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Looking for a solution with my sinking brake pedal when engine is running (vacuum present in booster). With the engine off I have a very solid brake pedal with little travel but as soon as the engine is started the pedal can be pushed almost to the floor limit. I've bled the system multiple times with a Motive Brake bleeder and exercised the ABS pump for brake bleeding, replaced the master cylinder with a new OEM part, swapped the ABS pump module with a known good used unit, checked for leaks and bad hoses but have found nothing wrong and still have the same sinking brake pedal, nothing seems to make a difference. The car stops very well but if I'm sitting at a stop light I can press harder on the brake pedal and there's just too much brake pedal travel and a spongy feel. I'm not finding any air getting into the system when re-bleeding all four wheels. Any suggestions would be welcomed. My next step is to rebuild the brake calipers and replaced all the rubber brake hoses. The new master cylinder and swapped ABS module make absolutely no difference.
Wow. You have pretty much done everything that anyone would suggest. Sometimes taking it to a mechanic, even the dealer would be adviseable. Don’t mess with brakes too much because that is the one item like insurance that you hope you never need to have fail in an emergency type situation.
Wow. You have pretty much done everything that anyone would suggest. Sometimes taking it to a mechanic, even the dealer would be adviseable. Don’t mess with brakes too much because that is the one item like insurance that you hope you never need to have fail in an emergency type situation.
One I receive the parts I've ordered and after I replace all the rubber hoses and rebuild the calipers and if this doesn't solve the problem, I might consider taking it to the dealer. I'm with you and don't want to take any chances with the brakes failing and other than the soft pedal the brakes do work very well. After each part replacement and after each time the brakes have been bled, I've done a test drive with hard braking and visual checks afterwards. The other day I modified the Motive brake bleeder I have so I could try the reverse brake bleed method as another attempt to make sure there's no air in the system, no evidence of any air and no improvement in brake pedal feel.
Looking for a solution with my sinking brake pedal when engine is running (vacuum present in booster). With the engine off I have a very solid brake pedal with little travel but as soon as the engine is started the pedal can be pushed almost to the floor limit. I've bled the system multiple times with a Motive Brake bleeder and exercised the ABS pump for brake bleeding, replaced the master cylinder with a new OEM part, swapped the ABS pump module with a known good used unit, checked for leaks and bad hoses but have found nothing wrong and still have the same sinking brake pedal, nothing seems to make a difference. The car stops very well but if I'm sitting at a stop light I can press harder on the brake pedal and there's just too much brake pedal travel and a spongy feel. I'm not finding any air getting into the system when re-bleeding all four wheels. Any suggestions would be welcomed. My next step is to rebuild the brake calipers and replaced all the rubber brake hoses. The new master cylinder and swapped ABS module make absolutely no difference.
Update, in addition to all that was done previously I've now rebuilt all four calipers and replaced all four brake hoses at each wheel, all OEM parts from Acura. I've also removed the new master cylinder and bench bled it again just to make sure no air was remaining, pedal the same, brakes work well but can still press the pedal down at a stoplight.
I finally purchased a master cylinder plug kit, Thexton 803p and wish I had purchased this kit earlier. For a brake problem like I'm dealing with this plug kit was something I needed from the beginning, it would have saved me a lot of time and expense. With the plug kit I plugged off one master cylinder line (two wheels) at the brake lines coming out of the ABS pump module and got a much better brake pedal, some travel initially but firm pedal with engine running. I then plugged off all four wheels and got a very solid brake pedal, very little brake travel initially and a very solid brake pedal. This eliminates the master cylinder and ABS pump module as the cause of the problem and this is why I had wished I had purchased this plug kit from the beginning even though it cost $70.
After bleeding the system again I then plugged off the one rear wheel and the pedal got a little firmer but still soft with long travel, then plugged off the front and rear wheel(same master cylinder line) and got a noticeably better pedal. I bleed the system again and plugged off the other two wheels and got a noticeably better pedal similar to the other two wheel circuit so I couldn't trace the problem to a single wheel or single two wheel master cylinder line. Each time I blocked off one or more wheel the pedal got better and better and noticeably more so when I blocked off the front wheels.
Even after all this my brake pedal is still not solid but at least I can rule out the master cylinder and ABS module and concentrate on problems with the brake lines, wheel calipers, rotors, brake pads since that's all that remains.
I'm confident the problem is not air in the brake lines and I've replaced the front rotors and pads so the next step is to replace the rear rotors and pads and possibly try a different set of brake pads up front since the front wheels is where most of the improvement came when these wheels were blocked off. Any other suggestions would be appreciated. I've read some threads where people have had a similar problem and have tried everything and claimed replacing the rotors back to OEM made a difference and others who have said the same thing about the brake pads. At this point I'm willing to try just about anything but certainly would like to avoid wasting money on the wrong parts.
Having done everything I could possibly do to improve the brake pedal firmness and stopping power of my brakes (2010 RDX) I've finally made some progress. In my previous post I've described all that I've done which includes checking, replacing or rebuilding everything in the braking system with no noticeable improvement. The most recent thing I've done that has finally made a very noticeable difference is I've replaced all the rubber brake hoses with Techna-Fit stainless steel braided lines. I had previously replaced all the rubber brake hoses with new OEM Acura parts with no improvement in brake pedal firmness. After replacing these hoses with the stainless braided lines the brake pedal firmness and stopping power is noticeably better. These Techna-Fit stainless braided lines are the only parts that has made a significant difference in the pedal feel and braking performance. I would recommend these brake lines for the 1st gen RDX for better braking.
Having done everything I could possibly do to improve the brake pedal firmness and stopping power of my brakes (2010 RDX) I've finally made some progress. In my previous post I've described all that I've done which includes checking, replacing or rebuilding everything in the braking system with no noticeable improvement. The most recent thing I've done that has finally made a very noticeable difference is I've replaced all the rubber brake hoses with Techna-Fit stainless steel braided lines. I had previously replaced all the rubber brake hoses with new OEM Acura parts with no improvement in brake pedal firmness. After replacing these hoses with the stainless braided lines the brake pedal firmness and stopping power is noticeably better. These Techna-Fit stainless braided lines are the only parts that has made a significant difference in the pedal feel and braking performance. I would recommend these brake lines for the 1st gen RDX for better braking.
Where did you get the Techna-Fit stainless braided lines?
Where did you get the Techna-Fit stainless braided lines?
I got them through lpiracing.com and I've also seen them available on Ebay. They did take about 3 weeks to be delivered because they were built to order. IF you need them sooner you might be able to get some pre-built ones for the 1st gen RDX off Ebay and I would ask the seller first.
I've seen something similar in a bad brake booster/brake booster switch on a different make (Volvo).
You said vacuum was present in the booster, was this when braking or just at idle? A small tear could present differently while operating. Cars often follow some logical flow so id say you have addressed everything directly already. Last step would be to recheck measurements of parts.
Where did you get the Techna-Fit stainless braided lines?
Here are a couple of photos of the installed Techna-Fit brake lines. The center support bracket needs to be moved to the ideal position along the lines and this is especially important for the front lines. The Techna-Fit lines I received were all the same length and all were the length of the longer rear brake lines so the front lines are longer than the original OEM ones. I had to adjust the bracket so the lines didn't get too close to the axle or too close the inside of the wheels. These lines appear to very high quality and they did improve the pedal feel, firmer with better stopping power.
05-02-2023, 12:32 PM
