I replaced the front disc pads a few months ago, and bled the brakes and everything works...fine...ish. No red warning light, etc. and about two weeks ago I had to do a panic stop because some knucklehead decided that day was a good one to die and tried to cross traffic he couldn't see because his view was blocked by truck. Brakes performed brilliantly, ABS kicked in when it should, and only damage to knucklehead's car is a possible stain on his seat.

However, I just know something isn't quite exactly right. I don't know if it's the pads' feel I don't like (Bosch QuietCast) or if there is still a tiny bit of air in the line. The peddle isn't squishy, yet I feel like I'm just having to push the peddle a wee skosh more than before. I'm probably the only one would notice it.

The 1990 MY Workshop Manual says to only bleed the front brakes after pad replacement. I thought it might be worth trying a second bleed, and was looking through the forum to see if there is a "best method" other than having my daughter on pedal duty. It seems there are recommendations for "Gravity Bleed" and others have used vacuum type, and I'm less certain of what to try this weekend after researching the various methods. It seems the best method varies by car and how the system is engineered.

Any help or suggestions would be welcome.

 

I may be wrong on this, but more than likely the brake bleeding instruction has absolutely nothing to do with removing air from the system. Typically you "bleed" the brakes when installing new pads, because you need to move the pistons back into the caliper. Rather than pushing possibly dirty fluid back through the system and also possibly over-flowing the reservoir if someone didn't know better than to "top off" their fluid not understand it is "low" because the pads are worn, the lines are cracked so the displaced fluid could go out of the system rather than backwards through it.

I could be wrong, maybe they mean something else, maybe they mean to bleed the system after doing this procedure simply to assure there is no air in the system. I would try re-bleeding. I would say it may be more likely that you accidentally introduced air when you bled the brakes per the instructions and THAT is why the system feels different than it did before. The pads wouldn't "squish" more, they would merely grab differently. Unless you mean you need to push more to get the same stopping distance, in which case the stopping distance may have changed due to the new pads. Did you bed them in?

Oh course there is always the chance that you are now paying attention to how far you are pushing because you are looking to see how the braking changed, and it's all in your head now that you are being overly critical.

No harm in trying a re-bleed though. If you try gravity bleeding be absolutely sure to keep the reservoir filled up. If you walk away and it bleeds out you are going to have a lot more air to deal with...

 

The thing I don't full grock about Gravity Bleeding is how does air get out of the lines? Air will tend to rise and fluid will tend go downward. Does the sheer mass of fluid push a small air bubble out the nipple, or does it rise through the fluid to escape at the reservoir?

 

No , not a dumb question , " the quite not right feeling "

Was that after you replaced the brake pads , and that's why you bleed them ,
Or was it after you bleed the brakes
Or was it after that day when the ABS kicked in ?

 

Since replacing the pads.

 

The first part of your question is correct .

" Does the sheer mass of fluid push a small air bubble out the nipple, "

 

Check out my blog. I have a section there where I bleed the brakes on ABS equipped car. The cheap pressure bleeder allows me to do this by myself.

When was your fluid changed last? If more than a couple of years might be good to change the fluid while you're at it.

 

I'll offer my opinion about brake feel and pads. I just recently changed the pads on my 89 Shooting Brake to sort a brake pull symptom. The pads that I removed were the ones that I'd installed when I rebuilt the brakes last year-maybe had 200 miles on them. I don't remember where I bought them but I'm pretty sure they were semi-metallic.

I took these pads off and replaced with a set of organic pads and holy sh*t is the brake pedal feel different. The former pads felt "normal" and required some shove to slow the car and the first cold stop wasn't great. The organic pads feel like I dropped an anchor they grab so hard-from first stop.

The trade? They get soft after 4 hard stops...

So, my guess is your new pads are just "different"

 

The fluid is really thick, the bubbles don't move through it that readily. If you have bled with a hose on the bleeder before, you have seen the bubbles trapped in the line. They were apparently suspended in the line, they weren't rapidly moving up and back into the system like bubbles in a soda.

