I changed the brake pads and discs at both front and rear a couple of days ago. Unfortunately I now have a very soft brake pedal, even though I did not open the nipple to bleed any brakefluid. I did however forget to open the reservoir tank on one wheel, and I also touched the brake pedal at a point to change from P to N. Could this be a reason for the soft pedal, or is it now simply a matter of bleeding out all the air wheel by wheel?
I'd appreciate your thoughts


( I also noticed I have a broken wheel stud at the rearwheel. Do I have to remove and replace the wheel bearing as well in order to fit a new one?? )

 

When replacing pads it is necessary to push the pistons back into the cylinders to make room for the new, thicker, pads. I think it is a good idea to attach a hose to the bleed nipple and open the nipple while pushing the piston in so the displaced brake fluid is bled off rather than being pumped back through the anti-lock valves or pump or the master cylinder. If you make sure the bleed hose goes upward before it enters your bleed container and you maintain positive pressure while the bleed nipple is open then you will be able to avoid air getting in, and you might bleed away any which is already in there.
Back to the soft pedal; perhaps a calliper is not sliding on its guide pins because they have dried out or become dirty/corroded and replacing the pads causes the calliper to slide on a different part of the guide pin. That could cause extra pedal travel and less effective brakes.
I would check the guide pins and bleed each wheel.

 

I would check carefully whether you have any leaks at the caliper seals - peel back the rubber boot if necessary to confirm.

What can happen is that if there is corrosion/pitting on the caliper piston (usually because of damaged rubber dust boot) on the outer side this shows no effects with the old pads. However, when you push the piston in to accommodate the new pads, the corrosion/pitting is now in line with the caliper seal and therefore a good seal is not achieved. This can also cause pistons to stick and cause binding of the brakes.

Attached picture probably explains it better.

Not saying this is definitely your issue but it's important to check. Can't see how air could be in there if you didn't open the bleed valve.

 

How do the brakes behave on the road, aside form the soft pedal?

I agree with the above remarks.

On a lightly different track........

Neither my X300 nor others I've driven have an old fashioned 'hard' pedal. In fact, many ABS cars have a soft-ish pedal.

Whenever brake work is done it is typical to be sensitive to the brake pedal height and feel. In my years in the repair business I've seen it many, many times. In fact, I just went thru the 'brake pedal feels soft' thing on my brother's truck after replacing the pads and shoes....with the hydraulic system never being opened up. Took a bit of time, and comparing to like vehicles, to convince him everything was OK.

I'm not saying there's nothing wrong. But, at the end of the day, if you check all the usual suspects and find nothing wrong.....it might be that there's nothing wrong

Cheers
DD

 

Hi guys and thanks for the input.
The brakes definitely feels too soft and the pedal travels almost to the floor. The brakes are working but it doesn't feel very safe.

The strange thing though, is that when I pushed back the pistons in the caliper to fit the pads, I noticed that the fluid level was almost approaching the top of the reservoir tank, so I sucked out quite a bit of brakefluid. I was expecting to refill more after the first test drive, but to my surprise the level was now at max again. Just as it was before I started, and I had not yet refilled any fluid.. How can this be possible??

 

I've read about some people bleeding the master cyl. (MC) with a hand vacuum pump and MC cap adapter after bleeding the wheels cyl's. Claims to help create a harder pedal. I know they sell MC cap adapter's with a hose made for this but I never tried it, its new to me

 

As your old brake pads were wearing down over the years, your brake fluid reservoir fluid level would gradually drop as more fluid was needed behind each of the pistons as they extended in the calipers to compensate for the wear in the pads. The reservoir would have been topped up during routine maintenance to keep the fluid at the correct level. When you pushed the pistons back to fit the new pads, the fluid returned to the reservoir, and would have caused it to overflow if you hadnt intervened. With new pads fitted, it would not be unusual for the reservoir not to need topping up.
As for your soft brake pedal, Doug makes a valid point about the pedal having an inherent degree of softness, but it does sound as if you are beyond this point, and in any event, safety first. Rebleeding the system would seem a sensible next step, using a pressure bleeder and low pressure.
I have heard of master cylinder seals "flipping" when pistons are pushed back, but it has never happened to me, although I am gentle pushing the calipers back. The symptoms would be not unlike yours....

 

countryjag, what is "low pressure" ie how high is safe? I made a pressure bleeder and tried to bleed my brakes but at 15psi it was painfully slow. I was wary of a small explosion involving brake fluid so did not try higher pressure and reverted to the tried-and-true assistant pushing the pedal method.

 

The system I use connects to the spare wheel to pressurise it. They reckon 20psi is plenty, and it works well for me at that. The fluid comes out gently and doesnt "spurt"; slowish, but worth being patient. The pedal pushing method seems to be less favoured on modern braking systems, and you do hear of master cylinder seals "flipping" as the piston travels to the bottom of the cylinder, where it doesnt usually go, and is then suddenly released and travels quickly back up the length of the cylinder.

 

Finally got the time to bleed the brakes. Connected a brake vacuum machine thingy and had a mate to help. Did the whole procedure starting at the rear with the wheel furthest away from the reservoir but it didn't help a bit 😔. Now what??

(The pedal still travels far and is soft. When pumping while breaking it feels perfect on the second push though. Just like before.. )

 

I'd carefully inspect the calipers for any abnormality......

- As mentioned above, check that there's nothing to prevent them from sliding easily.

-Any sign of leaks?

-Push the pistons back (with bleeders open). Any signs of excessive resistance?



Next, the hoses.....

- Have a helper press the pedal while you look at the hoses. Any sign of ballooning? A bit rare, but it happens




Next, bearings ....

- Any excessive play in the bearings that might cause disc run-out/wobble? If so, this might push the pads away from the discs. This distance has to be taken up when the brakes are applied and presents itself as a long pedal.



Next, air in the system.....

- Bleed the brakes again. You might have a stubborn air pocket.


I'm out of ideas after that....other than going back to the notion that you're mind is playing tricks on you. And that's not an insult. It happens all the time.

Perhaps replace the master cylinder as a guess?

Cheers
DD

 

A diagnostic tip is to clamp off the parts of the system and see what happens. i.e. clamp off both front calipers at the hose. Do you still have a soft pedal? If so that eliminates the calipers as the problem. Then try the back etc.

 

+1

Use the correct type of clamp on flexi brake pipes.



These apply sufficient pressure to stop the fluid flow but not too much to risk damage to the hose.

Graham

 

Wow, lots of good advice here. I really think b1mcp is on to something though, so I will inspect the calipers. I have a feeling something happened with one of them at the rear... Update is coming. I already ordered a repair kit, so I guess I'l have to remove hoses and everything on the caliper to inspect the seals?

 

Got the caliper repair kit.. but decided to just take it to the mechanic and try to get it through the MOT. I was thinking they could tell me what needed to be done as I'd probably fail the mot. But it passed! They said they checked the brakes but there was no air. So I am very surprised. And happy I guess. But the pedal is still soft on the first touch..
Anyway, I'm just happy it passed. Co2 level was a bit high at idle but they passed it anyway. New oil ,filter, plugs and airfilter was not enough to completely cure the Co2 issue but it was close enough to pass the mot.