Diagnosing a spongy brake pedal

[mashriqain]

The brake pedal is spongy. The brakes work okay and they don't need repeated pressing to work, they work the first time but pedal is spongy, compared to another where the brake pedal is firm (and I believe that is how it is supposed to be). What could be the possible reasons behind this?

• With the engine off, the pedal becomes firm when pressed two-three times.
• Brake pads have been changed.
• Brake fluid flush completed.
• Brake service done i.e. calipers greased.

[Teeboyuk]

Check the servo or u have a vacuum leak.

[syncview]

did this problem pop up after the mentioned work or it was as is before?

[mashriqain]

Check the servo or u have a vacuum leak.

Servo?

[mashriqain]

did this problem pop up after the mentioned work or it was as is before?

It was present before the work. The said work was long due and I was hoping that it would solve the spongy pedal issue or improve a little but it is still the same.

[syncview]

Car in question and how much has it run?

[syncview]

Servo?

servo as in the brake booster

[mashriqain]

Car in question and how much has it run?

Axio '07, about 29k right now (verified mileage)

[mashriqain]

servo as in the brake booster

Is there any definitive test to know whether brake booster is faulty?

[syncview]

could be because of air in the system which means you need to bleed properly

or

one more rubber brake line(s) are weak and need replacement however that would be rare at 29k but anything is possible

regarding the brake booster:

Do-It-Yourself Power Brake Booster Test

check all vacuum lines on the engine

[mashriqain]

^ The tests from above pass:

[h=3]Test 1[/h]

[h=3]Test 2[/h]

[h=3]Test 3[/h]

Read more: Do-It-Yourself Power Brake Booster Test Do-It-Yourself Power Brake Booster Test

As far as proper bleeding is concerned, the brake fluid was flushed today i.e. until the new brake fluid was seen coming out of the bleed valve for each wheel. So are there still chances of air stuck in the system?

[syncview]

there are if bleeding wasn't done properly, how was it bled?

also have a close look at the rubber lines that go into the calipers, they might be old and balloon out due to pressure when the pedal is pressed, this can cause a spongy pedal

[mashriqain]

there are if bleeding wasn't done properly, how was it bled?

also have a close look at the rubber lines that go into the calipers, they might be old and balloon out due to pressure when the pedal is pressed, this can cause a spongy pedal

• Old fluid removed from reservoir by syringe, not all the way, some fluid was still left.

• New fluid filled in resevoir.

• Bleeder valves opened one by one, pedal pressed repeatedly until fresh fluid was seen coming from bleeder valve. Then closed.

No further bleeding was done after completing this process.

[syncview]

Was this a two man or one man job?

If one man, then did you make a bottle with a pipe till it's lowest level dipped in brake fluid, which is put on a relatively higher place than the fender of the car and connected to the bleed valve, better explaned by xulfiqar in star2's thread about his Nissan sunny

If it was a two man operation then the bleed valve should have been tightened every time the pedalling was performed..another trick in this method was to use a brick under the pedal so the pedal doesn't hit the floor. Once the pedal gets firm, the bleed valve is opened till the pedal hits the brick and closed while the pedal is still pushed on the brick

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[ToxicDevil]

How many clicks does the handbrake take?

[mashriqain]

Was this a two man or one man job?

If one man, then did you make a bottle with a pipe till it's lowest level dipped in brake fluid, which is put on a relatively higher place than the fender of the car and connected to the bleed valve, better explaned by xulfiqar in star2's thread about his Nissan sunny

If it was a two man operation then the bleed valve should have been tightened every time the pedalling was performed..another trick in this method was to use a brick under the pedal so the pedal doesn't hit the floor. Once the pedal gets firm, the bleed valve is opened till the pedal hits the brick and closed while the pedal is still pushed on the brick

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It was a three man job... A lookout for the brake oil reservoir and adding when needed. A bottle with transparent tube in it was used. Already filled with brake fluid.

What was not performed was closing the valve after each pedal press as you have mentioned. Just on the last.

A question, if I am to use a pressure bleeding device i.e. vacuum/suction applied through bleed valves, it can be done without pedal presses? Correct?

[syncview]

Yep, correct

EDIT: also, you're not supposed to suck thru the bleed valve, you're supposed to apply pressure of about 15-18psi into the bleed valve so that the brake fluid and air come out from the reservoir

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[ahsanzs]

Material of the brake pads (assuming 4-wheel disc brake) is important. If you are using MK Kashiyama yellow box with purple printing leather brake pads then your brake pedal will be soft like a mattress. Reason mentioning MK is that it is favourite of mechanics and most recommended by spare parts shops.

If you are using something like Tasaki or Kentex the brake pedal will feel very firm on brake press. (This doesn't guarantee shortest stopping distance, though - user experience and machine performance are two different terms. What I am saying is that regardless of the brake performance, hard brake pads could give you your required pedal feel).

[Xulfiqar]

dont mash on the pedal if the pads are new - they need some time to burnish. When not burnished it may give a spongy pedal as the brake pads have not bedded.

I also never close any bleed nipples when bleeding the brakes on one man system without pressure, if your catch reservoir is above the nipple level then you dont need to close it as the weight of the liquid in the bleed discharge pipe ensures no air can be sucked back.

It is vital that the pedal be pumped slowly.

Now heres a bit of "somewhat" bad news - if you suspect the MC has trapped air.

If at any point of time the master cylinder went dry - its loaded with air which wont bleed unless you bleed it individually first, Its very easy - you need some cut up brake connections and some transparent bleed pipe.

remove all the brake pressure pipes - and connect your junk fittings, push the clear pipes over them and dip them all into the brake fluid reservoir on the cylinder, slowly pump the pedal half stroke each time and wait about 2 seconds between pumps - make sure you release the pedal completely on each pump. The air bubbles will be seen in the pipes and when the fluid goes clear - the MC is ready for service.

connect all your hardware back and bleed the wheel slave units.

[syncview]

I also never close any bleed nipples when bleeding the brakes on one man system without pressure, if your catch reservoir is above the nipple level then you dont need to close it as the weight of the liquid in the bleed discharge pipe ensures no air can be sucked back.

it should be above the nipple level or the reservoir level?