The pressure is great enough that no air comes past the flowing fluid, so as you replace fluid in the reservoir and let the old fluid run out, any trapped air comes out with it. Since the lines are being refilled from the reservoir all the way to the point of the bleeder, no air is ever introduced, so they are usually rock solid. Though some systems have odd points that can trap air, gravity bleeding usually works very well.

 

I agree, I was thinking he was probably mistaking the real pedal distance with the newly required pressure to get them to grab with the same force.

btw some organics get eaten really quick, so keep on eye on those new pads. If you have wires ceramic is the way to go

 

Don't be offended at what follows

It might be a mental thing.

It is very common to become hyper-sensitive to brake feel after doing brake repairs.

I've come across this many, many times over the years. Heck, I've even fallen victim myself.

For a long time, before we all got so spread out (or passed away) I took care of all the cars in my family: Mom and Dad's, brother's, my kids, the wife's, etc. As an experiment I would mention having done some brake work when, in fact, I never touched the brakes at all. Without fail I'd hear back within a day that "....the brakes feel a little mushy" or "....the pedal feels a little low".

I'm not saying there is nothing wrong with your brakes, or that the composition of the pads can't alter pedal feel.....but at the same time just be prepared for the possibility that there is nothing wrong and nothing to fix.

Cheers
DD

 

Mac , it's not your imagination , your pedal is feeling different because you made no mention that you replaced or machined your disc rotors .

If , your pads were worn out , there will be some degree of lip formed at the top and bottom of your disc , given that the new disc pad is flat and your disc isn't , the pad is sitting on those lips . You have created a slight gap between your pad and the disc rotor .

Because of this , when you brake the pad is flexing to take up that gap .
That's why you " feel like I'm just having to push the peddle a wee skosh more than before "

You had no air before replacing the pads , and have already bleed the brakes , you won't need to do any more bleeding , keep driving , the pads will wear in eventually , or you can check your disc rotors .

Good luck with that

 

Not sure if I'm understanding you correctly.

The circumferential lips at the top and bottom are areas not in contact with the pads. The contact areas wear down, the non-contact areas don't. Thus the lip.

This would mean that the new pads are a different dimensional size than the old ones ....and thus contact the brake discs in an area (the lips) that the old pads didn't.

New pads will contact the discs in the very same (worn) area that the old pads did

Cheers
DD

 

Hello Doug ,
Yes you are not understanding me correctly

Cheers ,

Sid

 

Well, OK....thanks for letting me know




Cheers
DD

 

To Doug's point on talking yourself into things. I recently replaced all the brakes (disc and drums) on my truck. I had clearly forgotten what a pig rear drums can be at times. In the first week I thought I heard and felt a lot of stuff, and had to convince myself just to let things settle. 1000klm later they are excellent and I am really only reminded of the feeling due to this thread.

 

Have to say I'm not understanding you correctly either.

 

That's correct. Normally, I usually assume new rotors when I replace pads, but I was surprised when I inspected the rotors that they looked nearly new so I didn't order new ones.

I may have botched the run-in because it was a cold day, and I was tired and in hurry to finish because we were going out that evening.

 

Not offended at all. Part of why I haven't posted about it before is because I was arguing with myself about the same thing.

I've been really tempted to have someone else who knows cars drive it, but the minute you ask, "did you feel anything with the brakes?" you've planted the seed and no longer have an unbiased sample.

Not to mention that nobody in my neighborhood (or possibly zip code) works on their own cars or knows much about them in the first place (I'm the one-eyed king among the blind around here, or at least the only own who owns tools not stored in a kitchen drawer).

My best sense is that it isn't nothing, but I admit I could be wrong.

 

Doug and Norri , I will try to get some pictures up soon , they might explain it better ,

Mac ,
No one knows your car better than you , yes were all human and can easily talk our selves in to almost anything , however you do have a gut feeling about something and I think that's why you started this thread .

Cheers ,