Soft brake pedal

#1

I just noticed a softer brake pedal. Most of the initial travel is soft. I have fresh fluid and fresh stainless lines (all 6 installed). What could be the cause and/or what are the usual suspects? Master? Booster?

#2

Stating the obvious air anywhere in the system will cause it to be soft. Some times getting a good bleed can be tricky. This does not sound like a MC or booster issue.

#3

Perhaps a sticking caliper…

#4

Thanks Scott. Any tips on getting a good bleed? I have a power bleeder, but I never get a good feeling after using it. After changing the SS lines, would one have to bleed the clutch as well?

Rob

#5

All of the pads have equal thickness.

#6

You should not need to bleed the clutch, but if you haven’t put a liter thru the system you’re not done with the SS brake line replacement effort yet. A lot of air gets in when you pull your brake lines. Bleed ~500ml out of RR, and ~200ml out of LR. Then ~150ml out of RF and ~100 out of LF.

I’ve had good luck with my power bleeder. Which, last week, announced end-of-life by spraying brake fluid all over the garage floor.

#7

[quote=“Ranger” post=63669]You should not need to bleed the clutch, but if you haven’t put a liter thru the system you’re not done with the SS brake line replacement effort yet. A lot of air gets in when you pull your brake lines. Bleed ~500ml out of RR, and ~200ml out of LR. Then ~150ml out of RF and ~100 out of LF.

I’ve had good luck with my power bleeder. Which, last week, announced end-of-life by spraying brake fluid all over the garage floor.[/quote]

I too am a member of the power bleeder squirt. Twice actually. Thanks for the tips!

Do you think there’s any difference/advantage/disadvantage of doing this while the car is on jack stands/lift, or should the corner being bled be the highest point?

#8

[quote=“Rob in VA” post=63673][quote=“Ranger” post=63669]You should not need to bleed the clutch, but if you haven’t put a liter thru the system you’re not done with the SS brake line replacement effort yet. A lot of air gets in when you pull your brake lines. Bleed ~500ml out of RR, and ~200ml out of LR. Then ~150ml out of RF and ~100 out of LF.

I’ve had good luck with my power bleeder. Which, last week, announced end-of-life by spraying brake fluid all over the garage floor.[/quote]

I too am a member of the power bleeder squirt. Twice actually. Thanks for the tips!

Do you think there’s any difference/advantage/disadvantage of doing this while the car is on jack stands/lift, or should the corner being bled be the highest point?[/quote]

Put the car up how ever is convenient. As long as the bleed nipple is at the top of the piston cavity the air will find it’s way out.

The engineer that designed our clutch slave had an off day I guess. That nipple is at the bottom.

#9

This thread reminds me. What is the general consensus on speed bleeders on racecars? Do they actually help? I am of the ol skool manual brake bleeding mindset, and I still have the OEM bleeders.

#10

[quote=“King Tut” post=63680]This thread reminds me. What is the general consensus on speed bleeders on racecars? Do they actually help? I am of the ol skool manual brake bleeding mindset, and I still have the OEM bleeders.[/quote]Up until recently my speedbleeders really kicked ass. With a Pressure bleeder thing I would lift the car, pull the tires, but bleed bottles on all 4 corners, and in a couple minutes I had a great bleed without a helper. The w/o a helper thing is key for me because the wife cuts me an awful lot of slack for obsessions AS LONG AS THE OBSESSION DOESN’T BOTHER HER.

Lately tho the speedbleeders don’t work very well and I’m not sure why. I used the crap out of them for 4yrs so they did pay their way. There’s not much too them so I’m not sure what’s wrong.

#11

I had speed bleeders that were having trouble on my last car. I took them off, cleaned them and they worked again. I guess there were some small particles that got in them?

Jason

#12

[quote=“jls8177” post=63693]I had speed bleeders that were having trouble on my last car. I took them off, cleaned them and they worked again. I guess there were some small particles that got in them?

Jason[/quote]
Anything special about how you cleaned them?

#13

Ok - so I just bled the shit out of the system. Very little air was in the system and I still have a soft pedal. With the car not started, the pedal will get stiff after a few pumps. With the car on, I can bury the pedal to the floor with little resistance. Could it be a stuck caliper like Fish suggested?

#14

Same symptoms I had with a sticking caliper… Could also be some sort of obstruction in a brake line. I’d take apart, clean, replace seals in the front calipers and flush lines if I were you.

