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Dodgy Brake Pedal Feel

RBwhatever
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RBwhatever Veteran

RBwhatever

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Posted (edited)

Hi guys,

I have just changed my brake pads all round using the tutorial on this site.

After I changed them my pedal hits the floor. Prior to changing them the pedal feel was good and took hardly any pressure to get the brakes to engage. Now it feel like I'm pushing into play-doh.

The brakes do engage but it takes a long travel of the pedal to do so. The pedal will also never go hard after pumping the brakes. It firms up about 2/3rds and just fades to the floor.

I have bled the brakes after finding this out and there is no air in the system at all. And all to no avail.

I have a theory:

In the sau guide there was one step that was not incorporated, but was in the Bendix brake fitting guide (I read the guide after I found I have this problem).

Clamp the brake hose and open the bleed screw on the caliper. Use a bleed hose to catch excess brake fluid in a suitable container as you push the pistons back into the caliper. Pistons should be pushed back by hand or using a piston retraction tool. Ensure all pistons can move without binding. Take care not to expose skin, clothing or paintwork to brake fluid.

Calipers with an integral park brake often require an alternate method to retract the piston. Consult the manufacturer's instructions.

http://www.bendix.com.au/Text/116433222907...-fit-Brake-Pads

I didn't do this step, but rather just pushed the caliper pistons back, forcing the brake fluid back through the system and into the resovior. After doing all four corners, it pushed enough fluid back to overflow the resovior.

Now, is it possible that forcing the fluid back through the master cylinder can damage the seals? Thus causing this problem?

Cheers guys.

Edited by KeyMaker
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https://www.sau.com.au/forums/topic/174008-dodgy-brake-pedal-feel/
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Kinks Grand Master

Kinks

Posted
Posted

I guess if you push enough brake fluid back up you end up with old dirty fluid in your reservoir. hit the brakes a few times and the dirt will rip your master cylinder seal and there go your brakes.

take it to a mechanic. the last thing you want is to end up with no brakes suddenly.

RBwhatever Veteran

RBwhatever

Posted
  • Author
Posted
I guess if you push enough brake fluid back up you end up with old dirty fluid in your reservoir. hit the brakes a few times and the dirt will rip your master cylinder seal and there go your brakes.

take it to a mechanic. the last thing you want is to end up with no brakes suddenly.

The fluid was changed by a mechanic 2 weeks prior to me changing the pads, so the fluid should have been pretty clean.

Taking it to a brake and clutch shop is on the cards to get it fixed.

Just trying to diagnose what went wrong and why.

ferni Grand Master

ferni

Posted
Posted

Doesn't make sense, changing pads shouldn't have that kind of effect on your pedal... when you first hit the pedal after fitting the pads it will be soft and you'll have to pump them up, since you've pushed the pistons back to fit the pads in... but then the pedal should be reasonably fine - it may be a little softer until you bed in the pads... due to the pad/disc not being flush, hence the need for bedding...

If your hitting the floor with your brake pedal you have to have air in the system.. If there is no air, then the fluid must be going somewhere? Any leaks around the brakes/lines? If not maybe something wrong with the master? Maybe try doing a full flush and bleeding them again? Or just take it to a pro :rolleyes:

RBwhatever Veteran

RBwhatever

Posted
  • Author
Posted (edited)
Doesn't make sense, changing pads shouldn't have that kind of effect on your pedal... when you first hit the pedal after fitting the pads it will be soft and you'll have to pump them up, since you've pushed the pistons back to fit the pads in... but then the pedal should be reasonably fine - it may be a little softer until you bed in the pads... due to the pad/disc not being flush, hence the need for bedding...

If your hitting the floor with your brake pedal you have to have air in the system.. If there is no air, then the fluid must be going somewhere? Any leaks around the brakes/lines? If not maybe something wrong with the master? Maybe try doing a full flush and bleeding them again? Or just take it to a pro :rolleyes:

Yeah doesn't make sense does it. It took me a while to get my head around it.

But yeah there's no air in the system as I've bled it twice already since the problem came about and it was bled 2 weeks prior, so I eliminated that possibility.

The peddle was soft with the first push, but it hasn't tightened up. It's consistently soft. It hasn't changed the feel even after bleeding.

I was thinking it would be a leak in the system somewhere. I can't be the caliper seals because then fluid would be leaking out from them. I can only think it's the master cylinder seals. It's not losing fluid, so it must be leaking internally.

I mean changing pads should just be a pull out drop in job and that's it. Pushing the pistons back without opening the bleed nipple is the only place where I could of gone wrong that I can think of, everything else is straight forward.

Edited by KeyMaker
tacker Mentor

tacker

Posted
Posted

But if the seals in the master cylinder are damaged how did it bleed, should have been a fair amount of fluid each time you pushed the pedal down. Two or three pumps is enough to remove any air in the caliper. And i would not think that pushing the pistons back would have enough volume to push dirty fluid back into the master cylinder.

But in saying that not sure how air could have got into your system while replacing pads only, so it could be your seal in the master but what are the odds of the seal failure happening what you change pads.

RBwhatever Veteran

RBwhatever

Posted
  • Author
Posted (edited)

Rightio, update time.

I got the car taken into the brake place today, explained my situation, and the guy said DO NOT PUSH THE PISTONS BACK WITHOUT OPENING THE BLEED NIPPLE AND WITHOUT CLAMPING THE BRAKE LINE.

Anyways he checked it out and it turns out to be one of the seals in my master cylinder is shot. He's replaces the two seals and does a little recondition and flushes the fluid again and puts in new brake fluid. And I was charged a decent $102 odd.

Now, after getting the car back, it feels 'better'. It wasn't the best or as good as it was before as it was still very spongy and still took about half the travel of the pedal to engage, but it did grab the disc a heap better.

Ok so I left a little detail out of the first post that I did not feel was relevant but in fact is very relevant.

When changing my brake pads I used silicon aka brake goo (same thing....no I'm not kidding) on the back of them and between the shims and between the shim and piston, just to make sure I didn't get squealing.

After getting my car back today and finding the pedal still spongy, I then proceeded to remove the pads again and remove all the silicon that I applied to the back of the pads. Fitted them again and hey presto, really good pedal feel and response. Now it only takes a push of the big toe to brake easily.

So all in all, it was a combination of two things.

1 is that I pushed the pistons back without opening the bleed nipples and clamping the lines thus damaging a seal in my master cylinder. The seal was probably due to die and this just triggered it.

2 Is the silicon that I applied to the back of the brake pads. I really didn't think it would affect it the feel that badly or at all but it did......a lot. I don't know why I haven't read this before. Guys have put the brake goo on and haven't said a thing about how the pedal feels afterwards.

So it's now fixed and I'm very happy :) I'll be posting that missing step up in the DIY tutorial, hopefully it doesn't have to happen to someone else.

Edited by KeyMaker
  • 1 month later...

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