mention it being checked out.

As for braking power with A/C, my car exhibits something similar but it's normal; the pedal goes down by about an inch or two whenever the compressor cuts out, which makes the car jerk forward if I've already stepped on the brakes about 70-80%.

Well the master cylinder was inspected since the brake was weak and the washers were the originals came with the car (19 years old) and the bass said 'washers thambila'. BTW terra, Don't you guys a get even a little bit of hissing sound ? (Due to the vacuum/fresh air suction mechanism)

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My van had the hissing sound, but it too was an 18 year old vehicle at the time of selling. It also had many many other sounds as well, but the brakes worked fine, for a van. My car makes no sound I can hear from the inside when pressing the brake pedal, other than the clunk sound made by the pedal itself.

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