#15

Have you tried bleeding with the brake pedal? I had similar symptoms with a bad master cylinder last spring. I used my power bleeder days before an event, but on track I could tell I had no rear brakes. I figured there was air in the system so I had a friend help me bleed the brakes in the paddock. Nothing come out of the rear calipers. The fronts bled fine. New master cylinder fixed it. Had I bled the brakes with the pedal instead of my power bleeder I might have noticed a problem before getting to the track.

#16

Stiff after a few pumps is classic MC failure, but it’s odd that the symptom is different with vac assist.

The last thing you did to the system was to change brake lines right? The system was never “right” after the brake lines were changed? It’d be a helova coincidence for the lines to get changed the same day the MC failed.

You’ve put how much fluid thru the system, especially how much thru RR, the first one that gets bled?

#17

[quote=“Ranger” post=63718]Stiff after a few pumps is classic MC failure, but it’s odd that the symptom is different with vac assist.

The last thing you did to the system was to change brake lines right? The system was never “right” after the brake lines were changed? It’d be a helova coincidence for the lines to get changed the same day the MC failed.

You’ve put how much fluid thru the system, especially how much thru RR, the first one that gets bled?[/quote]

At RA back in Dec. I noticed something wasn’t right w/ the brakes. Nothing too dramatic, but they didn’t feel as good as usual. VIR this month they felt worse, so I figured to flush the fluid and while I’m at it change the SS lines as a preventive kind of thing. The PO left rubber lines between the subframe, so I figured now’s a good time to address that as well.

I pumped 1.5 liters into the system. Almost a half of bottle was caught at each corner.

#18

I haven’t tried the two person variation.

#19

[quote=“Rob in VA” post=63719][quote=“Ranger” post=63718]Stiff after a few pumps is classic MC failure, but it’s odd that the symptom is different with vac assist.

The last thing you did to the system was to change brake lines right? The system was never “right” after the brake lines were changed? It’d be a helova coincidence for the lines to get changed the same day the MC failed.

You’ve put how much fluid thru the system, especially how much thru RR, the first one that gets bled?[/quote]

At RA back in Dec. I noticed something wasn’t right w/ the brakes. Nothing too dramatic, but they didn’t feel as good as usual. VIR this month they felt worse, so I figured to flush the fluid and while I’m at it change the SS lines as a preventive kind of thing. The PO left rubber lines between the subframe, so I figured now’s a good time to address that as well.

I pumped 1.5 liters into the system. Almost a half of bottle was caught at each corner.[/quote]

Recall this from page 1 “Bleed ~500ml out of RR, and ~200ml out of LR. Then ~150ml out of RF and ~100 out of LF.” It’s not clear to me that you pulled 500ml out of the RR, assuming that was the first one to bleed. If you didn’t quite pull enough out of that corner you could have moved the air pocket from the front of the car into the rear slave but not ejected it yet. Then when you went to the LR and pulled too much fluid you mostly just swapped out fluid in the shared line that runs front to back. You really have to move a lot of fluid thru the first rear wheel that you choose.

Note tho that your MC symptom of a couple pumps to firm doesn’t jibe with the theory of air in the lines.

#20

[quote=“Ranger” post=63722]Recall this from page 1 “Bleed ~500ml out of RR, and ~200ml out of LR. Then ~150ml out of RF and ~100 out of LF.” It’s not clear to me that you pulled 500ml out of the RR, assuming that was the first one to bleed. If you didn’t quite pull enough out of that corner you could have moved the air pocket from the front of the car into the rear slave but not ejected it yet. Then when you went to the LR and pulled too much fluid you mostly just swapped out fluid in the shared line that runs front to back. You really have to move a lot of fluid thru the first rear wheel that you choose.

Note tho that your MC symptom of a couple pumps to firm doesn’t jibe with the theory of air in the lines.[/quote]
Years ago I wanted to see how much fluid through the brake system to completely flush the system. I injected just a bit of dye into the reservoir at the MC intake ports and watched for the dye to at a wheel. I found that 350cc through the right rear wheel, 150cc through the left rear, and 150cc through each front caliper was more than enough. It really doesn’t matter whether you start with the right or left rear on an E30.

I agree with Scott that the braking being better after a couple of pumps doesn’t sound like air in the system. It sound to me more like a bad master cylinder.