Sinking brake pedal
#1
4th Gear
Thread Starter
Join Date: Jan 2023
Location: TX
Posts: 4
Likes: 0
Received 0 Likes
on
0 Posts
Sinking brake pedal
Hi everyone, recently, I noticed that while driving that the brakes felt a little "off", and what I noticed was that it seemed that more travel than usual was required to slow down the same amount. The problem occurred a couple times, but wasn't going on all of the time. Before I had a chance to get a good feel for what is going on, my radiator went bad, so after I replaced the radiator, I figured I might as well bleed my brakes (done with Techstream). Once I was back on the road, I haven't felt like the brakes have needed excessive travel to stop effectively. Now, I have noticed that if I am at a stop (such as a red light), after say 30 seconds, the brake pedal slowly starts sinking and requiring further travel to hold the vehicle at a stop. If I take my foot off the pedal and pump it, it will keep pressure for a while, but eventually loose it again at a stop.
I'm now trying to figure out what might be causing this, it doesn't seem like air since there is a fairly significant delay between initial pedal action and the change in pedal feel. According to the service manual, the suspected areas for "Low pedal or spongy pedal" are:
I'm now trying to figure out what might be causing this, it doesn't seem like air since there is a fairly significant delay between initial pedal action and the change in pedal feel. According to the service manual, the suspected areas for "Low pedal or spongy pedal" are:
- Fluid leaks in brake system
- Air in brake system
- Piston seals (Worn or damaged) (Front)
- Piston seals (Worn or damaged) (Rear)
- Master cylinder
#2
Moderator
A sinking brake pedal that can be pumped up usually means you need a new master cylinder. A leaking caliper would not feel that way, and would probably leak at the same time. You have not lost fluid.
You may want to bleed the brakes again to absolutely rule out air in the system before throwing a master cylinder on it.
A less likely failure would be the vacuum assist or a leaking vacuum hose on it.
How did you bleed them? Did you use a one man vacuum or pressure bleeder? Or those fast bleed brake bleeder valves? Or the old way with a helper?
You may want to bleed the brakes again to absolutely rule out air in the system before throwing a master cylinder on it.
A less likely failure would be the vacuum assist or a leaking vacuum hose on it.
How did you bleed them? Did you use a one man vacuum or pressure bleeder? Or those fast bleed brake bleeder valves? Or the old way with a helper?
#3
4th Gear
Thread Starter
Join Date: Jan 2023
Location: TX
Posts: 4
Likes: 0
Received 0 Likes
on
0 Posts
A sinking brake pedal that can be pumped up usually means you need a new master cylinder. A leaking caliper would not feel that way, and would probably leak at the same time. You have not lost fluid.
You may want to bleed the brakes again to absolutely rule out air in the system before throwing a master cylinder on it.
A less likely failure would be the vacuum assist or a leaking vacuum hose on it.
How did you bleed them? Did you use a one man vacuum or pressure bleeder? Or those fast bleed brake bleeder valves? Or the old way with a helper?
You may want to bleed the brakes again to absolutely rule out air in the system before throwing a master cylinder on it.
A less likely failure would be the vacuum assist or a leaking vacuum hose on it.
How did you bleed them? Did you use a one man vacuum or pressure bleeder? Or those fast bleed brake bleeder valves? Or the old way with a helper?
I bled the brakes the old way with a helper using Techstream to go through the process that includes the ABS system. I do have a vacuum bleeder that I may use to do it a second time unless there's some problem with that.
#4
4th Gear
Thread Starter
Join Date: Jan 2023
Location: TX
Posts: 4
Likes: 0
Received 0 Likes
on
0 Posts
Well, vacuum hose looks good as far as I can tell, rebled with the vacuum bleeder, no difference, put a new master cylinder on it and rebled with Techstream, it's maybe a little better, but the brake pedal is still sinking. Not really sure what to try next at this point. Might just need to have a professional look at it.
Trending Topics
#9
Pole Position
A vacuum leak anywhere on the engine could result in this issue, not just a leak in the vacuum hose going to brake booster. Too, the booster itself has a life span, and yours may be up! In other words, the vacuum leak may be happening inside the the booster.
Thread
Thread Starter
Forum
Replies
Last Post
danielnas
ES - 5th Gen (2007-2012)
5
03-12-20 05:11 PM
cenozoite
ES - 5th Gen (2007-2012)
9
01-29-18 03:04 PM