Brake Booster Problem

Iroshana · February 19, 2008

Hi all, I'm new for the forum and thanks for the admin to allowing me to use the forum.

I have a old Nissan Sunny SB12 (Diesel, Manual). There is a problem in the brake booster,. Sometimes when I press the brake its too hard to push down the paddle. Its not happening every time. I checked the vacuum hoses coming from the vacuum pump attached to the alternator. Found no damages at them.

Also I experienced that when I pressed the brake paddle 3-4 times, handbrake indicator on the dash board flashing for few seconds and engine getting slow for few seconds. I found there are 3 parellel indicators for the brake light on the dash board. One line goes for vacuum sensor.

Anybody got any idea on this matter? Am I to replace the booster or the vacuum pump?

-Iroshana

harshansenadhir · February 19, 2008

Iroshana said:
Hi all, I'm new for the forum and thanks for the admin to allowing me to use the forum.
I have a old Nissan Sunny SB12 (Diesel, Manual). There is a problem in the brake booster,. Sometimes when I press the brake its too hard to push down the paddle. Its not happening every time. I checked the vacuum hoses coming from the vacuum pump attached to the alternator. Found no damages at them.

Also I experienced that when I pressed the brake paddle 3-4 times, handbrake indicator on the dash board flashing for few seconds and engine getting slow for few seconds. I found there are 3 parellel indicators for the brake light on the dash board. One line goes for vacuum sensor.

Anybody got any idea on this matter? Am I to replace the booster or the vacuum pump?

-Iroshana

handbrake light comes when you press the paddle 3-4 times means the vacuum pressure has gone down than normal and engine takes a load bit coz in diesels the vacuum is filled by a separate pump unlike from the intake suction on petrols. This pump you'll find most of the times coupled with the alternator. check for pump as well as there's usually an O ring fixed tot he vacuum storage (brake booster) from the brake pedal side. check for that as well. last to check is the diaphragm. if the diaphragm is faulty you better replace the booster (though I once managed to repair it of one of my 504s ).

maithri · February 20, 2008

Iroshana,

The Brake servo is a vaccum cylinder, the vaccum created by a pump driven by the engine and applied through a hose. It is likely you may also have a non return valve to retain the vaccum when the engine is not running. Check the valve as well as the pipe first. A completely failed diaphragm in the servo will mean no servo at all-it's like a balloon once burst will not hold any more air/vaccum. Yours appear to be working but not too well, my guess is a lack of vaccum caused by a leaky hose/non return valve or a pump failing and not creating sufficient vaccum.

Maithri.

Iroshana · February 21, 2008

maithri said:
Iroshana,
The Brake servo is a vaccum cylinder, the vaccum created by a pump driven by the engine and applied through a hose. It is likely you may also have a non return valve to retain the vaccum when the engine is not running. Check the valve as well as the pipe first. A completely failed diaphragm in the servo will mean no servo at all-it's like a balloon once burst will not hold any more air/vaccum. Yours appear to be working but not too well, my guess is a lack of vaccum caused by a leaky hose/non return valve or a pump failing and not creating sufficient vaccum.

Maithri.

Maithri thanx for your information. I have seen on the internet that there should be a non-return valve at the booster. But I dont have something like that. Anyway my mechanic checked the brake system yesterday and he recommend me to replace the total system since the system is too old.

Is it possible for me to get a bigger size booster to make it too smart?

Iroshana · February 21, 2008

harshansenadhir said:
handbrake light comes when you press the paddle 3-4 times means the vacuum pressure has gone down than normal and engine takes a load bit coz in diesels the vacuum is filled by a separate pump unlike from the intake suction on petrols. This pump you'll find most of the times coupled with the alternator. check for pump as well as there's usually an O ring fixed tot he vacuum storage (brake booster) from the brake pedal side. check for that as well. last to check is the diaphragm. if the diaphragm is faulty you better replace the booster (though I once managed to repair it of one of my 504s ).

Thanx for your info. Is it OK to replace my booster with a bigger sized one? Will it make any difference in brake?

harshansenadhir · February 23, 2008

Iroshana said:
Thanx for your info. Is it OK to replace my booster with a bigger sized one? Will it make any difference in brake?

my advise is to go for the original one although you can improve the breaking power (NM) by installing a bigger one. then you'll probably have to replace it with the brake pump assembly if you fail to find a bigger booster which exactly fits the existing brake pump assembly. and what i'm not too sure is increasing the power of booster will harm the other components of the system such as caliper washers and other brake washers etc.. mithri might be able to shed a light on that

maithri · February 24, 2008

Your Mechanic may well be right but I prefer to see justification for such a drastic course of action. Sure it will cure the fault. But ask him to identify the problem area. Hydraulics, at wheels,pipes and hoses, load sensing valves if fitted,brake master cylinder, brake servo, vaccum pipes or vaccum pump.

It could also be a mechanical fault like worn wheel bearings causing the caliper pistons to be pushed back too far.

When replacing brake components I would never entertain second hand as a good option-specially any hydraulic components-never-buy new or repair existing using new seals and pistons etc if the bore is good.

Servo's are not easy to repair as the parts are hard to come by. They rarely fail due to wear and tare. So I suppose it's not viable for aftermarket parts suppliers to source and stock.

If you are going to modify the existing system be very careful over braking is as deadly as under braking so the mods have to be chosen very carefully.

I modified several Morris Travellers back in the 80's to front disc brakes and servo assistance they were fine and brought the car in to line with its modern day counterparts.

Maithri.

Iroshana · February 25, 2008

maithri said:
Your Mechanic may well be right but I prefer to see justification for such a drastic course of action. Sure it will cure the fault. But ask him to identify the problem area. Hydraulics, at wheels,pipes and hoses, load sensing valves if fitted,brake master cylinder, brake servo, vaccum pipes or vaccum pump.
It could also be a mechanical fault like worn wheel bearings causing the caliper pistons to be pushed back too far.

When replacing brake components I would never entertain second hand as a good option-specially any hydraulic components-never-buy new or repair existing using new seals and pistons etc if the bore is good.

Servo's are not easy to repair as the parts are hard to come by. They rarely fail due to wear and tare. So I suppose it's not viable for aftermarket parts suppliers to source and stock.

If you are going to modify the existing system be very careful over braking is as deadly as under braking so the mods have to be chosen very carefully.

I modified several Morris Travellers back in the 80's to front disc brakes and servo assistance they were fine and brought the car in to line with its modern day counterparts.

Maithri.

Mithri I really really appreciate your comments. It's very very useful for me. I'm going to give the car to the agents. I think they could solve the problem in proper way with original spares.