brakes....cannot get firm pedal

tomstir · Post by **tomstir** » 08 Mar 2013, 05:23

UUUUGGGGGG.... I can't seem to figure out what is going on with my brakes....

About a year and a half ago I replaced all rotors and pads and bled the system. The pedal never seemed to get firm and the brakes never had that "bite" to them I thought they had before. When thrashing around I could hammer the brakes on long sweepers and the pedal would slowly go almost to the floor and them it would feel like the abs would kit in. I rebled the brakes again and it felt better but not great.

About 6 month ago I decided to rebleed the system.....same results......so I started to read all the info I could find and thought that the master cylinder had gone bad because when I bled the brakes I was pushing the pedal to the floor.

I just finished replacing the broken spring seat and decided to order a new master cylinder and bleed the system again...this time with a piece of wood behind the bedal...........same results....the pedal feels better than the previous times but will slowly go to the floor when putting a lot of pressure on it.

I made my own pressure bleeder with a vitamin bottle cap and valve stem.....at first I could get 10-20pounds of pressure that would slowly leak out but not much fluid out of the calipers...after some modifications I was able to get 15pounds that would stay for several minutes but could not get any fluid out of the calipers.

Am I missing something? Is there some sort of check valve that I need to address? I never had the engine running and didn't think that made a difference...does it? I did read that if one gets air into the abs it is "dealer only" repairable...what do they do?

Thanks

tomstir

Post by **Ben850** » 08 Mar 2013, 07:30

I replaced the front caliper lines with braided stainless. For rotors, just OEM style Brembos, and Akebono ceramic pads.
It is a noticeable improvement. I'm fairly sure your brakes feel soft like mine did before.

On a side note, I did replace the calipers with rebuilt OEM. Ofcourse bled enough out to make sure all fluid was all fresh.

: Rebuilt calipers, Akebono ceramic, Brembo OEM rotors, and braided stainless lines.

Post by **rmmagow** » 08 Mar 2013, 07:45

I had this issue with my Mercedes. I ended up doing regular UP & DOWN bleed but with the car running. Fixed my problem. I have no real good explanation for why this worked other than maybe the MC was air bound.

Post by **jblackburn** » 08 Mar 2013, 08:06

Keep the reservoir full and push fluid out until you see it run completely clear. It may require 2 bottles of brake fluid, but if there are no leaks, it SHOULD firm up nicely.

I've never gotten the power bleeders to work well. The 2-person approach has always worked well for me.

Post by **cn90** » 08 Mar 2013, 09:05

Actually the 1-man bleeding works well. I made the cap using:
- Volvo 240 brake cap + adaptors for air compressor
- Air compressor set at 10-15 psi.

It works like a charm, actually this ATE cap fits Volvo, Mercedes, BMW etc.

Detail below:
https://www.matthewsvolvosite.com/forums ... hp?t=29243

PS: O.P., if your pedal is still mushy after a good bleed, perhaps you have air inside the ABS Hydraulic Unit..

Post by **erikv11** » 08 Mar 2013, 09:15

Yeah, 2-person bleeding always works. Hard to beat that, and nice to have some company in the garage.

OP already pointed out that probably there is air in the ABS unit. His question is if anyone knows what the dealer does to fix that. I'm curious too, that may be the clincher here.

Post by **confused_al** » 08 Mar 2013, 10:30

I just replaced the master cylinder for my Mercedes, even though I bench bled the tandem master cylinder but couldn’t avoid introduced some air into the system including ABS circuit. I did as Mercedes’ instructed and its rather easy.

In compare to normal bleeding, the differences are:
1. Mercedes instructs very high bleeder pressure setting for this procedure, 2 bar (29 psi);
2. Before starting engine, actuate brake pedal several times until the pressure is built up and maintained (pedal gets harder and harder).
3. Start engine and then bleed the system.

It’s not Volvo’s but I think that ATE system is similar. However, I wouldn’t use that high pressure in a Volvo, something like 20psi?

instarx · Post by **instarx** » 10 Mar 2013, 07:37

Sometimes old rubber brake lines can balloon when they are under pressure. They look normal when sitting, but when you apply a lot of pressure they can swell like a balloon in one spot and your pedal drops. I'd try replacing brake lines next.

Post by **cn90** » 10 Mar 2013, 11:47

The trick to prevent air in ABS Module when replacing Master Cylinder.

1. Remove the brake calipers, let's say just the front 2 calipers.
Remove brake pads, place piece of wood such as 3/4-inch thick oak (used for home flooring).
Use this wood in place of brake pads, now slowly apply the brake pedal until the piston touches the wood, this way the piston is extended but not completely out.
Whatever you do, make sure you don't eject the piston!

2. When removing the MC, use some ziploc + rubber band to cover the exposed metal lines.
At the most, there may be a 5-10 cc of air bubbles in the lines.

3. Replace the MC and tighten the metal lines.

4. Here is the trick: squeeze the caliper pistons back in, this will push brake fluid back into the system.
In the process of doing so, air that entered the metal lines earlier is now pushed back into the MC ---> up in the reservoir.

If you do it this way, you will never need to visit the dealer to cycle the ABS Module.

tomstir · Post by **tomstir** » 11 Mar 2013, 04:59

Thanks for the info guys.....

I drove my wifes 2002bmw and when stopped at a light I pushed on the brake pedal real hard and it too went down slowly...I have never had or felt any problems with it...I did the brakes several years ago and the dealer actually did a bleed on it since then.....do all newer cars do this? MY 1996 850 is the newest car I have worked on....l'm used to non power non abs systems.

instarx--- I looked at the brake lines while bleeding and did not notice any ballooning. I am thinking of replacing those lines....how would one keep air out while replacing those lines? I would think it was impossible.

confused_al---are you suggesting to use the pressure bleeding technique?

cn90--great right-ups....I used your strut replacement info a couple of weeks ago......do you think I have air in the abs? You mentioned "dealer abs cycle" is this common? Great tip with the "reverse piston" move to keep air out.

Does anyone know why when I pressurized my system that I could only get a small amout of fluid out of my calipers at first and then nothing? I did all of my bleeding with the engine off....would having the engine running allow the fluid to go through? Maybe with the engine off the abs is "locked up" and not allowing fluid to pass through.

thanks
tomstir